tag:theconversation.com,2011:/id/topics/atmospheric-science-25900/articlesAtmospheric science – The Conversation2024-02-26T13:38:23Ztag:theconversation.com,2011:article/2228512024-02-26T13:38:23Z2024-02-26T13:38:23ZHow is snow made? An atmospheric scientist describes the journey of frozen ice crystals from clouds to the ground<figure><img src="https://images.theconversation.com/files/576863/original/file-20240220-22-v6kq2o.jpg?ixlib=rb-1.1.0&rect=22%2C5%2C3764%2C2055&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some parts of the U.S. see well over 100 inches (2.5 meters) of snow per year.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/downhill-sledging-royalty-free-image/488074477?phrase=sledding+in+snow">Edoardo Frola/Moment Open via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>How is snow made? – Tenley, age 7, Rockford, Michigan</strong></p>
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<p>The thought of snow can conjure up images of powdery slopes, days out of school or hours of shoveling. For millions of people, it’s an inevitable part of life – but you may rarely stop to think about what made the snow.</p>
<p>As a <a href="https://www.eaps.purdue.edu/people/profile/ablanch.html">professor of atmospheric and planetary sciences</a>, <a href="https://scholar.google.com/citations?user=xClwTzUAAAAJ&hl=en&oi=ao">I’ve studied how ice crystals floating</a> in the sky become the snow that coats the ground.</p>
<p>It all starts in the clouds.</p>
<p>Clouds form when air near the Earth’s surface rises. This happens when sunlight warms the ground and the air closest to it, just like the Sun can warm your face on a cold winter day. </p>
<p>As the slightly warmer air rises, it cools – and the water vapor in that rising air condenses to form liquid water or water ice. From that, <a href="https://climatekids.nasa.gov/cloud-formation/#:%7E">a cloud is born</a>. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Cf6El0mI1fM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">You need just two things for snow to form.</span></figcaption>
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<h2>Endless pathways</h2>
<p>When temperatures are well below freezing on the ground, the clouds are primarily made of water in the form of ice. Under 32 degrees Fahrenheit – that’s zero degrees Celsius – the frozen water molecules arrange themselves into a hexagonal, or six-sided, crystalline shape. As ice crystals grow and clump together, they become too heavy to stay aloft. With the help of gravity, they begin to fall back down through and eventually out of the cloud.</p>
<p>What these ice crystals look like once they reach land depends on the temperature and humidity of the atmosphere. As the humidity – or the amount of water vapor in the cloud – increases, some of the ice crystals will grow intricate arms at their six corners. That branching process creates what we think of as the <a href="https://www.timeforkids.com/g2/snowflake-science-g2-5-plus/?rl=en-500">characteristic shapes of snowflakes</a>. </p>
<p>No two ice crystals take the same path through a cloud. Instead, every ice crystal experiences different temperatures and humidities as it travels through the cloud, whether going up or down. The ever-changing conditions, combined with the infinite number of paths the crystals could take, result in a unique growth history and crystalline shape for each and every snowflake. This is why you’ve likely heard the saying, “<a href="https://www.willyswilderness.org/post/no-two-snowflakes-are-alike-it-s-actually-true">No two snowflakes are exactly alike</a>.” </p>
<p>Many times, these differences are visible to the naked eye; sometimes a microscope is required to tell them apart. Either way, scientists who study clouds and snow can examine a snowflake and ultimately understand the path it took through the cloud to land on your hand. </p>
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<a href="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Snow crystals attached to a window." src="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=799&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=799&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=799&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">It takes approximately one hour for a snowflake to reach the ground.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/snowflakes-royalty-free-image/158720307?phrase=snowflakes">LiLi/iStock via Getty Images Plus</a></span>
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<h2>Liquid water as glue</h2>
<p>When snow falls from the sky, you don’t usually see individual ice crystals, but rather clumps of <a href="https://scied.ucar.edu/learning-zone/storms/snowflakes">crystals stuck together</a>. One way ice crystals aggregate is through what’s called mechanical interlocking. When ice crystals bump into each other, crystals with intricate branches and arms intertwine and stick to others. </p>
<p>This mechanism is the main sticking process in cooler, drier conditions – what people call a “<a href="https://compuweather.com/the-important-difference-between-wet-snow-and-dry-snow/">dry snow</a>.” The result is a snow perfect for skiing, and easily picked up by the wind, but that won’t hold together when formed into a snowball. </p>
<p>The second way to stick ice crystals together is to warm them up a bit. When ice crystals fall through a region of cloud or atmosphere where the temperature is slightly above freezing, the edges of the crystals start to melt. Just a tiny bit of liquid water allows ice crystals that bump into each other to stick together very efficiently, almost like glue. </p>
<p>The result? Large clumps of ice crystals falling from the sky, what we call a “<a href="https://www.acurite.com/blog/types-of-snow.html">wet snow</a>” – less than ideal for hitting the slopes but perfect for building a snowman. </p>
<p>Snow formed in clouds typically reaches the ground only in winter. But almost all clouds, no matter the time of year or location, <a href="https://scijinks.gov/clouds/">contain some ice</a>. This is true even for clouds in warm tropical regions, because the atmosphere above us is much colder and can reach temperatures below freezing even on the warmest of days. In fact, scientists who study weather discovered that clouds containing ice produce more rain than those that don’t contain any ice at all.</p>
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<p class="fine-print"><em><span>Alexandria Johnson receives funding from NASA. </span></em></p>There are an infinite number of paths an ice crystal can take before you touch it.Alexandria Johnson, Professor of Atmospheric and Planetary Sciences, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2236182024-02-23T17:16:47Z2024-02-23T17:16:47ZSatellites are burning up in the upper atmosphere – and we still don’t know what impact this will have on the Earth’s climate<figure><img src="https://images.theconversation.com/files/577600/original/file-20240223-16-tqd752.jpg?ixlib=rb-1.1.0&rect=25%2C16%2C5566%2C4174&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/satellite-hurtling-through-space-burning-enters-113962255">Paul Fleet / shutterstock</a></span></figcaption></figure><p>Elon Musk’s SpaceX has announced it will dispose of 100 Starlink satellites over the next six months, after it <a href="https://spacenews.com/spacex-to-deorbit-100-older-starlink-satellites/">discovered a design flaw</a> that may cause them to fail. Rather than risk posing a threat to other spacecraft, SpaceX will “de-orbit” these satellites to burn up in the atmosphere. </p>
<p>But atmospheric scientists are increasingly concerned that this sort of <a href="https://www.cbc.ca/radio/quirks/study-space-junk-pollution-1.7010373">apparent fly-tipping</a> by the space sector will cause further climate change down on Earth. One team recently, and unexpectedly, found <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10614211/">potential ozone-depleting metals</a> from spacecraft in the stratosphere, the atmospheric layer where the ozone layer is formed. </p>
<p>The relative “low earth orbit” where <a href="https://www.copernicus.eu/en/about-copernicus/infrastructure-overview/discover-our-satellites">satellites</a> monitoring Earth’s <a href="https://www.copernicus.eu/en">ecosystems</a> are found is increasingly congested – Starlink alone has more than 5,000 spacecraft in orbit. Clearing debris is therefore a priority for the space sector. Newly launched spacecraft must also be removed from orbit within 25 years (the US recently implemented a stricter <a href="https://www.fcc.gov/document/fcc-adopts-new-5-year-rule-deorbiting-satellites-0">five-year rule</a>) either by moving upwards to a so-called “graveyard orbit” or down into the Earth’s atmosphere. </p>
<p>Lower orbiting satellites are usually designed to use any remaining fuel and the pull of the Earth’s gravity to re-enter the atmosphere. In a controlled reentry, the spacecraft enters the atmosphere at a pre-set time to land in the most remote part of the Pacific Ocean at <a href="https://explorersweb.com/point-nemo-spacecraft-graveyard/">Point Nemo</a> (aka the spacecraft cemetery). In an uncontrolled re-entry, spacecraft are left to follow a “natural demise” and burn up in the atmosphere.</p>
<p>Nasa and the European Space Agency promote this form of disposal as part of a design philosophy called “design for demise”. It is an environmental challenge to build, launch and operate a satellite robust enough to function in the hostility of space yet also able to break up and burn up easily on re-entry to avoid dangerous debris reaching the Earth’s surface. It’s still a work in progress.</p>
<p>Satellite operators must prove their design and re-entry plans have a low “human-hit” rate before they are awarded a license. But there is limited concern regarding the impact on Earth’s upper atmosphere during the re-entry stage. This is not an oversight.</p>
<p>Initially, neither the space sector nor the astrophysics community considered burning up satellites on re-entry to be a serious environmental threat – to the atmosphere, at least. After all, the number of spacecraft particles released is small when compared with 440 tonnes of <a href="https://science.nasa.gov/solar-system/meteors-meteorites/">meteoroids</a> that enter the atmosphere daily, along with volcanic ash and human-made pollution from industrial processes on Earth.</p>
<h2>Bad news for the ozone layer?</h2>
<p>So are atmospheric climate scientists overreacting to the presence of spacecraft particles in the atmosphere? Their concerns draw on 40 years of research into the cause of the ozone holes above the south and north poles, that were first widely observed in the 1980s. </p>
<p>Today, they now know that ozone loss is caused by human-made <a href="https://gml.noaa.gov/hats/publictn/elkins/cfcs.html#:%7E:text=Chlorofluorocarbons%20(CFCs)%20are%20nontoxic%2C,as%20solvents%2C%20and%20as%20refrigerants.">industrial gases</a>, which combine with natural and very high altitude <a href="https://www.bas.ac.uk/data/our-data/publication/polar-stratospheric-clouds-satellite-observations-processes-and-role-in-ozone/">polar stratospheric clouds</a> or mother of pearl clouds. The surfaces of these ethereal clouds act as catalysts, turning benign chemicals into more active forms that can rapidly <a href="https://uk-air.defra.gov.uk/research/ozone-uv/moreinfo?view=arctic-ozone-hole">destroy ozone</a>.</p>
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<a href="https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Colourful cloud in night sky" src="https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577628/original/file-20240223-24-fpxid9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Mother of pearl cloud in the stratosphere above Norway.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/mother-pearl-cloud-norway-245-1849794832">Uwe Michael Neumann / shutterstock</a></span>
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<p>Dan Cziczo is an atmospheric scientist at Purdue University in the US, and a co-author of the recent study that found ozone depleting substances in the stratosphere. He explains to me that the question is whether the new particles from spacecraft will help the formation of these clouds and lead to ozone loss at a time when the Earth’s atmosphere is just <a href="https://theconversation.com/how-science-saved-the-ozone-layer-218839">beginning to recover</a>. </p>
<p>Of more concern to atmospheric scientists such as Cziczo is that only a few new particles could create more of these types of polar clouds – not only at the upper atmosphere, but also in the lower atmosphere, where cirrus clouds form. Cirrus clouds are the thin, wispy ice clouds you might spot high in the sky, above six kilometres. They tend to let heat from the sun pass through but then trap it on the way out, so in theory more cirrus clouds could add extra global warming on top of what we are already seeing from greenhouse gases. But this is uncertain and <a href="https://blogs.esa.int/campaignearth/2023/03/23/in-the-icy-mountains-of-norway-a-fons-researcher-is-studying-how-clouds-affect-global-warming/">still being studied</a>.</p>
<p>Cziczo also explains that from anecdotal evidence we know that the high-altitude clouds above the poles are changing – but we don’t know yet what is causing this change. Is it natural particles such as meteoroids or volcanic debris, or unnatural particles from spacecrafts? This is what we need to know.</p>
<h2>Concerned, but not certain</h2>
<p>So how do we answer this question? We have some research from atmospheric scientists, spacecraft builders and astrophysicists, but it’s not rigorous or focused enough to make informed decisions on which direction to take. Some astrophysicists claim that alumina (aluminium oxide) particles from spacecraft will cause chemical reactions in the atmosphere that <a href="https://www.space.com/starlink-satellite-reentry-ozone-depletion-atmosphere">will likely trigger ozone destruction</a>. </p>
<p>Atmospheric scientists who study this topic in detail have not made this jump as there isn’t enough scientific evidence. We know particles from spacecraft are in the stratosphere. But what this means for the ozone layer or the climate is still unknown.</p>
<p>It is tempting to overstate research findings to garner more support. But this is the path to research hell – and deniers will use poor findings at a later date to discredit the research. We also don’t want to use populist opinions. But we’ve also learnt that if we wait until indisputable evidence is available, it may be too late, as with the loss of ozone. It’s a constant dilemma.</p>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Fionagh Thomson has carried out consultancy work for the UK space agency. She is an elected member of the sustainability committees for the Royal Astronomical Society and the European Astronomical society. </span></em></p>We know particles from spacecrafts are in the stratosphere. But what this means for the ozone layer or the climate is still unknown.Fionagh Thomson, Senior Research Fellow (visual ethnographer), Durham UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2211542024-01-15T17:52:24Z2024-01-15T17:52:24ZCan technology clean up our air? An atmospheric scientist got a glimpse of the future<p>Every few years I visit CES (formerly the Consumer Electronics Show) in Las Vegas, a goliath event that is equal parts shameless spin and publicity, trade show and business conference. I’m an atmospheric scientist, and I want to get some insight into the technologies that might reduce our personal emissions in future.</p>
<p>In 2018, there was an explosion in interest in air-quality sensors alongside products aimed at cleaning air in the home. I wondered back then whether air filtration would gain traction in Europe and <a href="https://theconversation.com/air-purification-is-catching-on-but-it-may-be-doing-more-harm-than-good-111309">whether this was environmentally sustainable or socially equitable</a>. </p>
<p>That was in a pre-COVID world. While indoor air filters still aren’t ubiquitous, I see far more today than I’d have predicted in 2018. My futurologist skills are pretty poor.</p>
<p>All this matters because, thanks to various engineering successes, emissions of “traditional” air pollution particles from combustion (so-called PM2.5) in most rich countries are the lowest they’ve been in a <a href="https://royalsociety.org/topics-policy/projects/air-quality-climate-change/">century or more</a>. The key sources of air pollution are changing, vehicle emissions are improving and there are fewer large industrial emitters left to control.</p>
<p>Air pollution remains the largest global environmental factor that harms <a href="https://www.who.int/publications/i/item/9789240034228">public health</a>, but there is an increased focus on pollution in <a href="https://www.rcpch.ac.uk/resources/inside-story-health-effects-indoor-air-quality-children-young-people">day-to-day life</a> and what to do about it.</p>
<h2>An air-quality dimension to new tech</h2>
<p>CES involves a lot of walking because it is vast – seven miles on day one according to my smartwatch, six miles the next. Those miles deliver an endless stream of booths and stands offering new tech, large and small, and there is an air-quality dimension to a surprising number of them. </p>
<p>The first thing to note was the conspicuous absence of air-quality sensors, which haven’t quite delivered what was promised in 2018. This is probably due to a combination of continued accuracy issues of the sensors themselves, difficulty finding a niche in an often regulated marketplace, and the reality that just measuring pollution in lots of places and showing it on a nice website doesn’t directly make it any better.</p>
<p>Home air filtration is, however, still a major product sector and every appliance manufacturer has offerings – but these never really were “tech” in the first place. Indoor air cleaners remain pretty basic and any half-competent DIY-er could make their own. They’re just filter papers, a fan, a cheap particle counter, often now coupled with a dehumidifier to help reduce mould and spores indoors. For both combustion and biological particles they really can be effective if you can afford them. </p>
<p>There still aren’t convincing technological solutions to reducing indoor pollution from <a href="https://theconversation.com/common-products-like-perfume-paint-and-printer-ink-are-polluting-the-atmosphere-91914">“volatile organic compounds”, or VOCs</a>, however. These gases are released from personal care products, aerosol sprays, fires, candles, cooking, paints, glues, wood, furniture and many others. Modern energy-efficient buildings can have limited ventilation and often trap VOCs inside. Once they are in the air, they are difficult to collect and contain. </p>
<p>Some devices aim to oxidise VOCs to CO2 and water but this process may not be completely efficient and can <a href="https://news.mit.edu/2021/study-finds-indoor-air-cleaners-fall-short-removing-volatile-organic-compounds-1029">create byproducts</a> that are themselves harmful, such as formaldehyde. Technologies that removed the need to use VOCs in the first place would seem a simpler indoor air quality fix.</p>
<h2>Electrification means better air quality</h2>
<p>Electrification is everywhere at the consumer show, with the promise of phasing out fossil fuel burning from our lives. The pollution benefits of battery electric cars are now very well understood. </p>
<p>Perhaps more significant for the future will be the accumulating air quality benefits from replacing less visible polluting equipment – using heat pumps, solar and battery storage in place of gas and oil boilers, hydrogen fuel cells for trucks and backup generators, hydrogen engines for construction and farming, the list goes on. Compared to 2018, hydrogen is much more prominent, although accessing sufficient “green” supplies is another story.</p>
<p>Vehicle autonomy has been a part of CES for years but fully self-driving cars still seem some way off (or appear so to a complete non-expert like me). There is, however, growing <a href="https://secureenergy.org/savs-sf-case-study/">evidence</a> that using more autonomy could have a direct air quality benefit since it is aggressive stop-start driving that wears out tyres and suspends tiny polluting particles from the road into the air. </p>
<p>This could be reduced by smoother driving that is synchronised with nearby vehicles and urban traffic management, taking heavy-footed humans out of the equation. </p>
<p>Then come more distant transport technologies that might never come to pass – electric drones for everything, from food deliveries to air taxis for people, all displacing combustion-driven road vehicles.</p>
<p>I’m a technology enthusiast and came away with an optimistic view of the air pollution future. But I’m not naive and know that CES is ultimately about selling us stuff. </p>
<p>While it’s far less glitzy we can also get cleaner air by simply consuming less. It sounds (and is) simple, but I’m sure I’m not alone in feeling conflicted when offered different options. The latest mobile app-driven AI-guided e-scooter journey creates less urban air pollution than using a diesel car, but for those that can, it will always be cheaper and healthier just to walk.</p><img src="https://counter.theconversation.com/content/221154/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alastair Lewis is part of the National Centre for Atmospheric Science and receives funding from various UKRI schemes for research in areas associated with air pollution and atmospheric chemistry. He is currently a Royal Society Industry Fellow collaborating with Givaudan AG on consumer product impacts on air quality. He is Chair of the Defra Air Quality Expert Group and Department for Transport Science Advisory Council, however this article is written in a personal capacity.</span></em></p>A surprising number of new consumer tech products promise to improve air quality.Alastair Lewis, Professor of Atmospheric Chemistry at the National Centre for Atmospheric Science and University of York, University of YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2153952023-10-12T12:30:45Z2023-10-12T12:30:45ZWhat is a strong El Niño? Meteorologists anticipate a big impact in winter 2023-2024, but the forecasts don’t all agree<figure><img src="https://images.theconversation.com/files/553361/original/file-20231011-29-363wak.png?ixlib=rb-1.1.0&rect=32%2C873%2C3211%2C2058&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The El Niño pattern stands out in the warm sea surface temperature anomalies in the Pacific in 2023</span> <span class="attribution"><a class="source" href="https://www.climate.gov/maps-data/data-snapshots/data-source/sst-enso-region-monthly-difference-average">NOAA Climate.gov</a></span></figcaption></figure><p><em>Meteorologists have been talking for weeks about <a href="https://www.accuweather.com/en/winter-weather/us-winter-forecast-for-the-2023-2024-season/1583853">a snowy season ahead</a> in the southern Rockies and the Sierra Nevada. They anticipate <a href="https://www.powder.com/trending-news/el-nino-huge-snow-east">more storms</a> in the U.S. South and Northeast, and warmer, drier conditions across the already dry Pacific Northwest and the upper Midwest.</em></p>
<p><em>One phrase comes up repeatedly with these projections: <a href="https://www.wcpo.com/weather/weather-101/a-strong-el-nino-expected-this-winter-heres-what-that-means-for-our-weather">a strong El Niño</a> is coming.</em></p>
<p><em>It sounds ominous. But what does that actually mean? We asked <a href="https://scholar.google.com/citations?user=z7CXcXkAAAAJ&hl=en">Aaron Levine</a>, an atmospheric scientist at the University of Washington whose research focuses on El Niño.</em></p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wVlfyhs64IY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NOAA explains in animations how El Niño forms.</span></figcaption>
</figure>
<h2>What is a strong El Niño?</h2>
<p>During a normal year, the warmest sea surface temperatures are in the western Pacific and the Indian Ocean, in what’s known as the <a href="https://doi.org/10.1186/s40562-016-0054-3">Indo-Western Pacific warm pool</a>.</p>
<p>But every few years, the trade winds that blow from east to west weaken, allowing that warm water to slosh eastward and <a href="https://www.pmel.noaa.gov/elnino/schematic-diagrams">pile up along the equator</a>. The warm water causes the air above it to warm and rise, fueling precipitation in the central Pacific and shifting atmospheric circulation patterns across the basin.</p>
<p>This pattern is <a href="https://www.pmel.noaa.gov/elnino/what-is-el-nino">known as El Niño</a>, and it can <a href="https://www.climate.gov/media/13628">affect weather around the world</a>.</p>
<figure class="align-center ">
<img alt="An animation shows how warm water builds up along the equator off South America. The box where temperatures are measured is south of Hawaii." src="https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=272&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=272&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=272&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=342&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=342&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=342&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The box shows the Niño 3.4 region as El Niño begins to develop in the tropical Pacific, from January to June 2023.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>A strong El Niño, in the most basic definition, occurs once the average sea surface temperature in the equatorial Pacific is at least 1.5 degrees Celsius (2.7 Fahrenheit) warmer than normal. It’s measured in an imaginary box along the equator, roughly south of Hawaii, known as the <a href="https://svs.gsfc.nasa.gov/4695">Nino 3.4 Index</a>.</p>
<p>But El Niño is a coupled ocean-atmosphere phenomenon, and the atmosphere also plays a crucial role.</p>
<p>What has been surprising about this year’s El Niño – and still is – is that the atmosphere hasn’t responded as much as we would have expected based on the rising sea surface temperatures.</p>
<h2>Is that why El Niño didn’t affect the 2023 hurricane season the way forecasts expected?</h2>
<p>The 2023 Atlantic hurricane season is a good example. Forecasters often use El Niño as a predictor of <a href="https://www.weather.gov/ilx/swop-springtopics">wind shear</a>, which can tear apart Atlantic hurricanes. But with the atmosphere not responding to the warmer water right away, the impact on Atlantic hurricanes was lessened and it turned out to be a <a href="https://www.nytimes.com/article/tropical-storm-sean-hurricane.html">busy season</a>.</p>
<p><a href="https://doi.org/10.1175/JCLI-D-12-00097.1">The atmosphere is what transmits El Niño’s impact</a>. Heat from the warm ocean water causes the air above it to warm and rise, which fuels precipitation. That air sinks again over cooler water. </p>
<p>The rising and sinking creates giant loops in the atmosphere <a href="https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy">called the Walker Circulation</a>. When the warm pool’s water shifts eastward, that also shifts where the rising and sinking motions happen. The atmosphere reacts to this change like ripples in a pond when you throw a stone in. These ripples affect the jet stream, which steers weather patterns in the U.S.</p>
<p>This year, in comparison with other large El Niño events – such as <a href="https://www.climate.gov/news-features/blogs/enso/united-states-el-ni%C3%B1o-impacts-0">1982-83, 1997-98</a> and <a href="https://www.climate.gov/news-features/understanding-climate/2015-state-climate-el-ni%C3%B1o-came-saw-and-conquered">2015-16</a> – we’re not seeing the same change in where the precipitation is happening. It’s taking much longer to develop, and it’s not as strong.</p>
<p>Part of that, presumably, is related to the whole tropics being very, very warm. But <a href="https://doi.org/10.1029/2019GL086182">this is still an emerging field of research</a>.</p>
<p>How El Niño will change with global warming is a big and open question. El Niño <a href="https://www.climate.gov/news-features/understanding-climate/climate-variability-oceanic-nino-index">only happens every few years</a>, and there’s a fair amount of variability between events, so just getting a baseline is tough.</p>
<h2>What does a strong El Niño typically mean for US weather?</h2>
<p>During <a href="https://www.climate.gov/enso">a typical El Niño winter</a>, the U.S. South and Southwest are cooler and wetter, and the Northwest is warmer and drier. The upper Midwest tends to be drier, while the Northeast tends to be a little wetter. </p>
<p>The likelihood and the intensity generally scale with the strength of the El Niño event.</p>
<p>El Niño has traditionally been good for the mountain snowpack in California, which the state relies for a large percentage of its water. But it is often not so good for the Pacific Northwest snowpack.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two maps showing wetter, cooler weather in the Southeast and drier warmer air in the north during El Nino." src="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=834&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=834&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=834&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1047&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1047&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1047&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The jet stream takes a very different path in a typical El Niño vs. La Niña winter weather pattern. But these patterns have a great deal of variability. Not every El Niño or La Niña year is the same.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/media/14484">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>The <a href="https://www.climate.gov/news-features/featured-images/how-el-ni%C3%B1o-and-la-ni%C3%B1a-affect-winter-jet-stream-and-us-climate">jet stream plays a role</a> in that shift. When the polar jet stream is either displaced very far northward or southward, storms that would normally move through Washington or British Columbia are steered to California and Oregon instead.</p>
<h2>What do the forecasts show for the months ahead?</h2>
<p>Whether forecasters think a strong El Niño will develop depends on whose forecast model they trust.</p>
<p>This past spring, the <a href="https://www.weather.gov/media/climateservices/NWS%20Climate%20Forecast%20and%20Tools.pdf">dynamical forecast models</a> were <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table">already very confident</a> about the potential for a strong El Niño developing. These are big models that solve basic physics equations, starting with current oceanic and atmospheric conditions. </p>
<p>However, statistical models, which use statistical predictors of El Niño calculated from historical observations, were less certain.</p>
<p>Even in the <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table">most recent forecast model outlook</a>, the dynamical forecast models were predicting a stronger El Niño than the statistical models were.</p>
<p>If you go by just a sea surface temperature-based El Niño index, the forecast is for a fairly strong El Niño. </p>
<p>But the indices that incorporate the atmosphere are not responding in the same way. We’ve seen <a href="https://psl.noaa.gov/enso/enso.current.html">atmospheric anomalies</a> – as measured by cloud height monitored by satellites or sea-level pressure at monitoring stations – on and off in the Pacific since May and June, <a href="https://images.theconversation.com/files/553327/original/file-20231011-15-kprvx9.png">but not in a very robust fashion</a>. Even in September, they were nowhere near as large as they were in 1982, in terms of overall magnitude.</p>
<p>We’ll see if the atmosphere catches up by wintertime, when El Niño peaks.</p>
<h2>How long do El Niños last?</h2>
<p>Often during El Niño events – particularly strong El Niño events – the sea surface temperature anomalies collapse really quickly during the Northern Hemisphere spring. Almost all end in April or May.</p>
<p>One reason is that El Niño sows the seeds of its own demise. When El Niño happens, it <a href="https://doi.org/10.1175/1520-0469(1997)054%3C0811:AEORPF%3E2.0.CO;2">uses up that warm water</a> and the warm water volume shrinks. <a href="https://doi.org/10.1175/1520-0442(2000)013%3C3551:OOWWVC%3E2.0.CO;2">Eventually, it has eroded its fuel</a>.</p>
<p><iframe id="aOiS8" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/aOiS8/14/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The surface can stay warm for a while, but once the heat from the subsurface is gone and the trade winds return, the El Niño event collapses. At the end of past El Niño events, the sea surface anomaly dropped very fast and we saw conditions typically switch to La Niña – El Niño’s cooler opposite.</p><img src="https://counter.theconversation.com/content/215395/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aaron Levine receives funding from NOAA and has received funding in the past from the National Research Council. He is a member of the American Geophysical Union </span></em></p>An atmospheric scientist explains how El Niño works, this year’s oddities and why this phenomenon doesn’t last long.Aaron Levine, Atmospheric Research Scientist, CICOES, University of WashingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2137242023-09-19T12:18:13Z2023-09-19T12:18:13ZAs extreme downpours trigger flooding around the world, scientists take a closer look a global warming’s role<p>Torrential downpours sent muddy water racing through streets in <a href="https://www.washingtonpost.com/world/2023/09/14/libya-flood-death-toll-derna-news/">Libya</a>, <a href="https://twitter.com/WxNB_/status/1699014872015479212">Greece</a> and <a href="https://www.theguardian.com/world/2023/sep/05/boy-rescued-from-flood-waters-after-record-heavy-rain-in-spain">Spain</a> and flooded parts of <a href="https://www.straitstimes.com/asia/east-asia/hong-kong-hit-with-heavy-rain-flooding-days-after-typhoon">Hong Kong</a> and <a href="https://www.nytimes.com/2023/09/29/nyregion/nyc-flooding-video-photo.html">New York City</a> in September 2023. Thousands of people died in the city of Derna, Libya. Zagora, Greece, saw a record 30 inches of rain, the equivalent of <a href="https://public.wmo.int/en/media/news/storm-daniel-leads-extreme-rain-and-floods-mediterranean-heavy-loss-of-life-libya">a year and a half of rain falling in 24 hours</a>.</p>
<p>A few weeks earlier, monsoon rains triggered deadly landslides and flooding in <a href="https://www.youtube.com/watch?v=8VMBIlKjuKg">the Himalayas</a> that <a href="https://www.pbs.org/newshour/world/heavy-rain-landslides-have-killed-at-least-72-people-this-week-in-indias-himalayas">killed dozens of people</a> in India.</p>
<p>After severe flooding on almost every continent this year, including <a href="https://theconversation.com/epic-snow-from-all-those-atmospheric-rivers-in-the-west-is-starting-to-melt-and-the-flood-danger-is-rising-203874">mudslides and flooding in California</a> in early 2023 and devastating <a href="https://theconversation.com/how-climate-change-intensifies-the-water-cycle-fueling-extreme-rainfall-and-flooding-the-northeast-deluge-was-just-the-latest-209476">floods in Vermont and New York</a> in July, it can seem like extreme rainfall is becoming more common.</p>
<p>So, what role does global warming play in this? And importantly, what can we do to adapt to this new reality?</p>
<figure class="align-center ">
<img alt="A man and woman sit on a park bench with water up to the man's knees. The woman is sitting on the chair back. A car in the street is flooded up to the roof." src="https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544111/original/file-20230822-17-ybv7br.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A powerful storm system in 2023 flooded communities across Vermont and left large parts of the capital, Montpelier, underwater.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/michelle-whitehouse-and-her-husband-will-whitehouse-from-news-photo/1526471468">John Tully for The Washington Post via Getty Images</a></span>
</figcaption>
</figure>
<p>As a <a href="https://clasp.engin.umich.edu/people/mohammed-ombadi/">climate scientist</a> with a background in civil engineering, I am interested in exploring the links between the science of climate change and extreme weather events on one hand and the impacts those events have on our daily lives on the other. Understanding the connections is crucial in order to develop sound strategies to adapt to climate change.</p>
<h2>Thirstier atmosphere, more extreme precipitation</h2>
<p>As temperatures rise, the warmer atmosphere can <a href="https://sealevel.jpl.nasa.gov/ocean-observation/understanding-climate/air-and-water/">hold more water vapor</a>. Evaporation of water from land and oceans also increases. That water has to eventually come back to land and oceans. </p>
<p>Simply, as the atmosphere absorbs more moisture, it dumps more precipitation during storms. Scientists expect about a <a href="https://science2017.globalchange.gov/chapter/7/">7% increase</a> in precipitation intensity during extreme storms for every 1 degree Celsius (1.8 degrees Fahrenheit) of warming. </p>
<p>This increase in the amount of moisture that air can hold is what scientists call the <a href="https://doi.org/10.1073/pnas.2304077120">Clausius Clapeyron relationship</a>. But other factors, such as changes in wind patterns, <a href="https://doi.org/10.1073/pnas.2304077120">storm tracks and how saturated the air is</a>, also play a role in how intense the precipitation is.</p>
<h2>Liquid vs. frozen: Rain matters most</h2>
<p>One factor that determines the severity of floods is whether water falls as rain or snow. The almost instantaneous runoff from rain, as opposed to the slower release of water from melting snow, leads to more severe flooding, landslides and other hazards – particularly in mountain regions and areas downstream, where about a quarter of the global population lives. </p>
<p>A higher proportion of extreme rainfall rather than snow is believed to have been a key contributor to the <a href="https://www.bbc.com/news/world-asia-india-66519698">devastating floods and landslides in the Himalayas</a> in August 2023, though research is still underway to confirm that. Additionally, a <a href="https://doi.org/10.1029/2019WR025571">2019 examination of flood patterns</a> across 410 watersheds in the Western U.S. found that the largest runoff peaks driven by rainfall were more than 2.5 times greater than those driven by snowmelt.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Maps show the US and other regions of the Northern Hemisphere with rising rainfall intensity. Western North America and the Himalayas stand out" src="https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548585/original/file-20230915-29-73yoeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Rainfall intensity is projected to increase more in certain regions by the end of the 21st century, based on climate model data. Light colors show a twofold increase and dark colors indicate an eightfold increase in future rainfall extremes compared to the recent past.</span>
<span class="attribution"><span class="source">Mohammed Ombadi.</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In a <a href="https://doi.org/10.1038/s41586-023-06092-7">2023 study in the journal Nature</a>, my colleagues and I demonstrated that the intensity of extreme precipitation is increasing at a faster rate than the Clausius Clapeyron relationship would suggest – up to 15% per 1 C (1.8 F) of warming – in high-latitude and mountain regions such as the Himalayas, Alps and Rockies.</p>
<p>The reason for this amplified increase is that rising temperatures are shifting precipitation toward more rain and less snow in these regions. A larger proportion of this extreme precipitation is falling as rain.</p>
<p>In our study, we looked at the heaviest rains in the Northern Hemisphere since the 1950s and found that the increase in the intensity of extreme rainfall varied with altitude. Mountains in the American West, parts of the Appalachian Mountains, the Alps in Europe and the Himalayas and Hindu Kush mountains in Asia also showed strong effects. Furthermore, climate models suggest that most of these regions are likely to see a sevenfold-to-eightfold increase in the occurrence of extreme rainfall events by the end of the 21st century.</p>
<h2>Flooding isn’t just a short-term problem</h2>
<p>Deaths and damage to homes and cities capture the lion’s share of attention in the aftermath of floods, but increased flooding also has long-term effects on water supplies in reservoirs that are crucial for communities and agriculture in many regions. </p>
<p>For example, in the Western U.S., reservoirs are often kept as close to full capacity as possible during the spring snowmelt to provide water for the dry summer months. The mountains act as natural reservoirs, storing winter snowfall and then releasing the melted snow at a slow pace.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=419&fit=crop&dpr=1 600w, https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=419&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=419&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=527&fit=crop&dpr=1 754w, https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=527&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/548589/original/file-20230915-27-tbcn9v.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=527&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A series of atmospheric rivers in California dumped so much water on the region that Tulare Lake, which had dried up years earlier, reemerged as water spread across miles of California farmland.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/agribusiness-consultant-mark-grewel-stands-on-a-farm-road-news-photo/1249529651">Luis Sinco / Los Angeles Times via Getty Images</a></span>
</figcaption>
</figure>
<p>However, <a href="https://doi.org/10.1038/s41586-023-06092-7">our recent findings</a> suggest that with the world rapidly shifting toward a climate dominated by heavy downpours of rain – not snow – water resource managers will increasingly have to leave more room in their reservoirs to store large amounts of water in anticipation of disasters to minimize the risk of flooding downstream.</p>
<h2>Preparing for a fiercer future</h2>
<p>Global efforts to reduce greenhouse gas emissions have been increasing, but people still need to prepare for a fiercer climate. The destructive <a href="https://public.wmo.int/en/media/news/storm-daniel-leads-extreme-rain-and-floods-mediterranean-heavy-loss-of-life-libya">storms that hit the Mediterranean region</a> in 2023 provide a cogent case for the importance of adaptation. They shattered records for extreme precipitation across many countries and caused extensive damage.</p>
<p>A main factor that contributed to the catastrophe in Libya was the <a href="https://theconversation.com/libya-dam-collapse-happened-because-of-bad-management-not-bad-weather-213546">bursting of aging dams</a> that had managed water pouring down from <a href="https://www.washingtonpost.com/world/2023/09/12/deadly-libya-flooding-cause/">mountainous terrain</a>.</p>
<p>This underscores the importance of updating design codes so infrastructure and buildings are built to survive future downpours and flooding, and investing in new engineering solutions to improve resiliency and protect communities from extreme weather. It may also mean <a href="https://theconversation.com/managed-retreat-done-right-can-reinvent-cities-so-theyre-better-for-everyone-and-avoid-harm-from-flooding-heat-and-fires-163052">not building in regions</a> with high future risks of flooding and landslides.</p>
<p><em>This article, originally published Sept. 19, 2023, has been updated with flooding in New York City.</em></p><img src="https://counter.theconversation.com/content/213724/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mohammed Ombadi has received funding from Lawrence Berkeley National Laboratory to conduct the Nature study discussed in this article. </span></em></p>There’s a rule of thumb that rainfall intensity increases by about 7% per degree Celsius as temperatures rise. But the increase is much higher in the mountains, scientists found.Mohammed Ombadi, Assistant Professor of Climate and Space Sciences Engineering, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2047292023-05-30T21:47:09Z2023-05-30T21:47:09ZEarth’s energy budget is not in balance. Should we be concerned?<figure><img src="https://images.theconversation.com/files/523917/original/file-20230502-22-r5mboa.jpg?ixlib=rb-1.1.0&rect=2%2C4%2C995%2C655&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Human activity, through the emission of greenhouse gases, has caused the Earth's energy imbalance.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>A recent <a href="https://library.wmo.int/index.php?lvl=notice_display&id=22265#.ZEEef-xBzjC">report from the World Meteorological Organization</a> about the state of the climate indicates that the global mean temperature in 2022 was 1.15°C above the 1850-1900 (preindustrial reference period) average. Moreover, the last eight years have been the warmest since the beginning of instrumental temperature records 173 years ago.</p>
<p>In other words, the climate system has been out of balance for several decades.</p>
<p>As an expert in atmospheric science, I aim to shed light on Earth’s energy imbalance and its consequences for humankind.</p>
<h2>Earth’s energy imbalance</h2>
<p>Solar radiation is virtually <a href="https://www.weather.gov/jetstream/energy">Earth’s only energy source</a>, the other energy sources – such as Earth’s interior heat and tidal energy – being negligible. The Earth reflects around 30 per cent of the solar radiation and emits radiation towards space.</p>
<p>The <a href="https://meteofrance.com/comprendre-climat/monde/leffet-de-serre">greenhouse gases</a> (carbon dioxide, methane) let solar radiation pass, but not the radiation emitted by the Earth, thus trapping this energy. Earth’s near-surface temperature, which is 15°C, would be around -19°C without the greenhouse effect.</p>
<p>If the difference between the incoming energy – solar radiation – and outgoing energy – the sum of the solar radiation reflected by the Earth and the radiation emitted by the Earth – is not equal to zero, as is the case currently, we refer to this as <a href="https://essd.copernicus.org/articles/12/2013/2020/">Earth Energy Imbalance</a> (EEI).</p>
<p>It is <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf">human activity</a>, through the emission of greenhouse gases (generating an additional greenhouse effect), that has caused the Earth energy imbalance.</p>
<p>But where does the excess energy accumulate? It accumulates under the form of heat in the different components of the climate system (atmosphere, land, hydrosphere, cryosphere, biosphere). And this is what explains why the Earth is warming, or more globally, climate change.</p>
<h2>The ocean, heat accumulator</h2>
<p>Assessing the <a href="https://essd.copernicus.org/articles/12/2013/2020/">Earth heat inventory</a> through an international effort is essential to better understand the impact of Earth’s energy imbalance on the climate system.</p>
<p>Such an inventory corresponding to the period 1960-2020 has been provided by a <a href="https://essd.copernicus.org/articles/15/1675/2023/">recently published study</a>. This study shows that the Earth system has been accumulating heat since 1971. Moreover, the rate of heat accumulation corresponding to the period 2006-2020 is higher than that corresponding to 1971-2020. Most of the excess heat is stored in the ocean (89 per cent), mainly in the upper ocean (0-700 metres in depth). The rest of the excess heat is stored in the land (six per cent) and the atmosphere (one per cent), and has led to the melting of the components of the cryosphere – glaciers, ice sheets and sea ice (four per cent).</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=510&fit=crop&dpr=1 600w, https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=510&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=510&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=641&fit=crop&dpr=1 754w, https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=641&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/523506/original/file-20230429-26-xurb6x.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=641&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Earth heat inventory showing the percentage of heat stored in the different components of the climate system for the periods 2006-2020 and 1971-2020, as well as the total heat gain over the period 1971-2020.</span>
<span class="attribution"><span class="source">Schuckmann et al., 2023</span></span>
</figcaption>
</figure>
<p>In addition to storing excess heat, the ocean is also an important <a href="https://www.ncei.noaa.gov/news/quantifying-ocean-carbon-sink">CO₂ sink</a>, thus playing an essential role in the regulation of the climate. However, <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf">the ocean will become less efficient at capturing CO₂</a> with the increase in the cumulative emissions of this gas. Why? Because of the positive feedback between the ocean warming and the decrease in the capacity of the oceans to absorb CO₂.</p>
<p>Unfortunately, the current state of the ocean is concerning. In 2022, <a href="https://library.wmo.int/index.php?lvl=notice_display&id=22265#.ZEEef-xBzjC">the ocean heat content reached a record high</a>, and 58 per cent of the ocean surface experienced at least one marine heatwave. Since mid-March this year, the <a href="https://climatereanalyzer.org/clim/sst_daily/">mean ocean surface temperature</a> is the highest ever observed since the beginning of the satellite era. Among other negative impacts on the marine ecosystems, marine heatwaves cause <a href="https://oceanservice.noaa.gov/facts/coral_bleach.html">coral bleaching</a> events.</p>
<h2>The consequences of the imbalance</h2>
<p>Global warming has negative impacts on humanity and ecosystems, as the recently published <a href="https://www.ipcc.ch/report/ar6/syr/">Synthesis Report</a> of the Intergovernmental Panel on Climate Change (IPCC) reminds us. This report warns that, currently, between 3.3 and 3.6 billion people live in contexts that are very vulnerable to global warming.</p>
<p>The people who live in coastal areas are particularly affected. The risk of coastal floods increases with sea level rise, which is mainly due to the thermal expansion of the ocean and the melting of the land ice of glaciers and of the Antarctic and Greenland <a href="https://theconversation.com/the-antarctic-ice-sheet-is-melting-and-this-is-bad-news-for-humanity-200972">ice sheets</a>. To provide some numbers, the contributions of the ocean thermal expansion and of the land ice melting to <a href="https://library.wmo.int/index.php?lvl=notice_display&id=22265#.ZEEef-xBzjC">sea level rise</a> were, respectively, 55 per cent and 36 per cent for the period 2005-2019.</p>
<p>Global warming is not just a threat to our physical health, but also to our <a href="https://eos.org/features/the-mental-toll-of-climate-change?utm_campaign=ealert">mental health</a>. In effect, sudden-onset events (e.g., hurricanes, storms) can cause trauma. Changes in the climate variables (e.g., drought) can generate a sense of uncertainty. And the awareness of climate change can cause climate anxiety.</p>
<p>This goes to show that the imbalance of the climate system can lead to our own imbalance.</p>
<p>Given the numerous warnings from the scientific community about the harmful consequences of climate change for our societies, we may wonder: Could global warming lead to the collapse of society at a global scale, or even to the extinction of the human being?</p>
<p>Unfortunately, this subject has not received all the attention it deserves. Luke Kemp, researcher at the Centre for the Study of Existential Risk at the University of Cambridge, and his colleagues, have suggested a research agenda with the evocative name “<a href="https://www.pnas.org/doi/10.1073/pnas.2108146119">Climate Endgame</a>.”</p>
<h2>Win-win solution: Net zero emission</h2>
<p>Let’s go back to the origin of the problem: The Earth will continue to warm as long as this energy imbalance persists. Since human-caused emissions are responsible for Earth’s energy imbalance, the solution is, in principle, simple: emissions must be reduced to zero.</p>
<p>What can we do at an individual level? We can <a href="https://davidsuzuki.org/what-you-can-do/four-places-cut-carbon/">reduce our contribution to climate change</a> by using active transportation (walking, biking), by consuming less meat and dairy products, by reducing food waste, and by improving the energy efficiency of our homes, among other actions.</p>
<p>Hence, the climate game is not over. It is up to us to decide whether we want to solve the climate crisis.</p>
<p>But the window of opportunity is quickly closing…</p><img src="https://counter.theconversation.com/content/204729/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marta Moreno Ibáñez has received an excellence scholarship from the Trottier Family Foundation.</span></em></p>An expert in atmospheric science sheds light on Earth’s energy imbalance and its consequences for humankind.Marta Moreno Ibáñez, PhD candidate in Earth and atmospheric sciences, Université du Québec à Montréal (UQAM)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2049752023-05-04T14:25:46Z2023-05-04T14:25:46ZCloud seeding can increase rain and snow, and new techniques may make it a lot more effective – podcast<figure><img src="https://images.theconversation.com/files/524204/original/file-20230503-19-bx8o26.jpg?ixlib=rb-1.1.0&rect=418%2C594%2C6930%2C4308&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cloud seeding can increase rainfall and reduce hail damage to crops, but its use is limited.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/colorado-supercell-royalty-free-image/1303884216?phrase=Rain+storm&adppopup=true">John Finney Photography/Moment via Getty Images</a></span></figcaption></figure><p>When an unexpected rainstorm leaves you soaking wet, it is an annoyance. When a drought leads to fires, crop failures and water shortages, the significance of weather becomes vitally important.</p>
<p>If you could control the weather, would you?</p>
<p>Small amounts of rain can mean the difference between struggle and success. For <a href="https://climateviewer.com/2014/03/25/history-cloud-seeding-pluviculture-hurricane-hacking/">nearly 80 years</a>, an approach called cloud seeding has, in theory, given people the ability to get more rain and snow from storms and make hailstorms less severe. But only recently have scientists been able to peer into clouds and begin to understand how effective cloud seeding really is.</p>
<p>In this episode of “The Conversation Weekly,” we speak with three researchers about the simple yet murky science of cloud seeding, the economic effects it can have on agriculture, and research that may allow governments to use cloud seeding in more places.</p>
<iframe src="https://embed.acast.com/60087127b9687759d637bade/64536722a66d2600116de8f4" frameborder="0" width="100%" height="190px"></iframe>
<p><iframe id="tc-infographic-561" class="tc-infographic" height="100" src="https://cdn.theconversation.com/infographics/561/4fbbd099d631750693d02bac632430b71b37cd5f/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p><a href="https://scholar.google.com/citations?user=BSQl42wAAAAJ&hl=en&oi=ao">Katja Friedrich</a>, a professor of atmospheric and oceanic sciences at the University of Colorado, Boulder in the U.S., is a leading researcher on cloud seeding. “When we do cloud seeding, we are looking for clouds that have tiny super-cooled liquid droplets,” she explains. Silver iodide is very similar in structure to an ice crystal. When the droplets touch a particle of silver iodide, “they freeze, then they can start merging with other ice crystals, become snowflakes and fall out of the cloud.”</p>
<p>While the process is fairly straightforward, measuring how effective it is in the real world is not, according to Friedrich. “The problem is that once we modify a cloud, it’s really difficult to say what would’ve happened if you hadn’t cloud-seeded.” It’s hard enough to predict weather without messing with it artificially. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plane wing with a cylindrical device attached." src="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=370&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=370&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=370&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=465&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=465&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=465&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cloud seeding is usually done by planes equipped with devices – like the one attached to the wing of this plane – that spray silver iodide into the atmosphere.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Cloud_seeding#/media/File:Hagelflieger-EDTD.jpg">Zuckerle/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In 2017, Friedrich’s research group had a breakthrough in measuring the effect of cloud seeding. “We flew some aircraft, released silver iodide and generated these clouds that were like these six exact lines that were downstream of where the aircraft were seeding,” she says. They then had a second aircraft fly through the clouds. “We could actually <a href="https://doi.org/10.1073/pnas.1716995115">quantify how much snow we could produce</a> by two hours of cloud seeding.” That effect, according to research on cloud seeding, is an increase in precipitation of somewhere around 5% to 20% or 30%, depending on conditions.</p>
<p>Measuring the effect on precipitation – whether rain or snow – directly may have taken complex science and a bit of luck, but in places that have been using cloud seeding for long periods of time, the economic benefits are shockingly clear. </p>
<p><a href="https://www.ndsu.edu/agriculture/ag-home/directory/dean-bangsund">Dean Bangsund</a> is a researcher at North Dakota State University who studies the economics of agriculture. “We have a high amount of hail damage in North Dakota,” said Bangsund. For decades, the state government has been using cloud seeding to reduce hail damage, as cloud seeding leads to the formation of more pieces of smaller hail compared to fewer pieces of larger hail. “It doesn’t 100% eliminate hail; it’s designed to soften the impact.”</p>
<p>Every 10 years, the state of North Dakota does an <a href="https://www.cabdirect.org/cabdirect/abstract/20193399635">analysis on the economic impacts of the cloud seeding</a> program, measuring both reduction in hail damage and benefits from increased rain. Bangsund led the last report and says that for every dollar spent on the cloud seeding program, “we are looking at something that is anywhere from $8 or $9 in benefit on the really lowest scale, up to probably $20 of impact per acre.” With millions of acres of agricultural fields in the cloud seeding area, that is a massive economic benefit.</p>
<p>Both Freidrich and Bangsund emphasized that cloud seeding, while effective in some cases, cannot be used everywhere. There is also a lot of uncertainty in how much of an effect it has. One way to improve the effectiveness and applicability of cloud seeding is by improving the seed. <a href="https://scholar.google.com/citations?view_op=list_works&hl=en&hl=en&user=OxrNpiEAAAAJ&sortby=pubdate">Linda Zou</a> is a professor of civil infrastructure and environmental engineering at Khalifa University in the United Arab Emirates. </p>
<p>Her work has focused on developing a replacement for silver iodide, and her lab has <a href="https://www.technologyreview.com/2022/03/28/1048275/scientists-advance-cloud-seeding-capabilities-with-nanotechnology/">developed what she calls a nanopowder</a>. “I start with table salt, which is sodium chloride,” says Zou. “This desirable-sized crystal is then coated with a thin nanomaterial layer of titanium dioxide.” When salt gets wet, it melts and forms a droplet that can efficiently merge with other droplets and fall from a cloud. Titanium dioxide attracts water. Put the two together and you get a very effective cloud-seeding material. </p>
<p>From indoor experiments, Zou found that “with the nanopowders, there are 2.9 times the formation of larger-size water droplets.” These nanopowders can also form ice crystals at warmer temperatures and less humidity than silver iodide. </p>
<p>As Zou says, “if the material you are releasing is more reactive and can work in a much wider range of conditions, that means no matter when you decide to use it, the chance of success will be greater.”</p>
<hr>
<p>This episode was written and produced by Katie Flood. Mend Mariwany is the executive producer of The Conversation Weekly. Eloise Stevens does our sound design, and our theme music is by Neeta Sarl.</p>
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<hr><img src="https://counter.theconversation.com/content/204975/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>None of the interviewees work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p><p class="fine-print"><em><span> </span></em></p>Cloud seeding – spraying materials into clouds to increase precipitation – has been around for nearly 80 years. But only recently have scientists been able to measure how effective it really is.Daniel Merino, Associate Science Editor & Co-Host of The Conversation Weekly Podcast, The ConversationNehal El-Hadi, Science + Technology Editor & Co-Host of The Conversation Weekly Podcast, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2029522023-04-24T12:24:51Z2023-04-24T12:24:51ZCan rainbows form in a circle? Fun facts on the physics of rainbows<figure><img src="https://images.theconversation.com/files/521644/original/file-20230418-20-88ojk7.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C8959%2C5547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The higher your vantage point, the more likely you’ll see more of the rainbow’s circle. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/double-rainbow-hangs-in-the-sky-above-buildings-and-the-news-photo/1405823752">Chen Hui/VCG via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>Can rainbows form in a circle? – Henry D., age 7, Cambridge, Massachusetts</strong></p>
</blockquote>
<hr>
<p>The legend goes that there is a pot of gold hidden at the end of every rainbow. But is there really an “end” to a rainbow, and can we ever get to it?</p>
<p>Most us go through life seeing rainbows only as arches of color in the sky, but that’s only half of what is really a circle of color.</p>
<p>Normally, when you look at a rainbow, the Earth’s horizon in front of you hides the bottom half of the circle. But if you are standing on a mountain where you can see both above and below you, and the sun is behind you and it is misty or has just rained, chances are good that you will see more of the rainbow’s circle.</p>
<figure class="align-center ">
<img alt="A rainbow in the mist below a waterfall in Iceland." src="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&rect=0%2C52%2C5000%2C3270&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521643/original/file-20230418-23-n2b6wd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">How full this rainbow looks depends in part on how high up you’re standing while watching sunlight hit the waterfall’s mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/iceland-south-coast-skogarfoss-waterfall-rainbow-news-photo/452271798">Wolfgang Kaehler/LightRocket via Getty Images</a></span>
</figcaption>
</figure>
<p>To see the full circle, however, you will have to be in an airplane, literally above the clouds. Or you could create your own rainbow. I am <a href="https://www.uml.edu/Honors/People/chowdhury-partha.aspx">a physicist</a>, and I’ll explain how to do that in a minute.</p>
<h2>How a rainbow forms</h2>
<p><a href="https://scijinks.gov/rainbow/">Rainbows form</a> when sunlight from behind you hits millions of tiny round water droplets in front of you and bounces back to your eyes.</p>
<p>As a sunbeam hits a droplet at an angle, it bends into the water and separates out into a spectrum of colors. Scientists <a href="https://global.canon/en/technology/s_labo/light/001/02.html">call the bending of light “refracting</a>.” The colors separate because each “color” of light <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/rainbows/colours-of-the-rainbow">travels with a different speed</a> in water, or, for that matter, any transparent material that light can travel through, like glass in a prism.</p>
<p>When the colors hit the back wall of the water droplet, the angle is now too shallow for them to bend out into the air, so they reflect back into the water droplet and return to its entrance wall. From there, the colors can bend out again into air and reach your eye.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/q73VNpFA-0Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The United Kingdom’s Meteorology Office explains how light refracts, or bends, in a water droplet or a prism.</span></figcaption>
</figure>
<p>As you look at these droplets, the different colors happen to bunch up at a slightly different angle, and each color forms the <a href="https://atoptics.co.uk/rainbows/primcone.htm">circular rim of a cone</a> with your eye at the tip of the cone. And, voila, you have your own personal rainbow.</p>
<p>The droplets that send the colors to your eye cannot send them to anyone else, so even though everyone near you sees the same rainbow at a distance, each person really sees their own slightly different rainbow. It’s all in the eye of the beholder.</p>
<p>For rainbows to form, the shape of the water droplets has to be very close to a sphere for all of them to bend and reflect the colors in harmony. This happens for very small droplets, such as a fine mist, or just after a rain shower when the air is just moist. As the droplets get larger, gravity distorts their shape and the rainbow vanishes.</p>
<figure class="align-center ">
<img alt="An elephant in water closes its eyes while the photographer captures a rainbow across its trunk and forehead." src="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521647/original/file-20230418-764-w4nbr5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Even though it looks like this elephant is bathing in a rainbow, the elephant wouldn’t see it in the same way.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/an-elephant-is-pictured-under-a-rainbow-of-water-sprayed-to-news-photo/1242012110">Mads Claus Rasmussen / Ritzau Scanpix / AFP</a></span>
</figcaption>
</figure>
<p>A rainbow is not physically present where it appears to be, similar to your image in a mirror. So, I’m sorry to say that you can never actually reach your rainbow. And, alas, nobody can ever find that pot of gold.</p>
<p>But you can <a href="https://www.youtube.com/watch?v=dIdE-pqYqbs">create your own rainbow</a>. </p>
<h2>How to create and see a circular rainbow</h2>
<p>One experiment you can try in summer is to turn on a sprinkler hose using the “mist” setting. Remember to have the sun behind you. If you create a fine mist screen in front of you and look at your shadow, you might see a rainbow. </p>
<figure class="align-center ">
<img alt="A young boy plays in a fountain, with a rainbow overhead." src="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521649/original/file-20230418-20-u1rnce.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It might take some work, but you can see your own full-circle rainbows in the mist.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/young-boy-cools-off-under-a-rainbow-in-a-fountain-on-a-warm-news-photo/1266045824">Gary Hershorn/Getty Images</a></span>
</figcaption>
</figure>
<p>It is not difficult to see colors, but to see a full circle, you will need some patience and practice, just like scientists.</p>
<p>So next time you are on an airplane, grab the window seat. If you are flying a little above the cloud cover, keep a lookout for the small shadow of your plane on the clouds. That means the sun is behind you. </p>
<p>The clouds are tiny water droplets, so chances are you may see a small circle of color around the shadow of the airplane. This phenomenon is <a href="https://science.howstuffworks.com/nature/climate-weather/atmospheric/pilots-glory-rainbow-airplane-shadow.htm">nicknamed “pilot’s glory</a>,” because pilots who fly all the time and have a good view from the cockpit have a better chance of seeing it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An airplane's shadow has a circular rainbow around it as it flies over mountains." src="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521423/original/file-20230417-28-hkye8m.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The circular rainbow you see around an airplane’s shadow is called ‘pilot’s glory.’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/imatty35/6708114761/">Matthew Straubmuller/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>And if you really can’t wait to see what it looks like, there’s <a href="https://education.nationalgeographic.org/resource/rainbow/">always the internet</a>.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/202952/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Partha Chowdhury does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Each rainbow is personal – the rainbow you see isn’t exactly the same rainbow the next person sees. It’s all in the eye of the beholder.Partha Chowdhury, Professor of Physics, UMass LowellLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2038812023-04-20T12:40:04Z2023-04-20T12:40:04ZAllergy season is getting more intense with climate change – we’re creating better pollen forecasts to help<figure><img src="https://images.theconversation.com/files/521940/original/file-20230419-28-qacnzc.jpg?ixlib=rb-1.1.0&rect=308%2C37%2C7230%2C4622&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Allergy season is here.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/teenage-girl-with-allergy-blowing-nose-royalty-free-image/1198047425">Imgorthand/E+ via Getty Images</a></span></figcaption></figure><p>If you’re feeling the misery of allergy season in your sinuses and throat, you’re probably wondering what nature has in store for you this time – and in the future.</p>
<p>Pollen allergies affect over <a href="https://doi.org/10.1016/j.anai.2010.10.014">30% of the global population</a>, making them a significant <a href="https://doi.org/10.1016/j.anai.2010.10.014">public health</a> and <a href="https://doi.org/10.1016/j.rmed.2010.05.006">economic issue</a> as people feel ill and miss work. Our research shows that, as greenhouse gases warm the planet, their effects are driving longer and more intense pollen seasons.</p>
<p>To help allergy sufferers manage their symptoms in our changing climate, we’re building better pollen forecasts for the future.</p>
<p>As <a href="https://scholar.google.com/citations?user=3dWPwz8AAAAJ&hl=en">atmospheric</a> <a href="https://clasp.engin.umich.edu/people/zhang-yingxiao/">scientists</a>, we study how the atmosphere and climate affect trees and plants. In a 2022 study, we found that the U.S. will face <a href="https://www.nature.com/articles/s41467-022-28764-0">up to a 200% increase</a> in total pollen this century if the world continues producing carbon dioxide emissions at a high rate. Pollen season in general will start up to 40 days earlier in the spring and last up to 19 days longer than today under that scenario.</p>
<figure class="align-center ">
<img alt="6 maps showing differences in how types of plant pollen seasons will change. _Ambrosia_, better known as ragweed, has the greatest increase." src="https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=604&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=604&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=604&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=759&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=759&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=759&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The maps on the left show the recent average pollen season length in days for three types of plants: <em>Platanus</em>, or plane trees, such as sycamores; <em>Betula</em>, or birch; and <em>Ambrosia</em>, or ragweed. The maps on the right show the expected changes in total days by the end of the century if carbon dioxide emissions continue at a high rate.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41467-022-28764-0">Zhang and Steiner, 2022</a></span>
</figcaption>
</figure>
<p>While most studies focus on pollen overall, we zoomed in on more than a <a href="https://www.nature.com/articles/s41467-022-28764-0">dozen different types of grasses and trees</a> and how their pollen will affect regions across the U.S. in different ways. For example, species like oak and cypress will give the Northeast the biggest increase, but allergens will be on the rise just about everywhere, with consequences for human health and the economy.</p>
<h2>Why pollen is increasing</h2>
<p>Let’s start with the basics. Pollen – the dustlike grains produced by grasses and plants – contains the male genetic material for a plant’s reproduction.</p>
<p>How much pollen is produced depends on how the plant grows. Rising global temperatures will boost plant growth in many areas, and that, in turn, will affect pollen production. </p>
<p>Warmer temperatures will extend the growing season, allowing plants to grow and emit pollen for longer periods. But temperature is only part of the equation. We found that <a href="https://www.nature.com/articles/s41467-022-28764-0">a potentially greater driver of the future pollen increase</a> will be rising carbon dioxide emissions from sources such as vehicles and power plants. Carbon dioxide fuels photosynthesis, leading to increased growth and the potential for more pollen production. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dust-like pollen falls from pine cones" src="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cones on a Norway spruce in Virginia release pollen.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:2021-04-17_10_43_13A_Pollen_cones_releasing_pollen_on_a_Norway_Spruce_along_Tranquility_Court_in_the_Franklin_Farm_section_of_Oak_Hill,_Fairfax_County,_Virginia.jpg">Famartin/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Pollen changes will vary by region</h2>
<p>We looked at 15 different pollen types, rather than treating all pollen the same as many past studies have. Our study found that the amount of pollen increase in a specific region depends on the types of vegetation.</p>
<p>Typically, pollination starts with leafy deciduous trees in late winter and spring. Alder, birch and oak are the three top deciduous trees for causing allergies, though there are others, like mulberry. Grass pollen becomes more prevalent in the summer, followed by ragweed in late summer. In the Southeast, evergreen trees like mountain cedar and juniper (in the cypress family) start in January. In Texas, “cedar fever” is the equivalent of hay fever.</p>
<p>We found that in the Northeast, pollen seasons for a lot of allergenic trees will <a href="https://www.nature.com/articles/s41467-022-28764-0">increasingly overlap</a> as temperatures and carbon dioxide emissions rise. For example, it used to be that maple trees would release pollen first, and then birch would pollinate. Now we see more overlap of their pollen seasons.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2OsicNwv9jE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How pollen season spreads across the U.S. over one year. Yingxiao Zhang and Allison Steiner.</span></figcaption>
</figure>
<p>In general, pollen season changes are greater in the northern United States than in the South, because of larger temperature increases in northern areas in future climate projections.</p>
<p>Southeastern regions, including Florida, Georgia and South Carolina, can expect large grass and weed pollen increases in the future. The Pacific Northwest is likely to see peak pollen season a month earlier because of the early pollen season of alder. </p>
<p>Allergy problems are already on the rise. A study in 2021 found that the <a href="https://theconversation.com/pollen-can-raise-your-risk-of-covid-19-and-the-season-is-getting-longer-thanks-to-climate-change-156754">overall pollen season</a> was already about <a href="https://doi.org/10.1073/pnas.2013284118">20 days longer in North America</a> than it was in 1990 and pollen concentrations were up about 21%.</p>
<h2>Silver lining: We can improve pollen forecasting</h2>
<p>Most pollen forecasts right now provide a very broad estimate of where and when pollen counts will be high. Part of the problem is that there aren’t many <a href="https://pollen.aaaai.org/#/">observing stations</a> for pollen counts. Most are run by allergy clinics, and there are fewer than 200 of these stations distributed across the country. Michigan, where we live, doesn’t have any that are currently operating.</p>
<p>It’s a very labor-intensive process to measure different types of pollen. As a result, current forecasts have a lot of uncertainties. These likely are based in part on what a station has observed in the past and the weather forecast.</p>
<figure class="align-center ">
<img alt="A person's hands jostle a pine branch to collect pollen" src="https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pollen sampling for regional forecasts can be labor-intensive.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pollen_collection.jpg">HelenaAnna/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our model, <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022MS003329">if integrated into a forecasting framework</a>, could provide more targeted pollen forecasts across the country.</p>
<p>We can estimate where the trees are from satellite data and on-the-ground surveys. We also know how temperature influences when pollen comes out – what scientists call the <a href="https://www.britannica.com/science/phenology">phenology</a> of the pollen. With that information, we can use meteorological factors like wind, relative humidity and precipitation to figure out how much pollen gets into the air, and atmospheric models can show how it moves and blows around, to create a real-time forecast.</p>
<p>We’re currently working with a <a href="https://www.noaa.gov/">National Oceanic and Atmospheric Administration</a> lab about ways to integrate that information into a tool for air quality forecasting. Our next step is to evaluate these forecast tools and make information available to the public.</p>
<figure class="align-center ">
<img alt="Dozens of round, spiky pollen grains attached to a plant" src="https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ragweed pollen grains, magnified and colorized.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/ragweed-pollen-royalty-free-image/529469522">Bob Sacha/Corbis Documentary via Getty Images</a></span>
</figcaption>
</figure>
<p>There are still some unknowns when it comes to long-term pollen projections. For example, scientists don’t fully understand why plants produce more pollen in some years than others, and currently we cannot include these changes in our models. It’s also not fully clear how plants will respond if carbon dioxide levels go through the roof. Ragweed and residential trees are also hard to capture. There are very few ragweed surveys showing where these plants are growing in the U.S., but that can be improved.</p>
<p><em>This is an update to <a href="https://theconversation.com/pollen-season-is-getting-longer-and-more-intense-with-climate-change-heres-what-allergy-sufferers-can-expect-in-the-future-179158">an article</a> originally published March 15, 2022.</em></p><img src="https://counter.theconversation.com/content/203881/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Allison L. Steiner has received funding from NSF, NASA, DOE, and NOAA. She is currently the President of the Atmospheric Sciences section of the American Geophysical Union.</span></em></p><p class="fine-print"><em><span>Yingxiao Zhang does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Rising temperatures mean longer, earlier pollen seasons, but a bigger problem is what more carbon dioxide will do to the amount of pollen being released.Yingxiao Zhang, Ph.D. Student in Atmospheric Science, University of MichiganAllison L. Steiner, Professor of Atmospheric Science, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2038742023-04-17T12:43:14Z2023-04-17T12:43:14ZEpic snow from all those atmospheric rivers in the West is starting to melt, and the flood danger is rising<figure><img src="https://images.theconversation.com/files/521225/original/file-20230417-20-d354fm.jpeg?ixlib=rb-1.1.0&rect=0%2C2%2C1917%2C1336&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tulare Lake is reemerging as flood water spreads across miles of California farmland.
</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/agribusiness-consultant-mark-grewel-stands-on-a-farm-road-news-photo/1249529651">Luis Sinco / Los Angeles Times via Getty Images</a></span></figcaption></figure><p><em>To get a sense of the enormous amount of water atmospheric rivers dumped on the Western U.S. this year and the magnitude of the flood risk ahead, take a look at California’s Central Valley, where about <a href="https://ca.water.usgs.gov/projects/central-valley/about-central-valley.html">a quarter of the nation’s food</a> is grown.</em></p>
<p><em>This region was once home to the largest freshwater lake west of the Rockies. But the rivers that fed Tulare Lake were <a href="https://sarahamooneymuseum.org/a-look-back/tulare-lake-was-once-considered-largest-body-of-water-west-of-mississippi/">dammed and diverted</a> long ago, leaving it nearly dry by 1920. Farmers have been growing food on the fertile lake bed for decades.</em></p>
<p><em>This year, however, <a href="https://earthobservatory.nasa.gov/images/151174/return-of-tulare-lake">Tulare Lake is remerging</a>. Runoff and snowmelt from the Sierra Nevada have overwhelmed waterways and flooded farms and orchards. After similar storms in 1983, the lake covered <a href="https://www.upi.com/Archives/1983/05/30/The-massive-wall-of-debris-laden-water-that-roared-down/9734423115200/">more than 100 square miles</a>, and scientists say this year’s precipitation is looking a lot like 1983. Communities there and across the West are preparing for flooding and mudslide disasters as <a href="https://www.drought.gov/drought-status-updates/snow-drought-current-conditions-and-impacts-west-2023-04-06">record snow</a> begins to melt.</em></p>
<figure class="align-center ">
<img alt="Satellite images show farmland with only a few small lakes in early March, then a larger lake covering that farmland by early April." src="https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tulare Lake, long dry, begins to reemerge in March 2023 as flood water spreads across farm fields.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/images/151174/return-of-tulare-lake">NASA Earth Observatory</a></span>
</figcaption>
</figure>
<p><em>We asked Chad Hecht, a meteorologist with the Center for Western Weather and Water Extremes at the University of California San Diego’s Scripps Institution of Oceanography, how 2023’s storms compare to past extremes and what to expect in the future.</em></p>
<h2>How extreme were this year’s atmospheric rivers?</h2>
<p>California averages about 44 atmospheric rivers a year, but typically, only about six of them are strong storms that contribute most of the annual precipitation total and cause the kind of flooding we’ve seen this year.</p>
<p>This year, in a three-week window from about Dec. 27, 2022, to Jan. 17, 2023, we saw nine atmospheric rivers make landfall, five of them <a href="https://doi.org/10.1029/2022JD037180">categorized as strong</a> or greater magnitude. That’s how active it’s been, and that was only the beginning.</p>
<figure class="align-center ">
<img alt="Map of where atmospheric rivers arrived through the end of March 2023" src="https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Where atmospheric rivers hit during the first half of the 2023 water year, which started Oct. 1. The arrows show where the storms were strongest, but their impact reached far wider.</span>
<span class="attribution"><a class="source" href="https://cw3e.ucsd.edu/">Center For Western Weather and Water Extremes, Scripps Institution of Oceanography</a></span>
</figcaption>
</figure>
<p>In all, the state experienced 31 atmospheric rivers through the end of March: one extreme, six strong, 13 moderate and 11 weak. And other storms in between gave the Southern Sierra one of its wettest Marches on record. </p>
<p>These storms don’t just affect California. Their <a href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">precipitation</a> has pushed the snow-water equivalent levels <a href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">well above average across much of the West</a>, including in Oregon, Nevada, Utah, Idaho and the mountains of western Colorado, Arizona and New Mexico.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=726&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=726&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=726&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=912&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=912&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=912&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snow water equivalent is a measure of the water in snowpack. Many basins across the West were well over 200% of average in 2023.</span>
<span class="attribution"><a class="source" href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">NRCS/USDA</a></span>
</figcaption>
</figure>
<p>In terms of records, the big numbers this year were in California’s Southern Sierra Nevada. The region has had 11 moderate atmospheric rivers – double the average of 5.5 – and an additional four strong ones. </p>
<p>Overall, California has about <a href="https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_SWC.pdf">double its normal snowpack</a>, and some locations have experienced more than double the number of strong atmospheric rivers it typically sees. The result is that Northern Sierra snow water content is 197% of normal. The central region is 238% of normal, and the Southern Sierra is 296% of normal.</p>
<h2>What risks does all that snow in the mountains create?</h2>
<p>There is <a href="https://www.kcra.com/article/tahoe-ski-resorts-extend-season-snow-palisades/43403916">a lot of snow</a> in the Sierra Nevada, and it is going to come off the mountains at some point. It’s possible we are going to be looking at snowmelt into late June or July in California, and that’s far into summer for here.</p>
<p>Flooding is certainly a possibility. The closest year for comparison in terms of the amount of snow would be 1983, when the average statewide snow water content was 60.3 inches in May. That was a <a href="https://www.pressdemocrat.com/article/news/photos-a-look-back-at-the-1983-floods">rough year</a>, with <a href="https://www.washingtonpost.com/archive/politics/1983/06/01/rain-melting-snow-continue-to-menace-states-in-the-west/4aa62a9a-ce91-46f7-a579-607c4843a318/">flooding and mudslides</a> in <a href="https://www.sltrib.com/news/environment/2023/02/20/1983-downtown-salt-lake-turned/">several parts of the West</a> and extensive crop damage.</p>
<p><iframe id="V7dT9" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/V7dT9/8/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>This year, portions of the Southern Sierra Nevada have passed 1983’s levels, and <a href="https://www.latimes.com/california/story/2023-04-06/california-tulare-lake-storms-flooding-satellite-photos">Tulare Lake</a> is filling up again for the <a href="https://www.cnbc.com/2023/04/04/a-long-dormant-lake-has-reappeared-in-california-bringing-havoc-along-with-it.html">first time in decades</a>. Tulare Lake is an indication of just how extreme this year has been, and the risk is rising as the snow melts.</p>
<h2>The transition from extreme drought in 2022 to record snow was fast. Is that normal?</h2>
<p>California and some other parts of the West are known for weather whiplash. We frequently go from too dry to too wet. </p>
<p>2019 was another above-average year in terms of precipitation in California, but after that we saw <a href="https://droughtmonitor.unl.edu/DmData/TimeSeries.aspx">three straight years of drought</a>. We went from 13 strong or greater magnitude atmospheric rivers in 2017 to just three in 2020 and 2021, combined.</p>
<figure class="align-center ">
<img alt="Map showing well-above average precipitation across California, Nevada and Utah in particular." src="https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=724&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=724&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=724&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=910&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=910&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=910&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The onslaught of powerful atmospheric rivers pushed precipitation to well above average across large parts of the West in 2023, following three years of severe drought.</span>
<span class="attribution"><a class="source" href="https://cw3e.ucsd.edu/">Center for Western Weather and Water Extremes, Scripps Institution of Oceanography</a></span>
</figcaption>
</figure>
<p>California relies on these storms for <a href="https://water.ca.gov/News/Blog/2020/October/Atmospheric-Rivers-and-Their-Impact-on-California-Reservoirs">about half its water supply</a>, but if the West gets too many atmospheric rivers back to back, that starts to have harmful impacts, like the heavy snowpack that <a href="https://kslnewsradio.com/1994522/snow-causing-roofs-to-collapse-across-the-state-expert-offers-helpful-tips/">collapsed roofs</a> in the mountains this year, and <a href="https://youtu.be/sKx-wSICxQQ">flash flooding</a> and <a href="https://www.cbsnews.com/video/california-dangerous-mudslides-after-storms/#x">landslides</a>. These successive storms are typically referred to as <a href="https://cw3e.ucsd.edu/cw3e-publication-notice-atmospheric-river-families-definition-and-associated-synoptic-conditions/">atmospheric river families</a> and can result in exacerbated hydrologic impacts by quickly saturating soils and not allowing rivers and streams to recede back to base flow between storms.</p>
<h2>Are atmospheric rivers becoming more intense with a warming climate?</h2>
<p>There’s been <a href="https://theconversation.com/atmospheric-river-storms-can-drive-costly-flooding-and-climate-change-is-making-them-stronger-128902">a lot of research</a> on the impact of temperature because of how reliant California is on these storms for its water supply.</p>
<p>Atmospheric rivers are long, narrow corridors of water vapor in the sky that <a href="https://www.usgs.gov/news/featured-story/rivers-sky-6-facts-you-should-know-about-atmospheric-rivers">typically start in the tropics</a> as water evaporates and is pulled poleward by atmospheric circulations. They carry a lot of moisture – on average, their water vapor transport is more than <a href="https://doi.org/10.1175/JHM-D-17-0036.1">twice the flow of the Amazon River</a>. When they reach land, mountains <a href="https://www.noaa.gov/stories/what-are-atmospheric-rivers">force the air to rise</a>, which wrings out some of that moisture.</p>
<p>In a warming climate, the warmer air can hold more moisture. That can increase the capacity of atmospheric rivers, with more water vapor resulting in stronger storms.</p>
<figure class="align-center ">
<img alt="An animation shows two atmospheric rivers moving across the Pacific Ocean from the tropics." src="https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&rect=107%2C43%2C767%2C499&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=332&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=332&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=332&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An example of an atmospheric river approaching the West Coast.</span>
<span class="attribution"><a class="source" href="http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?color_type=tpw_nrl_colors&prod=global2&timespan=24hrs&anim=anigf">Space Science and Engineering Center, University of Wisconsin-Madison</a></span>
</figcaption>
</figure>
<p>Research by some of my colleagues at Scripps Institution of Oceanography also suggests that California will <a href="https://doi.org/10.1038/s41598-022-15474-2">see fewer storms that aren’t atmospheric rivers</a>. But the state will likely see <a href="https://doi.org/10.1038/s41598-017-11285-y">more intense atmospheric rivers</a> as temperatures rise. California will be even more reliant on these atmospheric rivers for its snow, which will result in drier dries and wetter wets.</p>
<p>So, we’re likely to see this whiplash continue, but to a more extreme level, with longer periods of dry weather when we’re not getting these storms. But when we do get these storms, they have the potential to be more extreme and then result in more flooding.</p>
<p>In the more immediate future, we’re likely <a href="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml">headed into an El Niño</a> this year, with warm tropical Pacific waters that shift weather patterns around the world. Typically, El Niño conditions are associated with more atmospheric river activity, especially in Central and Southern California.</p>
<p>So, we may see another wet year like this again in 2024.</p><img src="https://counter.theconversation.com/content/203874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chad Hecht receives funding from California Department of Water Resources, U.S. Army Corps of Engineers, Sonoma Water, Yuba Water Agency, & Orange County Water District. </span></em></p>This year’s Sierra snowpack is looking a lot like 1983’s, and that was a year of flooding and mudslide disasters. A meteorologist explains what’s ahead.Chad Hecht, Research and Operations Meteorologist, Center for Western Weather and Water Extremes, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2029252023-04-03T15:21:53Z2023-04-03T15:21:53ZCountries agreed to ban ozone-depleting chemicals in the 1980s – but we found five CFCs increasing to record levels in the atmosphere<p>Despite a global ban in place since 2010, atmospheric concentrations of five ozone-depleting chemicals have reached a record high.</p>
<p>Chlorofluorocarbons, or CFCs, are entirely man-made gases used in a variety of applications, including refrigeration, air conditioning or as chemical solvents. They have been increasingly regulated by a series of international treaties since the 1980s. The 1987 <a href="https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol">Montreal protocol</a>, which has been universally ratified, restricted the release of CFCs to the atmosphere where they contribute to the destruction of the ozone layer: a region high up in the stratosphere which absorbs harmful ultraviolet (UV) radiation and protects life below. </p>
<p>The goal of the Montreal protocol was to induce a decline in the atmospheric CFC concentration through controlling, and increasingly restricting, the production of these chemicals. This has worked well for many ozone-depleting substances, which is why the ozone layer is slowly recovering. And so the recent increase in atmospheric concentrations of five CFCs is quite surprising.</p>
<figure class="align-center ">
<img alt="Discarded aerosol canisters." src="https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519030/original/file-20230403-16-q8yjf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Montreal protocol has succeeded in eliminating the biggest sources of CFCs.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/circa-1990-bucket-full-empty-aerosol-106925534">Joseph Sohm/Shutterstock</a></span>
</figcaption>
</figure>
<p><a href="https://www.nature.com/articles/s41561-023-01147-w">Our findings</a>, while worrying, should be considered an early warning. The impact of all five CFCs on the recovery of the ozone layer is still small. Nevertheless, we do not fully understand where they are coming from, so this could change in the future, and we should not ignore the cumulative effect of these emissions on human health and the environment.</p>
<h2>The global picture</h2>
<p>Our team has been analysing air samples from all over the world, focusing on so-called “background” sites that are far away from the sources of these CFCs, or in fact any industrial emissions. An example is the Cape Grim observatory on the remote west coast of Tasmania. This is the basis for our assessment of the threat these chemicals pose, as it reveals global trends in their atmospheric concentration.</p>
<p>Our main findings for the period 2010-2020 were twofold. First, concentrations of CFC-13 and CFC-113a continued their previously observed – and puzzling – increase. Rising concentrations of CFC-113a even accelerated around 2016. Second, concentrations of CFC-114a and CFC-115 were stable since the 2000s, while those of CFC-112a had even started to decrease. However, all of them began increasing around 2013-2014.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two line graphs side by side" src="https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=273&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=273&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=273&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=343&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=343&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519027/original/file-20230403-26-jnky50.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=343&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Global emissions of the five CFCs weighted by their impact on ozone depletion (a) and the climate (b).</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41561-023-01147-w">Western et al. (2023)/Nature Geoscience</a></span>
</figcaption>
</figure>
<p>These observations, combined with additional knowledge about atmospheric circulation and how CFCs are removed from the atmosphere through chemical reactions, allowed us to estimate the global emissions of these five gases. Their damage to the ozone layer can be expressed through their ozone depletion potential, which states how much ozone would be destroyed compared to the same quantity of CFC-11, which is different for each CFC. </p>
<p>The result is a relief. Emissions between 2010 and 2020 only resulted in a very small loss of around 0.002% of global stratospheric ozone. </p>
<p>There is no time to relax, though, for two reasons. All five CFCs are also potent greenhouse gases and, once emitted, will remain in the atmosphere for decades to centuries. Their warming effect in 2020 was already approximately that of Switzerland’s total CO₂ emissions. And if those emissions continue on their upwards trajectory, their contribution to climate change will expand too. The persistence of these gases in the atmosphere must be taken seriously: all emissions are a legacy for future generations to contend with.</p>
<h2>Tracking down the sources</h2>
<p>The first step towards avoiding future emissions is to find out where the current ones are coming from. There were already some hints in previous studies, which we gathered and combined with our own information, such as on the exact timing of when emissions started accelerating.</p>
<p>We found that three of the five CFCs (CFC-113a, CFC-114a and CFC-115) can be produced during the manufacture of other chemicals, which is allowed under the Montreal protocol, most notably hydrofluorocarbons or HFCs. HFCs have replaced CFCs for many applications as an ozone-friendly alternative. However, like CFCs, they are greenhouse gases and their production is now being reduced in <a href="https://treaties.un.org/Pages/ViewDetails.aspx?src=IND&mtdsg_no=XXVII-2-f&chapter=27&clang=_en">many countries</a> under the 2016 Kigali Amendment to the Montreal Protocol, which could reduce climate-related warming <a href="https://acp.copernicus.org/articles/22/6087/2022/">by 0.5°C</a>. </p>
<p>It’s likely that the CFCs are leaking out during the production process, where they are either used as a feedstock (a chemical ingredient to make another chemical) or as a result of incomplete conversion of the feedstock to the target chemical. The production of HFCs really took off in developing countries after CFCs were banned in 2010, which is around the same time as the increase in emissions of these five CFCs.</p>
<p>The production of HFCs is predicted to <a href="https://acp.copernicus.org/articles/22/6087/2022/">further increase</a> over the next few years, which could result in increasing emissions of these CFCs. CFC-113a is used to make at least one hydrofluoroolefin or HFO, which are alternatives to HFCs that don’t heat the climate and may be used long into the future. Despite HFCs and HFOs being more benign alternatives to CFCs, there may still be some cost to ozone during their production if CFCs continue to leak into the atmosphere.</p>
<p>We were unable to find a plausible source for the other two CFCs, CFC-13 and CFC-112a. The fact that their emissions are increasing and we don’t know why is a concern in itself.</p>
<h2>Time to revisit Montreal?</h2>
<p>The Montreal protocol has been a huge success in mitigating emissions of ozone-depleting substances. Total CFC emissions are now <a href="https://csl.noaa.gov/assessments/ozone/2022/">only around 5% of their peak</a> in the late 1980s. Yet an increase in the atmospheric abundance of some CFCs is still at odds with the treaty’s goals – and their elimination, by clogging leaks in industrial processes, could present an easy win to reduce these country-sized emissions of ozone-depleting and climate-warming gases. </p>
<p>It will take careful consideration by countries signed up to the protocol to find the necessary controls for quashing these trend-bucking emissions. In the meantime, we will continue to use our eyes in the sky to monitor the progress of a whole host of Earth-damaging gases.</p>
<hr>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Luke Western receives funding from the European Commission under Horizon 2020. </span></em></p><p class="fine-print"><em><span>Johannes Laube received funding from the European Research Council. </span></em></p>Chlorofluorocarbons (CFCs) are also potent greenhouse gases which contribute to climate change.Luke Western, Research Associate in Atmospheric Science, University of BristolJohannes Laube, Honorary Lecturer, Centre for Ocean and Atmospheric Sciences, University of East AngliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2027042023-03-28T12:22:16Z2023-03-28T12:22:16ZWhy tornadoes are still hard to forecast – even though storm predictions are improving<figure><img src="https://images.theconversation.com/files/518829/original/file-20230331-18-ihfljb.jpg?ixlib=rb-1.1.0&rect=0%2C315%2C1649%2C1048&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A tornado touches down.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/noaanssl/47953539496">Morgan Schneider/OU CIMMS/NOAA NSSL</a></span></figcaption></figure><p><em>Meteorologists <a href="https://www.spc.noaa.gov">began warning about severe weather</a> with the potential for tornadoes <a href="https://www.wpc.ncep.noaa.gov/threats/threats.php">several days before</a> storms tore across <a href="https://earthobservatory.nasa.gov/images/151138/tornado-leaves-path-of-destruction-in-mississippi">the Southeast</a> and the <a href="https://www.nytimes.com/2023/03/31/us/midwest-storms-flood-weather.html">Central U.S.</a> in late March 2023. At one point, <a href="https://twitter.com/NWS/status/1641890452562403328">more than 28 million people</a> were under a <a href="https://www.weather.gov/safety/tornado-ww">tornado watch</a>. But pinpointing exactly where a tornado will touch down – like the tornadoes that hit <a href="https://www.bbc.com/news/world-us-canada-65072195">Rolling Fork, Mississippi</a>, on March 24, and towns in <a href="https://apnews.com/article/tornado-arkansas-storm-concert-79fe2da8a6b8bd92970032530b760d20">Arkansas</a>, <a href="https://www.bbc.com/news/world-us-canada-65072195">Illinois</a> and <a href="https://www.spc.noaa.gov/climo/reports/230331_rpts.html">multiple other states</a> on March 31 – still relies heavily on seeing the storms developing on radar. <a href="https://atmo.tamu.edu/people/profiles/faculty/nowotarskichristopher.html">Chris Nowotarski</a>, an atmospheric scientist, explains why, and how forecast technology is improving.</em></p>
<h2>Why are tornadoes still so difficult to forecast?</h2>
<p>Meteorologists have gotten a lot better at forecasting the conditions that make tornadoes more likely. But predicting exactly which thunderstorms will produce a tornado and when is harder, and that’s where a lot of severe weather research is focused today.</p>
<p>Often, you’ll have a line of thunderstorms in an environment that looks favorable for tornadoes, and one storm might produce a tornado but the others don’t. </p>
<p>The differences between them could be due to small differences in meteorological variables that aren’t resolved by our current observing networks or computer models. Even changes in the land surface conditions – fields, forested regions or urban environments – could affect whether a tornado forms. These small changes in the storm environment can have large impacts on the processes within storms that can make or break a tornado.</p>
<figure class="align-center ">
<img alt="Scientists stand near a truck outfitted with measuring devices with a dramatic storm on the horizon." src="https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517815/original/file-20230327-18-egyw14.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One way scientists gather data for understanding tornadoes is by chasing storms.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/noaanssl/52201476520/">Annette Price/CIWRO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>One of the strongest predictors of whether a thunderstorm produces a tornado relates to <a href="https://www.weather.gov/jetstream/tornado">vertical wind shear</a>, which is how the wind changes direction or speed with height in the atmosphere.</p>
<p>How wind shear interacts with rain-cooled air within storms, which we call “outflow,” and how much precipitation evaporates can influence whether a tornado forms. If you’ve ever been in a thunderstorm, you know that right before it starts to rain, you often get a gust of cold air surging out from the storm. The characteristics of that cold air outflow are important to whether a tornado can form, because tornadoes typically form in that cooler portion of the storm.</p>
<h2>How far in advance can you know if a tornado is likely to be large and powerful?</h2>
<p>The vast majority of violent tornadoes form from <a href="https://www.weather.gov/ama/supercell">supercells</a>, thunderstorms with a deep rotating updraft, called a “mesocyclone.” Vertical wind shear can enable the midlevels of the storm to rotate, and upward suction from this mesocyclone can intensify the rotation within the storm’s outflow into a tornado.</p>
<p>If you have a supercell on radar and it has strong rotation above the ground, that’s often a precursor to a tornado. Some research suggests that <a href="https://doi.org/10.1175/WAF-D-19-0099.1">a wider mesocyclone is more likely to create a stronger</a>, longer-lasting tornado than other storms.</p>
<p>Forecasters also look at the storm’s environmental conditions – temperature, humidity and wind shear. Those offer more clues that a storm is likely to produce a significant tornado.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/R7CD6MpTefs?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What radar showed as a tornado headed toward Rolling Fork, Mississippi, on March 24, 2023.</span></figcaption>
</figure>
<p>The percentage of tornadoes that <a href="https://www.weather.gov/safety/tornado-ww">trigger a warning</a> has increased over recent decades, due to <a href="https://www.weather.gov/jetstream/how">Doppler radar</a>, improved modeling and better understanding of the storm environment. About <a href="https://doi.org/10.1175/WAF-D-19-0119.1">87% of deadly tornadoes</a> from 2003 to 2017 had an advance warning.</p>
<p>The lead time for warnings has also improved. In general, it’s <a href="https://community.fema.gov/ProtectiveActions/s/article/Tornado-Alerts-and-Warnings">about 10 to 15 minutes</a> now. That’s enough time to get to your basement or, if you’re in a trailer park or outside, to find a safe facility. Not every storm will have that much lead time, so it’s important to get to shelter fast.</p>
<h2>What are researchers discovering today about tornadoes that can help protect lives in the future?</h2>
<p>If you think back to the <a href="https://www.imdb.com/title/tt0117998/">movie “Twister</a>,” in the early 1990s we were starting to do more field work on tornadoes. We were taking radar out in trucks and driving vehicles with roof-mounted instruments into storms. That’s when we really started to appreciate what we call the storm-scale processes – the conditions inside the storm itself, how variations in temperature and humidity in outflow can influence the potential for tornadoes.</p>
<p>Scientists can’t launch a weather balloon or send instruments into every storm, though. So, we also use computers to model storms to understand what’s happening inside. Often, we’ll run several models, referred to as ensembles. For instance, if nine out of 10 models produce a tornado, we know there’s a good chance the storm will produce tornadoes.</p>
<p>The National Severe Storms Laboratory has recently been experimenting with tornado warnings based on these models, called <a href="https://www.nssl.noaa.gov/projects/wof/">Warn-on-Forecast</a>, to increase the lead time for tornado warnings.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A destroyed home with just one wall standing and furniture strewn about in Rolling Fork, Mississippi, after the tornado March 24, 2023." src="https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517845/original/file-20230328-490-c5aoro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">An early warning can be the difference between life and death for people in homes without basements or cellars.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/aerial-view-of-a-destroyed-neighborhood-in-rolling-fork-news-photo/1249647508">Chandan Khanna/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>There are a lot of other areas of research. For example, to better understand how storms form, <a href="http://people.tamu.edu/%7Ecjnowotarski/research.html">I do a lot of idealized computer modeling</a>. For that, I use a model with a simplified storm environment and make small changes to the environment to see how that changes the physics within the storm itself. </p>
<p>There are also new tools in storm chasing. There’s been an explosion in the use of drones – scientists are putting sensors into unmanned aerial vehicles and <a href="https://www.colorado.edu/aerospace/2021/12/08/designing-flying-ai-systems-study-supercell-thunderstorms-close">flying them close to</a> and sometimes into the storm.</p>
<p>The focus of tornado research has also shifted from the Great Plains – the traditional “tornado alley” – <a href="https://doi.org/10.1175/JAMC-D-15-0342.1">to the Southeast</a>.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1641899393971265537"}"></div></p>
<h2>What’s different about tornadoes in the Southeast?</h2>
<p>In the Southeast there are some different influences on storms compared with the Great Plains. The Southeast has more trees and more varied terrain, and also more moisture in the atmosphere because it’s close to the Gulf of Mexico. There tend to be <a href="https://doi.org/10.1175/2008WAF2222132.1">more fatalities</a> in the Southeast, too, because <a href="https://theconversation.com/tornadoes-that-strike-at-night-are-more-deadly-and-require-more-effective-warning-systems-132955">more tornadoes form at night</a>.</p>
<figure class="align-center ">
<img alt="US map showing highest number of tornadoes in Mississippi, Alabama and western Tennessee." src="https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=458&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=458&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=458&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=575&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=575&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517812/original/file-20230327-18-9tncri.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=575&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A map of severe tornado days from 1986 to 2015 shows a large number in the Southeast.</span>
<span class="attribution"><a class="source" href="https://www.spc.noaa.gov/">NOAA Storm Prediction Center</a></span>
</figcaption>
</figure>
<p>We tend to see more tornadoes in the Southeast that are in lines of thunderstorms called “quasi-linear convective systems.” The processes that lead to tornadoes in these storms can be different, and scientists are learning more about that.</p>
<p>Some research has also suggested the start of <a href="https://doi.org/10.1002/joc.5285">a climatological shift</a> in tornadoes toward the Southeast. It can be difficult to disentangle an increase in storms from better technology spotting more tornadoes, though. So, more research is needed.</p>
<p><em>This article was updated March 31, 2023, with tornadoes in Arkansas and the central U.S.</em></p><img src="https://counter.theconversation.com/content/202704/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Nowotarski receives funding from NSF, NOAA, DOE, and NASA.</span></em></p>Researchers are turning to computer models, drones and other methods to improve tornado forecasting.Chris Nowotarski, Associate Professor of Atmospheric Science, Texas A&M UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1984042023-02-24T00:45:54Z2023-02-24T00:45:54ZCurious Kids: where does wind actually come from?<figure><img src="https://images.theconversation.com/files/507272/original/file-20230131-16-wacbvj.jpg?ixlib=rb-1.1.0&rect=66%2C26%2C4218%2C2932&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/YNM4KStg78I">Saad Chaudhry/Unsplash</a></span></figcaption></figure><blockquote>
<p>Where does wind come from? – Zoya, age 14, Bhopal, India</p>
</blockquote>
<p><a href="https://theconversation.com/au/topics/curious-kids-36782"><img src="https://images.theconversation.com/files/291898/original/file-20190911-190031-enlxbk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=90&fit=crop&dpr=1" width="100%"></a></p>
<p>The short answer is wind happens because the Sun heats some parts of the planet more than others, and this uneven heating starts a wind going. That means wind energy is really a kind of solar energy!</p>
<h2>All winds are made the same way</h2>
<p><a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjH3IOSyd_8AhU-zqACHcjqDE0QFnoECAsQAQ&url=https%3A%2F%2Fwww.nature.com%2Fscitable%2Fknowledge%2Flibrary%2Fwhere-do-winds-come-from-100578316%2F&usg=AOvVaw0K54CQ7PpdSsYr5Izp8obD">Wind systems on Earth</a> vary from the global-scale trade winds and jet streams to local sea breezes, but they all ultimately depend on Earth being unevenly heated by the Sun.</p>
<p>When the ground is heated during the day and gets very hot, it heats the air above it by a process called heat conduction. This makes the air expand to occupy a larger volume. According to something called the “<a href="https://www.britannica.com/science/ideal-gas-law">ideal gas law</a>”, the volume increases in direct proportion to the temperature.</p>
<p>In other words, the heated air is less dense. If this happens to all air, no wind will be created; the whole air layer will just be a bit thicker.</p>
<p>However, if it happens to air in one location but not its surroundings, the heated air will rise. This is the principle that allows hot air balloons to remain buoyant in the air: the total weight of the air in the balloon, plus the basket and people inside, must be about the same as the weight of the same volume of colder air outside the balloon.</p>
<p>If there is no load or tether, the balloon will just keep accelerating upward until it cools off.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A rocky desert scene with several colourful hot air balloons in the sky" src="https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507274/original/file-20230131-18-yczmof.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hot air balloons use the principle of the air changing density as it heats up and cools down.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/vCArUMDcHCQ">Timur Garifov/Unsplash</a></span>
</figcaption>
</figure>
<p>A rising hot air balloon doesn’t create any wind because it’s too small. But imagine if the same thing happens to all the air over a whole city or larger region!</p>
<p>When such a large amount of heated air rises away from the surface, other air near the ground has to flow in sideways to take its place. The larger the area over which this happens, the stronger the horizontal wind needs to be to get all that air into position.</p>
<p>This phenomenon gives us daytime sea breezes near coasts that can be fairly strong, where cooler ocean air flows in to replace the warmed continental air as it rises up. </p>
<p>Over many days, a similar process gives us monsoons, because the heating is stronger in summer and weaker in winter, leading to strong temperature contrasts and winds in summer (and often, opposite ones in winter).</p>
<p>In turn, this leads to seasonal shifts in the prevailing wind, which often bring rains during the warm season in tropical areas including India and the top end of Australia.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-the-australian-monsoon-69411">Explainer: what is the Australian monsoon?</a>
</strong>
</em>
</p>
<hr>
<h2>There are some very big wind systems</h2>
<p>The biggest wind systems on the planet are called the <a href="https://en.wikipedia.org/wiki/Atmospheric_circulation">general circulation of the atmosphere</a>. They include the <a href="http://www.bom.gov.au/climate/about/?bookmark=trades#:%7E:text=tropical%20Ridge%20ENSO-,What%20are%20they%3F,global%20circulation%20of%20the%20atmosphere.">trade winds or easterlies</a>, the middle-latitude <a href="https://www.climate-policy-watcher.org/global-climate-2/winds-westerlies.html">westerlies</a> and the <a href="https://oceanservice.noaa.gov/facts/roaring-forties.html">Roaring Forties</a>. </p>
<p>These large wind systems happen because the tropics get more Sun than the poles and (obviously) become a lot warmer. That warm air naturally starts to rise and wants to flow toward the poles, while polar air wants to come down to the tropics.</p>
<p>Of course, it takes a long time (many days) for the air to make such a long trip. Meanwhile Earth is constantly rotating, which means <a href="https://www.schooltube.com/media/Merry+Go+Round+and+the+Coriolis+Effect/1_uo3uoomf/129088791">things trying to move in a straight line will seem to gradually turn</a>.</p>
<p>The poleward-flowing wind gradually turns toward the east and becomes the middle-latitude westerlies (westerly means “from the west”). </p>
<p>The low-level wind heading toward the tropics turns toward the west and becomes the easterlies, also known as trade winds because ship captains have used these to cross the oceans for centuries. The middle-latitude westerlies are very strong at high altitude, approaching 300km per hour in some places!</p>
<p>You can see a great interactive visualisation <a href="https://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=-195.00,0.00,472">of all the winds on the planet here</a>.</p><img src="https://counter.theconversation.com/content/198404/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Steven Sherwood receives funding from the Australian Research Council. </span></em></p>It can be disruptive or refreshing, and we feel it every single day. But do you ever stop to think what creates wind on our planet?Steven Sherwood, Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1967132022-12-20T13:36:46Z2022-12-20T13:36:46Z2022’s US climate disasters, from storms and floods to heat waves and droughts<figure><img src="https://images.theconversation.com/files/501982/original/file-20221219-16-o96kqe.jpg?ixlib=rb-1.1.0&rect=500%2C20%2C1732%2C1091&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rain and fast snowmelt sent the Yellowstone River and nearby streams raging beyond their banks in June 2022.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/YEClimateChangePhotos2022/647437279ccf446abe297139183af11f/photo">AP Photo/David Goldman</a></span></figcaption></figure><p>The year 2022 will be remembered across the U.S. for its devastating flooding and storms – and also for its extreme heat waves and droughts.</p>
<p>The nation saw <a href="https://www.ncei.noaa.gov/access/billions/events/US/2022?disasters%5B%5D=all-disasters">18 disasters</a> that caused more than US$1 billion in damage each, well above the average. The year started and ended with widespread severe winter storms from Texas to Maine, affecting tens of million of people and causing significant damages. Then, March <a href="https://www.nbcnews.com/news/weather/march-sets-record-tornado-reports-rcna22537">set the record</a> for the most reported <a href="https://theconversation.com/tornadoes-climate-change-and-why-dixie-is-the-new-tornado-alley-178863">tornadoes</a> in the month – 233.</p>
<p>During a period of five weeks over the summer, <a href="https://www.washingtonpost.com/climate-environment/2022/08/23/flood-united-states-climate-explainer/">five 1,000-year rainfall events</a> occurred in <a href="https://www.weather.gov/lsx/July262022Flooding">St. Louis</a>, <a href="https://theconversation.com/climate-change-is-intensifying-the-water-cycle-bringing-more-powerful-storms-and-flooding-heres-what-the-science-shows-187951">eastern Kentucky</a>, <a href="https://news.yahoo.com/illinois-flash-flooding-rain-climate-change-184218523.html">southern Illinois</a>, California’s <a href="https://www.nps.gov/deva/learn/news/death-valley-experiences-1-000-year-rain-event.htm">Death Valley</a> and <a href="https://www.texastribune.org/2022/08/22/dallas-flooding-fort-worth/">Dallas</a>, causing devastating and sometimes deadly flash floods. Severe flooding in Mississippi <a href="https://theconversation.com/intense-heat-and-flooding-are-wreaking-havoc-on-power-and-water-systems-as-climate-change-batters-americas-aging-infrastructure-189761">knocked out Jackson’s troubled water supply</a> for weeks. A <a href="https://theconversation.com/climate-change-is-making-flooding-worse-3-reasons-the-world-is-seeing-more-record-breaking-deluges-and-flash-floods-185364">historic flood in Montana</a>, brought on by heavy rain and melting snow, forced large areas of Yellowstone National Park to be evacuated. </p>
<p>In the fall, <a href="https://www.weather.gov/ilm/HurricaneIan">hurricanes Ian</a> and <a href="https://www.weather.gov/sju/fiona2022">Fiona</a> deluged Florida and Puerto Rico with over 2 feet (0.6 meters) of rain in areas and deadly, destructive storm surge. Ian became <a href="https://apnews.com/article/floods-europe-pakistan-climate-and-environment-87a354ddc9f2333e3175d0578c50a592">one of the most expensive</a> hurricanes in U.S. history. And a <a href="https://theconversation.com/typhoon-merbok-fueled-by-unusually-warm-pacific-ocean-pounded-alaskas-vulnerable-coastal-communities-at-a-critical-time-190898">typhoon pounded</a> 1,000 miles (1,600 km) of the Alaska coast. </p>
<figure class="align-center ">
<img alt="A girl in rain boots walks through a mud-filled yard. Damaged mattresses and other belongings from a flooded house are piled nearby." src="https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Flash flooding swept through mountain valleys in eastern Kentucky in July 2022, killing more than three dozen people. It was one of several destructive flash floods.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/local-fire-chief-and-his-daughter-drop-off-goods-for-a-news-photo/1242236541">Seth Herald/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>While too much rainfall threatened some regions, extreme heat and too little precipitation worsened risks elsewhere.</p>
<p>Persistent heat waves lingered over many parts of the country, setting temperature records. Wildfires raged in <a href="https://tucson.com/news/local/photos-wildfires-in-arizona-2022/collection_6555f988-c4dd-11ec-a7da-effb4de9da49.html#1">Arizona</a> and <a href="https://www.nytimes.com/2022/12/10/business/new-mexico-climate-change-wildfires-floods.html">New Mexico</a> on the background of a <a href="https://www.nature.com/articles/s41558-022-01290-z">megadrought in the Southwestern U.S.</a> more severe than anything the region has experienced in at least 1,200 years. </p>
<p>Drought also left the <a href="https://theconversation.com/record-low-water-levels-on-the-mississippi-river-in-2022-show-how-climate-change-is-altering-large-rivers-193920">Mississippi River so low</a> near Memphis in the fall that barges couldn’t get through without additional dredging and upstream water releases. That snarled grain shipping during the <a href="https://www.bloomberg.com/graphics/2022-mississippi-river-drought-global-impact/?sref=Hjm5biAW">critical harvest period</a>. Along the Colorado River, officials discussed even tighter water use restrictions as <a href="https://www.washingtonpost.com/climate-environment/2022/12/17/colorado-river-crisis-conference/">water levels neared dangerously low levels</a> in the major reservoirs. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing disasters, including several severe storms" src="https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=327&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=327&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=327&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=410&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=410&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503887/original/file-20230110-13-zrsvbi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=410&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">2022 had 18 disasters that exceeded $1 billion each in damage.</span>
<span class="attribution"><a class="source" href="https://www.ncei.noaa.gov/access/billions/">NCEI/NOAA</a></span>
</figcaption>
</figure>
<p>The United States was hardly alone in its climate disasters.</p>
<p>In Pakistan, <a href="https://theconversation.com/pakistan-floods-what-role-did-climate-change-play-189833">record monsoon rains</a> inundated more than one-third of the country, killing over 1,500 people. In <a href="https://www.newyorker.com/magazine/2022/08/01/living-through-indias-next-level-heat-wave">India</a> and <a href="https://www.theguardian.com/world/2022/sep/07/china-reports-most-severe-heatwave-and-lowest-rainfall-on-record">China</a>, prolonged heat waves and droughts dried up rivers, disrupted power grids and threatened food security for billions of people. Widespread flooding and mudslides brought on by torrential rains also killed hundreds of people <a href="https://www.cnn.com/2022/05/13/africa/south-africa-floods-climate-intl/index.html">in South Africa</a>, <a href="https://www.reuters.com/world/americas/death-toll-brazilian-floods-rises-57-thousands-displaced-2022-05-29/">Brazil</a> and <a href="https://www.nytimes.com/2022/10/17/world/africa/nigeria-floods.html">Nigeria</a>.</p>
<p>In Europe, heat waves set record temperatures <a href="https://www.washingtonpost.com/world/2022/07/28/human-caused-climate-change-made-uk-heat-wave-10-times-more-likely-study-says/">in Britain</a> and other parts of the continent, leading to severe droughts, <a href="https://www.theguardian.com/environment/2022/aug/13/europes-rivers-run-dry-as-scientists-warn-drought-could-be-worst-in-500-years">low river flows that slowed shipping</a>, and wildfires in many parts of the continent. Much of East Africa is still in the grips of a multiyear drought – the <a href="https://news.un.org/en/story/2022/11/1131107">worst in over 40 years</a>, according to the United Nations – leaving millions of people vulnerable to food shortages and starvation. The last eight years have been the <a href="https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202213">warmest in over 140 years</a> of record-keeping.</p>
<p>This isn’t just a freak year: Such extreme events are occurring with increasing frequency and intensity.</p>
<h2>Climate change is intensifying these disasters</h2>
<p>The most <a href="https://theconversation.com/climate-change-is-intensifying-the-water-cycle-bringing-more-powerful-storms-and-flooding-heres-what-the-science-shows-187951">recent global climate assessment</a> from the United Nations Intergovernmental Panel on Climate Change found significant increases in both the frequency and intensity of extreme temperature and precipitation events, leading to more droughts and floods.</p>
<p>Extreme flooding and droughts are also <a href="https://doi.org/10.1038/s41586-022-04917-5">getting deadlier and more expensive</a>, despite an improving capacity to manage climate risks, a study published in 2022 found. Part of the reason is that today’s extreme events, enhanced by climate change, often exceed communities’ management capabilities.</p>
<figure class="align-center ">
<img alt="A woman with her eyes closed holds a screaming 1-year-old boy in a National Guard helicopter, with a guard member standing in the open helicopter door." src="https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A family had to be airlifted from their home in eastern Kentucky after it was surrounded by floodwater in July 2022.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/command-sergeant-major-tim-lewis-of-the-kentucky-national-news-photo/1242203173">Michael Swensen/Getty Images</a></span>
</figcaption>
</figure>
<p>Extreme events, by definition, occur rarely. A 100-year flood has a 1% chance of happening in any given year. So when such events occur with increasing frequency and intensity, they are a clear indication of a changing climate state.</p>
<h2>Climate models showed these risks were coming</h2>
<p>Much of this is well understood and consistently reproduced by climate models.</p>
<p>As the climate warms, a shift in temperature distribution leads to more extremes. For example, globally, a 1 degree Celsius increase in annual average temperature is associated with a 1.2 C to 1.9 C (2.1 Fahrenheit to 3.4 F) <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter11.pdf">increase in the annual maximum temperature</a>.</p>
<figure class="align-center ">
<img alt="A man works on a car with an older mechanic in overalls standing next to him under the shade of a large beach umbrealla." src="https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Heat waves, like the heat dome over the South in July 2022, can hit outdoor workers especially hard.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/community-mechanic-lloyd-bush-works-on-a-neighbors-vehicle-news-photo/1410189284">Brandon Bell/Getty Images</a></span>
</figcaption>
</figure>
<p>In addition, global warming leads to changes in how the atmosphere and ocean move. The temperature difference between the equator and the poles is the driving force for global wind. As the polar regions warm at much higher rates than the equator, the reduced temperature difference causes a weakening of global winds and leads to a <a href="https://e360.yale.edu/features/global-stilling-is-climate-change-slowing-the-worlds-wind">more meandering jet stream</a>.</p>
<p>Some of these changes can create conditions such as persistent high-pressure systems and atmospheric blocking that bring more intense heat waves. The <a href="https://theconversation.com/what-is-a-heat-dome-an-atmospheric-scientist-explains-the-weather-phenomenon-baking-california-and-the-west-185569">heat domes</a> over the Southern Plains and South in June and in the West in September were both examples.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1538941467686756352"}"></div></p>
<p>Warming can be further amplified by positive feedbacks.</p>
<p>For example, <a href="https://www.ncei.noaa.gov/news/global-climate-202212">higher temperatures</a> tend to dry out the soil, and less soil moisture reduces the land’s heat capacity, making it easier to heat up. More frequent and persistent heat waves lead to excessive evaporation, combined with decreased precipitation in some regions, causing more severe droughts and more frequent wildfires. </p>
<p><iframe id="zBAAz" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/zBAAz/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Higher temperatures <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/">increase the atmosphere’s capacity</a> to hold moisture at a rate of about 7% per degree Celsius. This increased humidity leads to heavier rainfall events. </p>
<p>In addition, storm systems are <a href="https://thinktv.pbslearningmedia.org/resource/nves.sci.earth.hurricane/water-vapor-fuels-hurricanes/">fueled by latent heat</a> – the large amount of energy released when water vapor condenses to liquid water. Increased moisture content in the atmosphere also enhances latent heat in storm systems, increasing their intensity. Extreme heavy or persistent rainfall leads to increased flooding and landslides, with devastating social and economic consequences.</p>
<p>Even though it’s difficult to link specific extreme events directly to climate change, when these supposedly rare events occur with greater frequency in a warming world, it is hard to ignore the changing state of our climate. </p>
<h2>The new abnormal</h2>
<p>This year might provide a glimpse of our near future, as these extreme climate events become more frequent.</p>
<p>To say this is the “new normal,” though, is misleading. It suggests that we have reached a new stable state, and that is far from the truth. Without serious effort to curb greenhouse gas emissions, this trend toward more extreme events will continue. </p>
<p><em>This article was updated Jan. 12, 2023, with the release of NOAA’s billion-dollar disaster list and global temperatures for 2022.</em></p><img src="https://counter.theconversation.com/content/196713/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shuang-Ye Wu does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Millions of people around the world suffered through deadly flooding and long-lasting heat waves in 2022. A climate scientist explains the rising risks.Shuang-Ye Wu, Professor of Geology and Environmental Geosciences, University of DaytonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1872342022-09-27T12:29:12Z2022-09-27T12:29:12ZHurricane hunters flew through Ian’s powerful winds to forecast intensity – here’s what happens when the plane plunges into the eyewall of a storm<figure><img src="https://images.theconversation.com/files/474652/original/file-20220718-24-9bzmk2.jpg?ixlib=rb-1.1.0&rect=152%2C8%2C2802%2C1675&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Flying into Hurricane Harvey aboard a a P-3 Hurricane Hunter nicknamed Kermit in 2018.</span> <span class="attribution"><span class="source">Lt. Kevin Doreumus/NOAA</span></span></figcaption></figure><p><em>As Hurricane Ian intensified on its way toward the Florida coast, <a href="https://www.omao.noaa.gov/find/media/video/dropsonde-launch-and-flight-center-tropical-storm-ian-noaa-wp-3d-orion-miss-piggy-september-25-2022-credit-lt-cmdr-kevin-doremus-0">hurricane hunters were in the sky</a> doing something almost unimaginable: flying through the center of the storm. With each pass, the scientists aboard these planes take measurements that satellites can’t and send them to forecasters at the National Hurricane Center.</em></p>
<p><em>Jason Dunion, a <a href="https://scholar.google.com/citations?user=BFiIdhQAAAAJ&hl=en">University of Miami meteorologist</a>, leads the National Oceanic and Atmospheric Administration’s 2022 hurricane field program. He described the technology the team is using to gauge hurricane behavior in real time and the experience aboard a <a href="https://www.omao.noaa.gov/learn/aircraft-operations/aircraft/lockheed-wp-3d-orion">P-3 Orion</a> as it plunges through the eyewall of a hurricane.</em> </p>
<h2>What happens aboard a hurricane hunter when you fly into a storm?</h2>
<p>Basically, we’re take a flying laboratory into the heart of the hurricane, all the way up to Category 5s. While we’re flying, we’re crunching data and sending it to forecasters and climate modelers.</p>
<p>In the <a href="https://www.omao.noaa.gov/learn/aircraft-operations/about/hurricane-hunters">P-3s</a>, we routinely cut through the middle of the storm, right into the eye. Picture <a href="https://scied.ucar.edu/video/dropsonde-animation-noaa">an X pattern</a> – we keep cutting through the storm multiple times during a mission. These might be developing storms, or they might be Category 5s.</p>
<figure class="align-center ">
<img alt="View out the aircraft window of the eyewall." src="https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486820/original/file-20220927-18-3ei8of.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In the eye of Hurricane Teddy in 2020. The eye is the calmest part of the storm, but it’s surrounded by the most intense part: the eyewall.</span>
<span class="attribution"><a class="source" href="https://www.omao.noaa.gov/learn/aircraft-operations/media/images">Lt. Cmdr. Robert Mitchell/NOAA Corps</a></span>
</figcaption>
</figure>
<p>We’re typically flying at an altitude of around 10,000 feet, about a quarter of the way between the ocean surface and the top of the storm. We want to cut through the roughest part of the storm because we’re trying to measure <a href="https://www.unidata.ucar.edu/data/NGCS/lobjects/chp/structure/">the strongest winds</a> for the Hurricane Center. </p>
<h2>That has to be intense. Can you describe what scientists are experiencing on these flights?</h2>
<p>My most intense flight was Dorian in 2019. The storm was near the Bahamas and <a href="https://www.nhc.noaa.gov/data/tcr/AL052019_Dorian.pdf">rapidly intensifying to a very strong Category 5</a> storm, with winds around 185 mph. It felt like being a feather in the wind.</p>
<p>When we were coming through the eyewall of Dorian, it was all seat belts. You can lose a few hundred feet in a couple of seconds if you have a down draft, or you can hit an updraft and gain a few hundred feet in a matter of seconds. It’s a lot like a rollercoaster ride, only you don’t know exactly when the next up or down is coming.</p>
<figure class="align-center ">
<img alt="View of Earth and a large hurricane from a portal on the space station." src="https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486822/original/file-20220927-12-shn7r8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Hurricane Dorian seen from the International Space Station.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/images/145559/a-devastating-stall-by-hurricane-dorian">NASA Expedition 60</a></span>
</figcaption>
</figure>
<p>At one point, we had G-forces of 3 to 4 Gs. That’s what <a href="https://www.spaceanswers.com/space-exploration/what-g-force-do-astronauts-experience-during-a-rocket-launch/">astronauts experience</a> during a rocket launch. We can also get <a href="https://twitter.com/TheAstroNick/status/1575179322599493632">zero G for a few seconds</a>, and anything that’s not strapped down will float off.</p>
<p>Even in the rough parts of the storm, scientists like myself are busy on computers working up the data. A technician in the back may have launched a dropsonde from the belly of the plane, and we’re checking the quality of the data and sending it off to modeling centers and the National Hurricane Center.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1575288070223630336"}"></div></p>
<h2>What are you learning about hurricanes from these flights?</h2>
<p>One of our goals is to better understand why storms <a href="https://theconversation.com/the-2020-atlantic-hurricane-season-was-a-record-breaker-and-its-raising-more-concerns-about-climate-change-150495">rapidly intensify</a>. </p>
<p>Rapid intensification is when a storm increases in speed by 35 mph in just a day. That equates to going from Category 1 to a major Category 3 storm in a short period of time. <a href="https://theconversation.com/hurricane-ida-turned-into-a-monster-thanks-to-a-giant-warm-patch-in-the-gulf-of-mexico-heres-what-happened-167029">Ida</a> (2021), <a href="https://www.nhc.noaa.gov/data/tcr/AL052019_Dorian.pdf">Dorian</a> (2019) and <a href="https://www.nhc.noaa.gov/data/tcr/AL142018_Michael.pdf">Michael</a> (2018) are just a few recent hurricanes that rapidly intensified. When that happens near land, it can catch people unprepared, and that gets dangerous fast.</p>
<p>Since rapid intensification can happen in a really short time span, we have to be out there with the hurricane hunters taking measurements while the storm is coming together.</p>
<figure class="align-center ">
<img alt="A pilot at the controls with the storm seen through the window" src="https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486826/original/file-20220927-24-tc8raz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A hurricane hunter flies through Hurricane Ida in 2021.</span>
<span class="attribution"><a class="source" href="https://www.omao.noaa.gov/learn/aircraft-operations/media/images">Lt. Cmdr. Kevin Doremus/NOAA Corps</a></span>
</figcaption>
</figure>
<p>So far, rapid intensification is <a href="https://www.science.org/content/article/why-scientists-had-trouble-predicting-hurricane-michael-s-rapid-intensification">hard to predict</a>. We might start to see the ingredients quickly coming together: Is the ocean warm to a great depth? Is the atmosphere nice and juicy, with a lot of moisture around the storm? Are the winds favorable? We also look at the inner core: What does the structure of the storm look like, and is it starting to consolidate?</p>
<p>Satellites can offer forecasters a basic view, but we need to get our hurricane hunters into the storm itself to really pick the hurricane apart.</p>
<h2>What does a storm look like when it’s rapidly intensifying?</h2>
<p>Hurricanes like to stand up straight – think of a spinning top. So, one thing we look for is alignment.</p>
<p>A storm that isn’t yet fully together might have low-level circulation, a few kilometers above the ocean, that isn’t lined up with its mid-level circulation 6 or 7 kilometers up. That isn’t a very healthy storm. But a few hours later, we might fly back into the storm and notice that the two centers are more lined up. That’s a sign that it could rapidly intensify.</p>
<p>We also look at the <a href="https://www.aoml.noaa.gov/news/planetary-boundary-layer-parametrization/">boundary layer</a>, the area just above the ocean. Hurricanes breathe: They draw air in at low levels, the air rushes up at the eyewall, and then it vents out at the top of the storm and away from the center. That’s why we get those huge updrafts in the eyewall.</p>
<p>So we might watch our dropsonde or tail doppler radar data for how the winds are flowing at the boundary layer. Is that really moist air rushing in toward the center of the storm? If the boundary layer is deep, the storm can also take a bigger inhale.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/474543/original/file-20220718-18-7tvint.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Cross-section of a hurricane.</span>
<span class="attribution"><a class="source" href="https://www.weather.gov/jetstream/tc_structure">National Weather Service</a></span>
</figcaption>
</figure>
<p>We also look at the structure. A lot of times the storm looks healthy on satellite, but we’ll get in with the radar and the structure is sloppy or the eye may be filled with clouds, which tells us the storm isn’t quite ready to rapidly intensify. But, during that flight, we might start to see the structure change pretty quickly.</p>
<p>Air in, up and out – the breathing – is a great way to diagnose a storm. If that breathing looks healthy, it can be a good sign of an intensifying storm.</p>
<h2>What instruments do you use to measure and forecast hurricane behavior?</h2>
<p>We need instruments that not only measure the atmosphere but also the ocean. The winds can steer a storm or tear it apart, but the ocean heat and moisture are its fuel.</p>
<p>We use <a href="https://www.eol.ucar.edu/content/what-dropsonde">dropsondes</a> to measure temperature, humidity, pressure and wind speed, and send back data every 15 feet or so all the way to the ocean surface. All of that data goes to the National Hurricane Center and to modeling centers so they can get a better representation of the atmosphere.</p>
<figure class="align-center ">
<img alt="A scientist in a flight suit puts a device into a tube in the bottom of the plane to drop it." src="https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486828/original/file-20220927-12-391k29.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A NOAA technician deploys an airborne expendable bathythermograph.</span>
<span class="attribution"><a class="source" href="https://www.omao.noaa.gov/learn/aircraft-operations/media/images">Paul Chang/NOAA</a></span>
</figcaption>
</figure>
<p>One P-3 has a laser – a <a href="https://www.aoml.noaa.gov/wp-content/uploads/2021/04/3_2021HFP_InstrumentDescriptions.pdf">CRL, or compact rotational raman LiDAR</a> – that can measure temperature, humidity and aerosols from the aircraft all the way down to the ocean surface. It can give us a sense of how juicy the atmosphere is, so how conducive it is for feeding a storm. The CRL operates continuously over the entire flight track, so you get this beautiful curtain below the aircraft showing the temperature and humidity.</p>
<p>The planes also have <a href="https://www.aoml.noaa.gov/real-time-doppler-radar/">tail doppler radars</a>, which measure how moisture droplets in the air are blowing to determine how the wind is behaving. That gives us a 3D look at the wind field, like an X-ray of the storm. You can’t get that from a satellite.</p>
<p>We also launch ocean probes call AXBTs – <a href="https://www.aoml.noaa.gov/phod/dhos/axbt.php">aircraft expendable bathythermograph</a> – out ahead of the storm. These probes measure the water temperature down several hundred feet. Typically, a surface temperature of 26.5 degrees Celsius (80 Fahrenheit) and above is favorable for a hurricane, but the depth of that heat is also important. </p>
<p>If you have warm ocean water that’s maybe 85 F at the surface, but just 50 feet down the water is quite a bit colder, the hurricane is going to mix in that cold water pretty quickly and weaken the storm. But deep warm water, <a href="https://theconversation.com/hurricane-ida-turned-into-a-monster-thanks-to-a-giant-warm-patch-in-the-gulf-of-mexico-heres-what-happened-167029">like we find in eddies</a> in the Gulf of Mexico, provides extra energy that can fuel a storm.</p>
<figure class="align-center ">
<img alt="Map showing Ida's track and the depth of heat" src="https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=570&fit=crop&dpr=1 600w, https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=570&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=570&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=716&fit=crop&dpr=1 754w, https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=716&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/476567/original/file-20220728-27592-3cxnt3.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=716&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The depth of ocean heat as Hurricane Ida headed for a warm eddy boundary on Aug. 28, 2021.</span>
<span class="attribution"><span class="source">University of Miami</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This year, we’re also testing a new technology – small drones that we can launch out of the belly of a P-3. They have about a 7- to 9-foot wingspan and are basically a weather station with wings.</p>
<p>One of these drones dropped in the eye could measuring pressure changes, which indicate whether a storm is getting stronger. If we could drop a drone in the eyewall and have it orbit there, it could measure where the strongest winds are – that’s another important detail for forecasters. We also don’t have a lot of measurements in the boundary layer because it’s not a safe place for a plane to fly. </p>
<h2>You also targeted the Cabo Verde islands off Africa for the first time this year. What are you looking for there?</h2>
<p>The Cabo Verde Islands are in the Atlantic’s hurricane nursery. The seedlings of hurricanes come off Africa, and we’re trying to determine the tipping points for theses disturbances to form into storms.</p>
<p>Over half the named storms we get in the Atlantic come from this nursery, including <a href="https://oceanweatherservices.com/blog/2022/03/20/what-should-we-expect-for-the-2022-hurricane-season/">about 80% of the major hurricanes</a>, so it’s important, even though the disturbances are maybe seven to 10 days ahead of a hurricane forming.</p>
<figure class="align-center ">
<img alt="The plane on a runway at sunrise." src="https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/486821/original/file-20220927-16-bc6a7c.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">NOAA’s P-3 Orion nicknamed ‘Kermit’ prepares to take off.</span>
<span class="attribution"><a class="source" href="https://www.omao.noaa.gov/learn/aircraft-operations/media/images">Lt. Cmdr Rannenberg/NOAA Corps</a></span>
</figcaption>
</figure>
<p>In Africa, a lot of thunderstorms develop along the Sahara desert’s southern border with the cooler, <a href="https://doi.org/10.1093/acrefore/9780190228620.013.510">moister Sahel region</a> in the summer. The temperature difference can cause ripples to develop in the atmosphere that we call tropical waves. Some of those tropical waves are the precursors for hurricanes. However, the <a href="https://www.aoml.noaa.gov/saharan-air-layer/">Saharan air layer</a> – huge dust storms that come rolling off Africa every three to five days or so – <a href="https://doi.org/10.1175/BAMS-D-20-0212.1">can suppress a hurricane</a>. These storms peak from June to mid-August. After that, tropical disturbances have a better chance of reaching the Caribbean.</p>
<p>At some point not too far in the future, the National Hurricane Center will have to do a seven-day forecast, rather than just five days. We’re figuring out how to improve that early forecasting.</p><img src="https://counter.theconversation.com/content/187234/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jason Dunion receives funding from NOAA, NASA, and the Office of Naval Research.</span></em></p>The meteorologist leading NOAA’s 2022 hurricane field program describes flying through eyewalls and the technology in these airborne labs for tracking rapid intensification in real time.Jason Dunion, Research Meteorologist, University of MiamiLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1906362022-09-21T13:01:42Z2022-09-21T13:01:42ZLooking back on America’s summer of heat, floods and climate change: Welcome to the new abnormal<figure><img src="https://images.theconversation.com/files/485658/original/file-20220920-11061-c1zwpd.jpg?ixlib=rb-1.1.0&rect=8%2C116%2C5958%2C3855&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Much of the South and Southern Plains faced a dangerous heat wave in July 2022, with highs well over 100 degrees for several days.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/johnny-bouldin-sits-outside-of-his-home-during-a-heatwave-news-photo/1410189259">Brandon Bell/Getty Images</a></span></figcaption></figure><p>The summer of 2022 started with a <a href="https://theconversation.com/climate-change-is-making-flooding-worse-3-reasons-the-world-is-seeing-more-record-breaking-deluges-and-flash-floods-185364">historic flood in Montana</a>, brought on by heavy rain and melting snow, that tore up roads and caused large areas of Yellowstone National Park to be evacuated. </p>
<p>It ended with a record-breaking heat wave in California and much of the West that pushed the <a href="https://theconversation.com/intense-heat-and-flooding-are-wreaking-havoc-on-power-and-water-systems-as-climate-change-batters-americas-aging-infrastructure-189761">power grid to the breaking point</a>, causing <a href="https://www.kron4.com/weather/san-jose-mayor-blasts-pge-for-heat-wave-power-outages/">blackouts</a>, followed by a tropical storm that <a href="https://www.latimes.com/california/story/2022-09-09/tropical-storm-kay-southern-california-mexico-heat-wave">set rainfall records</a> in southern California. A <a href="https://theconversation.com/typhoon-merbok-fueled-by-unusually-warm-pacific-ocean-pounded-alaskas-vulnerable-coastal-communities-at-a-critical-time-190898">typhoon flooded</a> coastal Alaska, and <a href="https://www.nytimes.com/2022/09/19/climate/puerto-rico-hurricane-fiona.html">a hurricane</a> hit Puerto Rico with more than <a href="https://www.accuweather.com/en/hurricane/fiona-rainfall-totals-in-puerto-rico-rival-hurricane-marias-downpours/1249695">30 inches of rain</a>.</p>
<p>In between, wildfires raged through California, Arizona and New Mexico on the background of a <a href="https://www.nature.com/articles/s41558-022-01290-z">megadrought in Southwestern U.S.</a> that has been more severe than anything the region has experienced in at least 1,200 years. Near Albuquerque, New Mexico, a five-mile stretch of the <a href="https://earthobservatory.nasa.gov/images/150244/rio-grande-runs-dry-then-wet">Rio Grande ran dry</a> for the first time in 40 years. Persistent heat waves lingered over many parts of the country, setting temperature records.</p>
<p>At the same time, during a period of five weeks between July and August, <a href="https://www.washingtonpost.com/climate-environment/2022/08/23/flood-united-states-climate-explainer/">five 1,000-year rainfall events</a> occurred in <a href="https://www.weather.gov/lsx/July262022Flooding">St. Louis</a>, <a href="https://theconversation.com/climate-change-is-intensifying-the-water-cycle-bringing-more-powerful-storms-and-flooding-heres-what-the-science-shows-187951">eastern Kentucky</a>, <a href="https://news.yahoo.com/illinois-flash-flooding-rain-climate-change-184218523.html">southern Illinois</a>, California’s <a href="https://www.nps.gov/deva/learn/news/death-valley-experiences-1-000-year-rain-event.htm">Death Valley</a> and in <a href="https://www.texastribune.org/2022/08/22/dallas-flooding-fort-worth/">Dallas</a>, causing devastating and sometimes deadly flash floods. Extreme rainfall also led to severe flooding in <a href="https://theconversation.com/intense-heat-and-flooding-are-wreaking-havoc-on-power-and-water-systems-as-climate-change-batters-americas-aging-infrastructure-189761">Mississippi</a>, <a href="https://www.gpb.org/news/2022/07/14/virginia-flooding-damages-more-100-homes-and-leaves-40-people-unaccounted-for">Virginia</a> and <a href="https://www.nytimes.com/2022/08/15/us/west-virginia-flash-floods.html">West Virginia</a>.</p>
<p><iframe id="P2HHH" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/P2HHH/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The United States is hardly alone in its share of climate disasters. </p>
<p>In Pakistan, <a href="https://theconversation.com/pakistan-floods-what-role-did-climate-change-play-189833">record monsoon rains</a> inundated more than one-third of the country, killing over 1,500 people. In <a href="https://www.newyorker.com/magazine/2022/08/01/living-through-indias-next-level-heat-wave">India</a> and <a href="https://www.theguardian.com/world/2022/sep/07/china-reports-most-severe-heatwave-and-lowest-rainfall-on-record">China</a>, prolonged heat waves and droughts dried up rivers, disrupted power grids and threatened food security for billions of people.</p>
<p>In Europe, heat waves set record temperatures <a href="https://www.washingtonpost.com/world/2022/07/28/human-caused-climate-change-made-uk-heat-wave-10-times-more-likely-study-says/">in Britain</a> and other places, leading to severe droughts and wildfires in many parts of the continent. <a href="https://www.cnn.com/2022/05/13/africa/south-africa-floods-climate-intl/index.html">In South Africa</a>, torrential rains brought flooding and mudslides that killed more than 400 people. The summer may have come to an end on the calendar, but climate disasters will surely continue.</p>
<p>This isn’t just a freak summer: Over the years, such extreme events are occurring in increasing frequency and intensity.</p>
<h2>Climate change is intensifying these disasters</h2>
<p>The most <a href="https://theconversation.com/climate-change-is-intensifying-the-water-cycle-bringing-more-powerful-storms-and-flooding-heres-what-the-science-shows-187951">recent international climate assessment</a> from the United Nations’ Intergovernmental Panel on Climate Change found significant increases in both the frequency and intensity of extreme temperature and precipitation events, leading to more droughts and floods.</p>
<p>A recent study published in the scientific journal Nature found that extreme flooding and droughts are also <a href="https://doi.org/10.1038/s41586-022-04917-5">getting deadlier and more expensive</a>, despite an improving capacity to manage climate risks. This is because these extreme events, enhanced by climate change, often exceed the designed levels of such management strategies.</p>
<figure class="align-center ">
<img alt="A girl in rain boots walks through a mud-filled yard. Damaged mattresses and other belongings from a flooded house are piled nearby." src="https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/484438/original/file-20220913-14-z0q39y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Flash flooding swept through mountain valleys in eastern Kentucky in July 2022, killing more than three dozen people. It was one of several destructive flash floods.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/local-fire-chief-and-his-daughter-drop-off-goods-for-a-news-photo/1242236541">Seth Herald/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>Extreme events, by definition, occur rarely. A 100-year flood has a 1% chance of happening in any given year. So, when such events occur with increasing frequency and intensity, they are a clear indication of a changing climate state.</p>
<p>The term “global warming” can sometimes be misleading, as it seems to suggest that as humans put more <a href="https://climate.nasa.gov/faq/19/what-is-the-greenhouse-effect/">heat-trapping greenhouse gases</a> into the atmosphere, the world is going to get a bit warmer everywhere. What it fails to convey is that warming temperatures also lead to a more violent world with more extreme climate disasters, as we saw this past summer.</p>
<h2>Climate models showed these risks were coming</h2>
<p>Much of this is well-understood and consistently reproduced by climate models.</p>
<p>As the climate warms, a shift in temperature distribution leads to more extremes. The magnitudes of changes in extreme temperature are often larger than changes in the mean. For example, globally, a 1 degree Celsius increase in annual average temperature is associated with 1.2 C to 1.9 C (2.1 Fahrenheit to 3.4 F) of <a href="https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter11.pdf">increase in the annual maximum temperature</a>.</p>
<figure class="align-center ">
<img alt="A man works on a car with an older mechanic in overalls standing next to him under the shade of a large beach umbrealla." src="https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485653/original/file-20220920-11202-l4elwo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Heat waves, like the heat dome over the South in July 2022, can hit outdoor workers especially hard.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/community-mechanic-lloyd-bush-works-on-a-neighbors-vehicle-news-photo/1410189284">Brandon Bell/Getty Images</a></span>
</figcaption>
</figure>
<p>In addition, global warming causes changes in the vertical profile of the atmosphere and equator-to-pole temperature gradients, leading to changes in how the atmosphere and ocean move. The temperature difference between equator and the poles is the driving force for global wind. As the polar regions warm at much higher rates then the equator, the reduced temperature difference causes a weakening of global winds and leads to a <a href="https://e360.yale.edu/features/global-stilling-is-climate-change-slowing-the-worlds-wind">more meandering jet stream</a>.</p>
<p>Some of these changes can create conditions such as persistent high-pressure systems and atmosphere blocking that favor more frequent and more intense heat waves. The <a href="https://theconversation.com/what-is-a-heat-dome-an-atmospheric-scientist-explains-the-weather-phenomenon-baking-california-and-the-west-185569">heat domes</a> over the Southern Plains and South in June and the West in September are examples.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1538941467686756352"}"></div></p>
<p>The initial warming can be further amplified by positive feedbacks. For example, warming increases snow melt, exposing dark soil underneath, which absorbs more heat than snow, further enhancing the warming. </p>
<p>Warming of the atmosphere also increases its capacity to hold water vapor, which is a strong greenhouse gas. Therefore, more water vapor in the air leads to more warming. Higher temperatures tend to dry out the soil, and less soil moisture reduces the land’s heat capacity, making it easier to heat up. </p>
<p>These positive feedbacks further intensify the initial warming, leading to more heat extremes. More frequent and persistent heat waves lead to excessive evaporation, combined with decreased precipitation in some regions, causing more severe droughts and more frequent wildfires.</p>
<p><iframe id="zBAAz" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/zBAAz/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Higher temperatures <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/">increase the atmosphere’s capacity</a> to hold moisture at a rate of about 7% per degree Celsius.</p>
<p>This increased humidity leads to heavier rainfall events. In addition, storm systems are <a href="https://thinktv.pbslearningmedia.org/resource/nves.sci.earth.hurricane/water-vapor-fuels-hurricanes/">fueled by latent heat</a>, or the large amount of energy released when water vapor condenses to liquid water. Increased moisture content in the atmosphere also enhances latent heat in storm systems, increasing their intensity. Extreme heavy or persistent rainfall leads to increased flooding and landslides, with devastating social and economic consequences.</p>
<p>Even though it’s difficult to link specific extreme events directly to climate change, when these supposedly rare events occur with increasing frequency in a warming world, it is hard to ignore the changing state of our climate. </p>
<figure class="align-center ">
<img alt="A woman with her eyes closed holds a screaming 1-year-old boy in a National Guard helicopter, with a guardsman standing in the open helicopter door." src="https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/485651/original/file-20220920-14-jz4qqj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A family had to be airlifted from their home in eastern Kentucky after it was surrounded by floodwater in July 2022.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/command-sergeant-major-tim-lewis-of-the-kentucky-national-news-photo/1242203173">Michael Swensen/Getty Images</a></span>
</figcaption>
</figure>
<h2>The new abnormal</h2>
<p>So this past summer might just provide a glimpse of our near future, as these extreme climate events become more frequent.</p>
<p>To say this is the new “normal,” though, is misleading. It suggests that we have reached a new stable state, and that is far from the truth.</p>
<p>Without serious effort to curb greenhouse gas emissions, this trend toward more extreme events will continue. Things will keep getting worse, and this past summer will become the norm a few years or decades down the road – and eventually, it will seem mild, like one of those “nice summers” we look back on fondly with nostalgia.</p><img src="https://counter.theconversation.com/content/190636/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shuang-Ye Wu does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Millions of people around the world suffered through long-lasting heat waves and deadly flash flooding in the summer of 2022. A climate scientist explains the rising risks.Shuang-Ye Wu, Professor of Geology and Environmental Geosciences, University of DaytonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1855692022-06-22T12:35:23Z2022-06-22T12:35:23ZWhat is a heat dome? An atmospheric scientist explains the weather phenomenon baking Texas and the Southwest<figure><img src="https://images.theconversation.com/files/534155/original/file-20230626-27-2k6wiq.png?ixlib=rb-1.1.0&rect=0%2C143%2C811%2C564&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A heat dome began sizzling Texas and its neighbors in mid-June 2023, with warm nights providing little relief.</span> <span class="attribution"><a class="source" href="https://graphical.mdl.nws.noaa.gov/sectors/sectorDay.php?view=public&sector=conus&element=T">National Weather Service</a></span></figcaption></figure><p>A heat dome occurs when a persistent region of high pressure traps heat over an area. The heat dome can stretch over several states and linger for days to weeks, leaving the people, crops and animals below to suffer through stagnant, hot air that can feel like an oven.</p>
<p>Typically, heat domes are tied to the behavior of <a href="https://www.youtube.com/watch?v=o203JXAnSA0">the jet stream</a>, a band of fast winds high in the atmosphere that generally runs west to east. </p>
<p>Normally, the jet stream has a <a href="https://www.weather.gov/jetstream/jet">wavelike pattern, meandering</a> north and then south and then north again. When these meanders in the jet stream become bigger, they move slower and can become stationary. That’s when heat domes can occur. </p>
<figure class="align-center ">
<img alt="Map of U.S. with a bubble over the Midwest showing arrows moving, with the ridge air sinking" src="https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/470123/original/file-20220621-23-no5s1r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Heat domes involve high-pressure areas that trap and heat up the air below.</span>
<span class="attribution"><a class="source" href="https://oceanservice.noaa.gov/facts/heat-dome.html">NOAA</a></span>
</figcaption>
</figure>
<p>When the jet stream swings far to the north, air piles up and sinks. The <a href="https://glossary.ametsoc.org/wiki/Heat_dome">air warms as it sinks</a>, and the sinking air also keeps skies clear since it lowers humidity. That allows the sun to create hotter and hotter conditions near the ground. </p>
<p>If the air near the ground passes over mountains and descends, it can <a href="https://blog.weather.us/downsloping/">warm even more</a>. This downslope warming played a large role in the extremely hot temperatures in the Pacific Northwest during a <a href="https://en.wikipedia.org/wiki/2021_Western_North_America_heat_wave">heat dome event in 2021</a>, when Washington set a state record with 120 degrees Fahrenheit (49 Celsius), and temperatures reached 121 F in British Columbia in Canada, surpassing the previous Canadian record by 8 degrees F (4 C).</p>
<h2>The human impact</h2>
<p>Heat domes normally persist for several days in any one location, but they can last longer. They can also move, influencing neighboring areas over a week or two. The heat dome that started in Texas and Mexico in <a href="https://origin.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdspd">June 2023</a> spread into the Southwest in July, with little relief in sight.</p>
<p>On rare occasions, the heat dome can be more persistent. That happened in the <a href="https://www.hsdl.org/c/tl/1980-us-heat-wave/">southern Plains in 1980</a>, when as many as 10,000 people died during weeks of high summer heat. It also happened over much of the United States <a href="https://doi.org/10.1038/s41558-020-0771-7">during the Dust Bowl years</a> of the 1930s.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1677793035487444992"}"></div></p>
<p>A heat dome can have serious impacts on people, because the stagnant weather pattern that allows it to exist usually results in weak winds and an increase in humidity. Both factors make the heat feel worse – <a href="https://theconversation.com/knowing-how-heat-and-humidity-affect-your-body-can-help-you-stay-safe-during-heat-waves-163700">and become more dangerous</a> – because the human body is not cooled as much by sweating.</p>
<p>The <a href="https://www.weather.gov/ama/heatindex">heat index</a>, a combination of heat and humidity, is often used to convey this danger by indicating what the temperature will feel like to most people. The high humidity also reduces the amount of cooling at night. Warm nights can leave people without air conditioners unable to cool off, which increases the risk of heat illnesses and deaths. With global warming, <a href="https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature">temperatures are already higher</a>, too.</p>
<p>One of the worst recent examples of the impacts from a heat dome with high temperatures and humidity in the U.S. occurred <a href="https://www.weather.gov/lot/1995_heatwave_anniversary">in the summer of 1995</a>, when an estimated <a href="https://www.chicagomag.com/Chicago-Magazine/July-2015/1995-Chicago-heat-wave/">739 people died in the Chicago area</a> over five days.</p>
<p><em>This article was updated July 10, 2023, with the heat dome in the Southwest.</em></p><img src="https://counter.theconversation.com/content/185569/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>William Gallus receives funding from the National Science Foundation. </span></em></p>Heat domes are a dangerous part of summer weather.William Gallus, Professor of Atmospheric Science, Iowa State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1793572022-05-02T12:37:24Z2022-05-02T12:37:24ZWhat do tornadoes look like on the inside?<figure><img src="https://images.theconversation.com/files/457168/original/file-20220408-11-604hh6.JPG?ixlib=rb-1.1.0&rect=6%2C3%2C2035%2C1529&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A tornado in Turkey, Texas.</span> <span class="attribution"><span class="source">Jana Houser</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What do tornadoes look like on the inside? – Madison, age 7, Noblesville, Indiana</strong></p>
</blockquote>
<hr>
<p>Scientists really don’t know the answer to this question. There are no visual observations from inside of a tornado, because these storms create very violent and dangerous conditions on the ground. </p>
<p>If we placed cameras in the path of a tornado, they would either be damaged by the strong winds and swirling debris, or become so caked with mud and water that they wouldn’t produce any useful pictures. And of course, it’s not safe for humans to try to observe tornadoes at close range. It’s important to always <a href="https://www.cdc.gov/nceh/features/tornadosafety/index.html">seek shelter when tornado conditions develop</a>. </p>
<p>We do have some ideas about the structure of the inside of tornadoes from instruments called <a href="https://www.nssl.noaa.gov/tools/radar/mobile/">mobile Doppler radars</a>. Scientists can drive these instruments to locations near the tornado, but stop at a safe distance. </p>
<p>The radar sends energy toward the tornado, and when it hits the storm, some of the energy is bounced back. Researchers can analyze that reflected energy to detect important characteristics about the tornado. These include where there is and is not rain within the storm, where there is debris, how fast the winds are, and how these properties change moving away from the center of the tornado toward its outer edges and up vertically through the storm cloud above it. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/jsDcQryQm3Q?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Researchers use mobile radar to study tornadoes and other kinds of storms across the U.S.</span></figcaption>
</figure>
<p>From these radar observations, we have learned that tornadoes usually have a clear area in their centers, or at least a zone that is rain- and debris-free. This area also has intense vertical winds that sometimes are strong enough to suck pavement up from roads. </p>
<p>This clear space is surrounded by a ring of heavy rain and debris that is often moving outward, away from the tornado’s center. That’s because the winds are spinning incredibly fast and creating <a href="https://www.livescience.com/52488-centrifugal-centripetal-forces.html">centrifugal force</a> that pulls these objects away from the middle of the storm. Sometimes areas of heavy rain that are a little farther removed from the tornado spiral inward toward the area of rotation, like the <a href="https://mynasadata.larc.nasa.gov/basic-page/hurricane-dynamics">spiral bands</a> that extend outward from the eye of a hurricane. </p>
<p>Some tornadoes have only <a href="https://en.wikipedia.org/wiki/Tornado#/media/File:F5_tornado_Elie_Manitoba_2007.jpg">one main funnel cloud</a>. Others have <a href="https://www.youtube.com/watch?v=zsyWlak3_6M">multiple small funnels</a> that rotate around each other. There are even tornadoes that <a href="https://www.spc.noaa.gov/faq/tornado/nofunnel.htm">don’t have a funnel cloud at all</a>. As long as winds are rotating in a tight circle all the way from the storm cloud down to the ground, it’s a tornado, even if atmospheric conditions haven’t condensed water vapor in the air into a visible funnel.</p>
<p>Scientists have also learned that many tornadoes don’t actually descend from the cloud to the ground. Rather, they <a href="https://www.al.com/news/huntsville/2015/05/do_tornadoes_actually_form_on.html">form at the ground</a> and quickly build upward – often in less than a minute. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/0PgnpaJ4i5I?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Tornadoes can form at the ground before radar detects rotating winds at low levels.</span></figcaption>
</figure>
<p>When that happens, your eyes may fool you if you’re watching for a funnel cloud coming down from the sky. There could already be tornado-strength winds at the surface, even without that funnel cloud. So be careful – when it comes to tornadoes, looks can be deceiving.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/179357/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jana Houser receives funding from the National Science Foundation. </span></em></p>You can’t photograph the inside of a twister, but radar offers some clues.Jana Lesak Houser, Associate Professor of Geography, Ohio UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1782952022-03-29T12:36:30Z2022-03-29T12:36:30ZHow fast can we stop Earth from warming?<figure><img src="https://images.theconversation.com/files/453654/original/file-20220322-21-4h6qc0.jpg?ixlib=rb-1.1.0&rect=17%2C180%2C3864%2C2403&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The ocean retains heat for much longer than land does. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/crowded-sunset-silhouette-royalty-free-image/1179557108">Aliraza Khatri's Photography via Getty Images</a></span></figcaption></figure><p>Global warming doesn’t stop on a dime. If people everywhere stopped burning fossil fuels tomorrow, stored heat would still continue to warm the atmosphere.</p>
<p>Picture how a radiator heats a home. Water is heated by a boiler, and the hot water circulates through pipes and radiators in the house. The radiators warm up and heat the air in the room. Even after the boiler is turned off, the already heated water is still circulating through the system, heating the house. The radiators are, in fact, cooling down, but their stored heat is still warming the air in the room.</p>
<p>This is known as <a href="https://doi.org/10.1038/s41558-020-00955-x">committed warming</a>. Earth similarly has ways of storing and releasing heat. </p>
<p>Emerging research is refining scientists’ understanding of how Earth’s committed warming will affect the climate. Where we once thought it would take 40 years or longer for global surface air temperature to peak once humans stopped heating up the planet, research now suggests <a href="https://doi.org/10.1088/1748-9326/9/12/124002">temperature could peak in closer to 10 years</a>.</p>
<p>But that doesn’t mean the planet returns to its preindustrial climate or that we avoid disruptive effects such as sea level rise.</p>
<p>I am a professor of climate science, and my research and teaching focus on the usability of climate knowledge by practitioners such as urban planners, public health professionals and policymakers. Let’s take a look at the bigger picture.</p>
<h2>How understanding of peak warming has changed</h2>
<p>Historically, the <a href="https://www.carbonbrief.org/timeline-history-climate-modelling">first climate models</a> represented only the atmosphere and were greatly simplified. Over the years, scientists <a href="https://celebrating200years.noaa.gov/breakthroughs/climate_model/welcome.html">added oceans</a>, land, ice sheets, chemistry and biology.</p>
<p>Today’s models can more explicitly represent the behavior of greenhouse gases, especially carbon dioxide. That allows scientists to better separate heating due to carbon dioxide in the atmosphere from the role of heat stored in the ocean.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/_WUNMzC98jI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Why global warming is ocean warming.</span></figcaption>
</figure>
<p>Thinking about our radiator analogy, increasing concentrations of greenhouse gases in Earth’s atmosphere keep the boiler on – holding energy near the surface and raising the temperature. Heat accumulates and is stored, <a href="https://climate.nasa.gov/vital-signs/ocean-heat/">mostly in the oceans</a>, which take on the role of the radiators. The heat is distributed around the world through weather and oceanic currents.</p>
<p>The <a href="https://bg.copernicus.org/articles/17/2987/2020/">current understanding</a> is that if all of the additional heating to the planet caused by humans was eliminated, a plausible outcome is that Earth would reach <a href="https://www.carbonbrief.org/explainer-will-global-warming-stop-as-soon-as-net-zero-emissions-are-reached">a global surface air temperature peak in closer to 10 years than 40</a>. The previous estimate of 40 or more years has been widely used over the years, <a href="https://theconversation.com/what-would-happen-to-the-climate-if-we-stopped-emitting-greenhouse-gases-today-35011">including by me</a>.</p>
<p>It is important to note that this is only the peak, when the temperature starts to stabilize – not the onset of rapid cooling or a reversal of climate change.</p>
<p>I believe there is <a href="https://bg.copernicus.org/articles/17/2987/2020/">enough uncertainty to justify caution</a> about exaggerating the significance of the new research’s results. The authors applied the concept of peak warming to global surface air temperature. Global surface air temperature is, metaphorically, the temperature in the “room,” and is not the best measure of climate change. The concept of instantly cutting off human-caused heating is also idealized and entirely unrealistic – doing that would involve much more than just ending fossil fuel use, including widespread changes to agriculture – and it only helps illustrate how parts of the climate might behave. </p>
<p>Even if the air temperature were to peak and stabilize, “<a href="https://youtu.be/AT5jdqHUeKM">committed ice melting</a>,” “committed sea level rise” and numerous other land and biological trends would continue to evolve from the accumulated heat. Some of these could, in fact, cause a <a href="https://doi.org/10.1130/G48580.1">release of carbon dioxide and methane</a>, especially from the Arctic and other high-latitude reservoirs that are <a href="https://yaleclimateconnections.org/2018/02/the-permafrost-bomb-is-ticking/">currently frozen</a>. </p>
<p>For these reasons and others, it is important to consider the how far into the future studies like this one look.</p>
<h2>Oceans in the future</h2>
<p>Oceans will continue to store heat and exchange it with the atmosphere. Even if emissions stopped, the excess heat that has been accumulating in the ocean since preindustrial times would influence the climate for another 100 years or more.</p>
<p>Because the ocean is dynamic, it has currents, and it will not simply diffuse its excess heat back into the atmosphere. There will be ups and downs as the temperature adjusts.</p>
<p>The oceans also influence the amount of carbon dioxide in the atmosphere, because carbon dioxide is both absorbed and emitted by the oceans. <a href="https://www.ncei.noaa.gov/products/paleoclimatology/paleo-perspectives/global-warming">Paleoclimate studies show</a> large changes in carbon dioxide and temperature in the past, with the oceans playing an important role.</p>
<figure class="align-center ">
<img alt="Chart showing ocean heating increasing fastest and going to greater depths over time." src="https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/453639/original/file-20220322-24-c0zec5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The chart shows how excess heat – thermal energy – has built up in ocean, land, ice and atmosphere since 1960 and moved to greater ocean depths with time. TOA CERES refers to the top of the atmosphere.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earth%27s_Heat_Accumulation.png">Karina von Schuckman, LiJing Cheng, Matthew D. Palmer, James Hansen, Caterina Tassone, et al.</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Countries aren’t close to ending fossil fuel use</h2>
<p>The possibility that a policy intervention might have measurable impacts in <a href="https://doi.org/10.1088/1748-9326/9/12/124002">10 years</a> rather than several decades could motivate more aggressive efforts to remove carbon dioxide from the atmosphere. It would be very satisfying to see policy interventions having present rather than notional future benefits.</p>
<p>[<em>Over 150,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-150ksignup">Sign up today</a>.]</p>
<p>However, today, countries aren’t anywhere close to ending their fossil fuel use. Instead, all of the <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/">evidence points to humanity experiencing rapid global warming</a> in the coming decades. </p>
<p>Our most robust finding is that the less carbon dioxide humans release, the better off humanity will be. Committed warming and human behavior point to a need to accelerate efforts both to reduce greenhouse gas emissions and to adapt to this warming planet now, rather than simply talking about how much needs to happen in the future.</p><img src="https://counter.theconversation.com/content/178295/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Rood receives funding from the National Oceanographic and Atmospheric Administration and the National Science Foundation. He is a co-principal investigator at the Great Lakes Integrated Sciences and Assessment Center at the University of Michigan.</span></em></p>If fossil fuel burning stopped, emerging research suggests air temperatures could level off sooner than expected. But that doesn’t mean the damage stops.Richard B. (Ricky) Rood, Professor of Climate and Space Sciences and Engineering, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1788632022-03-23T17:46:45Z2022-03-23T17:46:45ZTornadoes, climate change and why Dixie is the new Tornado Alley<figure><img src="https://images.theconversation.com/files/450763/original/file-20220308-27-79zxp9.jpg?ixlib=rb-1.1.0&rect=0%2C9%2C6144%2C4074&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The heart of U.S. tornado activity, once Tornado Alley, has shifted eastward.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/noaaphotolib/27906393336/in/gallery-194732561@N07-72157720311063131/">Brent Koops/NOAA Weather in Focus Photo Contest 2015</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p><em>Tornadoes and severe storms swept across the South in <a href="https://www.washingtonpost.com/weather/2022/04/05/severe-thunderstorms-tornadoes-south-southeast/">early April</a> 2022, following <a href="https://apnews.com/article/tornadoes-ap-news-alert-florida-a9d5ab5e1479a40a486d436072884181">a deadly and destructive March</a> when <a href="https://www.spc.noaa.gov/climo/online/monthly/2022_annual_summary.html">over 200 tornadoes</a> were reported. The March numbers, still preliminary, would be a record for the month, though detection has also improved. Severe storms have damaged homes from <a href="https://abcnews.go.com/US/killed-severe-weather-spawns-30-tornadoes-states/story?id=83784060">Texas to Florida</a>, and north to <a href="https://www.washingtonpost.com/weather/2022/04/05/severe-thunderstorms-tornadoes-south-southeast/">South Carolina</a> and <a href="https://weather.com/storms/severe/video/tornado-near-savannah-captured-on-video">Georgia</a> in recent weeks. We asked tornado scientist <a href="https://www.researchgate.net/profile/Ernest-Agee">Ernest Agee</a> to explain what causes tornadoes and how the center of U.S. tornado activity has shifted eastward from the traditional Tornado Alley in recent years.</em></p>
<h2>What causes tornadoes?</h2>
<p>Tornadoes start with thunderstorms. Think of the thunderstorm as the parent of the tornado. When atmospheric conditions favor the development of severe storms, tornadoes can form.</p>
<p>The recipe for a tornado requires a few important ingredients: low-level heat and moisture and cold air aloft, coupled with a favorable wind field that increases in speed with height, as well as changes in the wind direction in the lower levels.</p>
<p>The right combination of heat, moisture and wind can develop rotating thunderstorms capable of spinning off a tornado or a tornado family. Thunderstorms capable of spinning off tornadoes typically develop along and ahead of a <a href="https://www.wpc.ncep.noaa.gov/html/fntcodestxt.html">frontal boundary</a> – where warm and cold air masses meet – often accompanied above by a <a href="https://scijinks.gov/jet-stream/">strong jet stream</a>.</p>
<h2>Why do tornado outbreaks seem to be getting more frequent and intense? Is climate change playing a role?</h2>
<p>Studies do show tornadoes getting <a href="https://doi.org/10.1038/s41612-018-0048-2">more frequent, more intense and more likely to come in swarms</a>.</p>
<p>The most intense and longest-lasting tornadoes tend to come from what are known as <a href="https://www.weather.gov/ama/supercell">supercells</a> – powerful rotating thunderstorms. The <a href="https://www.noaa.gov/news/december-2021-tornado-outbreak-explained">December 2021 outbreak, with more than 60 tornadoes</a> that swept across Kentucky and neighboring states, came from a supercell. The <a href="https://www.weather.gov/bmx/event_04272011">2011 outbreak in Alabama</a> was another.</p>
<p>All of this unfolds under the umbrella of global warming. While it’s still <a href="https://theconversation.com/tornadoes-and-climate-change-what-a-warming-world-means-for-deadly-twisters-and-the-type-of-storms-that-spawn-them-173645">hard for climate models to assess</a> something as small as a tornado, they do <a href="https://doi.org/10.1038/s41612-018-0048-2">project increases in severe weather</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MJJG3-MVz1U?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Forecasting tornadoes. NOAA National Severe Storms Laboratory.</span></figcaption>
</figure>
<p>What’s interesting is that despite that increase, the per capita death toll from tornadoes has <a href="https://doi.org/10.1175/WCAS-D-18-0078.1">actually gone down</a> in the latter half of the past 100 years. So, as bad as these new outbreaks are, science and technology are saving lives at a faster rate than storms are killing people.</p>
<p>Scientists can now anticipate and forecast areas where tornadoes may develop. If you look at NOAA’s <a href="https://www.spc.noaa.gov/products/outlook/">Storm Prediction Center website</a>, you’ll see eight-day outlooks now. That’s based on scientific knowledge and technology able to target where conditions conducive to tornadoes are developing.</p>
<p>People also <a href="https://abc11.com/tornado-warning-severe-weather-alerts-watch-vs-accuweather/5321358/">know what to do now</a> and are more likely to get warnings, and more homes have <a href="https://www.fema.gov/emergency-managers/risk-management/safe-rooms">safe rooms</a> able to withstand a tornado. Social media also plays a big role today. A few years ago, I had a student who was on his family’s farm when he got a text warning that a tornado was coming. He and his family got to safety just before the tornado hit.</p>
<h2>The Southeast seems to be getting a lot more severe storms. Has Tornado Alley shifted?</h2>
<p>In 2016, my students and I published the first paper that clearly showed, statistically, the <a href="https://doi.org/10.1175/JAMC-D-15-0342.1">emergence of another center of tornado activity</a> in the Southeast, centered around Alabama.</p>
<p>Oklahoma still has tornadoes, of course. But the statistical center has moved. Other research since then has <a href="https://doi.org/10.1002/joc.5285">found similar shifts</a>.</p>
<figure class="align-center ">
<img alt="Map of U.S. showing tornado activity greatest from Louisiana through Alabama and north to Tennessee." src="https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=407&fit=crop&dpr=1 600w, https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=407&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=407&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=512&fit=crop&dpr=1 754w, https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=512&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/450797/original/file-20220308-21-1nm6thq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=512&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mean number of days per year with a tornado registering EF1 strength or greater within 25 miles, 1986-2015.</span>
<span class="attribution"><a class="source" href="https://www.spc.noaa.gov/wcm/">NOAA Storm Prediction Center</a></span>
</figcaption>
</figure>
<p>We found a notable decrease in both the total number of tornadoes and days with tornadoes in the traditional Tornado Alley in the central plains. At the same time, we found an increase in tornado numbers in what’s been dubbed Dixie Alley, extending from Mississippi through Tennessee and Kentucky into southern Indiana.</p>
<p>In the Great Plains, drier air in the western boundary of traditional Tornado Alley probably has something to do with the fact that tornadoes are a declining risk in Oklahoma while wildfire risk is growing. </p>
<p>Research by other scientists suggests that the <a href="https://doi.org/10.1175/EI-D-17-0011.1">dry line</a> between the wetter Eastern U.S. and the drier Western U.S., historically around the 100th meridian, has <a href="https://doi.org/10.1175/EI-D-17-0012.1">shifted eastward</a> by <a href="https://news.climate.columbia.edu/2018/04/11/the-100th-meridian-where-the-great-plains-used-to-begin-now-moving-east/">about 140 miles</a> since the late 1800s. The dry line can be a boundary for convection – the rising of warm air and sinking of colder air that can fuel storms.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1506617765347614725"}"></div></p>
<p>While scientists don’t have a full picture of the role climate change may be playing, we can certainly say we live in a warmer climate, and that a warming climate provides many of the ingredients for severe storms.</p>
<p>[<em><a href="https://memberservices.theconversation.com/newsletters/?source=inline-youresmart">Read The Conversation daily by subscribing to our newsletter</a></em>.]</p>
<p><em>This article was updated April 6, 2022, with more severe storms and tornadoes across the South.</em></p><img src="https://counter.theconversation.com/content/178863/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ernest Agee does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Studies show tornadoes are getting more common and more intense, and they’re shifting eastward to a new tornado hot spot.Ernest Agee, Professor Emeritus of Atmospheric Science, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1772332022-03-16T12:34:02Z2022-03-16T12:34:02ZCloud seeding might not be as promising as drought-troubled states hope<figure><img src="https://images.theconversation.com/files/446845/original/file-20220216-25-1vorff5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cloud seeding equipment near Winter Park in Colorado.</span> <span class="attribution"><a class="source" href="https://www.denverwater.org/tap/cloud-seedings-role-winter-season">Denver Water</a></span></figcaption></figure><p>On mountain peaks scattered across Colorado, <a href="https://cwcb.colorado.gov/focus-areas/supply/weather-modification-program">machines are set up to fire chemicals into the clouds</a> in attempts to generate snow. The process is called cloud seeding, and as global temperatures rise, more <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">countries</a> and <a href="https://www.theguardian.com/environment/2021/mar/23/us-stated-cloud-seeding-weather-modification">drought-troubled states</a> are using it in sometimes desperate efforts to modify the weather.</p>
<p>But cloud seeding isn’t as simple as it sounds, and it might not be as promising as people wish.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/cloud-seeding-might-not-be-as-promising-as-drought-troubled-states-hope-177233&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
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<hr>
<p>As an <a href="https://www.researchgate.net/scientific-contributions/William-R-Cotton-72102078">atmospheric scientist</a>, I have studied and <a href="https://www.cambridge.org/core/books/abs/human-impacts-on-weather-and-climate/rise-of-the-science-of-weather-modification-by-cloud-seeding/973C1181FD0E4220848FC83AFE05D2D2">written about weather modification</a> for 50 years. Cloud seeding <a href="https://doi.org/10.1073/pnas.1917204117">experiments that produce snow or rain</a> require the <a href="https://doi.org/10.1175/JAMC-D-18-0341.1">right kind of clouds</a> with enough moisture, and the right temperature and wind conditions. The percentage increases in precipitation are small, and it’s difficult to tell when snow or rain fell naturally and when it was triggered by seeding.</p>
<h2>How modern cloud seeding began</h2>
<p>The modern age of weather modification began in the 1940s in Schenectady, New York. </p>
<p>Vince Schaefer, a scientist working for General Electric, <a href="https://patentimages.storage.googleapis.com/7f/03/d4/b4e0d609dd15ee/US2570867.pdf">discovered that adding small pellets of dry ice</a> to a freezer containing “<a href="https://www.pnnl.gov/news-media/supercooled-water-stable-liquid-scientists-show-first-time">supercooled</a>” water droplets triggered a proliferation of ice crystals. </p>
<p><a href="https://rammb.cira.colostate.edu/wmovl/vrl/tutorials/euromet/courses/glossary/bergeron.htm">Other scientists had theorized</a> that the right mix of supercooled water drops and ice crystals could cause precipitation. <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/snow/how-does-snow-form">Snow forms</a> when ice crystals in clouds stick together. If ice-forming particles could be added to clouds, the scientists reasoned, moisture that would otherwise evaporate might have a greater chance of falling. Schaefer proved it could work.</p>
<p>On Nov. 13, 1946, Schaefer <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">dropped crushed dry ice</a> from a plane into supercooled stratus clouds. “I looked toward the rear and was thrilled to see long streamers of snow falling from the base of the cloud through which we had just passed,” <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">he wrote in his journal</a>. A few days later, he wrote that trying the same technique appeared to have improved visibility in fog.</p>
<figure class="align-center ">
<img alt="A man looks into a freezer looking amazed at what he sees." src="https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=827&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=827&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=827&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1040&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1040&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1040&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Vincent Schaefer, in foreground, examines snow created in a modified GE freezer in 1947, with Irving Langmuir, at left, and Bernard Vonnegut.</span>
<span class="attribution"><a class="source" href="https://nyheritage.contentdm.oclc.org/digital/collection/p16694coll20/id/5747/rec/33">General Electric Company/Museum of Science and Innovation</a></span>
</figcaption>
</figure>
<p>A colleague at GE, Bernie Vonnegut, searched through chemical tables for materials with a crystallographic structure similar to ice and discovered that <a href="https://doi.org/10.1063/1.1697813">a smoke of silver iodide particles</a> could have the same effect at temperatures below -20 C (-4 F) as dry ice.</p>
<p>Their research led to <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">Project Cirrus</a>, a joint civilian-military program that explored seeding a variety of clouds, including supercooled stratus clouds, cumulus clouds and <a href="https://vlab.noaa.gov/web/nws-heritage/-/almost-science-fiction-hurricane-modification-and-project-stormfury">even hurricanes</a>. Within a few years, communities and companies that rely on water were spending US$3 million to $5 million a year on cloud-seeding projects, particularly in the drought-troubled western U.S., <a href="https://www.nsf.gov/nsb/publications/1965/nsb1265.pdf">according to congressional testimony in the early 1950s</a>.</p>
<h2>But does cloud seeding actually work?</h2>
<p>The results of about 70 years of research into the effectiveness of cloud seeding are mixed.</p>
<p>Most scientific studies aimed at evaluating the effects of seeding cumulus clouds have shown little to no effect. However, the results of seeding wintertime <a href="https://cloudatlas.wmo.int/en/orographic-influences-on-clouds.html">orographic clouds</a> – clouds that form as air rises over a mountain – have <a href="https://doi.org/10.1073/pnas.1917204117">shown increases in precipitation</a>.</p>
<p>There are two basic approaches to cloud seeding. One is to seed supercooled clouds with silver iodide or dry ice, causing ice crystals to grow, consume moisture from the cloud and fall as snow or rain. It might be shot into the clouds in rockets or sprayed from an airplane or mountaintop. The second involves warm clouds and <a href="https://www.nytimes.com/2003/09/02/science/q-a-salt-and-humidity.html">hygroscopic</a> materials like salt particles. These particles take on water vapor, becoming larger to fall faster.</p>
<figure class="align-center ">
<img alt="A drawing of a plane flying" src="https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=906&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=906&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=906&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1139&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1139&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1139&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An illustration of cloud-seeding processes.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Cloud_seeding#/media/File:Cloudseedingimagecorrected.jpg">Naomi E. Tesla/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The amount of snow or rain tied to cloud seeding has varied, with <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">up to 14% reported in experiments in Australia</a>. In the U.S., studies have found a few percentage points of increase in precipitation. In a 2020 study, scientists <a href="https://doi.org/10.1073/pnas.1917204117">used radar to watch as 20 minutes of cloud seeding</a> caused moisture inside clouds to thicken and fall. In all, about one-tenth of a millimeter of snow accumulated on the ground below in a little over an hour.</p>
<p>Another study, in 2015, used climate data and a <a href="https://doi.org/10.1175/JAMC-D-17-0335.1">six-year cloud-seeding experiment</a> in the mountains of Wyoming to estimate that <a href="https://doi.org/10.1175/JAMC-D-14-0163.1">conditions there were right</a> for cloud seeding about a quarter of the time from November to April. But the results likely would increase the snowpack by <a href="https://doi.org/10.1175/JAMC-D-18-0341.1">no more than about 1.5%</a> for the season.</p>
<p>While encouraging, these experiments have by no means reached the level of significance that Schaefer and his colleagues had anticipated.</p>
<h2>Weather modification is gaining interest again</h2>
<p><a href="https://doi.org/10.1175/JAMC-D-18-0341.1">Scientists today are continuing to carry out randomized seeding experiments</a> to determine when cloud seeding enhances precipitation and by how much.</p>
<p>People have raised a few concerns about negative effects from cloud seeding, but those effects appear to be minor. Silver ion is a <a href="https://doi.org/10.1029/WR006i001p00088">toxic heavy metal</a>, but the amount of silver iodide in seeded snowpack is so small that extremely sensitive instrumentation must be used to detect its presence. </p>
<figure class="align-center ">
<img alt="A man attaches a row of canisters to an airplane wing." src="https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&rect=5%2C5%2C3637%2C2419&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Several companies attempt cloud seeding from airplanes.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/DroughtCloudSeeding/afa3c57641344d3f9165eedf834b388e/photo">AP Photo/Dave Kolpack</a></span>
</figcaption>
</figure>
<p>Meanwhile, extreme weather and droughts are increasing interest in weather modification. </p>
<p>The World Meteorological Organization reported in 2017 that weather modification programs, including suppressing crop-damaging hail and increasing rain and snowfall, were underway in <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">more than 50 countries</a>. My home state of Colorado has <a href="https://cwcb.colorado.gov/weather-modification-grant-program">supported cloud-seeding operations</a> for years. Regardless of the mixed evidence, many communities are counting on it to work.</p><img src="https://counter.theconversation.com/content/177233/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>William R. Cotton does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Several states are experimenting with weather modification to try to generate snow as water supplies shrink. An atmospheric scientist explains the history behind it – and the challenges.William R. Cotton, Professor Emeritus of Meteorology, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1791582022-03-15T16:08:24Z2022-03-15T16:08:24ZPollen season is getting longer and more intense with climate change – here’s what allergy sufferers can expect in the future<figure><img src="https://images.theconversation.com/files/452084/original/file-20220315-99009-sispwj.jpg?ixlib=rb-1.1.0&rect=0%2C15%2C1280%2C929&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ragweed pollen, instigator of headaches and itchy eyes across the U.S.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/ragweed-pollen-royalty-free-image/529469522">Bob Sacha/Corbis Documentary via Getty Images</a></span></figcaption></figure><p>Brace yourselves, allergy sufferers – research shows pollen season is going to get a lot longer and more intense with climate change.</p>
<p>Our study finds that the U.S. will face <a href="https://www.nature.com/articles/s41467-022-28764-0">up to a 200% increase</a> in total pollen this century if the world continues producing carbon dioxide emissions from vehicles, power plants and other sources at a high rate. Pollen season in general will start up to 40 days earlier in the spring and last up to 19 days longer than today under that scenario.</p>
<p>As <a href="https://scholar.google.com/citations?user=3dWPwz8AAAAJ&hl=en">atmospheric</a> <a href="https://clasp.engin.umich.edu/people/zhang-yingxiao/">scientists</a>, we study how the atmosphere and climate affect trees and plants. While most studies focus on pollen overall, we zoomed in on more than a <a href="https://www.nature.com/articles/s41467-022-28764-0">dozen different types of grasses and trees</a> and how their pollen will affect regions across the U.S. in different ways. For example, species like oak and cypress will give the Northeast the biggest increase, but allergens will be on the rise just about everywhere, with consequences for human health and the economy.</p>
<figure class="align-center ">
<img alt="6 maps showing differences in how types of plant pollen seasons will change. Ambrosia, better known as ragweed, has the greatest increase." src="https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=604&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=604&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=604&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=759&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=759&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451986/original/file-20220314-117573-11rcxij.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=759&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The maps on the left show the recent average pollen season length in days for three types of plants: platanus, or plane trees, such as sycamores; betula, or birch; and ambrosia, or ragweed. The maps on the right show the expected changes in total days by the end of the century if carbon dioxide emissions continue at a high rate.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41467-022-28764-0">Zhang and Steiner, 2022</a></span>
</figcaption>
</figure>
<p>If your head is pounding at just the thought of it, we also have some good news, at least for knowing in advance when pollen waves are coming. We’re working on using the model from this study to develop more accurate local pollen forecasts.</p>
<h2>Why pollen is increasing</h2>
<p>Let’s start with the basics. Pollen – the dust-like grains produced by grasses and plants – contains the male genetic material for a plant’s reproduction.</p>
<p>How much pollen is produced depends on how the plant grows. Rising global temperatures will boost plant growth in many areas, and that, in turn, will affect pollen production. But temperature is only part of the equation. We found that <a href="https://www.nature.com/articles/s41467-022-28764-0">the bigger driver of the future pollen increase</a> will be rising carbon dioxide emissions.</p>
<p>The higher temperature will extend the growing season, giving plants more time to emit pollen and reproduce. Carbon dioxide, meanwhile, fuels photosynthesis, so plants may grow larger and produce more pollen. We found that carbon dioxide levels may have a much larger impact on pollen increases than temperature in the future.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Dust-like pollen falls from pine cones" src="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451965/original/file-20220314-16-1h5t3qc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cones on a Norway Spruce in Virginia release pollen.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:2021-04-17_10_43_13A_Pollen_cones_releasing_pollen_on_a_Norway_Spruce_along_Tranquility_Court_in_the_Franklin_Farm_section_of_Oak_Hill,_Fairfax_County,_Virginia.jpg">Famartin/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Pollen changes will vary by region</h2>
<p>We looked at 15 different pollen types, rather than treating all pollen the same as many past studies have.</p>
<p>Typically, pollination starts with leafy deciduous trees in late winter and spring. Alder, birch and oak are the three top deciduous trees for causing allergies, though there are others, like mulberry. Then grasses come out in the summer, followed by ragweed in late summer. In the Southeast, evergreen trees like mountain cedar and juniper (in the cypress family) start in January. In Texas, “cedar fever” is the equivalent of hay fever.</p>
<p>We found that in the Northeast, pollen seasons for a lot of allergenic trees will <a href="https://www.nature.com/articles/s41467-022-28764-0">increasingly overlap</a> as temperatures and carbon dioxide emissions rise. For example, it used to be that oak trees would release pollen first, and then birch would pollinate. Now we see more overlap of their pollen seasons.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2OsicNwv9jE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How pollen season spreads across the U.S. over one year. Yingxiao Zhang and Allison Steiner.</span></figcaption>
</figure>
<p>In general, pollen season will change more in the north than in the south, because of larger temperature increases in northern areas.</p>
<p>Southeastern regions, including Florida, Georgia and South Carolina, can expect large grass and weed pollen increases in the future. The Pacific Northwest is likely to see peak pollen season a month earlier because of the early pollen season of alder. </p>
<h2>Silver lining: We can improve pollen forecasting</h2>
<p>Most pollen forecasts right now provide a very broad estimate. Part of the problem is that there aren’t many <a href="https://pollen.aaaai.org/#/">observing stations</a> for pollen counts. Most are run by allergy clinics, and there are less than 100 of these stations distributed across the country. Michigan, where we live, doesn’t have any.</p>
<p>It’s a very labor-intensive process to actually measure different types of pollen. As a result, current forecasts have a lot of uncertainties. These likely are based in part on what a station has observed in the past and the weather forecast.</p>
<figure class="align-center ">
<img alt="A person's hands jostle a pine branch to collect pollen" src="https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/451976/original/file-20220314-117573-o3yi1v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Pollen sampling for regional forecasts can be labor-intensive.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Pollen_collection.jpg">HelenaAnna/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Our model, if integrated into a forecasting framework, could provide more targeted pollen forecasts across the country.</p>
<p>We can estimate where the trees are from satellite data and on-the-ground surveys. We also know how temperature influences when pollen comes out – what we call the phenology of the pollen. With that information, we can use meteorological factors like wind, relative humidity and precipitation to figure out how much pollen gets into the air, and atmospheric models can show how it moves and blows around, to create a real-time forecast.</p>
<p>All of that information allows us to look at where pollen might be in space and time, so people dealing with allergies will know what’s coming in their area.</p>
<p>We’re currently talking with a <a href="https://www.noaa.gov/">National Oceanic and Atmospheric Administration</a> lab about ways to integrate that information into a tool for air quality forecasting.</p>
<figure class="align-center ">
<img alt="Dozens of round, spiky pollen grains attached to a plant" src="https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/452085/original/file-20220315-19-guleto.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ragweed pollen grains, magnified and colorized.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/ragweed-pollen-royalty-free-image/529469522">Bob Sacha/Corbis Documentary via Getty Images</a></span>
</figcaption>
</figure>
<p>There are still some unknowns when it comes to long-term pollen projections. For example, scientists don’t fully understand why plants produce more pollen in some years than others. There’s not a good way to include that in models. It’s also not fully clear how plants will respond if carbon dioxide levels go through the roof. Ragweed and residential trees are also hard to capture. There are very few ragweed surveys showing where these plants are growing in the U.S., but that can be improved.</p>
<h2>Pollen levels are already on the rise</h2>
<p>A study in 2021 found that the <a href="https://theconversation.com/pollen-can-raise-your-risk-of-covid-19-and-the-season-is-getting-longer-thanks-to-climate-change-156754">overall pollen season</a> was already about <a href="https://doi.org/10.1073/pnas.2013284118">20 days longer in North America</a> than it was in 1990 and pollen concentrations were up about 21%.</p>
<p>Increasing pollen levels in the future will have a much broader impact than a few sniffles and headaches. Seasonal allergies affect <a href="https://doi.org/10.1016/j.anai.2010.10.014">about 30% of the population</a>, and they have economic impacts, from <a href="https://doi.org/10.1016/j.anai.2010.10.014">health costs</a> to <a href="https://doi.org/10.1016/j.rmed.2010.05.006">missed working days</a>.</p><img src="https://counter.theconversation.com/content/179158/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Allison L. Steiner has received funding from NSF, NASA, DOE, and NOAA. She is currently a member of the NASEM Board on Atmospheric Sciences and Climate.</span></em></p><p class="fine-print"><em><span>Yingxiao Zhang does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Rising temperatures mean longer, earlier pollen seasons, but the bigger problem is what carbon dioxide will do to the amount of pollen being released. A 200% increase is possible this century.Yingxiao Zhang, Ph.D. Student in Atmospheric Science, University of MichiganAllison L. Steiner, Professor of Atmospheric Science, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1763392022-02-08T17:14:28Z2022-02-08T17:14:28ZOlympic skiers and snowboarders are competing on 100% fake snow – the science of how it’s made and how it affects performance<figure><img src="https://images.theconversation.com/files/444596/original/file-20220204-25-1wqc0jo.jpg?ixlib=rb-1.1.0&rect=14%2C74%2C4910%2C3136&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Snowmaking machines blow cold water, which freezes before it hits the ground.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/snow-cannon-in-winter-mountains-snow-gun-spraying-royalty-free-image/1337370791?adppopup=true">Alexander Uhrin/iStock via Getty Images</a></span></figcaption></figure><p>The winter Olympics conjure up images of snowy mountain ranges, frozen ice rinks and athletes in cold-weather gear. And for good reason. Winter Olympic venues have often been in places that receive an <a href="https://doi.org/10.1175/MWR-D-19-0007.1">average snowfall of 300 inches per year</a> or more.</p>
<p>However, barring some extremely anomalous weather patterns, the mountains surrounding the snow events for the Beijing Winter Olympics will be tones of brown and green and nearly devoid of snow. The region typically receives only <a href="https://en.wikipedia.org/wiki/Zhangjiakou">a few inches of snowfall</a> in each winter month. This means that basically all of the snow the athletes will be competing on will be human-made.</p>
<p>I am an <a href="https://scholar.google.com/citations?hl=en&user=f8naRg0AAAAJ">atmospheric scientist</a> who specializes in mountain weather and snow. I am also the co-founder of a snowmaking startup and an avid skier. There are distinct differences between natural and artificial snow, and it will be interesting to see if these differences have any effect on competition.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/GE8KpPzU_rQ?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Snowmaking guns spray tiny droplets of cooled water into the air.</span></figcaption>
</figure>
<h2>How to make fake snow</h2>
<p>Though artificial snow and natural snow are both frozen water, most skiers and snowboarders are able to immediately recognize that the two are very different.</p>
<p>Traditional snowmaking uses <a href="https://www.technoalpin.com/en-us/snow-guns/fan-guns/tr10">high pressure water, compressed air and specialized nozzles</a> to blow tiny liquid droplets into the air that then freeze as they fall to the ground. But snowmaking is not as simple as just making sure the air is sufficiently cold. </p>
<p>Pure water does not freeze until it is cooled to nearly -40 F (-40 C). It is only the presence of microscopic suspended particles in water that <a href="https://doi.org/10.1002/qj.49710444024">allow it to freeze at the familiar 32 F (0 C)</a>. These particles, known as ice nuclei, act as a sort of scaffolding to help ice crystals form.</p>
<p>Without these particles, water struggles to turn into ice. Different particles can raise or lower freezing temperatures depending on their specific molecular configuration. </p>
<p>Two of the best ice nuclei are <a href="https://doi.org/10.1175/JAMC-D-18-0341.1">silver iodide</a> and a protein produced by the bacteria <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC186742/"><em>Pseudomonas syringae</em></a>. Most snowmaking systems add a <a href="https://www.snomax.com/product.html">commercial form of the bacterial protein</a> to water to ensure most of the tiny droplets freeze before they hit the ground.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A woman making a tight turn on skis around a red gate." src="https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=391&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=391&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=391&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=491&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=491&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444589/original/file-20220204-25-eejikp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=491&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Skiers and snowboarders in downhill racing events, like U.S. Olympian Mikaela Shiffrin, often prefer the harder, faster artificial snow over natural snow.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/USWorldCupAlpineSkiing/891980327fe34d159be71c729d6ff316/photo?Query=mikaela%20shiffrin&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=2741&currentItemNo=8">AP Photo/Charles Krupa</a></span>
</figcaption>
</figure>
<h2>Sliding on human-made snow</h2>
<p>Natural snow starts as a tiny ice crystal on an ice nucleus in a cloud. As the crystal falls through the air, it <a href="https://doi.org/10.1088/0031-9112/27/8/028">slowly grows into the classic six-sided snowflake</a>. </p>
<p>By comparison, human-made snow freezes quickly from a single droplet of water. The resulting snow consists of billions of tiny spherical balls of ice. It may resemble natural snow to the naked eye on a ski run, but the natural and artificial snow “feel” very different.</p>
<p>Due to the fact that the tiny ice balls pack together quite densely – and that some of them may have not frozen until they touched the ground – artificial snow often feels hard and icy. Fresh natural “powder” snow, on the other hand, provides skiers and snowboarders an almost weightless feeling as they soar down the mountainside. This is largely because the natural snow crystals stack very loosely – a fresh layer of powder is as much as <a href="https://upcolorado.com/utah-state-university-press/item/2390-secrets-of-the-greatest-snow-on-earth">95% or more air</a>. </p>
<p>While fresh powder is what most recreational skiers dream of, Olympic skiers have different tastes. Racers want to be able to glide as fast as possible and use their sharp edges to make powerful, tight turns. The dense, icy conditions of artificial snow are actually better in these regards. In fact, race organizers often <a href="https://mountaintimes.info/elite-ski-racers-carve-water-injected-icy-course/">add liquid water to race courses of natural snow</a> which will freeze and ensure a durable, consistent surface for racers.</p>
<p>Another consideration is the fact that natural snowstorms produce dull, flat lighting and low visibility – hard conditions to race or jump in. Heavy natural snowfall will often cancel ski races, as <a href="https://www.washingtonpost.com/archive/sports/1998/02/09/mens-downhill-delayed-again-due-to-weather/cb89f1d0-5ae2-4b13-9c90-43257b4e9970/">happened during the snowy 1998 Nagano Games</a>. For racers, clear skies and artificial snow provide the advantage there, too.</p>
<p>But hard human-made snow does have its downsides. Freestyle skiers and snowboarders who are flying off jumps or sliding on rails high above the ground seem to <a href="https://www.sportecology.org/_files/ugd/a700be_9aa3ec697a39446eb11b8330aec19e30.pdf">prefer the softer surface of natural snow</a> for safety reasons. This is also true of Nordic skiers, who recently flagged the <a href="https://www.nbcnews.com/science/environment/climate-warms-athletes-flag-dangers-manmade-snow-rcna11915">dangers of artificial snow in the event of crashes</a> as icy, hard surfaces can lead to more injuries. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A zoomed in photo of a complex six-sided snowflake." src="https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444593/original/file-20220204-21-1vmybgg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Natural snowflakes grow slowly into six-sided crystals that are full of air when they pile up on the ground.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Snowflake_macro_photography_1.jpg#/media/File:Snowflake_macro_photography_1.jpg">Alexey Kljatov via WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Mimicking nature</h2>
<p>While Olympic athletes have mixed needs for their snow, for the vast majority of recreational skiers, natural snow is far better. Due to the air-filled crystals, it is much softer and more enjoyable to ski or snowboard on. </p>
<p>Scientists have been trying for decades to create more natural snow on demand. The first way that people tried to make “real” snow was by seeding natural clouds with silver iodide. The goal was to facilitate moisture in clouds turning into falling snow crystals. If you could make this process – called the <a href="https://glossary.ametsoc.org/wiki/Bergeron-findeisen_process">Wegener-Bergeron-Findeisen</a> process – occur more easily, it would theoretically increase the snowfall rate.</p>
<p>In practice, it has historically been difficult to prove the efficacy of seeding. However, recent work using large, meticulously deployed sets of atmospheric instruments has shown that – for a fraction of storms with the proper conditions – seeding clouds with silver iodide does indeed yield modest <a href="https://doi.org/10.1073/pnas.1917204117">increases in the total amount of snowfall</a>. </p>
<p>[<em>Over 140,000 readers rely on The Conversation’s newsletters to understand the world.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-140ksignup">Sign up today</a>.]</p>
<p>Another option – which doesn’t require storm clouds to seed in the first place – is to create snowmaking machines that can grow fluffy natural snow crystals. Scientists have been growing snowflakes in laboratories for many decades, but the process is delicate, and typically researchers only <a href="http://hdl.handle.net/2115/34465">produce a few flakes at a time</a>. Because ice crystals typically grow slowly, it has been tricky for researchers to scale the process up by the many orders of magnitude needed to grow enough snow for skiing. But in a quest to produce fluffy powder for skiers and snowboarders, my colleague Trey Alvey and I developed a process that can produce snowflakes in larger quantities using a technique that mimics the natural crystal formation process. We’re commercializing it through our company called <a href="https://www.quantum-snow.com">Quantum Snow</a>.</p>
<p>The dry, barren mountains hosting the 2022 Winter Olympic venues are not exactly a skiing destination. But thanks to snowmaking science, the athletes will have reliable, if icy, runs to compete on. And sports fans can all be thankful for the technology that allows them to enjoy the high-speed spectacle put on by the brave souls who compete in the skiing and snowboarding events.</p><img src="https://counter.theconversation.com/content/176339/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Veals works for, consults for and owns shares in Quantum Snow LLC. He receives funding from The National Science Foundation, U.S. Department of Energy, NASA, and NOAA. </span></em></p>Snowmaking machines can produce enough snow to cover a run, but artificial snow is very different from natural flakes that fall from the sky.Peter Veals, Professor of Atmospheric Science, University of UtahLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1762012022-02-02T13:06:53Z2022-02-02T13:06:53ZWhy a warming climate can bring bigger snowstorms<figure><img src="https://images.theconversation.com/files/443923/original/file-20220202-21-1vr2vha.jpg?ixlib=rb-1.1.0&rect=0%2C30%2C6720%2C4436&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Boston got socked with nearly 2 feet of snow in late January 2022.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/tall-snow-drifts-and-buried-cars-line-the-sidewalk-on-news-photo/1238082640">Scott Eisen/Getty Images</a></span></figcaption></figure><p>Many of the Northeast’s <a href="https://xmacis.rcc-acis.org/">heaviest snowfalls</a> in over a century of reliable record keeping have occurred since 1990. How can the spate of big snowstorms be reconciled with our warming climate? </p>
<p>I’m an <a href="https://scholar.google.com/citations?user=h3tGrwsAAAAJ&hl=en">atmospheric scientist</a>. Let’s look at an important law of physics and some theories that can help explain the changes.</p>
<p><iframe id="Pgnpr" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/Pgnpr/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Warmer air, more moisture</h2>
<p>First, warmer air can hold more moisture than cold air.</p>
<p>Think of the atmosphere like a sponge. Air holds about 4% more water vapor for each additional degree Fahrenheit increase in temperature (that’s about 7% per degree Celsius). The physical law that explains this relationship is known as <a href="https://eos.org/research-spotlights/extreme-precipitation-expected-to-increase-with-warming-planet">the Clausius-Clapyron relation</a>.</p>
<p>This increased atmospheric moisture is helping to intensify the water cycle. The Northeast and Mid-Atlantic have become wetter – not just in winter, but in spring, summer and fall, too. In addition to more total precipitation over a season and year, the additional moisture also fuels extreme events, like <a href="https://www.scientificamerican.com/article/vapor-storms-are-threatening-people-and-property/">more intense hurricanes and flooding rains</a>. The Northeast has seen an <a href="https://nca2018.globalchange.gov/chapter/2/">increase of more than 50% in the heaviest precipitation events</a> in recent decades, the largest increase of any region of the U.S.</p>
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Read more:
<a href="https://theconversation.com/how-is-snowfall-measured-a-meteorologist-explains-how-volunteers-tally-up-winter-storms-175628">How is snowfall measured? A meteorologist explains how volunteers tally up winter storms</a>
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<p>In the early 1900s, winters across the Northeast typically averaged around 22 degrees Fahrenheit. Now, 26 degrees is the <a href="https://theconversation.com/warming-is-clearly-visible-in-new-us-climate-normal-datasets-159684">official new “normal” temperature</a>, defined as the average over 1991-2020. A few recent winters have been over 30. </p>
<p>In the Northeast, then, we have an environment that has warmed yet is often still below freezing. Put another way, regions of the world that are cold enough for snow have warmed enough to now be visited by storms capable of holding and dropping more moisture. Rather than intense downpours, the region gets heavy snow. </p>
<h2>The warming ocean plays a role</h2>
<p>The historic blizzard that buried Boston under nearly 2 feet of snow in January 2022 was fueled by ocean waters in the western Atlantic that are warmer than normal. That’s also part of a consistent pattern.</p>
<p><iframe id="cPPU2" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/cPPU2/16/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The oceans have been absorbing more than 90% of the additional heat attributable to rising atmospheric greenhouse gases from human activities, particularly burning fossil fuels. The oceans now <a href="https://theconversation.com/ocean-heat-is-at-record-levels-with-major-consequences-174760">contain more heat energy</a> than any time since measurements began six decades ago.</p>
<p>Scientists are studying whether global warming may be driving a slowing of the ocean conveyor belt of currents that transport water around the globe. Satellite imagery and ocean measurements show that <a href="https://doi.org/10.1038/s43247-021-00143-5">warmer waters have “piled up</a>” along the East Coast, a possible indication of a slowing of the <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/oceans/amoc">Atlantic Meridional Overturning Circulation</a>.</p>
<p>Moisture evaporated from ocean water provides much of the energy for both tropical and mid-latitude extra-tropical cyclones, known commonly as nor’easters.</p>
<h2>The Arctic influences the snow pattern, too</h2>
<p>While tropical storm systems are fueled primarily by warm water, <a href="https://theconversation.com/what-is-a-bomb-cyclone-an-atmospheric-scientist-explains-175825">nor’easters gain energy from sharp temperature gradients</a> where cold and warm air masses meet. The frequency of cold air outbreaks is another aspect of climate change that may be contributing to recent increases in extreme snowfall events.</p>
<p>Recent research has suggested that a warming Arctic, including declines in Arctic sea ice and snow cover, is influencing behavior of the polar vortex, a band of strong westerly winds that forms in the stratosphere between about 10 and 30 miles above the Arctic every winter. The winds enclose a large pool of extremely cold air. </p>
<p>When the Arctic is relatively warm, the <a href="https://cpo.noaa.gov/Divisions-Programs/Communication-Education-and-Engagement/CEE-News/ArtMID/8293/ArticleID/2369/Research-Links-Extreme-Cold-Weather-in-the-United-States-to-Arctic-Warming">polar vortex tends to be weaker</a> and more easily elongates or “stretches,” allowing extremely cold air to dip south. Episodes of <a href="https://theconversation.com/how-arctic-warming-can-trigger-extreme-cold-waves-like-the-texas-freeze-a-new-study-makes-the-connection-166550">polar-vortex stretching have markedly increased in the past few decades</a>, leading, at times, to more severe winter weather in some places.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/6KEkSfgHJNk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is the polar vortex? NASA explains.</span></figcaption>
</figure>
<p>Arctic amplification, the enhanced warming to our north, may, paradoxically, be helping to shuttle cold air to the Eastern Seaboard during polar vortex disruptions, where the cold air can interact with warmer, moisture-laden air from the warmer-than-normal western Atlantic Ocean. The most recent stretched polar vortex event helped to bring together key ingredients for the historic blizzard.</p>
<h2>What’s ahead?</h2>
<p>Global climate models project an <a href="https://doi.org/10.1038/s41598-021-95979-4">increase in the most extreme snowfall events</a> across large areas of the Northern Hemisphere with future warming. In some other parts of the world, like Western Europe, <a href="https://theconversation.com/the-water-cycle-is-intensifying-as-the-climate-warms-ipcc-report-warns-that-means-more-intense-storms-and-flooding-165590">intensification of the hydrological cycle</a> will mean more winter rain than snow as temperatures rise.</p>
<p>For the east coast of North America, as well as Northern Asia, winter temperatures are expected to still be cold enough for storms to bring heavy snow – at least through mid-century. Climate models suggest that extreme snowfalls will become rarer, but not necessarily less intense, in the second half of the century, as more storms produce rain.</p>
<p>The sharp increase in high-impact Northeast winter storms is an expected manifestation of a warming climate. It’s another risk the U.S. will have to prepare for as extreme events become more common with climate change.</p><img src="https://counter.theconversation.com/content/176201/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael A. Rawlins receives funding from The Department of Energy, the National Aeronautics and Space Administration, and the National Science Foundation. </span></em></p>Winters are getting warmer, yet Bostonians were digging out from nearly 2 feet of snow from a historic blizzard in late January. Why is the Northeast seeing more big snowstorms like this?Michael A. Rawlins, Associate Director, Climate System Research Center, UMass AmherstLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1758252022-01-27T19:46:48Z2022-01-27T19:46:48ZWhat is a bomb cyclone? An atmospheric scientist explains<figure><img src="https://images.theconversation.com/files/443016/original/file-20220127-22-1gefps5.jpeg?ixlib=rb-1.1.0&rect=6%2C0%2C1042%2C946&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A bomb cyclone over the U.S. East Coast on Jan. 4, 2017.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/east-coast-bomb-cyclone-seen-by-noaas-goes-16-satellite">NOAA/CIRA</a></span></figcaption></figure><p>A bomb cyclone is a large, intense midlatitude storm that has low pressure at its center, weather fronts and an array of associated weather, from blizzards to severe thunderstorms to heavy precipitation. It becomes a bomb when its central pressure decreases very quickly – by at least 24 millibars in 24 hours. Two famed meteorologists, <a href="https://news.mit.edu/2006/obit-sanders">Fred Sanders</a> and <a href="https://www.mcgill.ca/meteo/facultystaff/gyakum">John Gyakum</a>, gave this pattern its name in a <a href="https://doi.org/10.1175/1520-0493(1980)108%3C1589:SDCOT%3E2.0.CO;2">1980 study</a>. </p>
<p>When a cyclone “bombs,” or undergoes bombogenesis, this tells us that it has access to the optimal ingredients for strengthening, such as high amounts of heat, moisture and rising air. Most cyclones don’t intensify rapidly in this way. Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.</p>
<p>The U.S. Eastern Seaboard is one of the <a href="https://doi.org/10.1175/1520-0493(2002)130%3C2188:ECDITS%3E2.0.CO;2">regions where bombogenesis is most common</a>. That’s because storms in the <a href="https://www.merriam-webster.com/dictionary/midlatitudes">midlatitudes</a> – a temperate zone north of the tropics that includes the entire continental U.S. – draw their energy from large temperature contrasts. Along the U.S. East Coast during winter, there’s a naturally potent thermal contrast between the cool land and the warm <a href="https://scijinks.gov/gulf-stream/#">Gulf Stream current</a>. </p>
<p>Over the warmer ocean, heat and moisture are abundant. But as cool continental air moves overhead and creates a large difference in temperature, the lower atmosphere becomes unstable and buoyant. Air rises, cools and condenses, forming clouds and precipitation.</p>
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<figcaption><span class="caption">UK meteorologist Alex Deakin explains how unstable air causes cumulus clouds to form.</span></figcaption>
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<p>Intense cyclones also require favorable conditions above the surface. Particularly strong upper-level winds, also known as “jet streaks,” and <a href="https://www.weather.gov/jetstream/longshort">high-amplitude waves</a> embedded within storm tracks can help force air to rise. </p>
<p>When a strong jet streak overlies a developing low-pressure system, it creates a feedback pattern that makes warm air rise at an increasing rate. This allows the pressure to drop rapidly at the center of the system. As the pressure drops, winds strengthen around the storm. Essentially, the atmosphere is trying to even out pressure differences between the center of the system and the area around it.</p>
<p>Weather forecasters are predicting that the northeastern U.S. will be affected by a <a href="https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdspd">potent winter storm on Jan. 28-30, 2022</a>. Forecast models are calling for a swath of snow from coastal North Carolina northward to Maine.</p>
<p>While precise locations and amounts of snowfall are still uncertain, parts of coastal New England appear most at risk of receiving <a href="https://www.wpc.ncep.noaa.gov/wwd/wssi/wssi.php">8-12 inches or more of heavy accumulating snow</a>. Coupled with winds forecast to be over 50 miles per hour along the coast, the storm is likely to produce blizzard conditions, storm surge, coastal flooding, wind damage and beach erosion. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/trvbHGTDHVg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Bomb cyclones are sometimes called ‘winter hurricanes,’ but they are a different type of storm.</span></figcaption>
</figure>
<p>This storm’s life is expected to begin offshore of the southeast U.S. as a weak low-pressure system. Just 24 hours later, global models predict that its central pressure will drop by 35-50 millibars. </p>
<p>If this storm develops as forecasts predict, aided by winds blowing at over 150 miles per hour in the upper atmosphere, very warm sea surface temperatures just offshore (2-4 degrees Fahrenheit warmer than average), and a highly unstable atmosphere, it will have the critical ingredients for a bomb cyclone. </p>
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<p class="fine-print"><em><span>Esther Mullens receives funding from the National Science Foundation. </span></em></p>The key ingredients for a storm to undergo bombogenesis are an unstable atmosphere, temperature differences and high-speed winds in the upper atmosphere.Esther Mullens, Assistant Professor of Geography, University of FloridaLicensed as Creative Commons – attribution, no derivatives.