tag:theconversation.com,2011:/global/topics/ozone-layer-1571/articlesOzone layer – The Conversation2024-03-08T13:38:33Ztag:theconversation.com,2011:article/2228582024-03-08T13:38:33Z2024-03-08T13:38:33ZAsthma meds have become shockingly unaffordable − but relief may be on the way<figure><img src="https://images.theconversation.com/files/579691/original/file-20240304-18-r33cu5.jpg?ixlib=rb-1.1.0&rect=25%2C51%2C8538%2C5469&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Its price will take your breath away.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/man-using-blue-asthma-inhaler-medication-royalty-free-image/1179346207?">Brian Jackson/Getty Images</a></span></figcaption></figure><p>The <a href="https://www.businessinsider.com/cost-asthma-medication-doubled-unjust-2023-7">price of asthma medication has soared</a> in the U.S. over the past decade and a half. </p>
<p>The jump – in some cases from around <a href="https://doi.org/10.1001/jamainternmed.2015.1665">a little over US$10</a> <a href="https://www.singlecare.com/blog/albuterol-sulfate-hfa-proventil-hfa-without-insurance/">to almost $100</a> for an inhaler – has meant that patients in need of asthma-related products <a href="https://www.businessinsider.com/cost-asthma-medication-doubled-unjust-2023-7">often struggle</a> to buy them. Others simply <a href="https://asthma.net/living/cannot-afford-inhalers">can’t afford</a> them. </p>
<p>To make matters worse, asthma <a href="https://www.fda.gov/drugs/buying-using-medicine-safely/generic-drugs">disproportionately affects</a> lower-income patients. Black, Hispanic and Indigenous communities have the <a href="https://aafa.org/asthma-allergy-research/our-research/asthma-disparities-burden-on-minorities/">highest asthma rates</a>. They also shoulder <a href="https://aafa.org/asthma-allergy-research/our-research/asthma-disparities-burden-on-minorities/">the heaviest burden</a> of asthma-related deaths and hospitalizations. Climate change will likely <a href="https://www.hsph.harvard.edu/c-change/subtopics/climate-change-and-asthma/">worsen asthma rates</a> and, consequently, these disparities.</p>
<p>I’m a health law professor at <a href="https://www1.villanova.edu/university/law/faculty-scholarship/faculty-directory/profiles/AnaSantosRutschman.html">Villanova University</a>, <a href="https://papers.ssrn.com/sol3/cf_dev/AbsByAuth.cfm?per_id=2667484">where I study</a> whether patients can get the medicines they need. And I’ve been watching this affordability crisis closely.</p>
<p>In many ways, it shows what happens when law and policy decisions aren’t aligned with public health needs. The good news, however, is that there finally seems to be some political will to rein in the price of asthma meds.</p>
<h2>Why inhaler prices are skyrocketing</h2>
<p>In 2008, the U.S. Food and Drug Administration <a href="https://www.fda.gov/drugs/frequently-asked-questions-popular-topics/transition-cfc-propelled-albuterol-inhalers-hfa-propelled-albuterol-inhalers-questions-and-answers">banned inhalers</a> that use chlorofluorocarbons, or CFCs – which were once widely used as propellants – because they can damage the ozone layer. The FDA was following a timeline set by an environmental treaty, the <a href="https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol">Montreal Protocol</a>, which the U.S. ratified in the late 1980s. </p>
<p>From 2009 onward, CFC inhalers were phased out and replaced with hydrofluoroalkane, or HFA, ones, which are more environmentally friendly. They’re also a lot pricier. For patients with insurance, the average out-of-pocket cost of an inhaler rose from $13.60 per prescription in 2004 to $25 immediately after the 2008 ban, <a href="https://doi.org/10.1001/jamainternmed.2015.1665">a 2015 study found</a>.</p>
<p>Today, the <a href="https://www.singlecare.com/blog/albuterol-sulfate-hfa-proventil-hfa-without-insurance/">average retail price</a> of an albuterol inhaler is $98. Unlike CFC inhalers, which have <a href="https://www.fda.gov/drugs/buying-using-medicine-safely/generic-drugs">generic versions</a>, HFA inhalers are <a href="https://www.scientificamerican.com/article/unlikely-victims-of-banning-cfcs/">covered by patents</a>. While <a href="http://doi.org/10.1089/jamp.2016.1297">the drug itself</a> hasn’t changed, the switch to a different device allowed companies to increase their prices.</p>
<p>In 2020, the FDA finally approved the <a href="https://www.fda.gov/news-events/press-announcements/fda-approves-first-generic-commonly-used-albuterol-inhaler-treat-and-prevent-bronchospasm">first generic version</a> of an albuterol inhaler. But generic competition still isn’t robust enough to lower prices meaningfully.</p>
<p>Patients with good insurance <a href="https://allergyasthmanetwork.org/advocacy-updates/united-healthcare-albuterol-epinephrine-cost/">may pay very little</a> or even nothing. But uninsured patients face steep market prices, and as of 2023, there were <a href="https://aspe.hhs.gov/sites/default/files/documents/e06a66dfc6f62afc8bb809038dfaebe4/Uninsured-Record-Low-Q12023.pdf">over 25 million</a> uninsured Americans. <a href="https://www.cdc.gov/asthma/asthma_stats/insurance_coverage.htm">Even insured patients may have trouble</a> affording their asthma meds, the CDC has found. </p>
<p>The same asthma medication for which U.S. patients pay top dollar is available elsewhere at much cheaper prices. Consider the following case for inhalers. The pharmaceutical company Teva sells <a href="https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ccd3aaec-4892-40d0-ad60-3e570178fbe1">QVAR RediHaler</a>, a corticosteroid inhaler, <a href="https://doi.org/10.1016/S2213-2600(24)00012-2">for $286</a> in the U.S.</p>
<p>In Germany, Teva sells that same inhaler for $9.</p>
<h2>Seeking meds from Mexico and Canada</h2>
<p>Some U.S. patients have traveled abroad to obtain cheaper asthma medication. After the 2008 ban on CFCs, it became common for patients to <a href="https://doi.org/10.1177/8755122515595052">visit border towns in Mexico</a> to purchase albuterol inhalers. They were sold for <a href="https://doi.org/10.1177/8755122515595052">as little as $3 to $5</a>. </p>
<p>A study of inhalers available to U.S. patients in Nogales, Mexico – about an hour south of Tucson, Arizona – found that Mexican products were <a href="http://doi.org/10.1177/8755122515595052">generally comparable to U.S. inhalers</a>. But researchers found some differences in performance, suggesting that American patients who use them could be getting a slightly different dose than their usual.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Asthma medication is seen on the shelves of a Mexican pharmacy." src="https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/580250/original/file-20240306-24-xrc96u.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">Asthma meds are considerably more affordable south of the border.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-interior-of-farmacia-san-pablo-news-photo/1041982048">Jeffrey Greenberg/Universal Images Group via Getty Images</a></span>
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<p>There have also been reports of Americans turning to Canadian pharmacies to purchase asthma inhalers at much cheaper prices. In one case, a U.S. pharmacy would have charged $857 for a three-month supply. A patient obtained it for <a href="https://www.seattletimes.com/life/wellness/canadian-pharmacy-provided-inhaler-at-a-fraction-of-us-cost/">$134 from a pharmacy in Canada</a>.</p>
<h2>One potential fix: Importing cheaper meds</h2>
<p>U.S. law has long <a href="https://www.fda.gov/about-fda/center-drug-evaluation-and-research-cder/frequently-asked-questions-about-drugs">prohibited</a> personal importation of pharmaceutical drugs. However, a recent development could <a href="https://www.reuters.com/business/healthcare-pharmaceuticals/us-fda-allow-florida-import-cheaper-drugs-canada-2024-01-05">pave the way for states</a> to import cheaper asthma drugs.</p>
<p>In January 2024, the <a href="https://www.reuters.com/business/healthcare-pharmaceuticals/us-fda-allow-florida-import-cheaper-drugs-canada-2024-01-05/">FDA authorized</a> the importation of certain prescription drugs from Canada for the first time. <a href="https://www.kff.org/policy-watch/what-to-know-about-the-fdas-recent-decision-to-allow-florida-to-import-prescription-drugs-from-canada/">For now</a>, this authorization is limited to Florida, and it covers only drugs for HIV/AIDS, prostate cancer and certain mental health conditions.</p>
<p>Should it prove successful, the program could serve as a blueprint for other states.</p>
<h2>Another possible solution: Price-capping</h2>
<p>Policymakers could also try borrowing a page from the insulin playbook. Insulin prices <a href="https://doi.org/10.1001/jamanetworkopen.2023.18074">climbed for almost two decades</a> before Congress acted, capping the cost of insulin for Medicare patients. The 2022 <a href="https://www.congress.gov/bill/117th-congress/house-bill/5376/text">Inflation Reduction Act</a> established an out-of-pocket ceiling of $35 per month for prescription-covered insulin products. </p>
<p>If this cap had been in effect two years earlier, it would have saved 1.5 million Medicare patients about $500 annually, <a href="https://www.hhs.gov/about/news/2023/08/16/first-anniversary-inflation-reduction-act-millions-medicare-enrollees-savings-health-care-costs.html">a recent study estimated</a>. It also would have saved Medicare <a href="https://www.hhs.gov/about/news/2023/08/16/first-anniversary-inflation-reduction-act-millions-medicare-enrollees-savings-health-care-costs.html">$761 million</a>.</p>
<p>A similar approach could be taken for asthma meds.</p>
<p>Congress could create an asthma-specific rule similar to the insulin case. Or it could place provisions for asthma-med prices into a larger piece of legislation.</p>
<p>While this approach depends on the political environment, there are signs the government is becoming more willing to act. In January 2024, the U.S. Department of Health and Human Services <a href="https://www.hhs.gov/about/news/2024/01/29/readout-hhs-officials-meeting-private-sector-patient-advocacy-leaders-improve-national-access-important-asthma-medications.html">hosted a meeting</a> to discuss the problem with manufacturers and other stakeholders.</p>
<p>It’s a start. And – together with other measures – it brings some hope that asthma meds might soon become more affordable to those in need.</p><img src="https://counter.theconversation.com/content/222858/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ana Santos Rutschman 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>An inhaler that costs nearly $300 in the US goes for just $9 in Germany. What gives?Ana Santos Rutschman, Professor of Law, Villanova School of LawLicensed 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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<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/2188392023-11-29T17:18:29Z2023-11-29T17:18:29ZHow science saved the ozone layer<figure><img src="https://images.theconversation.com/files/562385/original/file-20230125-16-qhyylf.png?ixlib=rb-1.1.0&rect=0%2C75%2C1198%2C1059&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Concentration of ozone (in Dobson units) as of mid-September 2022, based on measurements by the IASI infrared sounder over 15 years above Antarctica. The extent of damage and geographical distribution of the hole (in blue) varies according to weather conditions.</span> <span class="attribution"><span class="source">Anne Boynard/LATMOS</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>On 9 January 2023, the United Nations released its <a href="https://news.un.org/en/story/2023/01/1132277">latest report on the status of the ozone layer</a>. It highlighted that this protective barrier is on track toward recovery and should be fully restored by the second half of the 21st century.</p>
<p>There is an urgent need for solutions to help limit climate disruption, yet effective decision-making remains challenging. In light of this context, it is worthwhile to recall the scientific saga that led to the signing of the 1987 Montreal Protocol.</p>
<p>Resulting from the outstanding coordinated efforts of scientists, industrialists and policymakers, that text was the first environmental agreement to be unanimously ratified. Today, the treaty and its subsequent amendments are paving the way toward complete elimination of the substances that destroy the ozone layer.</p>
<h2>Indispensable ozone</h2>
<p>As pointed out by the 2023 annual report, the ozone hole over Antarctica returns every year from September to November. During this three-month period, ozone concentrations <a href="https://www.cnrs.fr/cw/dossiers/dosclim1/motscles/savoirPlus/dobson.html">falling below 220 Dobson units</a>.</p>
<p><a href="https://www.academie-sciences.fr/pdf/rapport/ozone0615.pdf">Ozone protects us from solar radiation</a> by absorbing the most powerful ultraviolet rays into the upper reaches of the atmosphere (10 to 50 km above the Earth’s surface). As such, no ozone means no life on Earth.</p>
<p>We have long known which chemical processes produce and destroy this atmospheric compound filling the stratosphere. In fact, ozone measurements have been carried out since the Interwar period (1919–39). But from the 1980s onward, more and more devices for monitoring the ozone have been developed, from ground-based instruments to weather balloons released on a regular basis by meteorological institutes, and satellites <a href="https://ozonewatch.gsfc.nasa.gov/monthly/SH.html">that monitor the distribution of ozone</a> worldwide.</p>
<p>Back in the 1980s, scientists were concerned about the <a href="https://csl.noaa.gov/assessments/ozone/1994/chapters/chapter11.pdf">impact of supersonic flights</a> and other potential disturbances on this stable atmospheric layer, which is less affected by air masses than those closer to Earth.</p>
<h2>A question mark above Antarctica</h2>
<p>In 1984, a discovery prompted a radical shift in priorities within the scientific community. Two independent teams – one from Japan, the other from the United States – had reported <a href="https://www.nature.com/articles/315207a0">observing a loss of ozone above the Antarctica each October</a> and this loss was becoming more severe by the year. The first puzzle in their findings was that the loss of concentration was observed in a region of the globe that should have been unaffected by human-induced emissions.</p>
<p>Suspicions were soon cast on chlorinated and compounds, the prime targets being <a href="https://gml.noaa.gov/hats/publictn/elkins/cfcs.html">chlorofluorocarbons</a> and halons. In the 1960s, these “magic” industrial compounds became widely available. From then on, they were used in everything from propellants to refrigeration and air conditioning, foam manufacture, fire extinguishers, and beyond.</p>
<p>These chemicals have the advantage of being very stable (remaining in the atmosphere between 50 and 100 years) and posing no harm to health. However, unlike most pollutants generated by human activity, they are not destroyed in the troposphere and can therefore reach the stratosphere.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=447&fit=crop&dpr=1 600w, https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=447&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=447&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=562&fit=crop&dpr=1 754w, https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=562&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/188770/original/file-20171004-28664-1lruby2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=562&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The ban on CFC gases has helped stabilise the formation of the hole in the ozone layer.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Aerosol.png">PiccoloNamek</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Chemists carried out laboratory experiments that demonstrated that chlorine and bromine atoms were able to mix with ozone molecules, thereby destroying them. (They went on to win a <a href="https://www.nobelprize.org/prizes/chemistry/1995/summary/">Nobel Prize for their discovery</a>.)</p>
<p>But the scientists still had other puzzles to solve. Why was this widespread destruction only occurring over the South Pole? And how come satellites had not raised any warnings?</p>
<p>In the latter case, the computer codes that processed the observations and discarded anomalous data were found to have been systematically rejecting the measured values, as these were much too low compared to the expected concentrations usually measured at the Earth’s poles.</p>
<p>In an effort to shed light on the phenomenon, observation campaigns led to the development of <a href="https://gml.noaa.gov/dv/iadv/graph.php?code=SPO&program=ozwv&type=vp">weather balloons and planes for measuring ozone at varying altitudes</a>.</p>
<p>Their observations indicated that the ozone had been completely destroyed across an area of 15 to 20 square kilometres (dubbed the “ozone hole”). But why was this depletion not as significant in higher regions of the atmosphere where the most ozone would be, specifically around 25 km above our heads?</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/O8k-FPTDqvE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Detection of unusual behaviour in the ozone hole from 2020 to 2022. (Copernicus ECMWF, 2022).</span></figcaption>
</figure>
<hr>
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<h2>1985: an awakening</h2>
<p>When <a href="https://www.nature.com/articles/321755a0">the puzzle was solved in 1985</a>, three “ingredients” were revealed to be at play: the dynamics of the stratosphere trapping very cold air masses in the form of vortexes during winter; specific cloud types (i.e., <a href="https://cloudatlas.wmo.int/fr/nitric-acid-and-water-polar-stratospheric-clouds.html">polar stratospheric clouds</a>) caused when temperatures inside these vortexes dropped to approximately -80°C; and greater levels of sunshine in spring, which would trigger a <a href="https://csl.noaa.gov/assessments/ozone/2002/qandas8.pdf">chain of catalytic reactions</a> on the surface of these clouds, involving stable chlorinated and brominated compounds built up over the preceding weeks.</p>
<p>These findings caused a domino effect, culminating in the United Nations <a href="https://ozone.unep.org/sites/default/files/2019-07/VC-Handbook-2019-French.pdf">signing the Vienna Convention</a> for the Protection of the Ozone Layer that same year. The text recognised the need for greater international cooperation with a view to limiting human-induced damage to this layer. Building on this consensus, the <a href="https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol">Montreal Protocol</a> came into existence two years later.</p>
<p>While industrialists at the time proposed to use more reactive substitutes that would decompose before reaching the stratosphere, the scientific community undertook to publish <a href="https://csl.noaa.gov/assessments/ozone/">scientific reports every four years</a>. These authoritative reports were to collate all available information on the ozone and its evolution.</p>
<p>As things stand, the ozone hole has not yet disappeared, as a considerable amount of CFCs and halons remain in the stratosphere. Nevertheless, concentrations of these are declining rapidly, and scientists today regard the ozone layer as being “in remission”. Indeed, measurements have shown for several years now that the ozone hole is no longer widening, but gradually shrinking.</p>
<p>Current knowledge predicts that it will be back in balance sometime between 2060 and 2070, once all the offending substances have disappeared from the stratosphere.</p>
<h2>Potential delays</h2>
<p>There are, however, several reasons for this rebalance to come into effect at a later date than indicated in current forecasts. The first is that all countries must stick to their commitments. In 2018, based on data from monitoring stations dotted across the planet, researchers <a href="https://www.nature.com/articles/s41586-018-0106-2">detected that concentrations of CFC-11 were not falling as quickly as they should have been</a>. Using back trajectory analysis, they ascertained that the relevant emissions were coming from provinces in eastern China.</p>
<figure class="align-center ">
<img alt="Carte montrant les zones d’émission du gaz CFC-11, dangereux pour la couche d’ozone" src="https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=479&fit=crop&dpr=1 600w, https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=479&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=479&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=602&fit=crop&dpr=1 754w, https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=602&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/506432/original/file-20230125-20-5tgpqi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=602&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Back trajectories to identify sources of CFC-11 emission measured by local stations in China.</span>
<span class="attribution"><a class="source" href="https://www.bbc.com/news/science-environment-48353341">Bristol University</a></span>
</figcaption>
</figure>
<p>Another cause, which partly explains why the process has already fallen slightly behind initial estimates, relates to the warming of the lower layers of the atmosphere. In essence, when the bottom of the atmosphere absorbs more energy, the stratosphere cools down due to a compensation effect. The colder it becomes, the faster the polar stratospheric clouds form, which in turn destroys more ozone.</p>
<p>The third potential reason is linked to climate engineering, specifically the technique of intentionally sending suspended particles into the stratosphere to mimic a volcanic eruption and deflect some of the Sun’s rays. An experiment was carried out to simulate the injection of particles over Antarctica. Its results found that although the global temperature would fall by 0.5°C, the ozone hole <a href="https://www.tf1info.fr/environnement-ecologie/video-climat-rechauffement-climatique-envoyer-des-ballons-de-soufre-dans-la-stratosphere-ce-projet-qui-inquiete-pour-la-couche-d-ozone-2244561.html">would revert to high levels of damage similar to those observed in the 1990s</a>.</p>
<h2>The way forward?</h2>
<p><a href="https://theconversation.com/la-protection-de-la-couche-dozone-une-source-dinspiration-pour-la-defense-du-climat-108125">Ozone layer restoration could serve as a template for mitigating climate disruption</a>. It is well established that human-induced greenhouse gas emissions trap infrared radiation and have already caused temperatures to rise.</p>
<p><a href="https://www.ipcc.ch/assessment-report/ar6/">IPCC reports</a> have been compiling the most recent scientific knowledge for decision-makers every five to six years. Ambitious international agreements <a href="https://unfccc.int/sites/default/files/french_paris_agreement.pdf">such as the 2015 Paris Agreement</a> have been put in place to keep the global temperature rise “well below 2°C”.</p>
<p>But the big difference here is scale. It is not enough to persuade a handful of industrialists to find the right chemical substitutes; what we need is a total sea change in the way our fossil fuel-dependent societies operate.</p>
<hr>
<p><em>This article is part of a project between The Conversation France and AFP Audio, supported financially by the European Journalism Centre, as part of the Bill and Melinda Gates Foundation “Solutions Journalism Accelerator” <a href="https://ejc.net/news/the-second-group-selected-in-the-solutions-journalism-accelerator-programme">“Solutions Journalism Accelerator”</a> initiative. AFP and The Conversation France have maintained their editorial independence at every stage of the project.</em></p><img src="https://counter.theconversation.com/content/218839/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Cathy Clerbaux has received funding from CNES (Centre National d'Etudes Spatiales, France) and the European H2020 program (ERC-advanced IASI-FT) to finance her team's research work.</span></em></p>In 1987, the Montreal Protocol established a ban on substances responsible for destroying the ozone layer, which is essential for protection against the sun’s rays.Cathy Clerbaux, Directrice de recherche au CNRS (LATMOS/IPSL), professeure invitée Université libre de Bruxelles, Sorbonne UniversitéLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2034482023-04-20T11:54:34Z2023-04-20T11:54:34ZNitrous oxide: why the environment isn’t amused about laughing gas<figure><img src="https://images.theconversation.com/files/520202/original/file-20230411-24-99jttk.jpg?ixlib=rb-1.1.0&rect=6%2C0%2C4578%2C2577&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-photo/london-england-august-2014-nitrous-oxide-1404940571">Lenscap Photography/Shutterstock</a></span></figcaption></figure><p>A young man breathes deeply from a gas-filled bag. He begins to feel a pleasurable sensation “particularly in the chest and extremities” before dancing around and then collapsing in a heap. A few minutes later he comes to and is consumed by a fit of giggles. The young man is a chemist, living in Bristol and his <a href="https://www.bbc.co.uk/sounds/play/b09hs6wr">name is Humphry Davy</a>. The year is 1799 and Davy has just discovered the euphoric effects of nitrous oxide (N₂O), which he names “laughing gas”. </p>
<p>Word soon spread through high society and <a href="https://www.abc.net.au/news/2019-02-20/laughing-gas-parties-discovery-of-anaesthesia/10811060">laughing gas parties</a> became all the rage. But, despite its pain relief properties, it wasn’t adopted in medical settings until the middle of the 19th century.</p>
<p>Now the UK government is considering outlawing possession of the gas over concerns about health risks <a href="https://www.bbc.co.uk/news/health-65088226">when used as a recreational drug</a>. But it is overlooking another threat it poses to humanity: it is a powerful greenhouse gas. </p>
<p>N₂O is one of the most popular recreational drugs among 16-24 year olds but <a href="https://www.gov.uk/government/news/publication-of-acmds-review-on-nitrous-oxide">heavy use can cause spine damage</a>. </p>
<p>The UK government has made it clear its intention to make possession of the gas a criminal offence. Meanwhile others, including former government drug advisor David Nutt, see criminalisation as <a href="https://news.sky.com/story/professor-david-nutt-former-government-adviser-says-alcohol-is-most-dangerous-drug-11909379">an overreaction</a>. The gas is now used in rocket fuel, as a aerosol propellant – particularly for whipped cream – as well anaesthetic gas and air. So banning private possession won’t do enough to tackle the damage it is doing to our planet.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=393&fit=crop&dpr=1 600w, https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=393&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=393&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=493&fit=crop&dpr=1 754w, https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=493&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/519871/original/file-20230406-1028-29woex.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=493&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Taking laughing gas in the house of a tooth-drawer, 1820.</span>
<span class="attribution"><span class="source">Wellcome Collection</span></span>
</figcaption>
</figure>
<p>Like carbon dioxide (CO₂), N₂O can <a href="https://publishing.rcseng.ac.uk/doi/full/10.1308/rcsbull.2020.147">absorb infrared radiation from the Sun</a>, but its structure allows it to do so much more efficiently. Its potency as a greenhouse gas is about <a href="https://www.nature.com/articles/s41586-020-2780-0">300 times that of carbon dioxide</a>. So the cans of whipped cream and the small canisters containing the gas, (known as whippits to recreational users) have a <a href="https://files.core.ac.uk/pdf/2612/81514516.pdf">surprising ‘carbon footprint’</a>. Each can or canister contains just eight grams of N₂O. But when released into the atmosphere this has the equivalent effect of 2.4 kilograms of CO₂, which is about the amount emitted from driving an SUV for ten miles.</p>
<h2>No laughing matter</h2>
<p>The concentration of N₂O <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhouse-gases">in the atmosphere is very low</a>, (335 parts per billion) about a thousand times lower than CO₂. But, like CO₂, N₂O levels are on the rise. Concentrations are about 20% higher than during Humphry Davy’s time. </p>
<p>Despite these low concentrations, N₂O’s potency means it still has a significant effect on the climate. <a href="https://insideclimatenews.org/news/11092019/nitrous-oxide-climate-pollutant-explainer-greenhouse-gas-agriculture-livestock/">It is the third most damaging greenhouse gas</a> and is responsible for about 6% of the warming we are observing today (<a href="https://www.eci.ox.ac.uk/research/energy/downloads/methaneuk/chapter01.pdf">methane is the second, accounting for 10%</a>).</p>
<p>Unfortunately N₂O’s impact doesn’t stop there. <a href="https://www.science.org/doi/10.1126/science.1176985">N₂O is now the main threat to the ozone layer</a> since CFC chemicals were banned in the 1980s. Once N₂O is released at ground level it takes about 100 years to migrate to the stratosphere (the second layer of Earth’s atmosphere) where UV light catalysis its conversion to nitric oxide (NO). This then reacts with ozone (O₃), forming another pollutant - nitrogen dioxide (NO₂), and molecular oxygen (O₂) - which already makes up 21% of the atmosphere.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sTvqIijqvTg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Whippits are a relatively minor source of human emissions of nitrous oxide, the vast majority (some 70%) <a href="https://www.nature.com/articles/s41612-022-00265-3">comes from agriculture</a>. <a href="https://escholarship.org/uc/item/0kb4505k">Nitrogen-based fertilisers</a>, critical for farming, break down into a variety of nitrogen compounds, including N₂O. Other sources include the burning of fossil and biomass fuels, emissions from industry (particularly in the <a href="https://pubmed.ncbi.nlm.nih.gov/17847387/">manufacturing of nylon</a>), and release while being used as an <a href="https://anaesthetists.org/Home/Resources-publications/Environment/Nitrous-oxide-project">anaesthetic in clinical settings</a>.</p>
<h2>The solution</h2>
<p>Many of these N₂O emissions can be tackled through simple changes of behaviour. Applying more sparing amounts of fertilisers at the right part of the growing season means more fertilisers being taken up by plants. As a result less fertiliser is left in the soil where it runs off into water ways and breaks down into N₂O. </p>
<p>Meanwhile, in clinical settings, huge amounts of N₂O are released through leaky valves, expired stock and <a href="https://www.manchestereveningnews.co.uk/news/greater-manchester-news/thieves-steal-nitrous-oxide-oxygen-17967243">theft for recreational use</a>. Some parts of the NHS are already putting systems in place to <a href="https://sustainablehealthcare.org.uk/what-we-do/sustainable-specialties/anaesthetics/nitrous-oxide-project">tackle many of these issues</a> through upgrading gas manifolds, security and stock control. </p>
<p>N₂O is one of the gases targeted for reductions in international agreements, such as the <a href="https://www.oecd.org/dev/1923119.pdf">Kyoto Protocol</a> and <a href="https://unfccc.int/news/rise-in-greenhouse-gas-concentrations-jeopardizes-paris-agreement-temperature-targets">Paris agreement</a>, so its reduction does form part of government targets to reduce emissions of warming gases. And there are alternatives to N₂O for clinical and medical use as well as in food industries. </p>
<p>Anaesthetists can choose from many other anaesthetics and analgesics, the nylon industry is moving away from processes that release the gas. And if you are tempted by strawberries and cream, use some elbow grease to whip up a bowl instead of turning to the aerosol can.</p><img src="https://counter.theconversation.com/content/203448/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Lorch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>People are becoming more aware of the health risks of laughing gas, but fewer people realise it’s a potent greenhouse gas.Mark Lorch, Professor of Science Communication and Chemistry, University of HullLicensed 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>
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<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">
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<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>
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</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>
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<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>
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<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>
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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><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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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/2013752023-03-08T19:06:36Z2023-03-08T19:06:36ZBushfire smoke eats up the ozone protecting us from dangerous radiation. The damage will increase as the world heats up<p>Can bushfire smoke reduce the concentration of ozone in the stratosphere? A decade ago, we might have been sceptical. But there’s a growing body of research showing a clear link. </p>
<p>Last year, MIT expert Susan Solomon and colleagues published a groundbreaking study showing the 900,000 tonnes of bushfire smoke and particles emitted during Australia’s 2019–20 Black Summer did, in fact, thin out the ozone umbrella that <a href="https://www.dcceew.gov.au/environment/protection/ozone/ozone-science/ozone-layer">protects us</a>. </p>
<p>Ozone floats around 20–25 kilometres above our heads, acting like airborne sunscreen. Its concentration is tiny – up to 15 parts per million – but it is highly effective at blocking damaging ultraviolet-B rays from the sun. Without this layer, many plants would die, while humans and other animals would be afflicted with skin cancers. </p>
<p>The Black Summer fires burned so much forest and scrub across the country they produced massive <a href="https://en.wikipedia.org/wiki/Flammagenitus_cloud">pyrocumulus clouds</a>. The fires were making their own weather, sending plumes of smoke into the higher reaches of our atmosphere, where smoke particles interacted with ozone. That single Australian summer of fire took out 1% of the atmosphere’s ozone – damage that will take <a href="https://www.theguardian.com/environment/2022/mar/01/smoke-from-black-summer-bushfires-depleted-ozone-layer-study-finds">a decade</a> to fix. </p>
<p>Now, Solomon’s researchers have found out how smoke actually does it. In their <a href="https://doi.org/10.1038/s41586-022-05683-0">new research</a>, they detail the chemistry involved. This research is important, as we enter what’s been dubbed the Pyrocene – the <a href="https://www.abc.net.au/news/2020-09-19/fire-expert-says-were-living-through-a-fire-age-pyrocene/12675874">age of fire</a> – with bushfires <a href="https://theconversation.com/climate-change-wildfire-risk-has-grown-nearly-everywhere-but-we-can-still-influence-where-and-how-fires-strike-185465#:%7E:text=The%20number%20of%20days%20with,frequent%20at%20the%20global%20level.">already growing</a> in size and intensity as the world heats up. </p>
<h2>So how does smoke break ozone?</h2>
<p>Australians became all too familiar with the sight and smell of bushfire smoke over the Black Summer. But what’s in it? </p>
<p>Particles in bushfire smoke are carbonaceous, consisting of burnt and partly burnt vegetable material alongside sulfates – compounds which can be pumped into the atmosphere by volcanoes, fossil fuel burning, or bushfires. </p>
<p>The problem is, these carbonaceous particles bind well to substances like hydrogen chloride which comes from the chemical compounds found in living plants. Other compounds with chlorine are also involved in the smoke, such as the reactive chlorine nitrate and hypochlorous acid. </p>
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Read more:
<a href="https://theconversation.com/bushfire-smoke-is-everywhere-in-our-cities-heres-exactly-what-you-are-inhaling-129772">Bushfire smoke is everywhere in our cities. Here's exactly what you are inhaling</a>
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<p>The tiny smoke particles act as transport, carrying these substances containing chlorine up higher and higher to the stratosphere. Once there, chlorine sets about <a href="https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science">destroying ozone</a>, molecule by molecule. Each chlorine atom can take apart hundreds of ozone molecules, meaning a small amount can have a disproportionate impact. </p>
<p>To find this out, Solomon and her colleagues relied heavily on models of the atmospheric chemistry. Their results agreed well with experimental observations made by satellite. So, although the chemical interactions have not been fully shown, the overall picture is probably correct.</p>
<p>You might remember it was chlorine atoms at the heart of our fears about the hole in the ozone layer. Almost 50 years ago, scientists discovered our protective ozone layer was thinning – and connected it to the chlorine-dense chlorofluorocarbons (CFCs) used in spray cans and refrigerators. </p>
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<a href="https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="ozone hole 2022" src="https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=617&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=617&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=617&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=775&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=775&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514124/original/file-20230308-16-bbpt5r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=775&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">In 2022, the ozone hole over Antarctica was the lowest it’s ever been. But that could change.</span>
<span class="attribution"><span class="source">Joshua Stevens/NASA Earth Observatory</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>The area of greatest loss was dubbed the “ozone hole”, which still appears over Antarctica each year in spring in smaller form.</p>
<p>The way we responded to the loss of stratospheric ozone is remarkable, in retrospect. In 1987, nations agreed to the Montreal Protocol, banning CFC manufacture and use. It worked, and concentrations of ozone are now recovering by around 1% a year. That figure is about what was lost during the Black Summer. </p>
<h2>What does this mean for the future?</h2>
<p>It means the ozone layer will be slowly degraded by wildfire smoke. Fires burn in both northern and southern hemispheres, and their smoke is swept around the globe by natural processes. That means we’re likely to see falling ozone concentrations in new places rather than just around the South Pole. Affected areas would include the mid-latitudes around the equator, where billions of people live.</p>
<p>Ozone does replenish itself. It’s continuously formed and destroyed in the stratosphere. The net balance of these competing processes has – until now – been a steady but small concentration of ozone. This layer makes life possible by absorbing the worst of the ultraviolet light pouring down from the sun and giving us a measure of protection from skin-damaging radiation. </p>
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<span class="caption">Tiny concentrations of ozone in the stratosphere play a remarkable role in protecting life on earth.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>A hotter world is one with <a href="https://www.carbonbrief.org/explainer-how-climate-change-is-affecting-wildfires-around-the-world/">more fire</a> in it, affecting areas like Siberian tundra, Californian mountains and Kenyan grasslands. </p>
<p>This research is yet another warning about the perils of unmitigated climate change. Bushfire smoke could undo the good work of the Montreal Protocol. </p>
<p>In retrospect, achieving this protocol seems relatively straightforward: ban one class of chemicals. To stop bushfire smoke eating away at our ozone umbrella means reversing climate change. And that is something we are struggling to do. </p>
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Read more:
<a href="https://theconversation.com/repairing-ozone-layer-is-also-reducing-co-in-the-atmosphere-new-study-166216">Repairing ozone layer is also reducing CO₂ in the atmosphere – new study</a>
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<img src="https://counter.theconversation.com/content/201375/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Rae was for 15 years a member of technical advisory groups to the Montreal Protocol</span></em></p>Over 30 years ago, the world banned CFC chemicals to save the ozone layer. But now, climate-fuelled bushfire smoke is putting it at renewed riskIan Rae, Honorary Professorial Fellow, School of Chemistry, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1989822023-02-02T19:15:28Z2023-02-02T19:15:28ZA rapidly growing rocket industry could undo decades of work to save the ozone layer – unless we act now<figure><img src="https://images.theconversation.com/files/507534/original/file-20230201-3038-cillry.jpg?ixlib=rb-1.1.0&rect=55%2C119%2C5241%2C3427&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Getty Images</span></span></figcaption></figure><p>The ozone layer is on track to heal within four decades, according to a recent <a href="https://news.un.org/en/story/2023/01/1132277">UN report</a>, but this progress could be undone by an upsurge in rocket launches expected during the same period.</p>
<p>The ozone layer protects life on Earth from the sun’s harmful ultraviolet (UV) rays. Destruction of the ozone layer became a major international issue in 1985 when the “ozone hole” was <a href="https://www.nature.com/articles/315207a0">discovered</a> over Antarctica. </p>
<p>Thanks to a coordinated global effort, the <a href="https://www.unep.org/ozonaction/who-we-are/about-montreal-protocol">Montreal Protocol</a> came into effect in 1987, leading to a ban on a class of chemicals called chlorofluorocarbons (CFCs), which were used in aerosols and refrigeration. A global crisis was <a href="https://www.bbc.com/future/article/20220321-what-happened-to-the-worlds-ozone-hole">avoided</a> as a result. </p>
<p>But the global space industry is growing rapidly, with an increasing number of annual rocket launches. As we show in our new <a href="https://doi.org/10.1080/03036758.2022.2152467">review</a>, the gases and particulates rockets emit as they punch through the atmosphere could lead to delays in the ozone layer’s recovery.</p>
<h2>Rocket fuel emissions are not regulated</h2>
<figure class="align-right ">
<img alt="Rocket on take-off" src="https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1131&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1131&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507709/original/file-20230201-17339-y1ilnp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1131&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Atmospheric emissions from rocket fuels are not regulated.</span>
<span class="attribution"><span class="source">Official SpaceX Images/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The launch industry today relies on four major fuel types for rocket propulsion: liquid kerosene, cryogenic, hypergolic and solid. The combustion of these fuels means contemporary rockets create a suite of gaseous and particulate exhaust products, including carbon dioxide, water vapour, black carbon, alumina, reactive chloride and nitrogen oxides. <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021EF002612">These products</a> are known to <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JD036373">destroy ozone</a>. </p>
<p>In the stratosphere, an upper level of the atmosphere where the protective ozone layer resides, emissions linger for much longer than lower down. Small amounts of an exhaust byproduct can have greater destructive effects in the upper atmosphere than when close to Earth’s surface.</p>
<p>A new fuel is methane, which is used in multiple rocket engines under development by major launch companies. The emissions products of methane are as yet poorly understood. </p>
<p>As we outline, rocket emissions in the upper atmosphere can affect the ozone layer but are not regulated. We argue this policy gap must be filled to ensure sustainable growth of the rocket launch industry and protection of the ozone layer. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/cornwall-space-launch-why-the-environmental-cost-of-rocket-launches-is-large-even-when-they-fail-197567">Cornwall space launch: why the environmental cost of rocket launches is large even when they fail</a>
</strong>
</em>
</p>
<hr>
<h2>Charismatic technology</h2>
<p>Solid rocket fuel contains a chemical that releases chlorine in the upper atmosphere and destroys ozone. CFCs were banned because they contain chlorine. </p>
<p>Fortunately, the number of launches to date is so small that the impacts on the ozone layer are currently insignificant. However, over coming decades the launch industry is set to expand considerably. <a href="https://www.cnbc.com/2017/10/31/the-space-industry-will-be-worth-nearly-3-trillion-in-30-years-bank-of-america-predicts.html">Financial estimates</a> indicate the global space industry could grow to US$3.7 trillion by 2040. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/space-tourism-rockets-emit-100-times-more-co-per-passenger-than-flights-imagine-a-whole-industry-164601">Space tourism: rockets emit 100 times more CO₂ per passenger than flights – imagine a whole industry</a>
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</em>
</p>
<hr>
<p>Rockets have exciting potential to enable industrial-level access to near-Earth space and exploration throughout the solar system. This makes them “<a href="https://morganya.org/research/Ames-charisma-aarhus.pdf">charismatic technology</a>” – and the promise of what the technology can enable drives deep emotional investment. </p>
<p>The allure of possibility can get in the way of even discussing how to make rockets achieve these aspirational goals without damage. We have to be able to have clear discussions.</p>
<figure class="align-center ">
<img alt="Rocket taking off into space" src="https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/507703/original/file-20230201-10216-nqytbc.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">Rockets hold an exciting promise of space exploration.</span>
<span class="attribution"><span class="source">Official SpaceX Images/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Collecting and sharing data</h2>
<p>Many communities – rocket launch providers, environmental regulators, atmospheric research scientists and government agencies – need to move forward together on an international level. Discussions on how to build best-practice operations for sustainability needn’t be stifling for space industry growth as potential actions are well within reach.</p>
<p>The greatest contribution each community can make, first off, is the collection and sharing of data. For example, those who build and launch rockets could estimate emissions during their design work and then measure actual emissions for their launch vehicles. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-new-era-of-spaceflight-promising-advances-in-rocket-propulsion-160396">A new era of spaceflight? Promising advances in rocket propulsion</a>
</strong>
</em>
</p>
<hr>
<p>Working with researchers to sample emission plumes in the atmosphere would help develop understanding of the real-world impacts of emissions on the ozone layer. The current lack of these measurements for modern launch vehicles limits the predictive power of atmospheric modelling. Making data easily accessible to researchers is necessary for meaningful progress.</p>
<p>To evaluate emissions at early stages of rocket development, we also need accurate models of the impact emissions have on the atmosphere. This is where coordination between the space industry and the ozone research community is essential – each community holds a complementary puzzle piece, both of which together inform regulatory discussion.</p>
<p>Creating sustainable global rocket launches is going to need coordination across aerospace companies, scientists and governments: it is achievable, but we need to start now. This is our chance to get ahead of the game.</p><img src="https://counter.theconversation.com/content/198982/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Laura Revell receives funding from the Royal Society of New Zealand Marsden fund, Deep South National Science Challenge and Ministry for Business, Innovation and Employment for research related to airborne microplastics, climate modelling and stratospheric ozone. She is funded by the Rutherford Discovery Fellowships from New Zealand Government funding, administered by the Royal Society Te Apārangi.</span></em></p><p class="fine-print"><em><span>Michele Bannister is funded by the Rutherford Discovery Fellowships from New Zealand Government funding, administered by the Royal Society Te Apārangi, for research related to Solar System exploration. She is a member of Aerospace Christchurch.</span></em></p><p class="fine-print"><em><span>Tyler F. M. Brown is a member of Aerospace Christchurch </span></em></p>Rocket emissions in the upper atmosphere can damage the ozone layer but are neither measured nor regulated. It’s a policy gap we have to close if the space industry is to grow sustainably.Laura Revell, Associate Professor in Environmental Physics, University of CanterburyMichele Bannister, Senior Lecturer in Astronomy, School of Physical and Chemical Sciences Te Kura Matū, University of CanterburyTyler Brown, Researcher, School of Physical and Chemical Sciences Te Kura Matū, University of CanterburyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1911722022-09-22T12:40:54Z2022-09-22T12:40:54ZCooling conundrum: HFCs were the ‘safer’ replacement for another damaging chemical in refrigerators and air conditioners – with a treaty now phasing them out, what’s next?<figure><img src="https://images.theconversation.com/files/486032/original/file-20220922-8022-dozc1l.jpg?ixlib=rb-1.1.0&rect=707%2C715%2C5018%2C3112&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Air conditioners are one source of leaking HFCs.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/apartment-building-in-upper-west-of-manhattan-royalty-free-image/502986175?adppopup=true">Bruce Yuanyue Bi/The Image Bank via Getty Images</a></span></figcaption></figure><p>The U.S. Senate voted to ratify an <a href="https://www.state.gov/u-s-ratification-of-the-kigali-amendment/">international treaty</a> on Sept. 21, 2022, agreeing to phase out a class of climate-warming chemicals that are widely used as coolants in refrigerators, air conditioners and heat pumps.</p>
<p>If you’re getting a sense of déjà vu, don’t be surprised.</p>
<p>These chemicals, called hydrofluorocarbons, or HFCs, were commercialized in the 1990s as a <a href="http://doi.org/10.1126/science.1216414">replacement for earlier refrigerants</a> that were based on chlorofluorocarbons, or CFCs. CFCs were destroying the ozone layer high in the Earth’s atmosphere, which is essential for protecting life from the Sun’s harmful ultraviolet radiation.</p>
<p>HFCs are less harmful than CFCs, but they create another problem – they have a <a href="https://www.ipcc.ch/report/safeguarding-the-ozone-layer-and-the-global-climate-system/">strong heat-trapping effect</a> that is contributing to global warming.</p>
<p>If HFCs can be phased down globally – as <a href="https://ozone.unep.org/all-ratifications">many countries</a> have agreed to do under the 2016 Kigali Amendment to the Montreal Protocol, the treaty just <a href="https://www.senate.gov/legislative/LIS/roll_call_votes/vote1172/vote_117_2_00343.htm">ratified by the U.S. Senate on a bipartisan vote</a> – that would <a href="https://csl.noaa.gov/news/2016/196_1016.html">avoid about half a degree Celsius</a> of temperature rise compared to preindustrial times. <a href="https://www.nrdc.org/experts/alex-hillbrand/china-accepts-kigali-amendment-will-phase-down-hfcs">China</a>, a major producer of these chemicals, ratified the amendment effective Sept. 15, 2021. And the U.S. Environmental Protection Agency finalized <a href="https://www.epa.gov/newsreleases/us-will-dramatically-cut-climate-damaging-greenhouse-gases-new-program-aimed-chemicals">a rule</a> in 2021 to cut HFCs production and imports.</p>
<p>Let’s take a closer look at what HFCs are and what might replace them next.</p>
<h2>How HFCs keep rooms and food cool</h2>
<p>Refrigerators and air conditioning use a technology known as a heat pump. It sounds almost miraculous – heat pumps use energy to take heat out of a cold place and dump it in a warm place.</p>
<p>Here’s <a href="https://www.danfoss.com/en/about-danfoss/our-businesses/cooling/the-fridge-how-it-works">how a refrigerator works</a>: A fluid – CFCs back in the old days, and now HFCs – circulates in the walls of the refrigerator, absorbing the ambient heat to keep the fridge cooled down. As that liquid absorbs the heat, it evaporates. The resulting vapor is pumped to the coils on the back of the refrigerator, where it is condensed back to a liquid under pressure. In the process, the heat that was absorbed from inside the fridge is released into the surrounding room. </p>
<p>Air conditioners and home heat pumps do the same thing: they use electric-powered compressors and evaporators to move heat into or out of a house.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/viM36llqxCU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How a refrigerator works.</span></figcaption>
</figure>
<p>Choosing the right fluid for a refrigerator means finding a substance that can be evaporated and condensed at the right temperatures by changing the pressure on the fluid.</p>
<p>CFCs seemed to fit the bill perfectly. They didn’t react with the tubing or compressors to corrode the equipment, and <a href="https://www.esrl.noaa.gov/gmd/hats/publictn/elkins/cfcs.html">they weren’t toxic or flammable</a>. </p>
<p>Unfortunately, the chemical stability of CFCs turned out to be a problem that threatened the whole world, as scientists discovered in the 1980s. Leaking CFCs, mostly from discarded equipment, remain in the atmosphere for a long time. Eventually they make their way to the stratosphere, where they are finally destroyed by UV radiation from the sun. But when they break down, they create chlorine that reacts with the protective ozone, letting dangerous radiation through to the Earth’s surface. </p>
<p>When production of CFCs was eliminated in the 1990s to protect the ozone layer, new refrigerants were developed and the industry shifted to HFCs.</p>
<h2>Why HFCs are a climate problem</h2>
<p>HFCs are like CFCs but much more reactive in air, so they never reach the stratosphere where they could harm Earth’s protective radiation shield. They largely saved the world from impending ozone disaster, and they are now found in refrigerators and heat pumps everywhere.</p>
<p>But while HFCs’ <a href="https://theconversation.com/explainer-hydrofluorocarbons-saved-the-ozone-layer-so-why-are-we-banning-them-86672">chemical reactivity</a> prevents them from depleting the ozone layer, their molecular structure allows them to absorb a lot of thermal radiation, making them a greenhouse gas. Like carbon dioxide on steroids, HFCs are extremely good at capturing infrared photons emitted by the Earth. Some of this radiant energy warms the climate.</p>
<p>Unlike carbon dixoide, reactive HFCs are consumed by chemistry in the air, so they only warm the climate for a decade or two. But a little bit goes a long way – each HFC molecule absorbs thousands of times as much heat as a carbon dixoide molecule, making them powerful climate pollutants.</p>
<figure class="align-center ">
<img alt="Chart showing increase by country, with the largest increase in China." src="https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=616&fit=crop&dpr=1 600w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=616&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=616&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=775&fit=crop&dpr=1 754w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=775&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=775&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 what HFCs’ growth was expected to look like before the Kigali Amendment or other control measures were in place.</span>
<span class="attribution"><a class="source" href="https://www.rivm.nl/en/hydrofluorocarbons/contribution-of-hfcs-to-greenhouse-effect">Netherlands National Institute for Public Health and the Environment</a></span>
</figcaption>
</figure>
<p>HFCs <a href="https://acp.copernicus.org/articles/17/2795/2017/acp-17-2795-2017.pdf">leaking from discarded cooling equipment</a> are estimated to contribute about 4% of global greenhouse gas emissions – about twice as much as aviation.</p>
<p>This is why it’s time to retire HFCs and swap them out for alternative refrigerants. They’ve done their job saving the ozone layer, but now HFCs are a major contributor to short-term global warming, and their <a href="https://www.ccacoalition.org/en/initiatives/hfc">use has been increasing</a> as demand for cooling increases around the world.</p>
<h2>What can replace HFCs?</h2>
<p>Because they are so powerful and short-lived, stopping the production and use of HFCs can have a <a href="https://www.drawdown.org/solutions/alternative-refrigerants">significant cooling effect</a> on the climate over the next couple of decades, buying time as the world converts its energy supply from fossil fuels to cleaner sources.</p>
<p>The good news is that there are <a href="https://ww2.arb.ca.gov/resources/documents/choosing-new-system">alternative refrigerants</a>.</p>
<p>Ammonia and hydrocarbons like butane evaporate at room temperature and have been used as refrigerants since the early 20th century. These gases are short-lived, but they have a downside. Their greater reactivity means their compressors and plumbing have to be more corrosion-resistant and leak-proof to be safe. </p>
<figure class="align-center ">
<img alt="Rows of freezer cases in a store." src="https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&rect=0%2C7%2C4653%2C3396&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.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">Designing refrigeration equipment for different chemicals will likely mean retooling the industry, which could raise costs.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/freezer-cases-in-supermarket-royalty-free-image/1134353358">Mint Image via Getty Images</a></span>
</figcaption>
</figure>
<p>The chemical industry has been developing newer alternatives intended to be safer for both people and climate, but as we saw with CFCs and HFCs, inert chemicals can have unintended consequence. Several industry leaders have <a href="https://www.ahrinet.org/news-events/news/ahri-commemorates-montreal-protocol-anniversary-applauds-pending-senate-consideration-kigali">supported efforts to phase out HFCs</a>.</p>
<p>So, it’s time for another generation of cooling equipment. Just as TVs and audio equipment and light bulbs have evolved over past decades, refrigerators and air conditioners will be replaced by a new wave of improved products. New refrigerators will look and work just like the ones we’re used to, but they will be much gentler on the climate system.</p>
<p><em>This updates <a href="https://theconversation.com/us-china-commit-to-phase-down-climate-warming-hfcs-from-refrigerators-and-air-conditioners-but-what-will-replace-them-this-time-160241">an article</a> originally published on May 4, 2021, with the U.S. Senate ratifying the Kigali Amendment.</em></p><img src="https://counter.theconversation.com/content/191172/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Scott Denning 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>The US Senate voted to ratify the Kigali Amendment, agreeing on a bipartisan vote to phase down climate-warming HFCs. Now what?Scott Denning, Professor of Atmospheric Science, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1809902022-04-08T14:25:53Z2022-04-08T14:25:53ZAxiom launch: why commercial space travel could be another giant leap for air pollution<figure><img src="https://images.theconversation.com/files/457152/original/file-20220408-41099-9cm6ps.jpg?ixlib=rb-1.1.0&rect=0%2C4%2C2995%2C1989&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">SpaceX is seeking to expand its remit to include commercial low-Earth orbit launches.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/spacex/16236321533">SpaceX/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>The <a href="https://www.space.com/spacex-axiom-ax1-mission-ready-to-launch">Axiom-1 mission</a> to send four private astronauts to the International Space Station is the first of many missions planned by NASA to expand the ISS for <a href="https://www.nasa.gov/press-release/nasa-selects-first-commercial-destination-module-for-international-space-station">commercial use</a> as part of what’s being called the <a href="https://www.nasa.gov/leo-economy/low-earth-orbit-economy">low-Earth orbit economy</a>. </p>
<p>The commander of the Axiom-1 mission has emphatically stated that this is not an example of <a href="https://www.inverse.com/innovation/axiom-space-ax1">space tourism</a>, as the crew have undergone training and the mission includes plans to conduct biomedical research. </p>
<p>Crew members – all men aged 52 to 71 – reportedly paid a whopping <a href="https://www.theverge.com/2021/1/26/22250327/space-tourists-axiom-private-crew-iss-price">US$55 million (£42.3 million)</a> per ticket, an amount that would no doubt fund a formidable biomedical research programme here on Earth. But beyond the ludicrous ticket price, I’m concerned about the potential environmental impacts of such space jaunts. </p>
<p>The mission is using a SpaceX Falcon 9 Block 5 rocket, with the crew located in the Crew Dragon spacecraft at its apex. The rocket has two stages: the reusable booster that holds most (about four-fifths) of the fuel and that returns to Earth for reuse, and a discarded second stage. </p>
<figure class="align-center ">
<img alt="A capsule approaches a larger structure in space, marked with a Dragon logo" src="https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457153/original/file-20220408-34202-rdmf2d.jpeg?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">An artist’s impression of the SpaceX Crew Dragon craft docking with the International Space Station.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:SpaceX_Crew_Dragon_docking_with_the_International_Space_Station.jpg">Wikimedia</a></span>
</figcaption>
</figure>
<p>The booster reaches an altitude of about <a href="https://www.youtube.com/watch?v=IBEH4t05AvM">140km</a> before returning to Earth. The energy required to propel the spacecraft to the ISS is achieved from the <a href="https://www.spacex.com/vehicles/falcon-9/">combustion reaction</a> between rocket-grade kerosene and liquid oxygen, releasing byproducts hazardous to the environment. </p>
<p>Rocket launches and returning reusable components release air pollutants and greenhouse gases into multiple atmospheric layers. In the middle and upper atmosphere, these can persist for <a href="https://www.essoar.org/doi/10.1002/essoar.10510460.1">years</a> compared with equivalent pollutants released at or near the Earth’s surface, which linger for weeks at most. This is because there are fewer chemical reactions or weather events to flush pollutants out of middle and upper layers. </p>
<h2>Potent pollutants</h2>
<p>The kerosene fuel used by SpaceX Falcon rockets is a mix of hydrocarbons, composed of carbon and hydrogen atoms. These react with liquid oxygen to form carbon dioxide (CO₂), water vapour (H₂O) and black carbon or soot particles that are released from the <a href="https://aerospace.org/sites/default/files/2018-05/RocketEmissions_0.pdf">rocket exhaust</a>. </p>
<p>CO₂ and H₂O are potent greenhouse gases, and black soot particles are very efficient at absorbing the sun’s rays. That means all these chemicals contribute to warming the Earth’s atmosphere. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ax-1-why-the-private-mission-to-the-international-space-station-is-a-gamechanger-180589">Ax-1: why the private mission to the International Space Station is a gamechanger</a>
</strong>
</em>
</p>
<hr>
<p>Nitrogen oxides (NOx), reactive air pollutants, also form during launch due to very high temperatures causing a bonding reaction between usually stable nitrogen and oxygen molecules. NOx is also produced when the rocket’s reusable components <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016EF000399">return to Earth</a>, due to extreme temperatures produced by friction on its heat shields as they whizz through the mesosphere at 40km-70km. </p>
<p>When these particles make contact with the ozone layer (in the stratosphere), they convert <a href="https://www.annualreviews.org/doi/10.1146/annurev.ea.07.050179.002303">ozone to oxygen</a>, depleting the fragile sheath that protects the planet from the sun’s harmful UV radiation. </p>
<figure class="align-center ">
<img alt="A countdown timer in front of a small lake, a rocket visible in the background" src="https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457150/original/file-20220408-25034-2ng7uv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Countdown begins for the commercial launch destined for the International Space Station.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nasahqphoto/51989259502/">NASA HQ Photo/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Although total CO₂ emissions from this launch will be small in comparison to those from the global aircraft industry, emissions per passenger will be around <a href="https://theconversation.com/space-tourism-rockets-emit-100-times-more-co-per-passenger-than-flights-imagine-a-whole-industry-164601">100 times</a> those from a long-haul flight. </p>
<p>Soot emissions are also much less than those from the aircraft industry, but when released into the middle and upper atmosphere, soot has a warming effect <a href="https://www.essoar.org/doi/10.1002/essoar.10510460.1">500 times greater</a> than at levels closer to Earth. This is in part because there are typically no clouds and few to no aerosols competing with soot to absorb the sun’s rays. </p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ukraine-war-how-it-could-play-out-in-space-with-potentially-dangerous-consequences-178557">Ukraine war: how it could play out in space – with potentially dangerous consequences</a>
</strong>
</em>
</p>
<hr>
<p>The potential opportunities of creating industry and trade networks within low-Earth orbit have been likened by an Axiom co-founder to the early days of <a href="https://www.reuters.com/lifestyle/science/first-private-astronaut-mission-space-station-readies-launch-2022-04-04/">developing the internet</a>, now an almost universally accessible technology. If we extend that analogy to imagine similarly high levels of access to the low-Earth orbit economy, rocket launches are likely to become far more common than just the <a href="https://space.skyrocket.de/doc_chr/lau2021.htm">146 launches</a> achieved in 2021.</p>
<p>Such a scenario would substantially alter Earth’s climate and undermine our significant progress in repairing the ozone layer. At the very least, research is urgently needed to assess the consequences of a flourishing low-Earth orbit economy for our planet down below.</p>
<hr>
<figure class="align-right ">
<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">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><strong><em>Don’t have time to read about climate change as much as you’d like?</em></strong>
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<p class="fine-print"><em><span>Eloise Marais receives funding from the European Commission and the UK Natural Environment Research Council. </span></em></p>Expanding the low-Earth orbit economy through increased commercial spaceflight will only push our planet further into its climate crisis.Eloise Marais, Associate Professor in Physical Geography, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1662162021-08-18T15:09:41Z2021-08-18T15:09:41ZRepairing ozone layer is also reducing CO₂ in the atmosphere – new study<figure><img src="https://images.theconversation.com/files/416734/original/file-20210818-23-19uzpwb.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5098%2C3548&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-photo/view-earth-space-blue-planet-deep-296927024">Studio23/Shutterstock</a></span></figcaption></figure><p>Spring 2060. In dark glasses, a wide sunhat and with what little exposed skin left caked in sun cream, a child stares at the woodland across from their house. It looks scraggly and stunted, and with far fewer leaves than in the old photos she has seen. Still, no time to dwell on it: there’s a <a href="https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/sun-uv-and-cancer/the-uv-index-and-sunburn-risk">UV index</a> of 20 and she’s already spent five minutes outside.</p>
<p>Thankfully, this is not our future. Due to steps the world took in the 1980s to protect the <a href="https://ozone.unep.org/20-questions-and-answers">ozone layer</a>, a region of the upper atmosphere that absorbs the Sun’s harmful ultraviolet (UV) radiation, we have one less environmental problem to worry about.</p>
<p>In the mid-1970s, scientists realised that the ozone layer was being depleted by the growing use of <a href="https://gml.noaa.gov/hats/publictn/elkins/cfcs.html">chlorofluorocarbons</a> (CFCs) as refrigerants and as propellants in aerosol cans, among other applications. With the 1987 signing of the <a href="https://theconversation.com/uk/topics/montreal-protocol-3788">Montreal Protocol</a>, which was later strengthened by numerous amendments and ratified by 197 countries, the world phased out CFCs. Today, CFC levels in the atmosphere are <a href="https://agage.mit.edu/data/agage-data">falling</a> and the ozone layer is <a href="https://csl.noaa.gov/assessments/ozone/2018/twentyquestions/#topics-5">beginning to recover</a>. </p>
<figure class="align-center ">
<img alt="A bin full of discarded aerosol cans." src="https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416732/original/file-20210818-23-1f52akf.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">CFCs are nontoxic and nonflammable, making them useful in everything from hair care to household cleaning.</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>But what if the Montreal Protocol was never signed? What would the world we managed to avoid have looked like? This is the subject of <a href="https://www.nature.com/articles/s41586-021-03737-3">a new study</a> led by me with an international team of collaborators.</p>
<p>In earlier research, scientists showed there would have been thousands more <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2012.01223.x/full">skin cancer cases</a> in such a world, where the ozone layer is thinner and higher levels of UV radiation reach the planet’s surface. There would also have been <a href="https://www.pnas.org/content/104/12/4814">additional climate warming</a>, since CFCs, like carbon dioxide (CO₂), are also greenhouse gases, although far more potent. Our focus was on what could have happened to vegetation.</p>
<p>Like humans, plants are damaged when <a href="https://www.sciencedirect.com/science/article/abs/pii/000527289090156X">exposed to high UV levels</a>. Plants absorb CO₂ as they grow, but when UV radiation increases by 10%, <a href="https://pubs.rsc.org/en/content/articlelanding/2011/pp/c0pp90035d/">plants accrue 3% less biomass</a>. Without the Montreal Protocol, we estimated that UV levels would have been 4.5 times higher on average globally than today at the end of the century. We also estimated that by 2050, European, Asian and North American UV levels would be higher than they are in the present-day tropics. </p>
<p>Overall, this means that more of the CO₂ humans emit would have remained in the atmosphere, rather than being locked up in plants and the soil. And this extra CO₂ would have led to more global warming.</p>
<h2>A world without the Montreal Protocol</h2>
<p>Using computer models to represent the climate, the atmosphere’s chemistry, vegetation and the carbon cycle, we simulated two worlds. The first assumed that <a href="https://www.nature.com/articles/249810a0">the 1974 paper</a> alerting the world to the dangers of CFCs was never published and their use grows at <a href="http://www.pnas.org/cgi/doi/10.1073/pnas.0610328104">3% a year</a>. The second is a world where CFCs are controlled and the ozone layer recovers, the world we live in now and are on track to inhabit. </p>
<p>Apart from the CFCs, the two simulated worlds are identical. In both, CO₂ and other greenhouse gas emissions follow an <a href="https://ar5-syr.ipcc.ch/topic_futurechanges.php#box_2_2">intermediate scenario</a> for the 21st century, which is one of several used to inform the UN’s <a href="https://theconversation.com/ipcc-report-how-to-make-global-emissions-peak-and-fall-and-whats-stopping-us-165830">Intergovernmental Panel on Climate Change reports</a>. </p>
<p>The world in which CFCs were phased out looks like what we would expect from <a href="https://theconversation.com/this-is-the-most-sobering-report-card-yet-on-climate-change-and-earths-future-heres-what-you-need-to-know-165395">warmer future climates</a>. Global temperatures increase, with all their <a href="https://theconversation.com/3-dangers-of-rising-temperatures-that-could-affect-your-health-now-105028">negative consequences</a>, but – as we expect for the real world – the ozone layer recovers to its historic levels by the middle of the century. In the other world, the <a href="https://www.earthobservatory.nasa.gov/features/WorldWithoutOzone">ozone layer drastically thins</a> and by the end of the century ozone concentrations everywhere fall below levels seen in the <a href="https://earthobservatory.nasa.gov/world-of-change/Ozone">Antarctic ozone hole</a>.</p>
<figure class="align-center ">
<img alt="A satellite image of the southern hemisphere depicting relative ozone levels in the atmosphere." src="https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416580/original/file-20210817-15-pzobqj.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">
<figcaption>
<span class="caption">The Antarctic ozone hole recorded at its greatest extent in September 2006.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Montreal_Protocol#/media/File:NASA_and_NOAA_Announce_Ozone_Hole_is_a_Double_Record_Breaker.png">NASA</a></span>
</figcaption>
</figure>
<p>By the 2050s, because of UV damage, plants in the world where CFC use continues unabated absorb half the carbon they do in the world where CFCs were phased out. By the end of the century, plants in this high-CFC world absorb less than 15% of the carbon they do in the other world, resulting in 30% less carbon stored in plants and soils. This means 30% more CO₂ in the atmosphere by the end of the century, which adds 0.8°C more warming to the climate.</p>
<p>By itself, this 0.8°C would be enough to take current global temperatures (just over 1°C above the <a href="https://climate.nasa.gov/vital-signs/global-temperature/">pre-industrial average</a>) to beyond the 1.5°C level that represents the most ambitious target of the <a href="https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement">Paris Agreement</a>. Adding the 1.7°C that would have resulted from the greenhouse effect of CFCs themselves means that an extra 2.5°C of warming was prevented by the Montreal Protocol.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Four different world maps depicting declines in carbon uptake by plants across the 21st century." src="https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/416738/original/file-20210818-13-7c7vgh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Plants would take up much less carbon worldwide by the late 21st century if CFC use continued unabated.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/articles/s41586-021-03737-3">Young et al. (2021)/Nature</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>While we have avoided the world from our simulations, threats to the ozone layer still exist. Some scientists favour counteracting climate change by emulating the global cooling effects of <a href="https://www.usgs.gov/natural-hazards/volcano-hazards/volcanoes-can-affect-climate">large volcanic eruptions</a> – injecting particles into the upper atmosphere in a process known as <a href="https://theconversation.com/should-we-engineer-the-climate-a-social-scientist-and-natural-scientist-discuss-104516">stratospheric sulphate geoengineering</a>. </p>
<p>But this could <a href="https://science.sciencemag.org/content/320/5880/1201.abstract">deplete the ozone layer</a>. Our study shows that the knock-on effect on the biosphere must be considered in any impact assessment of such actions. </p>
<p>For its effectiveness in acting on dire scientific warnings, it’s tempting to think of the Montreal Protocol as a model for <a href="https://ukcop26.org/">climate negotiations</a>. Yet with just a handful of companies making CFCs and alternative chemicals readily available, the ozone issue was far more straightforward than reducing emissions from fossil fuels.</p>
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<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/shrinking-hole-in-the-ozone-layer-shows-what-collective-action-can-achieve-62007">Shrinking hole in the ozone layer shows what collective action can achieve</a>
</strong>
</em>
</p>
<hr>
<p>Nevertheless, as well as protecting the ozone layer, the Montreal Protocol has itself been a phenomenally successful climate treaty. It has controlled not only the emissions of highly potent greenhouse gases like CFCs, but, as we have shown, it has avoided additional CO₂ levels through protecting the world’s plant life.</p><img src="https://counter.theconversation.com/content/166216/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Young receives funding from the Engineering and Physical Sciences Research Council. </span></em></p>New research shows how the Montreal Protocol protected vegetation, helping keep carbon out of the atmosphere.Paul Young, Senior Lecturer in Atmospheric and Climate Science, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1602412021-05-04T12:15:32Z2021-05-04T12:15:32ZUS, China commit to phase down climate-warming HFCs from refrigerators and air conditioners – but what will replace them this time?<figure><img src="https://images.theconversation.com/files/398511/original/file-20210504-23-1kgtfb9.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5139%2C3415&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">HFCs keep refrigerators cool, but their leaks are warming the planet.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/asian-boy-searching-through-refrigerator-royalty-free-image/470621975">Jed Share/Kaoru Share via Getty Images</a></span></figcaption></figure><p>The U.S. Environmental Protection Agency has <a href="https://www.epa.gov/newsreleases/us-will-dramatically-cut-climate-damaging-greenhouse-gases-new-program-aimed-chemicals">finalized a rule</a> to start eliminating a class of climate-warming chemicals that are widely used as coolants in refrigerators, air conditioners and heat pumps.</p>
<p>If that plan feels like déjà vu, it should.</p>
<p>These chemicals, called hydrofluorocarbons, or HFCs, were commercialized in the 1990s as a <a href="http://doi.org/10.1126/science.1216414">replacement for earlier refrigerants</a> that were based on chlorofluorocarbons, or CFCs. CFCs were destroying the ozone layer high in the Earth’s atmosphere, which is essential for protecting life from the Sun’s harmful ultraviolet radiation.</p>
<p>HFCs are less harmful than CFCs, but they create another problem – they have a <a href="https://www.ipcc.ch/report/safeguarding-the-ozone-layer-and-the-global-climate-system/">strong heat-trapping effect</a> that is contributing to global warming.</p>
<p>Several <a href="https://fas.org/sgp/crs/misc/IF11541.pdf">states have announced plans</a> over the past few years for phasing out HFCs. Now the EPA, following a <a href="https://www.ccacoalition.org/en/news/latest-us-pandemic-relief-bill-includes-hfc-phasedown">vote in Congress</a> in 2020, has established <a href="https://www.epa.gov/climate-hfcs-reduction/final-rule-phasedown-hydrofluorocarbons-establishing-allowance-allocation">federal regulations</a> to cut HFC production and imports starting in 2022, and aims to reduce their production and use by 85% within 15 years.</p>
<p>If HFCs can be phased down globally – as <a href="https://ozone.unep.org/all-ratifications">many countries</a> have agreed to do under the 2016 Kigali Amendment to the Montreal Protocol – that would <a href="https://csl.noaa.gov/news/2016/196_1016.html">avoid about half a degree Celsius</a> of temperature rise compared to preindustrial times. <a href="https://www.nrdc.org/experts/alex-hillbrand/china-accepts-kigali-amendment-will-phase-down-hfcs">China</a>, a major producer of these chemicals, ratified the amendment effective Sept. 15, 2021.</p>
<p>Let’s take a closer look at what HFCs are and what might replace them next.</p>
<h2>How HFCs keep rooms and food cool</h2>
<p>Refrigerators and air conditioning use a technology known as a heat pump. It sounds almost miraculous – heat pumps use energy to take heat out of a cold place and dump it in a warm place.</p>
<p>Here’s <a href="https://www.danfoss.com/en/about-danfoss/our-businesses/cooling/the-fridge-how-it-works">how a refrigerator works</a>: A fluid – CFCs back in the old days, and now HFCs – circulates in the walls of the refrigerator, absorbing the ambient heat to keep the fridge cooled down. As that liquid absorbs the heat, it evaporates. The resulting vapor is pumped to the coils on the back of the refrigerator, where it is condensed back to a liquid under pressure. In the process, the heat that was absorbed from inside the fridge is released into the surrounding room. Air conditioners and home heat pumps do precisely the same thing: they use electric-powered compressors and evaporators to move heat into or out of a house.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/viM36llqxCU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How a refrigerator works.</span></figcaption>
</figure>
<p>Choosing the right fluid for a refrigerator means finding a substance that can be evaporated and condensed at the right temperatures by changing the pressure on the fluid.</p>
<p>CFCs seemed to fit the bill perfectly. They didn’t react with the tubing or compressors to corrode the equipment, and <a href="https://www.esrl.noaa.gov/gmd/hats/publictn/elkins/cfcs.html">they weren’t toxic or flammable</a>. </p>
<p>Unfortunately, the chemical stability of CFCs turned out to be a problem that threatened the whole world, as scientists discovered in the 1980s. Leaking CFCs, mostly from discarded equipment, remain in the atmosphere for a long time. Eventually they make their way to the stratosphere, where they are finally destroyed by UV radiation from the sun. But when they break down, they create chlorine that reacts with the protective ozone, letting dangerous radiation through to the Earth’s surface. </p>
<p>When production of CFCs was eliminated in the 1990s to protect the ozone layer, new refrigerants were developed and the industry shifted to HFCs.</p>
<h2>Why HFCs are a climate problem</h2>
<p>HFCs are like CFCs but much more reactive in air, so they never reach the stratosphere where they could harm Earth’s protective radiation shield. They largely saved the world from impending ozone disaster, and they are now found in refrigerators and heat pumps everywhere.</p>
<p>But while HFCs’ <a href="https://theconversation.com/explainer-hydrofluorocarbons-saved-the-ozone-layer-so-why-are-we-banning-them-86672">chemical reactivity</a> prevents them from depleting the ozone layer, their molecular structure allows them to absorb a lot of thermal radiation, making them a greenhouse gas. Like carbon dioxide on steroids, HFCs are extremely good at capturing infrared photons emitted by the Earth. Some of this radiant energy warms the climate.</p>
<p>Unlike CO2, reactive HFCs are consumed by chemistry in the air, so they only warm the climate for a decade or two. But a little bit goes a long way – each HFC molecule absorbs thousands of times as much heat as a CO2 molecule, making them powerful climate pollutants.</p>
<figure class="align-center ">
<img alt="Chart showing increase by country, with the largest increase in China." src="https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=616&fit=crop&dpr=1 600w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=616&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=616&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=775&fit=crop&dpr=1 754w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=775&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/398515/original/file-20210504-17-1y4xkj8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=775&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">HFC emissions are increasing. The chart shows their anticipated growth without control measures in place.</span>
<span class="attribution"><a class="source" href="https://www.rivm.nl/en/hydrofluorocarbons/contribution-of-hfcs-to-greenhouse-effect">Netherlands National Institute for Public Health and the Environment</a></span>
</figcaption>
</figure>
<p>HFCs <a href="https://acp.copernicus.org/articles/17/2795/2017/acp-17-2795-2017.pdf">leaking from discarded cooling equipment</a> are estimated to contribute about 4% of global greenhouse gas emissions – about twice as much as aviation.</p>
<p>This is why it’s time to retire HFCs and swap them out for alternative refrigerants. They’ve done their job saving the ozone layer, but now HFCs are a major contributor to short-term global warming, and their <a href="https://www.ccacoalition.org/en/initiatives/hfc">use has been increasing</a> as demand for cooling increases around the world.</p>
<h2>What can replace HFCs?</h2>
<p>Because they are so powerful and short-lived, stopping the production and use of HFCs can have a <a href="https://www.drawdown.org/solutions/alternative-refrigerants">significant cooling effect</a> on the climate over the next couple of decades, buying time as the world converts its energy supply from fossil fuels to cleaner sources.</p>
<p>The good news is that there are <a href="https://ww2.arb.ca.gov/resources/documents/choosing-new-system">alternative refrigerants</a>.</p>
<p>Ammonia and hydrocarbons like butane evaporate at room temperature and have been used as refrigerants since the early 20th century. These gases are short-lived, but they have a downside. Their greater reactivity means their compressors and plumbing have to be more corrosion-resistant and leak-proof to be safe. </p>
<figure class="align-center ">
<img alt="Rows of freezer cases in a store." src="https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&rect=0%2C7%2C4653%2C3396&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/398507/original/file-20210504-15-1a8c5p2.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">Designing refrigeration equipment for different chemicals will likely mean retooling the industry, which could raise costs.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/freezer-cases-in-supermarket-royalty-free-image/1134353358">Mint Image via Getty Images</a></span>
</figcaption>
</figure>
<p>The chemical industry has been developing newer alternatives intended to be safer for both people and climate, but as we saw with CFCs and HFCs, inert chemicals can have unintended consequence. Several industry leaders have <a href="https://www.ahrinet.org/App_Content/ahri/files/RESOURCES/Kigali_JMS_04-19-18.pdf">supported efforts to phase out HFCs</a>.</p>
<p>So, it’s time for another generation of cooling equipment. Just as our TVs and audio equipment and light bulbs have evolved over past decades, our refrigerators and air conditioners will be replaced by a new wave of improved products. New refrigerators will look and work just like the ones we’re used to, but they will be much gentler on the climate system.</p>
<p><em>This article was updated Sept. 23, 2021, with EPA formalizing the new rule and China ratifying the Kigali Amendment.</em></p>
<p>[<em>Over 100,000 readers rely on The Conversation’s newsletter to understand the world.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=100Ksignup">Sign up today</a>.]</p><img src="https://counter.theconversation.com/content/160241/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Scott Denning 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>HFCs keep refrigerators cool, but when these short-lived climate pollutants leak, they warm the planet.Scott Denning, Professor of Atmospheric Science, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1554452021-03-23T02:53:31Z2021-03-23T02:53:31ZClimate explained: how particles ejected from the Sun affect Earth’s climate<figure><img src="https://images.theconversation.com/files/386315/original/file-20210224-17-sbtks2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Earth's magnetic field protects us from the solar wind, guiding the solar particles to the polar regions.</span> <span class="attribution"><a class="source" href="https://sohowww.nascom.nasa.gov/gallery/images/sunearth01.html">SOHO (ESA & NASA)</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287622/original/file-20190811-144878-bvgm9l.jpg?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">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em><strong><a href="https://theconversation.com/nz/topics/climate-explained-74664">Climate Explained</a></strong> is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.</em> </p>
<p><em>If you have a question you’d like an expert to answer, please send it to <a href="mailto:climate.change@stuff.co.nz">climate.change@stuff.co.nz</a></em></p>
<hr>
<blockquote>
<p><strong>When the Sun ejects solar particles into space, how does this affect the Earth and climate? Are clouds affected by these particles?</strong></p>
</blockquote>
<p>When we consider the Sun’s influence on Earth and our climate, we tend to think about solar radiation. We are acutely aware of the skin-burning dangers of ultraviolet, or UV, radiation. </p>
<p>But the Sun is an active star. It also continuously releases what is known as “<a href="https://en.wikipedia.org/wiki/Solar_wind">solar wind</a>”, made up of charged particles, largely protons and electrons, that travel at speeds of hundreds of kilometres per hour.</p>
<p>Some of these particles that reach Earth are guided into the polar atmosphere by our magnetic field. As a result, we can see the southern lights, aurora australis, in the southern hemisphere, and the northern equivalent, aurora borealis. </p>
<figure class="align-center ">
<img alt="Aurora Australis" src="https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=372&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=372&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=372&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=467&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=467&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389700/original/file-20210315-21-hbzclj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=467&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aurora australis observed above southern New Zealand.</span>
<span class="attribution"><span class="source">Shutterstock/Fotos593</span></span>
</figcaption>
</figure>
<p>This visible manifestation of solar particles entering Earth’s atmosphere is a constant reminder there is more to the Sun than sunlight. But the particles have other effects as well. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/why-is-the-suns-atmosphere-so-hot-spacecraft-starts-to-unravel-our-stars-mysteries-128242">Why is the sun's atmosphere so hot? Spacecraft starts to unravel our star's mysteries</a>
</strong>
</em>
</p>
<hr>
<h2>Solar particles and ozone</h2>
<p>When solar particles enter the atmosphere, their high energies ionise neutral atmospheric nitrogen and oxygen molecules, which make up 99% of the atmosphere. This “<a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL068279">energetic particle precipitation</a>”, named because it’s like a rain of particles from space, is a major source of <a href="https://progearthplanetsci.springeropen.com/articles/10.1186/s40645-014-0024-3">ionisation in the polar atmosphere</a> above 30km altitude — and it sets off a chain of reactions that produces <a href="https://aura.gsfc.nasa.gov/science/feature-20200701.html">chemicals</a> that facilitate the <a href="https://www.nobelprize.org/prizes/chemistry/1995/crutzen/lecture/">destruction of ozone</a>. </p>
<p>The impact of solar particles on atmospheric ozone was first observed in 1969. Since the early 2000s, thanks to new kinds of satellite observations, we have seen growing evidence that solar particles play an <a href="https://www.nature.com/articles/ncomms6197">important part</a> in influencing polar ozone. During particularly active times, when the Sun releases large amounts of particles into space, up to 60% of ozone at altitudes above 50km can be depleted. The effect can last for weeks.</p>
<p>Lower down in the atmosphere, below 50km, solar particles are important contributors to the year-to-year variability in polar ozone levels, often through <a href="https://progearthplanetsci.springeropen.com/articles/10.1186/s40645-014-0024-3">indirect pathways</a>. Here, solar particles again contribute to <a href="https://ozonewatch.gsfc.nasa.gov/facts/">ozone loss</a>, but a recent discovery showed they also help curb some of the <a href="https://doi.org/10.5194/acp-21-2819-2021">depletion in the Antarctic ozone hole</a>.</p>
<h2>How ozone affects the climate</h2>
<p>Most of the ozone in the atmosphere resides in a thin layer at altitudes of 20-25km — the “<a href="https://scied.ucar.edu/learning-zone/atmosphere/ozone-layer">ozone layer</a>”. </p>
<p>But ozone is everywhere in the atmosphere, from the Earth’s surface to altitudes above 100km. It is a greenhouse gas and plays a key role in heating and cooling the atmosphere, which makes it critical for climate. </p>
<p>In the southern hemisphere, <a href="https://doi.org/10.1002/qj.2330">changes in polar ozone</a> are known to influence regional climate conditions. </p>
<figure class="align-center ">
<img alt="Satellite image of Earth's atmosphere" src="https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/389699/original/file-20210315-17-gr8nv2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Solar particles ionise nitrogen and oxygen molecules in the atmosphere, which leads to other chemical reactions that contribute to ozone destruction.</span>
<span class="attribution"><span class="source">Shutterstock/PunyaFamily</span></span>
</figcaption>
</figure>
<p>Its depletion above Antarctica had a cooling effect, which in turn pulled the westerly wind jet that circles the continent closer. As the Antarctic hole recovers, this <a href="https://www.uow.edu.au/media/2019/ozone-depletion-driving-climate-change-in-southern-hemisphere.php">wind belt can meander further north</a> and affect rainfall patterns, sea-surface temperatures and ocean currents. The <a href="https://niwa.co.nz/climate/information-and-resources/southern-annular-mode">Southern Annular Mode</a> describes this north-south movement of the wind belt that circles the southern polar region.</p>
<p>Ozone is important for future climate predictions, not only in the thin ozone layer, but throughout the atmosphere. It is crucial we understand the factors that influence ozone variability, be it man-made or natural like the Sun. </p>
<h2>The Sun’s direct influence</h2>
<p>The link between solar particles and ozone is reasonably well established, but what about any direct effects solar particles may have on the climate? </p>
<p>We have observational evidence that solar activity influences <a href="https://doi.org/10.1029/2008JA014029">regional climate variability at both poles</a>. Climate models also suggest such polar effects link to larger climate patterns (such as the Northern and Southern Annular Modes) and influence conditions in mid-latitudes. </p>
<p>The details are not yet well understood, but for the first time the influence of <a href="https://doi.org/10.5194/gmd-10-2247-2017">solar particles on the climate system</a> will be included in climate simulations used for the upcoming Intergovernmental Panel on Climate Change (<a href="https://www.ipcc.ch/">IPCC</a>) assessment.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/solar-weather-has-real-material-effects-on-earth-118453">Solar weather has real, material effects on Earth</a>
</strong>
</em>
</p>
<hr>
<p>Through solar radiation and particles, the Sun provides a key energy input to our climate system. While these do vary with the Sun’s 11-year cycle of magnetic activity, they can not explain the recent rapid increase in global temperatures due to climate change.</p>
<p>We know rising levels of <a href="https://www.acs.org/content/acs/en/climatescience/greenhousegases.html">greenhouse gases</a> in the atmosphere are pushing up Earth’s surface temperature (the physics have been known <a href="https://www.sciencedirect.com/science/article/pii/S0160932716300308">since the 1800s</a>). We also know human activities have greatly <a href="https://www.esrl.noaa.gov/gmd/ccgg/trends/">increased greenhouse gases</a> in the atmosphere. Together these two factors explain the observed rise in global temperatures.</p>
<h2>What about clouds?</h2>
<p>Clouds are much lower in the atmosphere than where most solar particles penetrate. Particles know as galactic cosmic rays (coming from the centre of our galaxy rather than the Sun) may be linked to cloud formation. </p>
<p>It has been suggested cosmic rays could influence the formation of condensation nuclei, which act as “seeds” for clouds. But recent <a href="https://doi.org/10.1002/2017JD027475">research</a> at the <a href="https://home.cern/">CERN</a> nuclear research facility suggests the effects are insignificant. </p>
<p>This doesn’t rule out some other mechanisms for cosmic rays to affect cloud formation, but thus far there is little supporting evidence.</p><img src="https://counter.theconversation.com/content/155445/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Annika Seppälä is a Senior Lecturer at the University of Otago. She has previously received research funding from the European Council and the Academy of Finland.</span></em></p>When solar particles reach the Earth, they not only produce spectacular auroras but also contribute to the chemical reactions leading to ozone depletion, which in turn influences climate patterns.Annika Seppälä, Senior Lecturer in Geophysics, University of OtagoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1555802021-02-18T20:20:13Z2021-02-18T20:20:13ZEarth’s magnetic field broke down 42,000 years ago and caused massive sudden climate change<figure><img src="https://images.theconversation.com/files/385125/original/file-20210218-20-utxsk3.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5991%2C3988&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">vchal / shutterstock</span></span></figcaption></figure><p>The world experienced a few centuries of apocalyptic conditions 42,000 years ago, triggered by a reversal of the Earth’s magnetic poles combined with changes in the Sun’s behaviour. That’s the key finding of our new multidisciplinary study, published in <a href="https://science.sciencemag.org/cgi/doi/10.1126/science.abb8677">Science</a>.</p>
<p>This last major geomagnetic reversal triggered a series of dramatic events that have far-reaching consequences for our planet. They read like the plot of a horror movie: the ozone layer was destroyed, electrical storms raged across the tropics, solar winds generated spectacular light shows (auroras), Arctic air poured across North America, ice sheets and glaciers surged and weather patterns shifted violently.</p>
<p>During these events, life on earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna went extinct, while modern humans sought protection in caves.</p>
<p>The magnetic north pole – where a compass needle points to – does not have a permanent location. Instead, it usually wobbles around close to the geographic north pole – the point around which the Earth spins – over time due to movements within the Earth’s core.</p>
<p>For reasons still not entirely clear, magnetic pole movements can sometimes be more extreme than a wobble. One of the most dramatic of these pole migrations took place some 42,000 years ago and is known as the Laschamps Excursion – named after the village where it was discovered in the French Massif Central.</p>
<p>The Laschamps Excursion has been recognised around the world, including most recently in <a href="https://theconversation.com/we-found-the-first-australian-evidence-of-a-major-shift-in-earths-magnetic-poles-it-may-help-us-predict-the-next-155040">Tasmania, Australia</a>. But up until now, it has not been clear whether such magnetic changes had any impacts on climate and life on the planet. Our new work draws together multiple lines of evidence that strongly suggest the effects were indeed global and far-reaching.</p>
<h2>Ancient trees</h2>
<p>To investigate what happened, we analysed ancient New Zealand <a href="https://theconversation.com/lord-of-the-forest-new-zealands-most-sacred-tree-is-under-threat-from-disease-but-response-is-slow-100447">kauri trees</a> that had been preserved in peat bogs and other sediments for more than 40,000 years. Using the annual growth rings in the kauri trees, we have been able to create a detailed timescale of how Earth’s atmosphere changed over this time. The trees revealed a prolonged spike in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field as the poles switched, providing a way of precisely linking widely geographically dispersed records.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/NSig4MyLQ0o?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How the tree analysis works.</span></figcaption>
</figure>
<p>“The kauri trees are like the Rosetta Stone, helping us tie together records of environmental change in caves, ice cores, and peat bogs around the world,” says professor Alan Cooper, who co-lead this research project.</p>
<p>Using the newly-created timescale, we were able to show that tropical Pacific rain belts and the Southern Ocean westerly winds abruptly shifted at the same time, bringing arid conditions to places like Australia at the same time as a range of megafauna, including giant kangaroos and giant wombats <a href="https://theconversation.com/dna-evidence-proves-climate-change-killed-off-prehistoric-megafauna-45080">went extinct</a>. Further north, the vast Laurentide Ice Sheet rapidly grew across the eastern US and Canada, while in Europe the Neanderthals spiralled into extinction.</p>
<h2>Climate modelling</h2>
<p>Working with a computer programme that simulated the global interactions between chemistry and the climate, we investigated the impact of a weaker magnetic field and changes in the Sun’s strength. Importantly, during the magnetic switch, the strength of the magnetic field plummeted to less than 6% of what it is today. A compass back then would struggle to even find north.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large tree trunk" src="https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/385076/original/file-20210218-26-193rwr9.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">An ancient kauri tree log from Ngāwhā, New Zealand.</span>
<span class="attribution"><a class="source" href="http://www.nelsonskaihukauri.co.nz">Nelson Parker</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>With essentially no magnetic field, our planet totally lost its very effective shield against cosmic radiation, and many more of these very penetrating particles from space could access the top of the atmosphere. On top of this, the Sun experienced several “grand solar minima” throughout this period, during which the overall solar activity was generally much lower but also more unstable, sending out numerous massive solar flares that allowed more powerful ionising cosmic rays to reach Earth.</p>
<p>Our models showed that this combination of factors had an amplifying effect. The high energy cosmic rays from the galaxy and also enormous bursts of cosmic rays from solar flares were able to penetrate the upper atmosphere, charging the particles in the air and causing chemical changes that drove the loss of stratospheric ozone. </p>
<p>The modelled chemistry-climate simulations are consistent with the environmental shifts observed in many natural climate and environmental change archives. These conditions would have also extended the dazzling light shows of the aurora across the world – at times, nights would have been as bright as daytime. We suggest the dramatic changes and unprecedented high UV levels caused early humans to seek shelter in caves, explaining the apparent sudden flowering of cave art across the world 42,000 years ago.</p>
<p>It must have seemed like the end of days.</p>
<h2>The Adams Event</h2>
<p>Because of the coincidence of seemingly random cosmic events and the extreme environmental changes found around the world 42,000 years ago, we have called this period the “Adams Event” – a tribute to the great science fiction writer Douglas Adams, who wrote The Hitchhiker’s Guide to the Galaxy and identified “42” as the answer to life, the universe and everything. Douglas Adams really was onto something big, and the remaining mystery is how he knew?</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Qs1dLe3GsQY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Paleopocalypse! - A short video on the Adams Event, narrated by Stephen Fry.</span></figcaption>
</figure><img src="https://counter.theconversation.com/content/155580/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Fogwill receives funding from UKRI and the Australian Research Council. A huge thanks to Professor Alan Cooper, Honorary Researcher at the South Australian Museum, who co-led this study, Adjunct Professor Ken McCracken and Dr Jonathan Palmer at the University of New South Wales, Drew Lorrey at the New Zealand National Institute of Water and Atmospheric Research, Dr Janet Willmshurst at Landcare Research and our co-authors on the published article.
</span></em></p><p class="fine-print"><em><span>Professor Alan Hogg works for University of Waikato in Hamilton, New Zealand. He is an Associate Investigator in a Royal Society of New Zealand Marsden grant - MFP-NIW1803: Dr Andrew Lorrey, NIWA, Auckland, Principal Investigator.</span></em></p><p class="fine-print"><em><span>Chris Turney receives funding fromthe Australian Research Council and is a scientific advisor to cleantech graphite company, CarbonScape (<a href="https://www.carbonscape.com">https://www.carbonscape.com</a>).</span></em></p><p class="fine-print"><em><span>Zoë Thomas receives funding from the Australian Research Council.</span></em></p>Scientists have uncovered evidence of a global paleopocalyspe.Chris Fogwill, Professor of Glaciology and Palaeoclimatology, Head of School Geography, Geology and the Environment and Director of the Institute for Sustainable Futures, Keele UniversityAlan Hogg, Professor, Director, Carbon Dating Laboratory, University of WaikatoChristian Turney, Professor of Earth Science and Climate Change, Director of the Earth and Sustainability Science Research Centre, Director of Chronos 14Carbon-Cycle Facility, and UNSW Director of ARC Centre for Excellence in Australian Biodiversity and Heritage, UNSW SydneyZoë Thomas, ARC DECRA Fellow, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1478902020-10-10T12:47:44Z2020-10-10T12:47:44ZRemembering Mario Molina, Nobel Prize-winning chemist who pushed Mexico on clean energy – and, recently, face masks<figure><img src="https://images.theconversation.com/files/362769/original/file-20201009-15-1xhaoxs.jpg?ixlib=rb-1.1.0&rect=9%2C9%2C3172%2C2108&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Molina speaking about climate change at the Guadalajara International Book Fair in Mexico, Nov. 2018. </span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/nobel-prize-recipient-mario-molina-speaks-to-the-audience-news-photo/1074094970?adppopup=true">Leonardo Alvarez/Getty Images</a></span></figcaption></figure><p>Dr. Mario Molina, the Nobel Prize-winning scientist <a href="https://www.washingtonpost.com/local/obituaries/mario-molina-nobel-laureate-who-revealed-threat-to-ozone-layer-dies-at-77/2020/10/08/621f03f8-095f-11eb-9be6-cf25fb429f1a_story.html">who died on Oct. 7 at age 77</a>, did not become a scientist to change the world; he just loved chemistry. Born in Mexico City in 1943, Molina as a young boy conducted home experiments with <a href="https://www.infobae.com/america/mexico/2020/10/07/murio-mario-molina-premio-nobel-de-quimica-en-1995/">contaminated water just for the fun of it</a>. </p>
<p>But Molina came to understand the political importance of his <a href="https://www.nobelprize.org/prizes/chemistry/1995/summary/">work on atmospheric chemistry and ozone layer depletion</a>, which won him the <a href="https://www.nobelprize.org/prizes/chemistry/1995/summary/">Nobel in 1995, along with Paul J. Crutzen and F. Sherwood Rowland</a>. Getting that surprise call from Sweden <a href="https://www.youtube.com/watch?v=e3FECEaPOfE&feature=youtu.be">completely changed how he saw his role in the world</a>, Molina said in 2016. He felt a responsibility to share his knowledge of <a href="https://centromariomolina.org/mario-molina/biografia/">clean energy, air quality and climate change</a> broadly and to push <a href="https://www.nobelprize.org/prizes/chemistry/1995/summary/">decision-makers to use that information to protect the environment</a>.</p>
<p>As a Mexican, Dr. Molina was a point of pride for me. Though <a href="https://scholar.google.com/citations?user=LA4-pCYAAAAJ&hl=en">I am a social scientist</a>, not a chemist, his career inspired me to follow my dreams and to trust science to show us all the right path. </p>
<h2>Clean air now</h2>
<p>Mario Molina thought climate change was the biggest problem in the world long before most people did. </p>
<p>His research was instrumental in spurring negotiation of the 1987 <a href="https://youtu.be/UqW5WfFYczA">Montreal Protocol</a>, an international treaty that effectively banned fluorocarbons – harmful chemical compounds that damage the ozone layer. The agreement is credited with <a href="https://www.sciencemag.org/news/2016/06/ozone-layer-mend-thanks-chemical-ban">helping the ozone layer heal</a>. He understood that the environmental problem is global, and that what happens in China or the United States <a href="https://www.nobelprize.org/prizes/chemistry/1995/summary/">affects Mexico</a>, too.</p>
<p>After a long a career in academia, Molina and his wife, Luisa T. Molina – also an an atmospheric scientist – founded the <a href="https://centromariomolina.org/">Centro Mario Molina in 2005</a>, a Mexican center dedicated to environmental research and public policy. Together, they <a href="https://www.journals.elsevier.com/urban-climate/editorial-board/dr-luisa-t-molina#:%7E:text=California%20at%20Berkeley.-,Dr.,pollution%2C%20and%20stratospheric%20ozone%20chemistry.&text=Currently%2C%20she%20is%20also%20investigating,regional%20climate%20and%20air%20quality">co-directed the center, which conducts extensive work in Mexico City</a>. </p>
<p>The Molinas sounded the alarm in Latin America about <a href="http://peace-foundation.net.7host.com/Peace/file/Mexico%20City%20Project%20-Molina.pdf">air pollution and public health</a>, which remains a challenge in the region. But they also <a href="https://centromariomolina.org/ciudades-sustentables/">understood the role of economics</a> in environmental protection – and, importantly, the centrality of fossil fuels to the Mexican economy – so the Molinas worked with Mexican economists to address concerns that green energy would hurt prosperity. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Four men toast each other" src="https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=362&fit=crop&dpr=1 600w, https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=362&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=362&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=455&fit=crop&dpr=1 754w, https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=455&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/362770/original/file-20201009-15-3ez0cv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=455&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Molina (2nd-R) shortly after winning the Nobel Prize in Chemistry, celebrating at a reception with past Laureates from M.I.T., Oct. 11, 1995.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/nobel-prize-winner-for-chemistry-m-i-t-professor-mario-news-photo/1228950891?adppopup=true">Stuart Cahill/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>Through his organization, Molina also promoted cooperation between <a href="https://youtu.be/UqW5WfFYczA">scientists, goverment, industry and civil society</a> until 2013, when then-Mexican President Enrique Peña Nieto <a href="https://aristeguinoticias.com/0306/mexico/mario-molina-encabezara-sistema-nacional-del-cambio-climatico-epn/">appointed him</a> to head the country’s National System for Climate Change.</p>
<p>In 2018, when Mexico’s government changed, Molina was not invited to serve in the new administration. Mexico’s current president, Andrés Manuel López Obrador, <a href="https://www.washingtonpost.com/world/the_americas/mexicos-president-elect-promises-to-clean-up-the-environment--and-build-a-new-oil-refinery/2018/09/10/f91ac9d6-a336-11e8-a3dd-2a1991f075d5_story.html">came to power promising to build a new oil refinery in Mexico</a>.</p>
<p>Molina urged Mexico to transition to clean energy sources “<a href="http://centromariomolina.org/english2/wp-content/uploads/2020/06/22.-ComPrensa_CMM_Energ_28-05-2020-_ENGLISH.pdf">sooner rather than later</a>,” promising this policy change would promote “<a href="http://centromariomolina.org/english2/wp-content/uploads/2020/06/22.-ComPrensa_CMM_Energ_28-05-2020-_ENGLISH.pdf">public health, job creation and energy security for the country</a>.” In a May 2020 interview, Molina stressed clean energy “<a href="https://www.eleconomista.com.mx/arteseideas/Son-tiempos-para-acelerar-la-transicion-a-energias-limpias-Mario-Molina-20200528-0136.html">is an investment that society makes and very profitable</a>.”</p>
<p>“Mexico is going back to the previous century or the one before it, at a time when all the experts on the planet fully agree that we are in a climate crisis,” <a href="https://www.contrareplica.mx/nota--Mexico-esta-retrocediendo-al-siglo-anterior-Mario-Molina202014847">he said of Mexico’s continued reliance on fossil fuels just months before his death</a>. Molina criticized López Obrador for <a href="https://www.excelsior.com.mx/nacional/el-cambio-no-puede-esperar-mario-molina-habla-sobre-la-contaminacion/1313997">limiting the use of clean energy sources</a> and pushed for more wind energy in Mexico, a technology that’s only just emerging there. </p>
<h2>Scientist until the end</h2>
<p>Molina defended the importance of science in policy-making until the very end. </p>
<p>When the COVID-19 pandemic broke out, he was an early and <a href="https://www.infobae.com/america/mexico/2020/10/07/mario-molina-sus-ultimas-polemicas-por-el-uso-de-cubrebocas-ante-covid-19/">adamant advocate for face masks</a> and was aghast that the presidents of both Mexico and the United States <a href="https://www.theguardian.com/world/2020/jul/31/mexico-president-amlo-mask-coronavirus-corruption">refused to wear facial coverings</a>. He <a href="https://www.infobae.com/america/mexico/2020/10/07/mario-molina-sus-ultimas-polemicas-por-el-uso-de-cubrebocas-ante-covid-19/">said the government</a> should “force the use of face masks…because only in this way do we know that the curve can be flattened.”</p>
<p>[<em>Deep knowledge, daily.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=deepknowledge">Sign up for The Conversation’s newsletter</a>.]</p>
<p>Mario Molina graduated from the National Autonomous University of Mexico, or UNAM, and completed his graduate studies at the University of Fribourg and the University of California, Berkeley. Though he taught at M.I.T., he <a href="https://quimica.unam.mx/fallece-mario-molina-premio-nobel-de-quimica/?fbclid=IwAR2smRnABAjz_DcVt2BzNNhyE0ivcIcey1sGetiZqf48ggrbuA8xlibJtuw">remained loyal to UNAM</a>, working with faculty and students til the end.</p>
<p>The many Mexicans who, like me, were inspired by his life’s work mourn his passing.</p><img src="https://counter.theconversation.com/content/147890/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elena Delavega 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>Molina, who died on Oct. 8, ‘thought climate change was the biggest problem in the world long before most people did.’ His research on man-made depletion of the ozone layer won the 1995 Nobel Prize.Elena Delavega, Associate Professor of Social Work, University of MemphisLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1395192020-06-01T10:22:49Z2020-06-01T10:22:49ZPrehistoric climate change damaged the ozone layer and led to a mass extinction<figure><img src="https://images.theconversation.com/files/338387/original/file-20200528-51509-l9s17i.jpg?ixlib=rb-1.1.0&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-photo/planet-earth-spectacular-sunset-elements-this-1463607272">muartat/Shutterstock</a></span></figcaption></figure><p>Mass extinctions are very important to how life evolved on Earth. For example, when an asteroid <a href="https://theconversation.com/dinosaur-killing-asteroid-struck-at-worst-angle-to-cause-maximum-damage-new-research-139394">hit the Earth</a> 66 million years ago, the resulting dinosaur extinction led mammals <a href="https://theconversation.com/mass-extinctions-made-life-on-earth-more-diverse-and-might-again-122350">to take their place</a>. </p>
<p>My colleagues and I have <a href="https://advances.sciencemag.org/content/6/22/eaba0768">published new research</a> on the mass extinction that took place 359 million years ago at the boundary between the Devonian and Carboniferous geological periods. There have been many <a href="https://link.springer.com/article/10.1134/S0001437016050015">previous speculations</a> as to the cause of this event, including volcanic eruptions, asteroid impacts, climate change, sea level changes, wildfires and the rise of the first forests. </p>
<p>But we have shown that the extinctions on land at this time may have been caused by a catastrophic thinning of the ozone layer that let in damaging levels of ultra-violet radiation. <a href="https://phys.org/news/2018-02-thinning-ozone-layer-driven-earth.html">Something similar</a> contributed to the mass extinctions at the end of the Permian and Triassic periods, but these events were caused by volcanic eruptions. Our research suggests the Earth has a natural internal process triggered by a warming climate that can destroy the ozone layer, a serious warning for our own period of climate change. </p>
<p>The Late Devonian extinction played a <a href="https://www.pnas.org/content/107/22/10131">significant role</a> in the development of vertebrate life. It included the loss of the dominant group of armoured freshwater fish. The survivors were the sharks and the rather minor group of bony fish that subsequently spread out to dominate our younger oceans. </p>
<p>The event also shaped our own evolution because it led to the extinction of the first four-legged “tetrapods”. These were “fish” whose fins had evolved to become limbs with between six and eight fingers and toes. The first land-dwelling tetrapods with five fingers and toes – our ancestors – don’t appear in the fossil record until after this extinction. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/338380/original/file-20200528-51496-17hrmhk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Devonian Period saw the first tetrapods emerge.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/devonian-landscape-3d-render-759826384">Nicolas Primola/Shutterstock</a></span>
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<p>To find out exactly what caused the Late Devonian extinction, we looked for evidence of what happened in the atmosphere that was captured by fossilised plants from before and after the event. In particular, we looked at the resistant walls of the microscopic remains of pollen and spores, taken from fossils found in East Greenland and released by dissolving the rock samples in acid. </p>
<p>The resistant walls of spores and pollen are there to protect the cell contents from ultra-violet radiation. But there is a brief interval between the creation of a new cell and the formation of its protective wall when it is vulnerable.</p>
<p>The kinds of spores we examined are covered in small spines that are normally identical in length and have perfectly pointed tips. But most of the spines in our samples were malformed in a wild variety of shapes, suggesting the DNA of their cells was damaged by ultra-violet radiation. This suggests that the Earth’s protective ozone shield was down as the spores were formed.</p>
<p>Other spores and pollen had pigmented walls that acted as a protective tan, enabling those plants to survive. But a number of important plant groups quickly became extinct and the forest ecosystem collapsed. Those groups that survived were still disrupted and it took several million years to rebuild, creating quite a different ecosystem in the process. </p>
<p>Our samples came from a very large ancient lake that existed all year round despite being in a very arid part of the world. Such lakes only form when glaciers collapse and the world’s seasonal monsoon is very active due to solar heat, so the global climate must have been in a warming period.</p>
<h2>Extinction mechanism</h2>
<p>Other scientists <a href="https://science.sciencemag.org/content/337/6096/835">have shown</a> that high summer temperatures over continental areas can increase the transport of water vapour high into the atmosphere. This water vapour carries with it organic carbon compounds that include chlorine, which are produced naturally by a wide variety of plants, algae and fungi. Once these compounds are near the ozone layer, they release the chlorine and this breaks down ozone molecules.</p>
<p>This produces a positive feedback loop because a collapsing terrestrial ecosystem will release a flush of nutrients into the oceans, which can cause a rapid increase in algae. So the more the ozone layer is damaged, the more plants die, and the more ozone-damaging compounds are released. Later on, the ozone layer will naturally recover as the climate cools and the algae helps remove carbon dioxide from the atmosphere.</p>
<p>The discovery of this potential new extinction mechanism indicates that a warming climate, such as we have now, has the potential to erode the ozone layer to let in damaging ultra-violet radiation. This has consequences for all life on Earth, both on the land and in shallow waters. </p>
<p>We believe it is as important as recognising that asteroid impacts caused mass extinctions. Once we knew about the consequences of asteroid impacts, there followed an intense collective research effort to <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073191">assess the threat</a>. We now <a href="https://astronomy.com/news/2018/07/tracking-asteroids">plot the paths</a> of all large extra-terrestrial objects likely to come close to the Earth’s orbit.</p>
<p>Similarly, we now need to focus effort on understanding the links between global warming and the production and atmospheric transport of chlorine-bearing carbon compounds that have the potential to cause similar destruction of our ozone layer.</p>
<p>We now need to make further studies of the rocks with malformed spores to work out the duration of the extinction and the likely rate of temperature change required to push enough ozone-destroying chemicals high into the atmosphere. We also want to do ultra-violet malformation experiments on living fern-like plants which have spiny spores.</p><img src="https://counter.theconversation.com/content/139519/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Marshall receives funding from NERC and National Geographic. He is affiliated with CASP and the Etches Collection as a charitable trustee. </span></em></p>New research on the Late Devonian extinction suggests the ozone layer could be naturally depleted as the temperature rises.John Marshall, Professor of Earth Science, University of SouthamptonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1304382020-02-17T13:36:45Z2020-02-17T13:36:45ZThe unexpected link between the ozone hole and Arctic warming<figure><img src="https://images.theconversation.com/files/315338/original/file-20200213-11011-1plchfk.jpg?ixlib=rb-1.1.0&rect=191%2C295%2C4662%2C2936&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Temperatures are warming faster in the Arctic than anywhere else in the world. Water and sewer pipes in Iqaluit, Nunavut, are cracking during the winter as the ground shifts.</span> <span class="attribution"><span class="source">THE CANADIAN PRESS/Sean Kilpatrick</span></span></figcaption></figure><p>One of the <a href="https://doi.org/10.1029/JC085iC10p05529">earliest climate model predictions</a> of how human-made climate change would affect our planet showed that the Arctic would warm about two to three times more than the global average. Forty years later, this “Arctic amplification” has been observed firsthand.</p>
<p><a href="https://www.noaa.gov/media-release/unprecedented-arctic-warmth-in-2016-triggers-massive-decline-in-sea-ice-snow">Record-breaking Arctic warming</a> and the <a href="https://www.nytimes.com/interactive/2017/09/22/climate/arctic-sea-ice-shrinking-trend-watch.html">dramatic decline of sea ice</a> are having severe <a href="https://doi.org/10.1126/science.1235225">consequences on sensitive ecosystems</a> in the region.</p>
<p>But why has the Arctic warmed more than the tropics and the mid-latitudes?</p>
<p><a href="https://doi.org/10.1038/s41558-019-0677-4">We now know</a> that this is due, in part, to tiny concentrations of very powerful greenhouse gases — ozone-depleting substances such as chlorofluorocarbons (CFCs).</p>
<h2>A wonder gas?</h2>
<p>The ozone layer is the protective layer in the stratosphere, roughly 20-50 kilometres above the Earth, that absorbs harmful ultraviolet radiation from the sun. <a href="https://ozone.unep.org/20-questions-and-answers">Ozone-depleting substances</a> are potent greenhouse gases, but they are more commonly known for their devastating effect on the ozone layer.</p>
<p>These chemicals were invented in the 1920s. They were touted as “wonder gases” used as refrigerants, solvents and propellants, in refrigerators, air conditioners and packing materials. It wasn’t until the 1980s when <a href="https://doi.org/10.1038/315207a0">scientists discovered a hole in the ozone layer</a> above Antarctica that they realized the full extent of the ozone-depleting nature of these chemicals.</p>
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<a href="https://theconversation.com/what-are-ozone-depleting-substances-9203">What are ozone depleting substances?</a>
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<p>In 1987, 197 countries <a href="https://ozone.unep.org/treaties/montreal-protocol">agreed to phase out their use of ozone-depleting substances by ratifying the Montréal Protocol</a>. The success of this historic international agreement has reduced the emissions of CFCs to nearly zero; however, the recovery of the ozone hole has been slower as CFCs remain in the atmosphere for decades.</p>
<p>Due to the effect of ozone-depleting substances on the ozone layer, climate scientists who study these chemicals and their <a href="https://doi.org/10.1002/qj.2330">climate impacts</a> have been focused on the consequences of ozone depletion. The climate impact of ozone-depleting substances themselves has been typically considered small given the very tiny concentrations of these gases in the atmosphere, and has been largely unexplored.</p>
<h2>Experimenting with climate models</h2>
<p>My colleagues and I were interested in understanding how ozone-depleting substances might have influenced late-20th century warming from 1995 to 2005. We specifically chose this time period in order to capture the rapid rise in ozone-depleting substances in the atmosphere over this time. Since the early 2000s, atmospheric concentrations have been declining. </p>
<p>One way that climate scientists approach problems like this one is to use <a href="https://www.carbonbrief.org/qa-how-do-climate-models-work">computer models of the Earth</a> to understand what the effects of different phenomena, such as volcanic eruptions, and greenhouse gases, such as methane, might have on air temperatures, ocean circulation patterns, rainfall and so on.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=476&fit=crop&dpr=1 754w, https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=476&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/315341/original/file-20200213-11044-9d8ts7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=476&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">A snowmobiler navigates the ice near Iqaluit, Nunavut.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Sean Kilpatrick</span></span>
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</figure>
<p>To explore the contribution of ozone-depleting substances to late-20th century warming, we ran a climate model over the period from 1955 to 2005. One of the simulations incorporated all of the various <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/Fig8-18-1.jpg">historical climate drivers</a> — those that warm the climate, like carbon dioxide, methane, nitrous oxide and ozone-depleting substances, and those that cool the climate, like volcanic particulate matter. The second simulation had all the historical climate drivers, except the ozone-depleting substances.</p>
<p>This is one of the first times the role of ozone-depleting substances had been isolated. Typically, climate model experiments that examine the roles of different climate drivers will lump all greenhouses gases together. </p>
<p>Comparing the two model simulations revealed that global warming was reduced by one-third and Arctic warming by one-half when the ozone-depleting substances were not included in our simulation.</p>
<h2>Arctic amplification</h2>
<p>Why do ozone-depleting substances have such a large impact despite their very small atmospheric concentrations? First, these chemicals are very <a href="https://www.ghgprotocol.org/sites/default/files/ghgp/Global-Warming-Potential-Values%20%28Feb%2016%202016%29_1.pdf">potent greenhouse gases</a>, a fact that we have known for a long time. Second, in the late-20th century, warming from carbon dioxide is partially cancelled out by the cooling that comes from particulate matter in the atmosphere, allowing CFCs and other ozone-depleting substances to contribute substantially to warming.</p>
<p>Finally, when it comes to Arctic amplification, we know that this phenomenon arises from <a href="https://doi.org/10.1038/ngeo2071">feedbacks within the climate system</a> that act to enhance warming, and this is exactly what we find in our model simulations. In the simulation without ozone-depleting substances, the climate feedbacks were weaker than in the simulation with them, resulting in less Arctic amplification. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/315332/original/file-20200213-10980-rbmmcs.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">
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<span class="caption">Climate warming could extend the growing season in Nuuk, Greenland, by two months by the end of the 21st century.</span>
<span class="attribution"><span class="source">AP Photo/David Goldman</span></span>
</figcaption>
</figure>
<p>Understanding why the feedbacks differ is the aim of our future research but, in the meantime, our work clearly demonstrates the significant impact of ozone-depleting substances on Arctic climate.</p>
<p>Thirty years ago, those who signed the Montréal Protocol were not thinking about climate change. Yet, research such as ours underscores the important role this agreement will play in <a href="https://doi.org/10.1073/pnas.0610328104">mitigating future warming</a> as the concentrations of ozone-depleting substances decline over time. </p>
<p>That said, without massive reductions in carbon dioxide emissions in the coming decades, the gains we will achieve through the Montréal Protocol will be quickly overwhelmed. Further action is needed to protect the Arctic — and our planet.</p><img src="https://counter.theconversation.com/content/130438/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Karen Smith receives funding from the US National Science Foundation. </span></em></p>New research finds that chlorofluorocarbons (CFCs) and other ozone-depleting substances have boosted the effects of climate change in the Arctic.Karen Smith, Assistant professor, teaching stream, University of TorontoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1037512018-09-25T06:24:14Z2018-09-25T06:24:14ZAntarctica’s ‘moss forests’ are drying and dying<figure><img src="https://images.theconversation.com/files/237876/original/file-20180925-149958-iv4fh9.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lush moss beds in East Antarctica's Windmill Islands.</span> <span class="attribution"><span class="source">Sharon Robinson</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The lush moss beds that grow near East Antarctica’s coast are among the only plants that can withstand life on the frozen continent. But our new research shows that these slow-growing plants are changing at a far faster rate than anticipated.</p>
<p>We began monitoring plant ecosystems 18 years ago, near Australia’s Casey Station in the Windmill Islands, East Antarctica.</p>
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<a href="https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237870/original/file-20180925-149979-14gmguu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&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">Casey Station is on East Antarctica’s coast. Click map to zoom.</span>
<span class="attribution"><span class="source">Australian Antarctic Data Centre</span></span>
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<p>As we <a href="https://www.nature.com/articles/s41558-018-0280-0">report in Nature Climate Change today</a>, within just 13 years we observed significant changes in the composition and health of these moss beds, due to the drying effects of weather changes prompted by damage to the ozone layer.</p>
<h2>Living on the edge</h2>
<p>Visitors to Antarctica expect to see a stark landscape of white and blue: ice, water, and sky. But in some places summer brings a surprisingly verdant green, as lush mosses emerge from under their winter snow blanket.</p>
<p>Because it contains the best moss beds on continental Antarctica, Casey Station is dubbed the <a href="http://www.antarctica.gov.au/about-antarctica/wildlife/plants/casey-the-daintree-of-antarctica">Daintree of the Antarctic</a>. Individual plants have been growing here for at least 100 years; fertilised by <a href="https://phys.org/news/2012-07-antarctic-moss-survive-due-ancient.html">ancient penguin poo</a>.</p>
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Read more:
<a href="https://theconversation.com/drones-help-scientists-check-the-health-of-antarctic-mosses-revealing-climate-change-clues-83817">Drones help scientists check the health of Antarctic mosses, revealing climate change clues</a>
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<p>Antarctic mosses are extremophiles, the only plants that can survive the continent’s frigid winters. They live in a frozen desert where life-sustaining water is mostly locked up as ice, and they grow at a glacial pace – typically just 1 mm a year.</p>
<p>These mosses are home to <a href="https://www.britannica.com/animal/tardigrade">tardigrades</a> and other organisms, all of which survive harsh conditions by drying out and becoming dormant. When meltwater is available, mosses soak it up like a sponge and spring back to life.</p>
<p>The short summer growing season runs from December to March. Day temperatures finally rise above freezing, providing water from melting snow. Overnight temperatures drop below zero and mosses refreeze. Harsh, drying winds reach speeds of 200 km per hour. This is life on the edge.</p>
<h2>Tough turf</h2>
<p>When we first began monitoring the moss beds, they were dominated by <em>Schistidium antarctici</em>, a species found only in Antarctica. These areas were typically submerged through most of the summer, favouring the water-loving Schistidium. But as the area dries, two hardy, global species have encroached on Schistidium’s turf.</p>
<p>Like tree rings, mosses preserve a record of past climate in their shoots. From this we found nearly half of the mosses showed evidence of drying.</p>
<p>Healthy green moss has turned red or grey, indicating that plants are under stress and dying. This is due to the area drying because of colder summers and stronger winds. This increased desertification of East Antarctica is caused by both climate change and <a href="https://theconversation.com/the-ozone-hole-leaves-a-lasting-impression-on-southern-climate-34043">ozone depletion</a>.</p>
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<a href="https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=451&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=451&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=451&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237875/original/file-20180925-149964-1p2jdu.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>
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<span class="caption">Moss beds, with moss in the foreground showing signs of stress.</span>
<span class="attribution"><span class="source">Sharon Robinson</span>, <span class="license">Author provided</span></span>
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</figure>
<p>Since the 1970s, man-made substances have thinned Earth’s protective sunscreen, the ozone layer, creating a hole that appears directly over Antarctica during the southern spring (September–November). This has <a href="https://theconversation.com/the-ozone-hole-leaves-a-lasting-impression-on-southern-climate-34043">dramatically affected the southern hemisphere’s climate</a>. Westerly winds have moved closer to Antarctica and strengthened, shielding much of continental East Antarctica from global warming.</p>
<p>Our study shows that these effects are contributing to drying of East Antarctica, which is in turn altering plant communities and affecting the health of some native plant species. East Antarctica’s mosses can be viewed as sentinels for a rapidly drying coastal climate.</p>
<p>But there is good news. The ozone layer is slowly recovering as pollutants are phased out thanks to the <a href="https://theconversation.com/saving-the-ozone-layer-why-the-montreal-protocol-worked-9249">1987 Montreal Protocol</a>. What is likely to happen to Antarctic coastal climates when ozone levels recover fully by the middle of this century?</p>
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<a href="https://theconversation.com/the-ozone-hole-leaves-a-lasting-impression-on-southern-climate-34043">The ozone hole leaves a lasting impression on southern climate</a>
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<p>Unlike <a href="https://theconversation.com/the-freak-warm-arctic-weather-is-unusual-but-getting-less-so-92590">other polar regions</a>, East Antarctica has so far experienced <a href="https://www.scar.org/library/scar-publications/occasional-publications/3508-antarctic-climate-change-and-the-environment-1/">little or no warming</a>.</p>
<p>Antarctic ice-free areas are currently less than 1% of the continent but are <a href="https://theconversation.com/the-winners-and-losers-of-antarcticas-great-thaw-80140">predicted to expand over the coming century</a>. Our research suggests that this may isolate moss beds from snow banks, which are their water reservoirs. Ironically, increased ice melt may be bad news for some Antarctic mosses.</p>
<p>East Antarctica is drying – first at the hands of ozone depletion, and then by climate change. How its native mosses fare in the future depends on how we control greenhouse gas emissions. But with decisive action and continued monitoring, we can hopefully preserve these fascinating ecosystems for the future.</p><img src="https://counter.theconversation.com/content/103751/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Melinda Waterman has received funding from an Australian Postgraduate Award Scholarship, Australian Institute of Nuclear Science and Engineering postgraduate award, an Endeavour Research Fellowship and University of Wollongong’s Global Challenges Program.</span></em></p><p class="fine-print"><em><span>Sharon Robinson receives funding from the Australian Research Council, the Australian Institute of Nuclear Science and Engineering, the Antarctic Science Grants and the University of Wollongong’s Global Challenges Program</span></em></p><p class="fine-print"><em><span>Johanna Turnbull does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Mosses are the only plants that can withstand life in East Antarctica’s frozen landscape. But a new study shows that life is getting even harder, as ozone loss and climate change make conditions even drier.Melinda Waterman, Associate lecturer, University of WollongongJohanna Turnbull, Associate Lecturer in Biology, University of WollongongSharon Robinson, Professor, University of WollongongLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1005242018-07-29T20:17:14Z2018-07-29T20:17:14ZThe ozone hole is both an environmental success story and an enduring global threat<figure><img src="https://images.theconversation.com/files/229266/original/file-20180725-194124-4jtn2t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Researchers release a balloon carrying instruments to measure ozone levels above Antarctica.</span> <span class="attribution"><a class="source" href="https://www.nature.com/news/antarctic-ozone-hole-is-on-the-mend-1.20183">Kelli-Ann Bliss/NOAA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The headlines in recent months read like an international eco-thriller. </p>
<p>At Mauna Loa Observatory, perched high on a Hawaiian volcano, <a href="https://www.bbc.com/news/science-environment-44138984">researchers</a> measure unusual levels of CFC-11 in the atmosphere. The measurements baffle the scientific community: CFC-11, a potent ozone-depleting gas, has been carefully monitored since it was banned under the 1987 Montreal Protocol. But the measurements are soon <a href="https://doi.org/10.1038/s41586-018-0106-2">confirmed</a> by observing stations in Greenland, American Samoa and Antarctica. The <a href="https://www.nytimes.com/2018/06/24/world/asia/china-ozone-cfc.html">evidence</a> points to illegal production of the banned chemical, threatening the fragile recovery of Earth’s UV-shielding ozone layer. But the identity of the environmental super-villain remains a mystery. </p>
<p>Then, a breakthrough. By running global climate models backwards, a team of scientists in Boulder, Colorado, <a href="https://doi.org/10.1038/s41586-018-0106-2">trace the source</a> of CFC-11 to East Asia. The trail is picked up by the <a href="https://eia-international.org/">Environmental Investigation Agency</a>, a tiny activist organisation based above a coffee shop in Islington, London. EIA dispatches investigators to China and <a href="https://eia-international.org/report/blowing-it">uncovers</a> rampant illegal production of CFC-11 for insulation foam used in the Chinese construction industry. “This is an environmental crime on a massive scale,” says <a href="https://eia-international.org/new-eia-report-uncovers-illegal-cfc-11-production-use-china">Clare Perry</a>, EIA’s climate campaign leader. </p>
<p>Meanwhile, scientists and diplomats from around the world converge on Vienna for a meeting of the United Nations working group on the Montreal Protocol. EIA’s blockbuster report is <a href="https://www.nature.com/articles/d41586-018-05743-4">high on the agenda</a>. But can the international community band together once more to protect the ozone layer and save “the world’s most successful environmental treaty”? </p>
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Read more:
<a href="https://theconversation.com/after-30-years-of-the-montreal-protocol-the-ozone-layer-is-gradually-healing-84051">After 30 years of the Montreal Protocol, the ozone layer is gradually healing</a>
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<h2>A model of cooperation</h2>
<p>The last time the ozone hole was front-page news, President Ronald Reagan was still eating jelly beans in the Oval Office. In 1985 <a href="https://www.nature.com/articles/315207a0">British scientists</a> announced the discovery of a shocking decline in atmospheric ozone concentrations high above Antarctica. The “ozone hole”, as it became known, was caused by <a href="https://www.nature.com/articles/249810a0">ozone-eating chemicals</a> called chlorofluorocarbons (CFCs) used as refrigerants in air conditioners and propellants in aerosol spray cans. </p>
<p>The discovery galvanised public opinion, particularly over concerns about the risk of skin cancer, cataracts and sunburn associated with increased exposure to ultraviolet radiation. In Australia and New Zealand, popular ad campaigns featuring a <a href="https://www.youtube.com/watch?v=b7nocIenCYg">dancing seagull</a> encouraged the beach-goers to “Slip on a shirt, slop on sunscreen, and slap on a hat!”. </p>
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<figcaption><span class="caption">The 1981 “Slip! Slop! Slap!” ad campaign by Cancer Council Victoria (Australia).</span></figcaption>
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<p>Although many uncertainties over the science remained – which were eagerly exploited by the chemical industry – President Reagan <a href="https://www.wsj.com/articles/clearing-the-air-about-reagan-and-ozone-1444338641">recognised the danger</a> posed by the ozone hole and vigorously backed international negotiations to ban CFCs, including CFC-11. On January 1 1989, the <a href="http://www.environment.gov.au/protection/ozone/montreal-protocol">Montreal Protocol on Substances that Deplete the Ozone Layer</a> became law. </p>
<p>In his signing statement, Reagan heralded the Montreal Protocol as “a model of cooperation” and “a product of the recognition and international consensus that ozone depletion is a global problem”. It <a href="https://www.nytimes.com/2013/12/10/science/the-montreal-protocol-a-little-treaty-that-could.html">remains</a> his signature environmental achievement. </p>
<h2>An enduring impact on Earth’s climate</h2>
<p>Three decades after Montreal, the ozone layer is showing signs of recovery. In January 2018, a <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL074830">NASA study</a> found that the ozone hole was the smallest it had been since 1988, the year before the Montreal protocol went into effect. But a full recovery will take decades. “CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time,” said NASA scientist <a href="https://www.nasa.gov/feature/goddard/2018/nasa-study-first-direct-proof-of-ozone-hole-recovery-due-to-chemicals-ban">Anne Douglass</a>, one of the authors of the study. “As far as the ozone hole being gone, we’re looking at 2060 or 2080.”</p>
<p>In the meantime, CFCs continue to impact Earth’s climate in some unexpected ways. CFCs are powerful greenhouse gases, with more than 5,000 times the warming potential of an equivalent weight of carbon dioxide. It is estimated that banning CFCs and other ozone-depleting chemicals has delayed global warming by as much as a <a href="https://www.nature.com/articles/ngeo1999">decade</a>. </p>
<p>However, those gains are <a href="https://www.youtube.com/watch?v=IeVxBM8Avo4">threatened</a> by the ozone-friendly, but heat-trapping, chemicals that have replaced CFCs in our air conditioners and insulation. The latest amendment to the Montreal Protocol will phase out the use of this new class of chemicals by 2028. </p>
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Read more:
<a href="https://theconversation.com/explainer-hydrofluorocarbons-saved-the-ozone-layer-so-why-are-we-banning-them-86672">Explainer: hydrofluorocarbons saved the ozone layer, so why are we banning them?</a>
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<p>Even more surprising is the complex influence of the ozone hole on Earth’s atmosphere and oceans. The loss of UV-absorbing ozone over the South Pole has changed the <a href="http://science.sciencemag.org/content/339/6119/563">pattern of winds</a> around Antarctica. Strengthened winds blowing over the Southern Ocean draw more deep water towards the surface, where it is “ventilated” by contact with the atmosphere. </p>
<p>Deep Antarctic water is rich in carbon, making it a poor absorber of atmospheric CO₂. That means that the ocean has become <a href="http://science.sciencemag.org/content/339/6119/568">less efficient</a> at removing excess carbon dioxide from the atmosphere, reducing its ability to offset global warming.</p>
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<figcaption><span class="caption">Darryn Waugh on the ozone threat.</span></figcaption>
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<h2>Lessons from a world avoided</h2>
<p>The success of the Montreal Protocol holds lessons for today’s efforts to confront human-induced climate change. Vigorous <a href="http://www.thehole.org/">leadership</a> by Reagan and the then British prime minister, Margaret Thatcher, a trained chemist, was crucial during the negotiations of the treaty. The protocol began <a href="https://theconversation.com/saving-the-ozone-layer-why-the-montreal-protocol-worked-9249">modestly</a> and was designed to be flexible so that more ozone-depleting substances could be phased out by later amendments. Developing countries were also provided with incentives and institutional support to meet their compliance targets. </p>
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<figcaption><span class="caption">Lessons from the World Avoided: Dr Sean Davis at TEDx Boulder 2017.</span></figcaption>
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<p>But perhaps the most important lesson is the need for action, even when the science is not yet conclusive. “We don’t need absolute certainty to act,” says <a href="https://tedxboulder.com/videos/lessons-from-the-world-avoided">Sean Davis</a>, a climate scientist at the US National Oceanic and Atmospheric Administration. “When Montreal was signed, we were less certain then of the risks of CFCs than we are now of the risks of greenhouse gas emissions.” </p>
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<p><em>Professor Darryn Waugh will present a public lecture about the enduring impact of the ozone hole on climate at UNSW Sydney on July 30, 2018. Details and registration information are available <a href="https://www.science.unsw.edu.au/events/enduring-impact-ozone-hole-climate">here</a>.</em></p><img src="https://counter.theconversation.com/content/100524/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Darryn Waugh receives funding from NASA and the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Shane Keating does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Almost 30 years ago the world responded to the realisation that our ozone layer was in trouble. The resulting Montreal Protocol was a rare example of global cooperation, but there’s no room for complacency.Shane Keating, Senior Lecturer in Mathematics and Oceanography, UNSW SydneyDarryn Waugh, Professor, Earth and Planetary Sciences, Johns Hopkins UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/914702018-04-20T10:37:02Z2018-04-20T10:37:02ZIs Earth’s ozone layer still at risk? 5 questions answered<figure><img src="https://images.theconversation.com/files/215468/original/file-20180418-163966-4zh3w7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">False-color image of ozone concentrations above Antarctica on Oct. 2, 2015.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/feature/goddard/annual-antarctic-ozone-hole-larger-and-formed-later-in-2015">NASA/Goddard Space Flight Center</a></span></figcaption></figure><p><em>Editor’s note: Curbing damage to Earth’s protective ozone layer is widely viewed as one of the most important successes of the modern environmental era. Earlier this year, however, a <a href="http://dx.doi.org/10.5194/acp-18-1379-2018">study</a> reported that ozone concentrations in the lower level of the stratosphere had been falling since the late 1990s – even though the <a href="http://ozone.unep.org/en/treaties-and-decisions/montreal-protocol-substances-deplete-ozone-layer">Montreal Protocol</a>, a global treaty to phase out ozone-depleting chemicals, had been in effect since 1989. This raised questions about whether and how human activities could still be damaging the ozone layer. Atmospheric chemist <a href="https://scholar.google.com/citations?user=Gb0ClrsAAAAJ&hl=en">A.R. Ravishankara</a>, who co-chaired a United Nations/World Meteorological Organization Scientific Assessment panel on stratospheric ozone from 2007 to 2015, provides perspective.</em></p>
<h2>1. What’s the prevailing view among atmospheric scientists today about the state of the ozone layer?</h2>
<p>The overall picture is clear: The Montreal Protocol reduced use of ozone-depleting chemicals and will lead to healing of the ozone layer. This is an important goal because stratospheric ozone protects us from exposure to ultraviolet radiation, which can increase the risk of cataracts, skin cancer and other detrimental effects. </p>
<p>Of course, this forecast would be wrong if nations deviate from their treaty commitments, or if the scientific community fails to detect possible emissions of gases that could deplete the ozone layer but are not covered by the treaty. </p>
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<a href="https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=355&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=355&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=355&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=446&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=446&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215462/original/file-20180418-163998-h02rtb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=446&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">The ozone layer in the stratosphere shields life on Earth from most UV-B and UV-C, the most harmful varieties of ultraviolet radiation.</span>
<span class="attribution"><a class="source" href="https://scied.ucar.edu/ozone-layer">NASA</a></span>
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<p>Our understanding of stratospheric ozone depletion has grown steadily since the mid-1970s, when Mario Molina and F. Sherwood Rowland first suggested that the ozone layer could be depleted by <a href="https://www.britannica.com/science/chlorofluorocarbon">chlorofluorocarbons</a>, or CFCs – research that <a href="https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1995/press.html">earned a Nobel Prize</a>. In 1985 Joseph Farman reported on the formation of an <a href="https://celebrating200years.noaa.gov/historymakers/solomon/welcome.html">“ozone hole”</a> – actually, a large-scale thinning of the ozone layer – that develops over Antarctica every austral spring. </p>
<p>Further work by <a href="https://www.sciencehistory.org/historical-profile/susan-solomon">Susan Solomon</a> and colleagues clearly attributed the ozone hole to CFCs and other ozone-depleting chemicals that contained the elements chlorine and bromine. They also highlighted unusual reactions that take place on <a href="https://theconversation.com/explainer-what-are-the-nacreous-clouds-lighting-up-the-winter-skies-54095">polar stratospheric clouds</a>. </p>
<p>In 1987, the United States and 45 other countries signed the Montreal Protocol, which required them to phase out use of ozone-depleting substances. Today 197 nations have ratified the treaty, which has prevented large-scale ozone layer depletion and its harmful consequences. Ozone-depleting substances are also greenhouse gases that trap heat in the atmosphere, so phasing them out under the Montreal Protocol has also <a href="https://doi.org/10.1073/pnas.0610328104;%20https://public.wmo.int/en/media/press-release/joint-press-release-unepwmo-ozone-layer-track-recovery">helped to slow climate change</a>. </p>
<p>It takes decades to cleanse CFCs and other ozone depleting substances from the atmosphere, so even after the Montreal Protocol went into effect, their concentrations did not peak until around 1998 and are still high. Nonetheless, based on atmospheric observations, laboratory studies of chemical reactions and numerical models of the stratosphere, there is general consensus among scientists that the ozone layer is on track to recover around 2060, give or take a decade. We also know that the future of the ozone layer is intricately intertwined with climate change. </p>
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<figcaption><span class="caption">Ozone is constantly created and destroyed in Earth’s atmosphere as oxygen interacts with ultraviolet light, but man-made chemicals can disrupt this process.</span></figcaption>
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<h2>2. What could explain the continued decline in ozone in the lower stratosphere that was reported earlier this year?</h2>
<p>Of course, there are still some gaps in our knowledge of the ozone layer, and these two new reports have spotlighted such gaps. </p>
<p>The <a href="http://dx.doi.org/10.5194/acp-18-1379-2018">first study</a> reported that although ozone concentrations were increasing in the upper stratosphere, they were still declining in the lower stratosphere. It suggested several possible causes, such as increases in uncontrolled, very short-lived gases produced from human activities that can deplete the ozone layer, as well as changes in atmospheric circulation due to climate change. </p>
<p>The <a href="http://dx.doi.org/10.1038/ngeo2363">second study</a> identified rising levels of certain chlorinated chemicals, referred to as very short-lived substances, that could continue to deplete the ozone layer. </p>
<p>These reports were a little surprising, but not shocking. Scientists expect that we will continue to add to our knowledge of ozone layer, and our understanding will emerge as we digest these findings. The Montreal Protocol requires the scientific community to carry out <a href="https://www.esrl.noaa.gov/csd/assessments/ozone/">scientific assessments of ozone depletion</a> every four years precisely because we expect that new information like this will continue to emerge. One of those reviews is under way now and will be published later this year. </p>
<p>If industrial activities causing this decline in the lower stratosphere, Montreal Protocol member countries can amend the treaty to address these new threats. They did so in 2016 to <a href="https://www.unenvironment.org/news-and-stories/news/kigali-amendment-montreal-protocol-another-global-commitment-stop-climate">phase out hydrofluorocarbons</a> – coolants, used in air conditioners and refrigerators, that were found to be powerful greenhouse gases. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=357&fit=crop&dpr=1 600w, https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=357&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=357&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=449&fit=crop&dpr=1 754w, https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=449&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/215465/original/file-20180418-164001-n377gx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=449&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">U.S. Secretary of State John Kerry delivers a speech to delegates from Montreal Protocol member countries in Kigali, Rwanda, Oct. 14, 2016. At the meeting nations agreed on a deal to phase out hydrofluorocarbons from air conditioners and refrigerators.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Rwanda-Climate-Meeting/79739f353573440f9ca6c365f09c6fc0/2/0">AP Photo</a></span>
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<h2>3. If ozone levels in the lower stratosphere have been decreasing for 20 years, why are scientists just detecting that trend now?</h2>
<p>Ozone levels change naturally from year to year, so scientists need to look at data over long time periods to tease out trends. The potential for short-lived chlorine and bromine gases to affect the ozone layer has been recognized for a while. More recently, scientists have been measuring concentrations in the atmosphere of dichloromethane, a liquid that is widely used as a solvent, and deduced that if it continues to increase, it will be a potential problem. Trends in emissions of these compounds are uncertain, but some recent results suggest that they are not increasing as rapidly as they appeared to be a few years ago.</p>
<h2>4. Did these studies find any changes in the ozone hole?</h2>
<p>No, they did not. They examined ozone changes within 60 degrees of the equator, not over the Antarctic. We do not expect very short-lived substance emissions to significantly influence the ozone hole unless they increase drastically, but this is one more reason to keep an eye on them. </p>
<h2>5. Do these recent findings make you question whether the Montreal Protocol is effective?</h2>
<p>No! Indeed, they strengthen my trust in it. </p>
<p>With any environmental agreement, whether it addresses ozone depletion, acid rain, climate change or other issues, it is important to be vigilant during the “accountability phase” – the period after policy decisions have been made and before the targeted results are expected. I am confident that if scientific findings warrant it, Montreal Protocol countries will take further action, and that my granddaughters will see the day when we eliminate the ozone hole.</p><img src="https://counter.theconversation.com/content/91470/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>A.R. Ravishankara currently receives funding from Colorado State University and the Kauvar Foundation. In his career he has received funding from NASA, NOAA, NSF, AFOSR, DOE, US EPA and the Chemical Manufacturers Association. He worked at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory, Chemical Sciences Division, for nearly 30 years and served as its director from 2006 through 2014.</span></em></p>Earth’s ozone layer shields us from harmful ultraviolet radiation. Nations have been working to reduce ozone-depleting chemicals since the 1980s, but recent studies show that there is still work to do.A.R. (Ravi) Ravishankara, Professor of Chemistry and Atmospheric Science, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/869072018-01-23T11:19:48Z2018-01-23T11:19:48ZHealthy to eat, unhealthy to grow: Strawberries embody the contradictions of California agriculture<figure><img src="https://images.theconversation.com/files/193852/original/file-20171108-14159-4dgdct.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Suspected infestation of Macrophomina phaseolina, a "novel" soil pathogen, in the non-fumigated buffer zone of a strawberry field</span> <span class="attribution"><span class="source">Julie Guthman</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Agricultural abundance is a pillar of the California dream. In 2016 the state turned out <a href="https://www.cdfa.ca.gov/statistics/">more than US$45 billion worth</a> of meat, milk and crops. Long before nutritionists agreed that fresh fruits and vegetables should be the center of American diets, California farmers had planted much of their land in these products, and today they produce <a href="https://www.cdfa.ca.gov/farm_bill/">half of the nation’s fruits, vegetables and nuts</a>. </p>
<p>But although fruits and vegetables are vaunted as healthy foods, their impact as crops is quite different. On many California produce farms wages are low, working conditions are poor, and farmers use enormous quantities of pesticides and precious water. This is the central contradiction of California agriculture.</p>
<p>For the past five years I have been studying California’s strawberry industry, which currently is the state’s <a href="https://www.cdfa.ca.gov/statistics/">sixth</a> most important commodity in terms of the value of crops sold. Strawberries are attractive, reasonably nutritious and occasionally tasty fruits and can be grown and eaten within California nearly year-round. But the industry’s growth has relied on heavy use of toxic chemicals and now growers face heightened restrictions on some of their most favored chemicals: soil fumigants. Unfortunately, less toxic or non-chemical strategies that would allow strawberries to be grown for a mass market, maintaining affordable prices, are elusive and likely to remain so. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=388&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=388&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=388&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=488&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=488&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202607/original/file-20180119-110084-46utwf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=488&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Strawberry pickers in Salinas, Calif., photographed April 27, 2009.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/1/10/Xp3-dot-us_DSC8991.jpg">Holgerhubbs</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<h2>Chemical dependence</h2>
<p>Although strawberry production once was scattered throughout the state, by the 1960s it had concentrated in coastal zones to take advantage of sandy soils and mild temperatures. Thereafter, the industry saw tremendous growth in productivity. In Monterey and Santa Cruz counties alone, <a href="https://doi.org/10.3733/ca.2016a0001">acreage more than tripled and production increased tenfold</a> from 1960 to 2014. Much of this growth was enabled by advances in plant breeding and use of plastic tarps to absorb heat, allowing growers to increase the length of strawberry seasons. </p>
<p>But the main driver of growth has been the use of pre-plant chemical fumigants. Growers hire pest control companies to fumigate soils before planting strawberries in order to kill soil-borne pests – most importantly, plant pathogens such as <em>Verticillium dahliae</em> and <em>Macrophomina phaseolina</em>. Without such treatment, these pathogens cause strawberry plants to wilt and die. </p>
<p>Now, however, the industry’s fumigant of choice – methyl bromide – can no longer be used in strawberry fruit production. In 1991 methyl bromide was banned under the <a href="http://ozone.unep.org/en/treaties-and-decisions/montreal-protocol-substances-deplete-ozone-layer">Montreal Protocol on Substances that Deplete the Ozone Layer</a>. The United States was supposed to phase out use by 2005, a deadline that was extended to 2015 and didn’t really take effect until two years later. Even so, this toxic chemical can still be used in nursery production to ensure that starter plants are virus- and pathogen-free. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202609/original/file-20180119-110103-1x1y52i.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">Recently fumigated field in Watsonville, Calif., Oct. 11, 2009.</span>
<span class="attribution"><a class="source" href="https://flic.kr/p/791REj">Benketaro</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>One potential replacement, methyl iodide, was approved for use in late 2010. But it was <a href="http://calag.ucanr.edu/Archive/?article=ca.2016a0003">withdrawn from the market in 2012</a>, following an activist campaign and lawsuit that accused California regulators of performing an inadequate review of potential health risks to workers and the general public. Among other things, the chemical is a known <a href="http://www.stpp.ucla.edu/sites/default/files/Final%20Report%20SRC.pdf">neurotoxin and carcinogen</a>. </p>
<p>Other fumigants are still allowed, but their use is increasingly restricted by buffer zones and township quotas. Consequently, growers are contending with <a href="https://doi.org/10.1080/15538362.2012.697000">heightened levels of plant disease</a>, some from pathogens that had never before been evident in California strawberry fields. </p>
<h2>An embedded system</h2>
<p>Can California find a less toxic way to raise <a href="http://edis.ifas.ufl.edu/LyraEDISServlet?command=getImageDetail&image_soid=FIGURE%207&document_soid=FE971&document_version=1">90 percent of the nation’s fresh strawberries</a>? Although the strawberry industry is <a href="http://www.calstrawberry.com/Portals/0/images/2013-CSC_enviroreport_web.pdf">investing significant resources into non-chemical alternatives to manage soil-borne disease</a>, the obstacles are formidable. The entire production system, including reliance on fumigants, is <a href="https://doi.org/10.3733/ca.2017a0017">embedded into the cost of land</a>. </p>
<p>Fumigation has allowed growers to plant on the same blocks of land, year after year, and not worry about soil disease. With fumigation available to control pathogens, strawberry breeders have emphasized productivity, beauty and durability rather than pathogen resistance. Meanwhile, nursery production has shifted away from prime fruit growing regions along the coast to take advantage of different environments for plant propagation, enabling coastal land to be used solely for growing fruit. </p>
<p>Together these innovations have allowed growers to keep prime strawberry land in production every year for much of the year, yielding exceptional amounts of fruit. High land prices reflect these expectations and make it unprofitable to grow strawberries using less intensive methods. The Pacific Ocean’s natural summer air-conditioning is attractive to suburbanites as well as strawberries, so coastal development is putting additional pressure on the cost of strawberry land while at the same time increasing public pressure to control use of fumigants. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=397&fit=crop&dpr=1 754w, https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=397&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/202622/original/file-20180119-110106-1rcwmmh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=397&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Official logo of the California Strawberry Commission.</span>
<span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/f/fe/California_Strawberry_Commission_Logo_-_Color.jpg">CA Strawberry Commission</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Chemical-free strawberries for the few</h2>
<p>Informed and concerned consumers ingrained with California’s deep culture of environmentalism have turned to organic strawberries, which they see as a more sustainable option. As conventional growers took note of this vibrant market, <a href="https://doi.org/10.3733/ca.2016a0001">organic strawberry production rose fivefold between 2000 and 2012</a>, to reach about <a href="http://www.organicproducenetwork.com/article/351/organic-strawberries-in-short-supply?utm_source=OPN+Connect+Weekly+Newsletter&utm_campaign=1ad7c5557e-EMAIL_CAMPAIGN_2018_01_11&utm_medium=email&utm_term=0_558944fdc9-1ad7c5557e-123782331">3,300 acres planted in 2017</a>, which represents 12 percent of all strawberry acreage. </p>
<p>But although organic growers use non-chemical soil fumigation methods or rotate strawberries with crops that have a mild disease-suppressing effect, such as broccoli, few of them fundamentally alter the production system in other ways. In my research, I have observed that some growers are finding land away from prime areas that can be quickly certified for organic production, but have no long-term plans to manage soil diseases when they inevitably arise – a practice that is not in the spirit of organic production. </p>
<p>A small but dedicated set of growers have learned how to raise strawberries for the long haul without fumigants. However, even they use starter plants produced on fumigated soil, since no nurseries produce organic plants. Crucially, for these growers strawberries are a minor crop in what are otherwise highly diversified systems. And most of these producers are located outside of prime strawberry growing regions, where land is cheaper. Their approach therefore is not nearly replicable for growers producing for the mass market.</p>
<p>These exceptions tell us as much about the limits of California strawberry production as does mainstream production. Consumers who want organic strawberries must be willing to live with compromises, pay premium prices – and eat their broccoli. For others, the dream of affordable year-round strawberries grown without toxic chemicals is already an impossible one.</p><img src="https://counter.theconversation.com/content/86907/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Julie Guthman has received funding from the National Science Foundation in support of this research. She is currently a co-principal investigator on a USDA-funded project that aims to develop pathogen-resistant strawberries. </span></em></p>California produces 90 percent of the US strawberry crop, but growers face curbs on toxic chemicals that have helped their industry expand. Can a system centered on mass production become more sustainable?Julie Guthman, Professor of Social Sciences, University of California, Santa CruzLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/866722017-11-02T01:31:28Z2017-11-02T01:31:28ZExplainer: hydrofluorocarbons saved the ozone layer, so why are we banning them?<figure><img src="https://images.theconversation.com/files/192924/original/file-20171102-19867-30e4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Sunrise over the Earth. Hydrofluorocarbons were created to protect the ozone layer, but their stable nature makes them an extremely potent greenhouse gas.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>On October 28, Australia <a href="http://www.environment.gov.au/minister/frydenberg/media-releases/mr20171028.html">ratified the Kigali Amendment to the Montreal Protocol</a>. Australia is the <a href="https://treaties.un.org/pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXVII-2-f&chapter=27&clang=_en">tenth country to ratify</a>, joining others as diverse as Mali, Norway and Rwanda in a global commitment to dramatically reduce hydrofluorocarbons (HFCs) in the atmosphere. Once 20 countries have ratified the amendment, it will become binding.</p>
<p>HFCs were designed specifically to replace ozone-destroying compounds previously used in air conditioners and refrigerants. Unfortunately, we now know that HFCs are massively potent greenhouse gases – thousands of times more powerful than carbon dioxide (albeit released in far smaller quantities). </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-30-year-old-ozone-layer-treaty-has-a-new-role-fighting-climate-change-84025">The 30-year-old ozone layer treaty has a new role: fighting climate change</a>
</strong>
</em>
</p>
<hr>
<p>If the Kigali Amendment becomes binding, the hunt will begin for a replacement for HFCs and their uses in industry. In a strange twist, the least environmentally harmful option may well be carbon dioxide.</p>
<h2>Where do HFCs come from?</h2>
<p>HFCs are made of carbon, fluorine and hydrogen. They are exclusively synthetic, meaning they have no known natural sources. To understand why they came into existence requires a quick history lesson.</p>
<p>Throughout the second half of the 20th century, another class of compounds called chlorofluorocarbons (CFCs) were widely used. CFCs are very stable, which made them ideal for many practical uses, including in refrigeration, foam packaging, and even aerosol cans for hair spray.</p>
<p>However, scientists soon discovered that <a href="https://theconversation.com/what-are-ozone-depleting-substances-9203">CFCs had a major downside</a>. Because they are so stable, they can survive in the atmosphere long enough to eventually reach the ozone layer. Once there, they break down in sunlight and <a href="https://theconversation.com/explainer-what-is-the-antarctic-ozone-hole-and-how-is-it-made-9202">destroy ozone in the process</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-the-antarctic-ozone-hole-and-how-is-it-made-9202">Explainer: what is the Antarctic ozone hole and how is it made?</a>
</strong>
</em>
</p>
<hr>
<p>The <a href="http://ozone.unep.org/en/handbook-montreal-protocol-substances-deplete-ozone-layer/27571">Montreal Protocol</a> was a global agreement developed to stop this harmful ozone destruction. The protocol mandated a time frame to completely abolish CFCs. To replace them, new compounds were developed that do not destroy ozone: HFCs.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/192791/original/file-20171101-19858-7o7dkz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The usage of CFCs and their replacements, including HFCs, since 1950.</span>
<span class="attribution"><span class="source">UNEP 2011. HFCs: A Critical Link in Protecting Climate and the Ozone Layer</span></span>
</figcaption>
</figure>
<p>But the solution to one environmental problem became the cause of another: these replacements are potent contributors to warming the climate.</p>
<h2>Why are HFCs so bad?</h2>
<p>All greenhouse gases work by absorbing infrared radiation, which would otherwise escape into space. But not all greenhouse gases are created equal. The potency of a greenhouse gas depends on three properties:</p>
<ul>
<li><p>how long it remains in the atmosphere (its “lifetime”)</p></li>
<li><p>how much radiation it absorbs</p></li>
<li><p>whether the specific wavelength of radiation it absorbs would otherwise be absorbed by something else in the atmosphere (like water).</p></li>
</ul>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=848&fit=crop&dpr=1 600w, https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=848&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=848&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1066&fit=crop&dpr=1 754w, https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1066&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/192790/original/file-20171101-19845-1c413uu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1066&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 warming potentials of five greenhouse gases. The area of each circle represents the global warming potential, calculated for a 100-year time horizon.</span>
<span class="attribution"><a class="source" href="http://wedocs.unep.org/handle/20.500.11822/8014">Author created/Data from UNEP 2011 report HFCs: A Critical Link in Protecting Climate and the Ozone Layer</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Combined, these three properties can be used to determine the <a href="https://www.epa.gov/ghgemissions/understanding-global-warming-potentials">global warming potential</a> for each greenhouse gas. This is a measure of how potent the gas is relative to carbon dioxide (CO₂). By definition, CO₂ has a global warming potential of 1. Methane, commonly considered the <a href="https://theconversation.com/world-greenhouse-gas-levels-made-unprecedented-leap-in-2016-86545">second most important greenhouse gas</a>, has a global warming potential of 34 – meaning that 1 tonne of methane would trap 34 times more heat than 1 tonne of CO₂.</p>
<p>The global warming potentials for the three most abundant HFCs range from 1,370 to 4,180. In other words, these gases trap thousands of times more heat in our atmosphere than an equivalent amount of CO₂.</p>
<h2>What will replace HFCs?</h2>
<p>The nearly 200 countries that signed the original Montreal Protocol have <a href="http://www.unenvironment.org/news-and-stories/press-release/whats-next-kigali-deal-curb-potent-greenhouse-gases">unanimously agreed</a> that the climate risks posed by HFCs are too significant to ignore. Developed countries will begin phasing out HFCs in 2019. Developing countries will follow suit between 2024 and 2028.</p>
<p>So what will our refrigerators and air conditioners use instead? Several replacements are being considered. </p>
<p>Some groups are promoting another class of fluorine-containing compounds called <a href="https://www.chemours.com/Refrigerants/en_US/products/Opteon/Stationary_Refrigeration/">hydrofluoroolefins (or HFOs)</a>. These have a short lifetime in the atmosphere and so pose much less of a climate risk. However, <a href="http://www.greenpeace.org/international/Global/international/documents/climate/HFOs-the-new-generation-of-f-gases.pdf">environmental groups have raised concern</a> about the potentially toxic chemicals produced when HFOs break down.</p>
<p>Another option is to use mixtures of hydrocarbons such as butane. Hydrocarbons pose safety risks as they are <a href="http://refrigerants.danfoss.com/hydrocarbons/">highly flammable</a> and may also adversely affect air quality. Ammonia is another alternative that has been used as a refrigerant for a long time but is <a href="http://www.cbc.ca/news/canada/toronto/ammonia-spill-evans-kipling-etobicoke-evacuation-1.4304763">highly toxic</a>.</p>
<p>And, finally, there is the surprise candidate: CO₂. Although using CO₂ as a refrigerant poses technical challenges, it is <a href="http://refrigerants.danfoss.com/co2/#/">non-toxic and non-flammable</a> and a much weaker greenhouse gas than the HFCs it would replace. Strangely, from an environmental perspective, CO₂ may actually be the “best” refrigerant available.</p>
<h2>A cooler future ahead?</h2>
<p>The Montreal Protocol has long been considered one of the greatest environmental success stories of all time. It brought together the world’s governments and chemical industries to <a href="https://theconversation.com/after-30-years-of-the-montreal-protocol-the-ozone-layer-is-gradually-healing-84051">protect the ozone layer</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/after-30-years-of-the-montreal-protocol-the-ozone-layer-is-gradually-healing-84051">After 30 years of the Montreal Protocol, the ozone layer is gradually healing</a>
</strong>
</em>
</p>
<hr>
<p>The adoption of the Kigali Amendment will be another feather in the cap of this important agreement. HFCs aren’t overly prevalent yet – but without Kigali they are expected to grow rapidly. By banning them now, we will avoid their impacts before it is too late.</p>
<p>Estimates suggest that phasing out HFCs will <a href="https://www.atmos-chem-phys.net/13/6083/2013/acp-13-6083-2013.pdf">prevent up to 0.5°C of future warming</a>. Even if this estimate turns out to be <a href="https://www.climateinteractive.org/insights/the-kigali-deal-on-hfcs-is-important-but-wont-save-us-another-half-a-degree/">overly optimistic</a>, getting rid of the HFCs will be an important step towards achieving the <a href="http://unfccc.int/paris_agreement/items/9485.php">Paris Agreement</a> goal of limiting warming to well below 2°C.</p>
<p><br></p>
<p><em>This article was updated on November 3, to reflect that the United Kingdom have not yet ratified the Kigali Amendment.</em></p><img src="https://counter.theconversation.com/content/86672/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jenny Fisher receives funding from the Australian Research Council, the Department of the Environment, and the L'Oréal-UNESCO For Women in Science program. </span></em></p><p class="fine-print"><em><span>Stephen Wilson receives funding from the Australian Research Council, the Department of the Environment and the Bureau of Meteorology. </span></em></p>Australia has ratified an agreement to phase out hydrofluorocarbons, a manmade compound once hailed as the saviour of the ozone layer. What went wrong?Jenny Fisher, Senior Lecturer in Atmospheric Chemistry, University of WollongongStephen Wilson, Associate Professor, University of WollongongLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/840512017-09-14T19:35:27Z2017-09-14T19:35:27ZAfter 30 years of the Montreal Protocol, the ozone layer is gradually healing<figure><img src="https://images.theconversation.com/files/185938/original/file-20170914-19479-zu6q9g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Clouds over Australia's Davis Research Station, containing ice particles that activate ozone-depleting chemicals, triggering the annual ozone hole.</span> <span class="attribution"><span class="source">Barry Becker/BOM/AAD</span>, <span class="license">Author provided</span></span></figcaption></figure><p>This weekend marks the 30th birthday of the <a href="http://ozone.unep.org/en/handbook-montreal-protocol-substances-deplete-ozone-layer/27571">Montreal Protocol</a>, often dubbed the world’s most successful environmental agreement. The treaty, signed on September 16, 1987, is slowly but surely reversing the damage caused to the ozone layer by industrial gases such as chlorofluorocarbons (CFCs).</p>
<p>Each year, during the southern spring, a hole appears in the ozone layer above Antarctica. This is due to the extremely cold temperatures in the winter stratosphere (above 10km altitude) that allow byproducts of <a href="https://theconversation.com/what-are-ozone-depleting-substances-9203">CFCs</a> and related gases to be converted into forms that destroy ozone when the sunlight returns in spring. </p>
<p>As ozone-destroying gases are phased out, the annual ozone hole is generally getting smaller – a rare success story for international environmentalism.</p>
<p>Back in 2012, our <a href="https://theconversation.com/au/topics/saving-the-ozone-3785">Saving the Ozone series</a> marked the Montreal Protocol’s silver jubilee and reflected on its success. But how has the ozone hole fared in the five years since?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-what-is-the-antarctic-ozone-hole-and-how-is-it-made-9202">Explainer: what is the Antarctic ozone hole and how is it made?</a>
</strong>
</em>
</p>
<hr>
<p>The <a href="https://theconversation.com/explainer-what-is-the-antarctic-ozone-hole-and-how-is-it-made-9202">Antarctic ozone hole</a> has continued to appear each spring, as it has since the late 1970s. This is expected, as levels of the <a href="http://ozone.unep.org/en/handbook-montreal-protocol-substances-deplete-ozone-layer/2182">ozone-destroying halocarbon gases controlled by the Montreal Protocol</a> are still relatively high. The figure below shows that concentrations of these human-made substances over Antarctica have fallen by 14% since their peak in about 2000.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185927/original/file-20170913-19328-5n8tbz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Past and predicted levels of controlled gases in the Antarctic atmosphere, quoted as equivalent effective stratospheric chlorine (EESC) levels, a measure of their contribution to stratospheric ozone depletion.</span>
<span class="attribution"><span class="source">Paul Krummel/CSIRO</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>It typically takes a few decades for these gases to cycle between the lower atmosphere and the stratosphere, and then ultimately to disappear. The most recent official assessment, <a href="https://www.esrl.noaa.gov/csd/assessments/ozone/2014/">released in 2014</a>, predicted that it will take 30-40 years for the Antarctic ozone hole to <a href="https://theconversation.com/ozone-hole-closing-for-the-year-but-full-recovery-is-decades-away-33588">shrink to the size it was in 1980</a>.</p>
<h2>Signs of recovery</h2>
<p>Monitoring the ozone hole’s gradual recovery is made more complicated by variations in atmospheric temperatures and winds, and the amount of microscopic particles called aerosols in the stratosphere. In any given year these can make the ozone hole bigger or smaller than we might expect purely on the basis of halocarbon concentrations. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185937/original/file-20170914-19457-nh9mh.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">Launching an ozone-measuring balloon from Australia’s Davis Research Station in Antarctica.</span>
<span class="attribution"><span class="source">Barry Becker/BOM/AAD</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The 2014 assessment indicated that the size of the ozone hole varied more during the 2000s than during the 1990s. While this might suggest it has become harder to detect the healing effects of the Montreal Protocol, we can nevertheless tease out recent ozone trends with the help of <a href="http://blogs.reading.ac.uk/ccmi/">sophisticated atmospheric chemistry models</a>. </p>
<p>Reassuringly, a <a href="https://theconversation.com/shrinking-hole-in-the-ozone-layer-shows-what-collective-action-can-achieve-62007">recent study</a> showed that the size of the ozone hole each September has shrunk overall since the turn of the century, and that more than half of this shrinking trend is consistent with reductions in ozone-depleting substances. However, <a href="http://www.nature.com/nature/journal/v549/n7671/full/nature23681.html">another study</a> warns that careful analysis is needed to account for a variety of natural factors that could confound our detection of ozone recovery.</p>
<h2>The 2015 volcano</h2>
<p>One such factor is the presence of ozone-destroying volcanic dust in the stratosphere. Chile’s Calbuco volcano seems to have played a role in <a href="http://onlinelibrary.wiley.com/doi/10.1002/2016GL071925/abstract">enhancing the size of the ozone hole in 2015</a>.</p>
<p>At its maximum size, the 2015 hole was the <a href="http://www.environment.gov.au/system/files/resources/bde22641-eeb6-4502-9c54-8239c2c64c0f/files/2015-ozone-summary-report.pdf">fourth-largest ever observed</a>. It was in the <a href="http://www.environment.gov.au/protection/ozone/publications/antarctic-ozone-hole-summary-reports">top 15% in terms of the total amount of ozone destroyed</a>. Only 2006, 1998, 2001 and 1999 had more ozone destruction, whereas other recent years (2013, 2014 and 2016) ranked near the middle of the observed range.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=717&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=717&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=717&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=901&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=901&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185928/original/file-20170913-19318-h6yofi.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=901&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Average ozone concentrations over the southern hemisphere during October 1-15, 2015, when the Antarctic ozone hole for that year was near its maximum extent. The red line shows the boundary of the ozone hole.</span>
<span class="attribution"><span class="source">Paul Krummel/CSIRO/EOS</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Another notable feature of the 2015 ozone hole was that it was at its biggest observed extent for much of the period from mid-October to mid-December. This coincided with a period during which the jet of westerly winds in the Antarctic stratosphere was particularly unaffected by the warmer, more ozone-rich air at lower latitudes. In a typical year, the influx of air from lower latitudes helps to limit the size of the ozone hole in spring and early summer.</p>
<h2>The 2017 hole</h2>
<p>As noted above, the ozone holes of 2013, 2014 and 2016 were relatively unremarkable compared with that of 2015, being close to the long-term average for overall ozone loss.</p>
<p>In general respects, these ozone holes were similar to those seen in the late 1980s and early 1990s, before the peak of ozone depletion. This is consistent with a gradual recovery of the ozone layer as levels of ozone-depleting substances gradually decline.</p>
<p>This year’s hole began to form in early August, and the timing was similar to the long-term average. Stratospheric temperatures during the Antarctic winter were slightly cooler than in 2016, which would favour enhancement of the chemical changes that lead to ozone destruction in spring. However, temperatures climbed above average in mid-August during a disturbance to the polar winds, delaying the hole’s expansion. As of the second week of September, the warmer-than-average temperatures have continued but the ozone hole has grown <a href="https://ozonewatch.gsfc.nasa.gov/">slightly larger than the long-term average since 1979</a>. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/saving-the-ozone-layer-why-the-montreal-protocol-worked-9249">Saving the ozone layer: why the Montreal Protocol worked</a>
</strong>
</em>
</p>
<hr>
<p>While annual monitoring continues, which includes measurements under the Australian Antarctic Program, a more comprehensive assessment of the ozone layer’s prospects is set to arrive late next year. Scientists across the globe, coordinated by the UN Environment Program and the World Meteorological Organisation, are busy preparing the next report required under the Montreal Protocol, called the <a href="https://www.esrl.noaa.gov/csd/assessments/ozone/2018/">Scientific Assessment of Ozone Depletion: 2018</a>. </p>
<p>This peer-reviewed report will examine the recent state of the ozone layer and the atmospheric concentration of ozone-depleting chemicals, how the ozone layer is projected to change, and links between ozone change and climate. </p>
<p>In the meantime we’ll <a href="http://www.wmo.int/pages/prog/arep/gaw/ozone/">watch the 2017 hole</a> as it peaks then shrinks over the remainder of the year, as well as the ozone holes of future years, which will tend to grow less and less large as the ozone layer heals.</p><img src="https://counter.theconversation.com/content/84051/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Klekociuk is employed by the Australian Antarctic Division and is funded by the Department of the Environment and Energy of the Australian government.</span></em></p><p class="fine-print"><em><span>Paul Krummel is employed by CSIRO and receives funding from MIT, NASA, Australian Bureau of Meteorology, Department of the Environment and Energy, and Refrigerant Reclaim Australia.</span></em></p>The treaty to limit the destruction of the ozone layer is hailed as the most successful environmental agreement of all time. Three decades on, the ozone layer is slowly but surely returning to health.Andrew Klekociuk, Adjunct Senior Lecturer, University of TasmaniaPaul Krummel, Research Group Leader, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/693582016-11-25T02:16:47Z2016-11-25T02:16:47ZPlease, Donald Trump, don’t send climate science back to the pre-satellite era<figure><img src="https://images.theconversation.com/files/147498/original/image-20161125-15351-u7ulac.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">You can only truly understand the weather by flying above the clouds.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Bob Walker, an adviser to US President-elect Donald Trump, has set alarm bells ringing by <a href="https://www.theguardian.com/environment/2016/nov/22/nasa-earth-donald-trump-eliminate-climate-change-research">recommending</a> that NASA’s climate monitoring programs be axed.</p>
<p>But his dismissal of the “politicised science” at NASA’s <a href="https://science.nasa.gov/earth-science">Earth Science Division</a> shows an ignorance of the breadth, role and significance of its <a href="https://theconversation.com/five-reasons-why-cutting-nasas-climate-research-would-be-a-colossal-mistake-69336">contributions to society</a> in the United States and worldwide.</p>
<p>It’s unclear what exactly Walker means by his comment that “future programs should definitely be placed with other agencies”. Is the plan merely to shuffle the deckchairs – same science, different badge — or is it code for cutting the research observation and monitoring efforts altogether? </p>
<p>If the former, it is hard to see what it would achieve, beyond risking a loss of expertise as other agencies attempt to develop the same capabilities as NASA. But the latter is a frightening prospect, because it would effectively take us back to what climate scientists refer to as the “pre-satellite era”. </p>
<p>The global climate system is, well, global. There are places where there is no one around to take measurements, such as the vast expanses of our oceans, the central desert of Australia, and the Arctic and Antarctic regions. But what happens in these remote areas affects the climate elsewhere; the atmosphere has no boundary and the oceans are linked. </p>
<p>Before satellites, the patchiness of weather and climate observations for much of the globe made it hard to detect the patterns that govern rainfall, temperatures and winds. </p>
<p>Now we have a continuous global view of Earth, courtesy of NASA’s Earth observation satellite program. Cutting this research and returning to the pre-satellite era would leave us ignorant not only of Earth’s climate processes, but also of whether or not our environmental policies are effective. </p>
<h2>The value of satellites</h2>
<p>For more than three decades in the early 20th century, the British meteorologist Sir Gilbert T. Walker searched the sparse climate records for patterns that could explain why the Indian monsoon failed in some years. After some laborious number-crunching, he put forward the concept of the “Southern Oscillation”, describing sea-level pressure differences between Darwin and Tahiti in the South Pacific. His <a href="http://www.bom.gov.au/climate/current/soi2.shtml">Southern Oscillation Index</a> is still used today. </p>
<p>When sea-level pressure is lower in Tahiti than Darwin, it causes wind patterns that bring drought to India and northeast Australia, Walker suggested. But the Southern Oscillation was only part of the story. </p>
<p>Almost half a century later, in the late 1960s, early NASA satellite data provided an unprecedented look at the patterns of clouds above the Pacific Ocean. This helped the meteorologist Jacob Bjerknes to link Walker’s sea-level pressure oscillations with other variables such as wind, rainfall (clouds) and ocean temperature variations right across the tropical Pacific. </p>
<p>Crucially, he identified a low-rainfall zone in the central-eastern equatorial Pacific – of which Walker, with his patchy data, had been completely unaware. The “chain reaction” between the atmosphere and ocean now known as the <a href="https://theconversation.com/explainer-el-nino-and-la-nina-27719">El Niño-Southern Oscillation</a> emerged in part from NASA satellite imagery.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/147499/original/image-20161125-15348-dgkwu7.jpg?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"></a>
<figcaption>
<span class="caption">A visualisation of the strong El Niño that developed in 1997, using NASA sea-surface height data from the TOPEX/Poseidon satellite.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Of course, the holy grail when it comes to El Niño is to forecast events ahead of time, because El Niño is a major factor in bringing droughts and floods to countries bordering the Pacific Oceans. This has huge consequences for millions of livelihoods. Australia’s Bureau of Meteorology uses NASA satellite and model data to <a href="http://www.bom.gov.au/climate/enso/">forecast an impending El Niño three to six months ahead of time</a>, while real-time observations help to assess the impacts once the event actually arrives. </p>
<p>This level of forecasting and monitoring was a pipe dream in the pre-satellite era. The same could be said about a host of other global phenomena – from <a href="https://www.nasa.gov/mission_pages/hurricanes/main/index.html">severe storms</a>, to <a href="https://www.nasa.gov/mission_pages/fires/main/index.html">massive wildfires</a>, to <a href="http://aqast.org">air pollution</a>.</p>
<h2>Verifying policy decisions</h2>
<p>If President-elect Trump really needs yet more <a href="http://iopscience.iop.org/article/10.1088/1748-9326/11/4/048002">certainty</a> that human-induced global warming is not a <a href="https://twitter.com/realdonaldtrump/status/265895292191248385?lang=en">hoax</a> and that the recently enacted <a href="http://unfccc.int/paris_agreement/items/9485.php">Paris Agreement</a> will have a meaningful impact, then one of the best ways to achieve this would be to boost NASA’s Earth Science Division.</p>
<p>NASA satellites recently demonstrated the success of US and European environmental regulations in <a href="https://www.nasa.gov/press-release/new-nasa-satellite-maps-show-human-fingerprint-on-global-air-quality">improving air quality over the past decade</a>. NASA has also been central to monitoring the effectiveness of the <a href="http://ozone.unep.org/en/treaties-and-decisions/montreal-protocol-substances-deplete-ozone-layer">Montreal Protocol</a>, the global agreement to safeguard the ozone layer. By keeping a close watch on the <a href="http://ozonewatch.gsfc.nasa.gov">size and extent of the ozone hole</a>, NASA has helped to show that it is <a href="http://ozone.unep.org/Assessment_Panels/SAP/SAP2014_Assessment_for_Decision-Makers.pdf">beginning to recover</a> and that the policy is working.</p>
<h2>Our advice to Trump</h2>
<p>Gilbert T. Walker <a href="http://docs.lib.noaa.gov/rescue/mwr/Suppl/no39-1940.pdf">wrote in 1940</a>: </p>
<blockquote>
<p>I think that the relationships of world weather are so complex that our only chance of explaining them is to accumulate the facts empirically. </p>
</blockquote>
<p>His present-day namesake and Trump adviser Bob Walker also says “<a href="https://www.theguardian.com/environment/2016/nov/22/nasa-earth-donald-trump-eliminate-climate-change-research">we need good science to tell us what the reality is</a>”. One of President-elect Trump’s best chances of achieving this aim is to continue funding scientists to observe Earth from space. </p>
<p>So our advice to Trump is to look beyond the cheap talk about politicisation and appreciate the importance of the work done by NASA’s Earth Science Division. This is not, as Bob Walker asserts, “politically correct environmental monitoring” (whatever that is), but essential data that are already being used to ensure society’s <a href="https://www.youtube.com/watch?v=ag-Zo0izSNg&feature=youtu.be">health and wellbeing</a>. </p>
<p>As for climate change science, the division’s <a href="http://data.giss.nasa.gov/gistemp/">reports on global temperatures</a> are solely based on robust data. What’s being politicised here is not the science but the story that the science tells: that the planet is warming. Let’s not shoot the messenger.</p><img src="https://counter.theconversation.com/content/69358/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Helen McGregor receives funding from the Australian Research Council and the University of Wollongong. McGregor is a member of the Australian Meteorological and Oceanographic Society, the American Geophysical Union and the Australasian Quaternary Association. </span></em></p><p class="fine-print"><em><span>Jenny Fisher receives funding from the Australian Research Council, the Department of the Environment, NASA, and the University of Wollongong. Fisher is a member of the Australian Meteorological and Oceanographic Society and the American Geophysical Union.</span></em></p>Far from being “politicised science”, as a Trump advisor has claimed, NASA’s satellite monitoring has been a crucial help in understanding the planet we live on.Helen McGregor, ARC Future Fellow, University of WollongongJenny Fisher, Lecturer in Atmospheric Chemistry, University of WollongongLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/671452016-10-18T03:07:45Z2016-10-18T03:07:45ZHow a saviour of the ozone hole became a climate change villain – and how we’re going to fix it<figure><img src="https://images.theconversation.com/files/142103/original/image-20161018-12443-1vs1xny.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Montreal Protocol has successfully reduced the use of chemicals that destroy the Earth's ozone layer. </span> <span class="attribution"><span class="source">Atmosphere image from www.shutterstock.com</span></span></figcaption></figure><p>Over the weekend, <a href="http://unep.org/newscentre/Default.aspx?DocumentID=27086&ArticleID=36283&l=en">international leaders meeting in Kigali, Rwanda</a>, agreed to a remarkable deal to phase-out hydrofluorocarbons (HFCs), used as refrigerants and propellants. HFCs are potent greenhouse gases. </p>
<p>The agreement ended a decade of negotiations under the <a href="http://ozone.unep.org/en/treaties-and-decisions/montreal-protocol-substances-deplete-ozone-layer">Montreal Protocol</a>, established in 1987 to protect the ozone layer. Under the new agreement, developed nations will reduce HFCs 85% below current levels by 2036. </p>
<p>So how will the deal work? </p>
<h2>Fixing the ozone hole</h2>
<p>The Montreal Protocol was established under the Vienna Convention for the protection of the ozone layer. It followed evidence that chlorine atoms were damaging the stratospheric ozone, which protects the Earth from the most energetic ultraviolet radiation coming from the sun. </p>
<p>These chlorine atoms came from refrigerant and propellant gases, the chlorofluorocarbons (CFCs), that we were releasing into the atmosphere.</p>
<p>By 1990, nations had agreed to restrict production and consumption of CFCs and a timetable for their eventual phase-out over the next two decades. More time was allowed for developing countries and a multilateral fund was established to help them meet their targets. </p>
<p>With just a few exceptions, complete phase-out has been achieved. As well as ozone protection, there was a climate benefit from phasing-out the CFCs because they are much stronger greenhouse gases than carbon dioxide.</p>
<p>Related gases that were less damaging to the ozone layer, the hydrochlorofluorocarbons (HCFCs), were next targeted and they will have been phased out by about 2020. </p>
<p>In developed countries such as Australia they have largely disappeared already, although there is still a lot of one HCFC, R-22, in older air-conditioners. Other ozone-depleting substances such as the fumigant methyl bromide and a number of solvents were also targeted for elimination under the Montreal Protocol.</p>
<h2>New villain</h2>
<p>Major replacements for the CFCs were the hydrofluorocarbons (HFCs). Their molecules contain no chlorine so they are “ozone friendly” but like the CFCs these substances are serious global warmers. </p>
<p>HFCs are not manufactured in Australia but we import several thousand tonnes each year, which is a small proportion of world production. <a href="http://ris.dpmc.gov.au/2016/09/16/hydrofluorocarbons-hfcs/">Our imports will be capped</a> from 2018 following a recent government decision.</p>
<p>Nations under the Montreal Protocol realised that by using HFCs to replace ozone-depleting substances they had contributed to another environmental problem – global warming and climate change. </p>
<p>Despairing of any action under the climate change-centred <a href="http://unfccc.int/kyoto_protocol/items/2830.php">Kyoto Protocol</a>, the representatives of developed countries began to push for addition of HFCs to the Montreal Protocol where production and consumption data could be monitored and there was potential for an agreement to phase them out.</p>
<p>The process was fractious. Some parties argued that the Montreal Protocol could not be extended to cover substances that were not ozone-depleting. Others pointed to a clause in the preamble to the protocol that would allow HFCs to be covered. </p>
<p>This was a practical view, but perhaps it also contained an element of guilt: “we created the problem so it’s up to us to fix it”. </p>
<p>Resistance came from developing countries that were struggling financially to achieve the phase-out of HCFCs and did not want the expense of retooling for whatever would replace the HFCs. </p>
<p>In the corridors one could hear cynical voices saying that the phase-outs of CFCs and HCFCs would leave delegates and officers with nothing to do, so an extension to HFCs was needed to keep the “Montreal Club” alive.</p>
<h2>Send in the replacements</h2>
<p>Sensing that change was likely, the chemical industry in the US had already produced HFC replacements that are neither ozone-depleting nor global warming - the hydrofluoroolefins (HFOs).</p>
<p>These substances are designed to rapidly degrade in the lower atmosphere so that releases would not contribute to environmental problems. Other industrial players, strongly backed by environment groups, opted for natural refrigerants such as ammonia (already coming into widespread use in Australia), carbon dioxide (yes, the villain in new clothes!), and low-boiling hydrocarbons such as isobutane that can be “dropped in” to air-conditioners to replace the HFC R-134a.</p>
<p>Last week in Kigali, countries agreed to a phase-out schedule they could live with. Reductions will occur in steps: developed countries have until 2036 to reduce HFC consumption to 85% of current levels, while developing countries have until the mid-2040s. This is too slow for some observers but the experience of the last decade’s negotiations showed that measured pace would be important in securing the agreement.</p>
<p>Australian delegates had been involved all along in the group pushing for the extension of the Montreal Protocol to cover the HFCs. More than that, our lead delegate, Patrick McInerney (Department of the Environment) was co-chair of the working group that fashioned the Kigali consensus and enabled the 197 parties to bring the matter to conclusion.</p>
<p>Even the most pedantic observer, while questioning the validity of extending the Montreal Protocol, would have to agree that it was the right thing to do.</p><img src="https://counter.theconversation.com/content/67145/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ian Rae is was co-chair of the Chemicals Technical Options Committee and a member of the Technology and Economic Advisory Panel for the Montreal Protocol 2005-2013.</span></em></p>Hydrofluorocarbons were created to replace ozone-damaging chemicals – but they turned out to be major contributors to climate change.Ian Rae, Honorary Professorial Fellow, School of Chemistry, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/620072016-07-04T15:54:36Z2016-07-04T15:54:36ZShrinking hole in the ozone layer shows what collective action can achieve<figure><img src="https://images.theconversation.com/files/129618/original/image-20160706-12717-1eeovek.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ban on CFCs in aerosol sprays and refrigerants has led to a steady shrinking of the ozone hole.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Aerosol.png">PiccoloNamek</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The hole in the ozone layer was <a href="http://www.nature.com/nature/journal/v315/n6016/abs/315207a0.html">first discovered in 1985</a> by scientists from the British Antarctic Survey, who described how ozone levels above the Antarctic were steadily dropping compared to the previous decade. This was quickly recognised as a severe environmental problem – and the culprit was identified as the unchecked use of chlorofluorocarbons, or CFCs.</p>
<p>Soon after, the Montreal Protocol banning the use of CFCs was signed and came into effect in 1989. Now, 27 years later, we have published evidence that shows the <a href="http://science.sciencemag.org/content/early/2016/06/29/science.aae0061">ozone hole is beginning to close</a>. </p>
<p>CFCs are a family of non-toxic, non-flammable chemical compounds developed in the 1930s as a safe alternative to dangerous substances such as ammonia for refrigeration and spray can propellants. As CFCs were thought to be risk-free, their use grew enormously. </p>
<p>The chlorine atom is the component of CFCs that is responsible for ozone destruction. Very little chlorine exists naturally in the upper atmosphere as it generally emerges near Earth’s surface – for example from salt (sodium chloride, or NaCl) in sea spray – in water-soluble forms that are “washed out” of the atmosphere by snow and rain. CFCs on the other hand are not water soluble, so are extremely efficient at carrying chlorine high into the stratosphere at the level of the ozone layer. Once in the stratosphere, ultraviolet radiation breaks free the chlorine atom to destroy ozone and react with other substances. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/129218/original/image-20160704-19103-rvyokw.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">
<figcaption>
<span class="caption">The ozone hole over Antarctica in September 2006.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>The reason there is an ozone hole in the Antarctic is that it is the coldest place on Earth – it is so cold that clouds form in the Antarctic stratosphere. Those clouds provide surfaces on which the man-made chlorine from the CFC may go on to destroy ozone much more efficiently. Together with sunlight, this special chemistry is what makes springtime (late August to October) ozone depletion worse in the Antarctic.</p>
<h2>Ozone layer on the mend</h2>
<p>Our study, led by Professor Susan Solomon of the Massachusetts Institute of Technology alongside colleagues from the National Centre for Atmospheric Research in Boulder, Colorado, shows that the rapid worldwide agreement to sign and implement the Montreal Protocol has paid off. Signed by all the countries in the world, it was the first universally ratified treaty in United Nations history. </p>
<p>We show that the average size of the ozone hole above Antarctica each September has shrunk from about 20m square kilometres to 16m square kilometres since 2000. There are other metrics that indicate the ozone layer is on the mend – such as observations that the ozone hole is opening about 10 days later than in 2000. These observations became even more meaningful through our study’s computer model simulations which meant we were able to attribute more than half of the hole’s shrinking to the reduction in CFCs. </p>
<p>While a trend showing the hole is shrinking is evident, the size has varied from year to year. This is in part due to the effects of volcanic eruptions. For example, the fourth-largest ozone hole occurred in October 2015 following the eruption of <a href="http://www.bbc.co.uk/news/world-latin-america-32544075">Calbuco volcano in Chile</a>. The mechanism by which volcanic eruptions affect ozone levels is well-known: eruptions emit sulphur dioxide, which is converted into tiny airborne particles (aerosols) that enhance chemical conditions for chlorine to destroy ozone. </p>
<p>What is surprising here is that Calbuco was a relatively modest eruption – this underscores the need to monitor and describe such volcanic events carefully in order to account for natural variability in documenting the recovery of the ozone layer.</p>
<p>Regardless of the annual ups and downs of the size of the ozone hole, it’s now clear that banning CFCs through the Montreal Protocol almost 30 years ago was the right decision. Because of swift international action, that decision is now bearing fruit and the Antarctic ozone hole is starting to heal – perhaps to close completely by as early as the 2050s.</p>
<p>But even while we are on the way to resolving one environmental issue, the next is already upon us: man-made climate change. While the ozone hole is a relatively contained problem and involved only a single CFC-producing industry, the factors contributing to climate change involve many huge, established worldwide industries worth many trillions of dollars. The task ahead of us is great, nonetheless, tackling the ozone hole problem shows what can be achieved if we collectively set our minds to solving a problem.</p><img src="https://counter.theconversation.com/content/62007/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anja Schmidt receives funding from NERC, the Royal Society, and the NSF. </span></em></p><p class="fine-print"><em><span>Ryan Neely receives funding from NERC and the NSF. </span></em></p>What the Montreal Protocol has done for the ozone hole threat other international accords could do for climate change – if we all agree.Anja Schmidt, Academic Research Fellow in Volcanic Impacts and Hazards, University of LeedsRyan Neely, Lecturer in Observational Atmospheric Science, University of LeedsLicensed as Creative Commons – attribution, no derivatives.