tag:theconversation.com,2011:/us/topics/northern-hemisphere-5526/articlesNorthern hemisphere – The Conversation2023-07-10T20:11:22Ztag:theconversation.com,2011:article/2087612023-07-10T20:11:22Z2023-07-10T20:11:22ZDoes the direction water rotates down the drain depend on which hemisphere you’re in? Debunking the Coriolis effect in your sink<figure><img src="https://images.theconversation.com/files/534774/original/file-20230629-15-plnypv.jpg?ixlib=rb-1.1.0&rect=581%2C1032%2C4218%2C2604&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The idea that the Coriolis force influences how water drains frequently appears in popular culture and urban legends.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/es/image-photo/jet-water-flows-into-sink-concept-1399159301">frantic00 / Shutterstock</a></span></figcaption></figure><p>In countries near the Earth’s equator, tourists are often dazzled by a demonstration of a mysterious physical phenomenon. A presenter will position three buckets of water – one in the Northern Hemisphere, one in the Southern Hemisphere, and one directly on the equator – and let the water drain out.</p>
<p>Tourists are shown that, as the water drains, the water in the northern bucket rotates in one direction, the water in the southern bucket rotates in the other direction, and the water at the equator doesn’t rotate at all.</p>
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<figcaption><span class="caption">Tourists in countries near the equator, like Uganda and Ecuador, are amazed by attractions that claim to demonstrate the Coriolis effect.</span></figcaption>
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<p>The demonstrator might claim that this strange phenomenon is governed by physics, that it’s an example of the <a href="https://education.nationalgeographic.org/resource/coriolis-effect/">Coriolis effect</a>.</p>
<p>The intriguing nature of the Coriolis effect has led to its frequent appearances in urban legends and popular culture, from <a href="http://www.lghs.net/ourpages/users/dburns/ScienceOnSimpsons/Clips_files/Coriolis.m4v">TV shows</a> to <a href="http://www.gamefaqs.com/boards/939217-call-of-duty-4-modern-warfare/43834255/480093367">video games</a>.</p>
<p>The Coriolis effect is based on the idea that the spinning of the Earth introduces a physical force, known as the Coriolis force, which affects the way objects appear to move to us Earthbound observers. The Coriolis force causes objects on the Earth’s surface to be deflected in different directions depending on whether they are above or below the equator. The effect is strongest near the poles and weakest at the equator.</p>
<p>The Coriolis effect is legitimately responsible for the behavior of some natural phenomena, like hurricanes, that meterologists and physical oceanographers like <a href="https://scholar.google.com/citations?user=YdRRHIQAAAAJ">the two</a> <a href="https://0-scholar-google-com.brum.beds.ac.uk/citations?user=cQOa614AAAAJ&hl=fr">of us</a> study. But in domestic settings, the spinning of the Earth actually has very little effect on how water behaves. Math can explain how this works – or doesn’t work – in a kitchen sink.</p>
<h2>The math behind the phenomenon</h2>
<p>Geophysicists use certain mathematical equations, known as the <a href="https://www.britannica.com/science/Navier-Stokes-equation">Navier-Stokes equations</a>, to describe the behavior of fluids. Roughly, the Navier-Stokes equations relate the change of fluid velocity – how the fluid moves – to the forces acting on the fluid, subject to a few physical constraints. For example, the equations assume that the overall amount of fluid in the system doesn’t change over time.</p>
<p>But just because physicists and mathematicians can write down these equations, it doesn’t mean we can solve them. In fact, these equations are so difficult to solve that you would <a href="https://theconversation.com/millennium-prize-the-navier-stokes-existence-and-uniqueness-problem-4244">win a Millennium Prize and US$1 million</a> if you could do it.</p>
<p>Although there is no known complete solution to Navier-Stokes equations, meteorologists and physical oceanographers can still obtain useful partial solutions. One way to obtain these partial solutions is to compare various terms in the Navier-Stokes equations to determine which ones are most important. </p>
<p>These comparisons are often recorded as ratios and have no associated physical unit, thereby earning them the name “<a href="https://www.sciencedirect.com/topics/chemistry/dimensionless-number">dimensionless numbers</a>.”</p>
<h2>What happens in your sink?</h2>
<p>In the context of the Coriolis effect, perhaps the most important dimensionless number is the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/rossby-number">Rossby number</a>, named for the early 20th-century meteorologist <a href="https://www.britannica.com/biography/Carl-Gustaf-Arvid-Rossby">Carl-Gustav Rossby</a>. The Rossby number compares the dynamics of the fluid with the Earth’s rotation rate, taking into account how big the system is and how fast it’s moving. </p>
<p>A small Rossby number indicates that the Coriolis force has a strong effect on the system, while a large Rossby number signifies that the Coriolis force has a negligible effect. For example, the Rossby number for an average hurricane is of the order of 1, indicating that the dynamics of the fluid and the Earth’s rotation rate are of similar relevance. It is <a href="https://education.nationalgeographic.org/resource/coriolis-effect-1/">true that hurricanes</a> tend to rotate clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere.</p>
<p>The same math that applies to large-scale phenomena like hurricanes also applies to the water in your bathroom sink. In this setting, the system is relatively small, and so the Rossby number will be much larger than 1 – more than 10,000 times larger. This observation indicates that the Coriolis force is negligible on water draining in a bathroom sink.</p>
<p>In fact, the Rossby number predicts that the water would need to move at an almost imperceptible speed for the Coriolis force to become significant. So even though the way water swirls down the drain may be consistent, that isn’t due to the Coriolis effect.</p>
<h2>So what did the tourists see?</h2>
<p>The same logic applies to the equatorial attractions. Given the size of the system, physical oceanographers can comfortably conclude that the Coriolis force is not responsible for what the tourists see in those buckets or bowls. </p>
<p>This conclusion is also supported by examining the same kind of presentation in different countries. </p>
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<figcaption><span class="caption">Different videos of the Coriolis effect show the water spinning in different directions in the same hemisphere.</span></figcaption>
</figure>
<p>The water in the Northern Hemisphere rotates counterclockwise in one video but clockwise in another video. If the rotation were due to the Coriolis effect, the result would be the same in both videos. </p>
<p>Although physical oceanographers can’t deny what the tourists see, we know that the magic trick isn’t due to the Coriolis effect at such a small scale.</p><img src="https://counter.theconversation.com/content/208761/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Las personas firmantes no son asalariadas, ni consultoras, ni poseen acciones, ni reciben financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y han declarado carecer de vínculos relevantes más allá del cargo académico citado anteriormente.</span></em></p>This physical effect does explain how some massive natural phenomena like hurricanes behave. But on the scale of water in your sink – not so much.Francisco José Machín Jiménez, Profesor Titular de Universidad. Oceanógrafo Físico, Universidad de Las Palmas de Gran CanariaBorja Aguiar González, Personal Docente e Investigador, Universidad de Las Palmas de Gran CanariaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1734032022-01-10T13:36:59Z2022-01-10T13:36:59ZHow the Earth’s tilt creates short, cold January days<figure><img src="https://images.theconversation.com/files/439145/original/file-20220102-17-1b3kzl8.jpg?ixlib=rb-1.1.0&rect=0%2C6%2C4163%2C2765&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Sun rises in Midland, Michigan, shortly after 8a.m. on Jan. 13, 2017.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/Q6LNQ5">Christian Collins/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p><em>Above the equator, winter officially <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/seasons/winter/when-does-winter-start">begins in December</a>. But in many areas, January is when it really takes hold. Atmospheric scientist <a href="https://scholar.google.com/citations?user=B5TfCvMAAAAJ&hl=en">Deanna Hence</a> explains the weather and climate factors that combine to produce wintry conditions at the turn of the year.</em></p>
<h2>How does the Earth’s orbit influence our daylight and temperatures?</h2>
<p>As the Earth orbits the sun, it spins around an axis – picture a stick going through the Earth, from the North Pole to the South Pole. During the 24 hours that it takes for the Earth to rotate once around its axis, every point on its surface faces toward the Sun for part of the time and away from it for part of the time. This is what causes daily changes in sunlight and temperature. </p>
<p>There are two other important factors: First, the Earth is round, although it’s <a href="https://oceanservice.noaa.gov/facts/earth-round.html">not a perfect sphere</a>. Second, its axis is tilted about 23.5 degrees relative to its path around the Sun. As a result, light falls directly on its equator but strikes the North and South poles at angles. </p>
<p>When one of the poles points more toward the Sun than the other pole, that half of the planet gets more sunlight than the other half, and it’s summer in that hemisphere. When that pole tilts away from the Sun, that half of the Earth gets less sunlight and it’s winter there.</p>
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<a href="https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Graphic of Earth tilting on its axis, with Northern Hemisphere toward the sun." src="https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/438275/original/file-20211217-23072-g37bxk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Earth’s tilt as it orbits around the Sun puts that one part of the planet more directly exposed to the Sun’s rays.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/tilt-of-the-earths-axis-and-earths-season-royalty-free-illustration/695485360">iStock via Getty Images</a></span>
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<p>Seasonal changes are the most dramatic at the poles, where the changes in light are most extreme. During the summer, a pole receives 24 hours of sunlight and the Sun never sets. In the winter, the Sun never rises at all.</p>
<p>At the equator, which gets consistent direct sunlight, there’s very little change in day length or temperature year-round. People who live in high and middle latitudes, closer to the poles, can have very different ideas about seasons from those who live in the tropics.</p>
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<figcaption><span class="caption">As the Earth orbits the Sun, sunlight strikes the surface at varying angles because of the planet’s tilt. This creates seasons.</span></figcaption>
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<h2>There’s an old saying, “As the days lengthen, the cold strengthens.” Why does it often get colder in January even though we’re gaining daylight?</h2>
<p>It depends on where you are in the world and where your air is coming from. </p>
<p>Earth’s surface constantly absorbs energy from the Sun and stores it as heat. It also emits heat back into space. Whether the surface is warming or cooling depends on the balance between how much solar radiation the planet is absorbing and how much it is radiating away. </p>
<p>But Earth’s surface isn’t uniform. Land typically heats up and cools off much faster than water. Water requires more energy to raise and lower its temperature, so it warms and cools more slowly. Because of this difference, water is a better heat reservoir than land – especially big bodies of water, like oceans. That’s why we tend to see bigger swings between warm and cold inland than in coastal areas.</p>
<p>The farther north you live, the longer it takes for the amount and intensity of daylight to start significantly increasing in midwinter, since your location is tilting away from the Sun. In the meantime, those areas that are getting little sunlight keep radiating heat out to space. As long as they receive less sunlight than the heat they emit, they will keep getting colder. This is especially true over land, which loses heat much more easily than water. </p>
<p>As the Earth rotates, air circulates around it in the atmosphere. If air moving into your area comes largely from places like the Arctic that don’t get much sun in winter, you may be on the receiving end of bitterly cold air for a long time. That happens in the Great Plains and Midwest when cold air swoops down from Canada.</p>
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<p>But if your air comes across a body of water that keeps a more even temperature through the year, these swings can be significantly evened out. Seattle is downwind from an ocean, which is why it is many degrees warmer than Boston in the winter even though it’s farther north than Boston.</p>
<h2>How quickly do we lose daylight before the solstice and gain it back afterward?</h2>
<p>This depends strongly on your location. The closer you are to one of the poles, the faster the rate of change in daylight is. That’s why Alaska can go from having hardly any daylight in the winter to hardly any darkness in the summer. </p>
<p>Even for a particular location, the change is not constant through the year. The rate of change in daylight is slowest at the solstices – December in winter, June in summer – and <a href="https://www.bostonglobe.com/metro/2019/09/11/why-losing-daylight-quickly-and-what-know-about-autumnal-equinox/ooZUrhowvIUpSgV1LfOUoO/story.html">fastest at the equinoxes</a>, in mid-March and mid-September. This change occurs as the area on Earth receiving direct sunlight swings from 23.5 N latitude – about as far north of the equator as Miami – to 23.5 S latitude, about as far south of the equator as Asunción, Paraguay. </p>
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<figcaption><span class="caption">This satellite view captures the four changes of seasons. On the equinoxes, March 20 and Sept. 20, the line between night and day is a straight north-south line, and the sun appears to sit directly above the equator. Earth’s axis is tilted away from the Sun at the December solstice and toward the Sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the Sun and the light is spread evenly.</span></figcaption>
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<h2>What’s happening on the opposite side of the planet right now?</h2>
<p>In terms of daylight, folks on the other side of the planet are seeing the exact opposite of what we’re seeing. Right now, they’re at the peak of their summer and are enjoying the largest amounts of daylight that they’re going to get for the year. I do research on <a href="https://www.nsf.gov/news/news_summ.jsp?cntn_id=296639&org=NSF&from=news">Argentinian hailstorms</a> and <a href="https://www.researchgate.net/profile/Deanna-Hence-2">Indian Ocean tropical cyclones</a>, and both of those warm-weather storm seasons are well into their peaks right now.</p>
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<p>But there’s a key difference: The Southern Hemisphere has a lot less land and a lot more water than the Northern Hemisphere. Thanks to the influence of the southern oceans, land masses in the Southern Hemisphere tend to have fewer very extreme temperatures than land in the Northern Hemisphere does.</p>
<p>So even though a spot on the <a href="https://www.geodatos.net/en/antipodes">opposite side of the planet from your location</a> may receive exactly as much sunlight now as your area does in summer, the weather there may be different from the summer conditions you are used to. But it still can be fun to imagine a warm summer breeze on the far side of the Earth – especially in a snowy January.</p><img src="https://counter.theconversation.com/content/173403/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Deanna Hence receives funding from NASA, the National Science Foundation, and the Illinois Campus Research Board.</span></em></p>The winter solstice is past, but bundle up – January is when winter really arrives in many parts of the Northern Hemisphere.Deanna Hence, Assistant Professor of Atmospheric Sciences, University of Illinois at Urbana-ChampaignLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1005822018-07-26T05:06:50Z2018-07-26T05:06:50ZIt’s a savage summer in the Northern Hemisphere – and climate change is slashing the odds of more heatwaves<p>In Australia we know about sweltering summer heat. We all remember the images of <a href="https://www.theguardian.com/environment/2015/jan/09/koala-mittens-needed-to-help-bushfire-victims-with-burnt-paws">burned koala paws</a>, <a href="https://www.theguardian.com/environment/planet-oz/2014/jan/16/australia-tennis-open-climate-change-extreme-heat">collapsing tennis players</a> and, far more seriously, the tragic events of <a href="http://www.abc.net.au/innovation/blacksaturday/#/stories/mosaic">Black Saturday</a>. </p>
<p>Aussies may <a href="https://www.news.com.au/finance/work/at-work/poms-told-not-to-go-outside-health-warnings-issued-during-britains-record-hot-weather/news-story/b6abc1af8f9934bf41e64a1d894bf5a9">scoff</a> at Britain’s idea of a heatwave, but this time it’s the real deal and it’s no laughing matter. </p>
<p>Extreme heat has hit locations throughout the Northern Hemisphere, in places as far apart as <a href="https://www.bbc.com/news/world-us-canada-44730887">Montreal</a>, <a href="https://www.theguardian.com/uk-news/2018/jun/28/uk-heatwave-glasgow-bakes-on-hottest-day-on-record">Glasgow</a>, <a href="https://www.bbc.com/news/world-asia-44935152">Tokyo</a> and <a href="https://www.nytimes.com/2018/07/19/world/europe/heat-wave-sweden-fires.html">Lapland</a>. In the past few weeks heat records have tumbled in a wide range of places, most notably:</p>
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<li>a new <a href="https://www.washingtonpost.com/news/capital-weather-gang/wp/2018/07/06/africa-may-have-witnessed-its-all-time-hottest-temperature-thursday-124-degrees-in-algeria/?utm_term=.155b5a918fcd">record high temperature for Africa of 51.3°C in Algeria</a></li>
<li>a <a href="https://edition.cnn.com/2018/07/23/asia/japan-heatwave-deadly-intl/index.html">record high temperature in Japan of 41.1°C near Tokyo</a></li>
<li>a <a href="https://edition.cnn.com/travel/article/hottest-low-temperature-quriyat-oman-wxc/index.html">world record hottest overnight minimum of 42.6°C in Oman</a>.</li>
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Read more:
<a href="https://theconversation.com/why-hot-weather-records-continue-to-tumble-worldwide-86158">Why hot weather records continue to tumble worldwide</a>
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<p>Heat has not been the only problem. Much of northern Europe is experiencing a very persistent drought, with little to no measurable rainfall in months. This has caused the normally lush green fields of England and other European countries to <a href="https://www.bbc.com/news/in-pictures-44923654">turn brown</a> and even reveal previously hidden <a href="https://www.bbc.com/news/uk-44767497">archaeological monuments</a>.</p>
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<p>There have also been major wildfires in <a href="https://www.bbc.com/news/in-pictures-44696612">northern England</a>, <a href="https://www.thelocal.se/20180725/extreme-risk-swedish-wildfires-could-spread-to-south-of-the-country">Sweden</a> and, most recently and devastatingly, <a href="https://www.bbc.com/news/world-europe-44948173">Greece</a>. The Greek wildfires came off the back of a very dry winter and spring.</p>
<h2>What’s behind the widespread extreme heat?</h2>
<p>The <a href="https://www.metoffice.gov.uk/learning/wind/what-is-the-jet-stream">jet stream</a>, a high-altitude band of air that pushes weather systems around at lower altitudes, has been weaker than normal. It has also been positioned unusually far to the north, particularly over Europe. This has kept the low-pressure systems that often drive wind and rain over northern Europe at bay.</p>
<p>The jet stream has remained locked in roughly the same position over the Atlantic Ocean and northern Europe for the past couple of months. This has meant that the same weather types have remained over the same locations most of the time.</p>
<p>Weather is typically more transient than it has been recently. Even when we do have blocking high-pressure systems associated with high temperatures in northern Europe, they don’t normally linger as long as this.</p>
<h2>Is it driven by climate change?</h2>
<p>Although climatologists have made great strides in recent years in the field of <a href="https://theconversation.com/columns/andrew-king-103126">event attribution</a> – identifying the human climate fingerprint on particular extreme weather events – it is hard to quantify the role of climate change in an event that is still unfolding. </p>
<p>Until the final numbers are in we won’t be able to tell just how much climate change has altered the likelihood or intensity of these particular heat extremes.</p>
<p>Having said that, we can use past analyses of extreme heat events, together with future climate change projections, to infer whether climate change is playing a role in these events.</p>
<p>We also know that <a href="https://theconversation.com/why-hot-weather-records-continue-to-tumble-worldwide-86158">increasing numbers of hot temperature records</a> are being set, and that the increased probability of hot temperature records can indeed be <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017EF000611">attributed to the human influence on the climate</a>.</p>
<p>In Europe especially, there is already a <a href="https://www.carbonbrief.org/mapped-how-climate-change-affects-extreme-weather-around-the-world">large body of literature</a> that has looked at the role of human-caused climate change in heat extremes. In fact, <a href="https://www.nature.com/articles/nature03089">the very first event attribution study</a>, led by Peter Stott from the UK Met Office, found that human-caused climate change had at least doubled the likelihood of the <a href="https://www.britannica.com/event/European-heat-wave-of-2003">infamous European heatwave of 2003</a>.</p>
<p>For all manner of heat extremes in Europe and elsewhere, including in <a href="http://www.ametsoc.net/eee/2015/21_japan_heat.pdf">Japan</a>, a clear and discernible link with climate change has been made.</p>
<p>Research has also shown that heat extremes similar to those witnessed over the past month or two are expected to become more common as global temperatures continue to climb. The world has so far had <a href="http://www.globalwarmingindex.org/">around 1°C of global warming</a> above pre-industrial levels, but at the global warming limits proposed in the <a href="https://theconversation.com/the-paris-climate-agreement-at-a-glance-50465">Paris climate agreement</a>, hot summers like that of 2003 in central Europe would be a <a href="http://iopscience.iop.org/article/10.1088/1748-9326/aa8e2c">common occurrence</a>. </p>
<p>At 2°C of global warming, the higher of the two Paris targets, 2003-like hot summers would <a href="https://theconversation.com/europe-will-benefit-hugely-from-keeping-global-warming-to-1-5-c-85009">very likely happen in most years</a>.</p>
<p>Similarly, we know that <a href="https://www.carbonbrief.org/guest-post-unprecedented-summer-heat-europe-1-5c-warming">heat exposure</a> and <a href="https://www.nature.com/articles/s41558-018-0210-1">heat-induced deaths</a> in Europe will increase with global warming, even if we can limit this warming to the levels agreed in Paris.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/yes-the-arctics-freakishly-warm-winter-is-due-to-humans-climate-influence-70648">Yes, the Arctic's freakishly warm winter is due to humans' climate influence</a>
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<h2>But summers have always been hot, haven’t they?</h2>
<p>For most parts of the world summers have got warmer, and the hottest summer on record is relatively recent – such as 2003 in parts of central Europe and 2010 in much of eastern Europe. One exception is central England, where the hottest summer <a href="https://www.carbonbrief.org/guest-post-unprecedented-summer-heat-europe-1-5c-warming">remains 1976</a>, although it may be challenged this year.</p>
<p>While extreme hot summers and heatwaves did happen in the past, they were less common. One big difference as far as England is concerned is that its extreme 1976 heatwave was a global outlier, whereas this year’s isn’t.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1021130752199725059"}"></div></p>
<p>In 1976 northwestern Europe had higher temperature anomalies than almost anywhere else on the globe. In June 2018 the same region was unusually warm, but so was most of the rest of the Northern Hemisphere.</p>
<p>So while the persistent weather patterns are driving much of the extreme heat we’re seeing across the Northern Hemisphere, we know that human-caused climate change is nudging the temperatures up and increasing the odds of new heat extremes.</p><img src="https://counter.theconversation.com/content/100582/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew King receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Ben Henley receives funding from an Australian Research Council Linkage Project.</span></em></p>From Greece, to the UK, to Japan and even Sweden, a slew of places in the Northern Hemisphere are suffering extreme heat. And the chances of extreme heat records tumbling are growing all the time.Andrew King, ARC DECRA fellow, The University of MelbourneBen Henley, Research Fellow in Climate and Water Resources, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/828492017-09-14T16:47:59Z2017-09-14T16:47:59ZGhana is boosting Africa’s ascent to astronomical heights<figure><img src="https://images.theconversation.com/files/185644/original/file-20170912-19546-1n7hkdm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The refurbished radio telescope in Kutunse, Ghana paves the way for astronomy in Africa.</span> <span class="attribution"><span class="source">SKA</span></span></figcaption></figure><p><em>The <a href="https://theconversation.com/the-science-behind-the-square-kilometre-array-40870">Square Kilometre Array (SKA)</a> is the world’s largest radio telescope project, which will collect data over one million square kilometres from radio astronomy telescopes on the African and Australian continents.
In the long run the two-phased SKA could possibly help scientists answer questions in astrophysics, cosmology and fundamental physics. Phase one of the project entailed setting radio telescopes in <a href="http://www.ska.ac.za/about/the-project/">South Africa</a> and <a href="http://www.ska.gov.au/Pages/default.aspx">Australia</a>. Phase two will include more telescopes being added by partner countries, New Zealand and the eight African countries namely: Botswana, Ghana, Kenya, Mauritius, Madagascar, Mozambique, Namibia and Zambia. The full array should be up and running by 2030, but the first phase is expected to be operational by 2023. The launch of Ghana’s radio telescope is a critical part of this process. Dr Bernard Duah Asabere explained its significance.</em></p>
<p><strong>How did Ghana get involved in the project and how does it fit in?</strong></p>
<p>Ghana has had a redundant satellite communication antenna in Kutunse – a suburb 25 kilometres north-west of the capital, Accra.</p>
<p>Between 2011 and 2017 this antenna has been undergoing refurbishment for use as a radio astronomy telescope. At the end of the first engineering phase, the refurbished telescope is capable of participating in global network observations using a technique known as <a href="http://www.ska.ac.za/science-engineering/avn/">Very Long Baseline Interferometry</a> (VLBI). It also be used in single dish or standalone operational mode.</p>
<p>Interferometry is a technique in which collections of telescopes scattered over a large area function as a single radio telescope. The Very Long Baseline Interferometry technique is most well-known for:</p>
<ul>
<li><p>imaging distant cosmic radio sources, </p></li>
<li><p>tracking spacecraft, and </p></li>
<li><p>for applications in astrometry. </p></li>
</ul>
<p>But the technique can also measure the time differences between the arrival of radio waves from separate antennas to the same source in the sky. This helps astronomers get a better image resolution of an object or a region in the universe. </p>
<p>Put simply, if different telescopes at different locations are all tuned to observe the same source in the sky at the same time, astronomers can get fine details of the specific object being observed.</p>
<p>The countries that make up the African SKA project are each building their own radio telescopes or converting redundant telecommunication dishes so that they function as a network known as the African VLBI Network (AVN). </p>
<p>Ghana now becomes the first country in the African SKA partners besides South Africa to have a <a href="http://www.ska.ac.za/media-releases/ghana-and-south-africa-celebrate-first-success-of-african-network-of-telescopes/">telecommunication antenna</a> converted to realise the African VLBI Network. With Ghana’s telescope now operational, it means that South Africa and Ghana will be able to do joint observations. When the other seven African SKA partner countries get theirs ready, they will join the African’s network. </p>
<p>Kenya, Mozambique and Zambia are contending to add the <a href="https://furtherafrica.com/2017/08/28/eight-african-countries-commit-to-developing-radio-astronomy/">next </a>telescope to the network.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185643/original/file-20170912-19550-ts7kx9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A full view of the refurbished radio telescope in Ghana that forms part of the Square Kilometre Array project.</span>
<span class="attribution"><span class="source">supplied</span></span>
</figcaption>
</figure>
<p><strong>How did we know the Ghanaian telescope was ready and what will it do?</strong> </p>
<p>Across the globe there are several very long base interferometry networks: Europe has one, as does Australia and America. Any telescope across the world is able to join an observation in one of these networks.</p>
<p>After Ghana re-engineered the antenna into a functional radio astronomy telescope, it needed to do a science commissioning of the facility to see if the refurbishment was successful and it could track and observe astronomical sources in the sky and join international observations. </p>
<p>When Ghana tested its telescope it was able to detect methanol masers, observe pulsars and also succeeded in participating in an observation with 15 other telescopes which form part of the European very long base interferometry network. </p>
<p>Until now South Africa has been the only country on the continent that had been joining in VLBI observations with other countries’ networks because it was the only country with a radio telescope on the continent. </p>
<p>With radio telescopes in Ghana and South Africa, an African network is now given birth to. Aside being a part of the African network, Ghana could join other telescopes on the globe to do science observations. </p>
<p><strong>What is the significance of Ghana’s telescope for astronomy in Africa?</strong></p>
<p>There are many celestial objects to observe in the Universe: planets, masers, galaxies, meteorites, stars and even regions in the sky. And there are global questions that astronomy community is interested in addressing. This includes questions like: is there any life outside earth? Are there other stars that are as prominent as the sun? How did the universe come into being? These are questions that the SKA will attempt to address. </p>
<p>If Africa has its own network, astronomers on the continent can choose what celestial objects and regions it wants to observe. </p>
<p>If we look at most of the existing telescopes across the world, there has been a hole in Africa. Telescopes situated in the Northern hemisphere are unable to see the region of the sky in the southern hemisphere. With an African very long base interferometry network set up, astronomers in Africa can now observe both the northern and southern hemispheres of the sky from the continent. </p>
<p><strong>What is Ghana bringing to the party and what does it hope to get out of this SKA collaboration?</strong></p>
<p>The facility at Kutunse will be used as a science instrument but also as a training facility. Ghana will help the other seven countries that form part of the African network refurbish their unused antennae. </p>
<p>Although this technology is not new and has been done in Australia, Peru, Japan and the UK, no other country in Africa has done this. </p>
<p>For Ghana, developing the skills, regulations and institutional capacity in the partner countries is a vital part of building the square kilometre array on the continent over the next decade. This is because it will optimise African participation in the SKA.</p>
<p>Ghana will build it robust research community in a field never before accessible to the country.</p>
<p>But there is also the prospect of improving the radio astronomy capacity in the country. <a href="http://skatelescope.ca/wp-content/uploads/2017/05/01_asabere.pdf">Ghana’s radio astronomy development strategy</a> forms part of the broader Ghana Science, Technology and Innovation Development Plan.</p><img src="https://counter.theconversation.com/content/82849/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bernard Duah Asabere is the manager and lead local scientist of the Radio Astronomy Observatory. </span></em></p>Astronomy on the continent has been given a much needed boost with Ghana’s converted radio telescope between it and South Africa, to conduct scientific observations.Dr. Bernard Duah Asabere, Manager of the Ghana Radio Telescope Observatory, Ghana Space Science and Technology InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/750252017-04-12T00:38:52Z2017-04-12T00:38:52ZWhy Easter is called Easter, and other little-known facts about the holiday<figure><img src="https://images.theconversation.com/files/164906/original/image-20170411-26706-ygcz2u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What is the origin of Easter eggs?</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/kmorrow/26078653846/in/photolist-FJtVdS-e9Yznm-7R1yKK-bwABoa-e2SXf7-J5nqH-4Au4JD-hetpL-9Gjjdw-bwBiti-bwQLss-4Au3Ur-bwABHg-bwAKNk-4Au4cc-e9nZwK-4A1TNi-nn4YSq-ct1go-6jw4Mp-aduWrh-4A1XNX-aduZEW-ERwqPz-GPZj1-4NEJR6-FVb8R-qrPBTD-qazARZ-9Bc7et-9Bcdd6-qazxUB-f8viFr-bKZQHX-aduTCu-7QFDLx-GQ2F8-bKTaze-7R1zpv-SRVxdx-ngZzP2-bwBjUR-bLGDPk-7R4Q1Q-bwAKfB-7R4P2o-7R4NnS-8kyJoK-bwBkjF-bwBfsH">Katie Morrow</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>The date of Easter, when the resurrection of Jesus is said to have taken place, changes from year to year.</p>
<p>The reason for this variation is that Easter always falls on the first Sunday after the first full moon following the spring equinox. </p>
<p>I am a <a href="https://liberalarts.utexas.edu/rs/faculty/bl23254">religious studies scholar</a> specializing in early Christianity, and my research shows that this dating of Easter goes back to the complicated origins of this holiday and how it has evolved over the centuries. </p>
<p>Easter is quite similar to other major holidays like Christmas and Halloween, which have evolved over the last 200 years or so. In all of these holidays, Christian and non-Christian (pagan) elements have continued to blend together.</p>
<h2>Easter as a rite of spring</h2>
<p>Most major holidays have some connection to the changing of seasons. This is especially obvious <a href="http://www.ucpress.edu/book.php?isbn=9780520258020">in the case of Christmas.</a> The New Testament gives no information about what time of year Jesus was born. <a href="https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0009640712001941">Many scholars believe,</a> however, that the main reason Jesus’ birth came to be celebrated on December 25 is because that was the date of the winter solstice according to the Roman calendar. </p>
<p>Since the days following the winter solstice gradually become longer and less dark, it was ideal symbolism for the birth of <a href="https://www.biblegateway.com/passage/?search=John+8%3A12&version=NRSV">“the light of the world”</a> as stated in the New Testament’s Gospel of John.</p>
<p>Similar was the case with Easter, which falls in close proximity to another key point in the solar year: the vernal equinox (around March 20), when there are equal periods of light and darkness. For those in northern latitudes, the coming of spring is often met with excitement, as it means an end to the cold days of winter.</p>
<p>Spring also means the coming back to life of plants and trees that have been dormant for winter, as well as the birth of new life in the animal world. Given the symbolism of new life and rebirth, it was only natural to celebrate the resurrection of Jesus at this time of the year. </p>
<p>The naming of the celebration as “Easter” seems to go back to the name of a pre-Christian goddess in England, Eostre, who was celebrated at beginning of spring. The only reference to this goddess comes from the writings of the Venerable Bede, a British monk who lived in the late seventh and early eighth century. As religious studies scholar <a href="https://www.morningside.edu/about-morningside/directory/bruce-forbes/">Bruce Forbes</a> <a href="http://www.ucpress.edu/book.php?isbn=9780520284722">summarizes</a>: </p>
<blockquote>
<p>“Bede wrote that the month in which English Christians were celebrating the resurrection of Jesus had been called Eosturmonath in Old English, referring to a goddess named Eostre. And even though Christians had begun affirming the Christian meaning of the celebration, they continued to use the name of the goddess to designate the season.”</p>
</blockquote>
<p>Bede was so influential for later Christians that the name stuck, and hence Easter remains the name by which the English, Germans and Americans refer to the festival of Jesus’ resurrection.</p>
<h2>The connection with Jewish Passover</h2>
<p>It is important to point out that while the name “Easter” is used in the English-speaking world, many more cultures refer to it by terms best translated as “Passover” (for instance, “Pascha” in Greek) – a reference, indeed, to the Jewish festival of Passover. </p>
<p>In the Hebrew Bible, Passover is a festival that commemorates the liberation of the Jewish people from slavery in Egypt, as narrated in the <a href="https://www.biblegateway.com/passage/?search=Exodus+1&version=NRSV">Book of Exodus.</a> It was and continues to be the <a href="http://undpress.nd.edu/books/P00562">most important Jewish seasonal festival,</a> celebrated on the first full moon after the vernal equinox. </p>
<p>At the time of Jesus, Passover had special significance, as the Jewish people were again under the dominance of foreign powers (namely, the Romans). Jewish pilgrims streamed into Jerusalem every year in the hope that God’s chosen people (as they believed themselves to be) would soon be liberated once more. </p>
<p>On one Passover, Jesus traveled to Jerusalem with his disciples to celebrate the festival. <a href="https://www.biblegateway.com/passage/?search=Mark+11&version=NRSV">He entered Jerusalem</a> in a triumphal procession and created a disturbance in the Jerusalem Temple. It seems that both of these actions attracted the attention of the Romans, and that as a result Jesus was executed around the year A.D. 30. </p>
<p>Some of Jesus’ followers, however, believed that <a href="https://theconversation.com/the-case-for-christ-whats-the-evidence-for-the-resurrection-75530">they saw him alive</a> after his death, experiences that gave birth to the Christian religion. As Jesus died during the Passover festival and his followers believed he was resurrected from the dead three days later, it was logical to commemorate these events in close proximity. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=466&fit=crop&dpr=1 600w, https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=466&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=466&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/164909/original/image-20170411-26726-yti74v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Resurrection.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/paullew/3433334101/in/photolist-6eoJBx-9xYfQ5-98NWB9-9N1nNo-9xYfQy-6fNEPP-o7Mj6Z-6pJn3Z-8sJRH9-7QE7vk-bGjYtg-e5gTkP-9xVhht-NVXW6G-e4JMZq-8XKaCa-btuxmL-98KQGt-ndsCqj-ndsyLb-9xkuGb-4oW1Nr-e6CLoh-nZaHVF-9xYfPN-e4tsNB-byop5C-ndvC59-6fNEGM-ndsxFe-61PcSp-ENimSF-nfymPn-e5gTKz-61TfaY-9xVhFe-9xkuJy-nfvk3c-e5gTXK-e5nxao-e8ieQd-9xYghy-3hf7MX-dkeTq9-jPwBPc-5CWHP-72VmSJ-koYM94-nfB5hj-4NzxoC">Fr Lawrence Lew, O.P.</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>Some early Christians <a href="http://www.ucpress.edu/book.php?isbn=9780520284722">chose to celebrate</a> the resurrection of Christ on the same date as the Jewish Passover, which fell around day 14 of the month of Nisan, in March or April. These Christians were known as Quartodecimans (the name means “Fourteeners”). </p>
<p>By choosing this date, they put the focus on when Jesus died and also emphasized continuity with the Judaism out of which Christianity emerged. Some others instead preferred to hold the festival on a Sunday, since that was when Jesus’ tomb was <a href="https://www.biblegateway.com/passage/?search=Mark+16%3A1-8&version=NRSV">believed to have been found</a>.</p>
<p>In A.D. 325, the Emperor Constantine, who favored Christianity, convened a meeting of Christian leaders to resolve important disputes at the Council of Nicaea. The most fateful of its decisions was about the status of Christ, whom the council recognized as <a href="https://global.oup.com/academic/product/nicaea-and-its-legacy-9780198755050?lang=en&cc=us">“fully human and fully divine.”</a> This council also resolved that Easter should be fixed on a Sunday, not on day 14 of Nisan. As a result, <a href="http://www.ucpress.edu/book.php?isbn=9780520284722">Easter is now celebrated</a> on the first Sunday after the first full moon of the vernal equinox. </p>
<h2>The Easter bunny and Easter eggs</h2>
<p>In early America, the Easter festival was far more popular among Catholics than Protestants. For instance, <a href="http://www.penguinrandomhouse.com/books/122132/the-battle-for-christmas-by-stephen-nissenbaum/9780679740384/">the New England Puritans regarded</a> both Easter and Christmas as too tainted by non-Christian influences to be appropriate to celebrate. Such festivals also tended to be opportunities for heavy drinking and merrymaking. </p>
<p>The fortunes of both holidays changed in the 19th century, when they became occasions to be spent with one’s family. This was done partly out of a desire to make the celebration of these holidays less rowdy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/164908/original/image-20170411-26706-n6gf07.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">Children on an egg hunt.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/101074613@N07/13931110871/in/photolist-e8m1e2-nczvAe-vXZqW-6g57iV-4ARtrd-9B26Qu-8oLCnU-6eLyDP-4BCnLn-6fbdLu-6cCZtG-9AY4wn-cBsJ9-6vs6WD-8oLBPq-cv7Zd-4xeJQi-cv8UN-LWQBH-cv7XV-ngMDaB-dUqjhE-4PMtkY-e5WmSZ-8oHr2z-cBsJ6-7TGya6-dUqjpo-4ymiPP-7QXEuY-H9GUG-e7H5C4-bxgmDS-6E8nst-9AYffM-6f2bE3-FiS5Z-7QUkPX-ctfKZ-bvNZCj-ebV3b3-cxDyP-ne3zUK-6hZQVz-4B6i9o-5trmcj-nwzWK2-n94T57-raSFdA-ndXvWM">Susan Bassett</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>But Easter and Christmas also became reshaped as domestic holidays because understandings of children were changing. Prior to the 17th century, children were rarely the center of attention. As historian <a href="http://www.penguinrandomhouse.com/authors/22224/stephen-nissenbaum">Stephen Nissenbaum</a> <a href="http://www.penguinrandomhouse.com/books/122132/the-battle-for-christmas-by-stephen-nissenbaum/9780679740384/">writes</a>, </p>
<blockquote>
<p>“…children were lumped together with other members of the lower orders in general, especially servants and apprentices – who, not coincidentally, were generally young people themselves.” </p>
</blockquote>
<p>From the <a href="http://www.penguinrandomhouse.com/books/4742/centuries-of-childhood-by-philippe-aries/9780394702865/">17th century onward,</a> there was an increasing recognition of childhood as as time of life that should be joyous, not simply as preparatory for adulthood. This “discovery of childhood” and the doting upon children had profound effects on how Easter was celebrated.</p>
<p>It is at this point in the holiday’s development that Easter eggs and the Easter bunny become especially important. Decorated eggs had been part of the Easter festival at least <a href="http://www.ucpress.edu/book.php?isbn=9780520284722">since medieval times</a>, <a href="http://www.tandfonline.com/doi/abs/10.1080/0015587X.1984.9716293?journalCode=rfol20">given the obvious symbolism of new life.</a> A <a href="https://omnigraphics.com/shop/encyclopedia-of-easter-carnival-and-lent/#description">vast amount of folklore surrounds Easter eggs,</a> and in a number of Eastern European countries, the process of decorating them is <a href="http://www.cs.unc.edu/%7Eyakowenk/pysanky/">extremely elaborate.</a> Several Eastern European legends describe <a href="https://omnigraphics.com/shop/encyclopedia-of-easter-carnival-and-lent/#description">eggs turning red (a favorite color for Easter eggs)</a> in connection with the events surrounding Jesus’ death and resurrection.</p>
<p>Yet it was only in the 17th century that a <a href="http://www.ucpress.edu/book.php?isbn=9780520284722">German tradition of an “Easter hare”</a> bringing eggs to good children came to be known. Hares and rabbits had a long association with spring seasonal rituals because of their amazing powers of fertility. </p>
<p>When German immigrants settled in Pennsylvania in the 18th and 19th centuries, they brought this tradition with them. The wild hare also became supplanted by the more docile and domestic rabbit, in another indication of how the focus moved toward children.</p>
<p>As Christians celebrate the festival this spring in commemoration of Jesus’ resurrection, the familiar sights of the Easter bunny and Easter eggs serve as a reminder of the holiday’s very ancient origins outside of the Christian tradition.</p>
<p><em>This is an updated version of a piece published on March 21, 2018</em>.</p><img src="https://counter.theconversation.com/content/75025/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brent Landau 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>A scholar explains the rich historical roots of Easter and how it has evolved over the centuries.Brent Landau, Lecturer in Religious Studies, The University of Texas at AustinLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/643012016-08-24T20:27:15Z2016-08-24T20:27:15ZThe Industrial Revolution kick-started global warming much earlier than we realised<figure><img src="https://images.theconversation.com/files/135283/original/image-20160824-30259-wgdjb1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Britain's industrial pioneers couldn't have known how they would affect the climate.</span> <span class="attribution"><span class="source">Henry Gastineau</span></span></figcaption></figure><p>In the early days of the Industrial Revolution, no one would have thought that their burning of fossil fuels would have an almost immediate effect on the climate. But our new study, <a href="http://nature.com/articles/doi:10.1038/nature19082">published today in Nature</a>, reveals that warming in some regions actually began as early as the 1830s. </p>
<p>That is much earlier than previously thought, so our discovery redefines our understanding of when human activity began to influence our climate. </p>
<p>Determining when global warming began, and how quickly the planet has warmed since then, is essential for understanding how much we have altered the climate in different parts of the world. Our study helps to answer the question of whether our climate is already operating outside thresholds that are considered safe for human society and functional ecosystems. </p>
<p>Our findings show that warming did not develop at the same time across the planet. The tropical oceans and the Arctic were the first regions to begin warming, in the 1830s. Europe, North America and Asia followed roughly two decades later. </p>
<p>Surprisingly, the results show that the southern hemisphere began warming much later, with Australasia and South America starting to warm from the early 20th century. This continental-scale time lag is still evident today: while some parts of Antarctica have begun to warm, a clear warming signal over the entire continent is still not detectable. </p>
<p>The warming in most regions reversed what would otherwise have been a cooling trend related to high volcanic activity during the preceding centuries. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/kKPFUdcrLP0?wmode=transparent&start=40" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Global warming got underway much earlier in the north.</span></figcaption>
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<p>By pinpointing the date when human-induced climate change started, we can then begin to work out when the warming trend broke through the boundaries of the climate’s natural fluctuations, because it takes some decades for the global warming signal to “emerge” above the natural climate variability.</p>
<p>According to our evidence, in all regions except for Antarctica, we are now well and truly operating in a greenhouse-influenced world. We know this because the only climate models that can reproduce the results seen in our records of past climate are those models that factor in the effect of the carbon dioxide released into the atmosphere by humans.</p>
<p>These remarkable findings were pieced together from the most unusual of sources – not thermometers or satellites, but rather from natural climate archives. These include coral skeletons, ice cores, tree rings, cave deposits and ocean and lake sediment layers, all of which record the climate as they grow or accumulate. </p>
<p>These archives provide long records that extend back 500 years – well before the Industrial Revolution – and provide a critical baseline for the planet’s past climate, one that is impossible to obtain otherwise. </p>
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<a href="https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/135282/original/image-20160824-30228-gvuwcc.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">Corals can help reveal the climate of centuries past, long before weather records began.</span>
<span class="attribution"><span class="source">Eric Matson/AIMS</span>, <span class="license">Author provided</span></span>
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<p>But why is there no clear warming fingerprint yet seen across Antarctica? The answer most likely lies in the vast Southern Ocean, which isolates the frozen continent from the warming happening elsewhere. </p>
<p>The westerly winds that circulate through the Southern Ocean around Antarctica keep warm air masses from lower latitudes at bay. Ozone depletion and rising greenhouse gas concentrations during the 20th century have also caused this wind barrier to get stronger. </p>
<p>The Southern Ocean currents that flow around Antarctica also tend to <a href="http://www.nature.com/ngeo/journal/v9/n7/full/ngeo2731.html">move warmer surface waters away from the continent</a>, to be replaced with cold deeper water that hasn’t yet been affected by surface greenhouse warming. This process could potentially delay Antarctica’s warming by centuries.</p>
<h2>Ocean insulation</h2>
<p>The delay in warming observed in the rest of the southern hemisphere is something we do not yet fully understand. It could simply be because fewer records are available from the southern hemisphere, meaning that we still don’t have a full picture of what is happening. </p>
<p>Alternatively, like Antarctica, the southern hemisphere’s oceans could be holding back warming – partly through winds and currents, but perhaps also because of “thermal inertia”, whereby the ocean can absorb far more heat energy than the atmosphere or the land before its temperature markedly increases. Bear in mind that the southern half of the globe has much more ocean than the north.</p>
<p>Essentially, then, the coolness of the southern hemisphere’s vast oceans could be “insulating” Australasia and South America from the impact of global warming. The question is, for how long?</p>
<p>If our evidence of delayed warming in the southern hemisphere holds true, it could mean we are in in for more climate surprises as global warming begins to overcome the thermal inertia of our surrounding oceans. Could the <a href="https://theconversation.com/this-summers-sea-temperatures-were-the-hottest-on-record-for-australia-heres-why-56906">recent record warming of Australian waters</a>, and the <a href="https://theconversation.com/how-will-the-barrier-reef-recover-from-the-death-of-one-third-of-its-northern-corals-60186">subsequent damage to the Great Barrier Reef</a>, be an early sign that this is already occurring? </p>
<p>Recent research suggest that the mass bleaching event of the reef was made <a href="https://theconversation.com/great-barrier-reef-bleaching-would-be-almost-impossible-without-climate-change-58408">175 times more likely by climate change</a>. Following the recent severity of such extremes, a better understanding of how anthropogenic greenhouse warming is already impacting the southern hemisphere is critical. </p>
<h2>What to do about it</h2>
<p>Leading scientists from around the world <a href="https://www.ipcc.ch/report/sr15/">met in Geneva</a> last week to discuss the goal of limiting average global warming to 1.5°C – the more ambitious of the two targets enshrined in the <a href="https://theconversation.com/the-paris-climate-agreement-at-a-glance-50465">Paris climate agreement</a>. </p>
<p>Last year, global temperatures crossed the <a href="https://www.ncdc.noaa.gov/bams">1°C threshold</a>, and 2016 is <a href="http://climate.nasa.gov/news/2465/2016-climate-trends-continue-to-break-records/">on track to be 1.2-1.3°C above our climate baseline</a>.</p>
<p>But here’s the kicker. That baseline is relative to 1850–1900, when most of our thermometer-based temperature records began. What our study shows is that for many parts of the world that estimate isn’t good enough, because global warming was already under way, so the real baseline would be lower.</p>
<p>The small increases in greenhouse gases during the 19th century had a small effect on Earth’s temperatures, but with the longer perspective we get from our natural climate records we see that big changes occurred. These fractions of a degree of extra warming might seem insignificant at first, but as we nudge ever closer to the 1.5°C guardrail (and <a href="https://theconversation.com/we-have-almost-certainly-blown-the-1-5-degree-global-warming-target-63720">potentially beyond</a>), the past tells us that <a href="https://theconversation.com/without-a-longer-term-view-the-paris-agreement-will-lock-in-warming-for-centuries-64169">small changes matter</a>.</p>
<hr>
<p><em>Helen McGregor will be online to answer your questions from 2pm AEST today. Post a query in the comments below.</em></p><img src="https://counter.theconversation.com/content/64301/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, Australia. </span></em></p><p class="fine-print"><em><span>Joelle Gergis receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Nerilie Abram receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Steven Phipps receives funding from the Australian Antarctic Science Program, the Australian Research Council, the International Union for Quaternary Research, the National Computational Infrastructure Merit Allocation Scheme, the New Zealand Marsden Fund, the University of Tasmania and UNSW Australia.</span></em></p>The first signs that humans were warming the climate appeared much earlier in the northern hemisphere - way back in the 1830s. But now the trend is emerging all over the globe.Helen McGregor, ARC Future Fellow, University of WollongongJoelle Gergis, ARC DECRA Climate Research Fellow, School of Earth Sciences, The University of MelbourneNerilie Abram, QEII Research Fellow, Australian National UniversitySteven Phipps, Paleo Ice Sheet Modeller, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/512792015-12-22T05:22:10Z2015-12-22T05:22:10ZWant to understand the decolonisation debate? Here’s your reading list<figure><img src="https://images.theconversation.com/files/105753/original/image-20151214-9515-br507i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">South Africa was hit by an unprecedented wave of student protests against fee hikes, racism and for the decolonisation of curriculum. </span> <span class="attribution"><span class="source">Reuters/Mike Hutchings</span></span></figcaption></figure><p><em>In 2015 the decolonisation debate, epitomised by the <a href="http://mg.co.za/article/2015-03-26-rhodesmustfall-protest-spreads-to-other-campuses">#RhodesMustFall</a> campaign, took centre stage in South Africa. The protests sought to remove all vestiges of racism and <a href="http://www.dispatchlive.co.za/opinion/decolonise-africas-mind/">colonialism</a> from university campuses. Below is my selection of the top five books that those interested in decolonisation might find helpful.</em></p>
<p><strong>1)</strong> <a href="http://www.amazon.com/Theory-South-Euro-America-Evolving-Imagination/dp/1594517657">Theory from the South: Or, How Euro-America is Evolving toward Africa</a> by Jean and John Comaroff. The book subverts the hallowed notion that knowledge comes from the global North, while the global South only provides the data. </p>
<p>The Comaroffs argue that it is the global South, particularly Africa, that is at the vanguard of global trends. They highlight themes relating to personhood, porous national boundaries and individual versus cultural rights. </p>
<p>They also reflect on democratic one-party states and offer critical perspectives on history as well as economic changes and political activism. In all, African perspectives offer innovative theoretical “scaffolding” to address global issues including xenophobia, economic downturn, democracy and HIV/AIDS. </p>
<p><strong>2)</strong> <a href="http://library.wur.nl/WebQuery/clc/1938849">Southern Theory: The Global Dynamics of Knowledge in Social Science</a> by Raewyn Connell describes southern theory from places such as Australia, Latin America, and Asia. She argues that while theory from the global North is universally accepted, southern theory is labelled according to its geographical place of origin. It is thus made out to be applicable only in those spaces. </p>
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<p>Connell also argues that the oligopolistic publishing industry relies on a few “celebrity” authors. Almost all of them come from the North and write in globally dominant languages. While this shows the cards stacked firmly against intellectuals from the so-called periphery, Connell asserts that such authors still have agency.</p>
<p><strong>3)</strong> <a href="http://www.ohioswallow.com/book/African+Intellectuals+and+Decolonization">African Intellectuals and Decolonization</a> is an anthology edited by Nicholas M. Creary. The essays explore themes relating to the struggle to decolonise African knowledge and the roles that African and Africanist intellectuals play in that struggle. </p>
<p>The first part unpicks representation and retrospection. It debunks commonly held perspectives that Africa’s decolonisation has failed or that it is all-encompassing. The second part explores perspectives on the struggle to decolonise African publics.</p>
<p>The third explores the decolonisation of knowledge. It reveals ways in which the tradition of Western metaphysical thought served to support colonialism and continues to impose Eurocentric values and norms onto African contexts.</p>
<p>Distinctly different African contexts are thus made to fit European models and are essentially misunderstood. The book’s abiding theme is the call from African scholars for African scholarship out of African contexts.</p>
<p><strong>4)</strong> <a href="http://www.amazon.com/Decolonizing-Methodologies-Research-Indigenous-Peoples/dp/1848139500">Decolonizing Methodologies: Research and Indigenous Peoples</a> by Linda Tuhiwai Smith. This offers a passionate discussion of the ways in which Eurocentric research methodologies and theories have affected indigenous communities. These communities are often put under a microscope, not unlike flora and fauna. </p>
<p>The book maps the historical implications of research from the global North. The second part describes indigenous methodologies coming out of work done by indigenous researchers and their communities. </p>
<p>The last two chapters, added to the second edition, describe the implications of choosing this kind of research and what it means to link research to activist scholarship.</p>
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<img alt="" src="https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=939&fit=crop&dpr=1 600w, https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=939&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=939&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1179&fit=crop&dpr=1 754w, https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1179&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/105107/original/image-20151209-15567-nmbhzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1179&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p>The book is written for indigenous researchers, but has also been well received by projects such as <a href="http://ccms.ukzn.ac.za/projects/rethinking-indigeneity.aspx">Rethinking Indigeneity</a> which I’m working on. </p>
<p>The first book from the project, by Keyan <a href="https://books.google.co.za/books/about/Where_Global_Contradictions_are_Sharpest.html?id=P_aTuPARGAkC&redir_esc=y">Tomaselli</a>, argues that the periphery is, in fact, the prism through which Northern methodological contradictions are best brought to the surface.</p>
<p><strong>5)</strong> Then there is the great granddad from whence much of the above discussion derives: Ngugi’ wa Thiong’o’s <a href="http://www.complete-review.com/reviews/kenya/ngugi1.htm">Decolonising the Mind: The Politics of Language in African Literature</a>. </p>
<p>Many of the works published on decolonisation originate from Ngugi’s idea of decolonising the African mind. Imperialism, he writes, has left its mark on the minds of the previously colonised. They personalise what was once far off and different and become detached from their immediate surrounds and culture. </p>
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<p>Africans are groomed for such thinking from childhood in colonial and missionary schools. They see Africa, its languages, cultures, traditions and practices as backward, dark, evil and generally disdainful. </p>
<p>The continent is carved up in terms of imperial markers and its peoples are identified in terms of their colonisers. Tragically, African leaders in the postcolony wish for the return to colonial rule, with themselves as the new masters.</p>
<p>Ngugi argues that African intellectuals bear responsibility for popularising the decolonisation struggle. The liberation of African minds is the ultimate goal.</p>
<p>The decolonisation <a href="https://theconversation.com/search?date=all&language=en&page=2&q=Rhodesmustfall&sort=relevancy&type=all">struggle</a> continues. The protests it has sparked in recent times should motivate us to take stock of its progress.</p><img src="https://counter.theconversation.com/content/51279/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shanade Bianca Barnabas received funding from the National Research Foundation during her PhD research. </span></em></p>Many works published on decolonisation originate from Ngugi wa Thiongo’s idea of decolonising the African mind. Imperialism, he writes, has left its mark on the minds of the previously colonised.Shanade Bianca Barnabas, Post doctoral research fellow, University of JohannesburgLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/140832013-05-15T23:23:05Z2013-05-15T23:23:05ZHow cold has it really been in the northern hemisphere?<figure><img src="https://images.theconversation.com/files/23885/original/m5hzxg36-1368650130.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's a good job they come with built-in jumpers.</span> <span class="attribution"><span class="source">PA/Niall Carson</span></span></figcaption></figure><p>If you are one of the many people with a larger than normal heating bill for recent months, you would probably be under the impression that it has been exceptionally cold in the northern hemisphere. We’ve experienced heavy snow on multiple occasions in the UK and seen images in the news of similarly frigid conditions in parts of mainland Europe and the United States. </p>
<p>In fact, some places experienced cold conditions, while other places experienced warmth that was anomalous for the time of year. These events were driven by unusual atmospheric circulation, which redistributed typical weather patterns across the northern hemisphere.</p>
<h2>Warm, with pockets of cold</h2>
<p>While some places were cold, the northern hemisphere was warmer than average in March, and indeed across the winter, consistent with long-term warming trends. The US National Climatic Data Centre (NCDC) has recently described such conditions as “<a href="http://www.ncdc.noaa.gov/news/local-isnt-global-pockets-cold-warming-world">pockets of cold in a warming world</a>”.</p>
<p>The last time the northern hemisphere recorded a month — any month — that was cooler than the 1961-1990 long-term average was in February 1994. The last time a whole northern hemisphere winter was colder than average was 1984.</p>
<p>Cold weather still happens — but it is less frequent, and most often less cold, than it was during most of the 20th century.</p>
<p>The month of March has been locally reported as being intensely cold in the northern hemisphere. But when averaged over the globe or the hemispheres, March 2013 was actually notable for its warmth. Globally, temperatures were 0.46°C above the 1961-1990 average, almost exactly matching average values of the last decade, and it was the tenth-warmest March on record for both the northern and southern hemispheres. In the northern hemisphere, it was a spring of extremes in particular places. But overall the warm regions more than cancelled out the cold regions, as the hemispheric average shows.</p>
<h2>What happened in March 2013?</h2>
<p>The major influence on the extreme conditions — both warm and cold — in March in the northern hemisphere was a highly abnormal air pressure pattern.</p>
<p>Under normal circumstances, winter sees high pressure systems sitting over subtropical latitudes and low pressure at higher latitudes (the “Azores high” and “Icelandic low”). The westerly winds between those two systems — the north Atlantic “storm track” — direct relatively mild maritime air over Europe, making its winters much warmer than those of most other places at the same latitude.</p>
<p>For example, the average winter temperature in Paris is more than 10°C warmer than Montreal, and 25°C warmer than Harbin in northeastern China, despite Paris being further north than these cities.</p>
<p>In March 2013 this situation was reversed, with persistent high pressure over the Arctic and sub-Arctic, and low pressure in the central Atlantic. Monthly averaged air pressure was well above normal near and north of Iceland, and well below normal west of Portugal.</p>
<p>This also reversed the usual airflow, directing easterly winds over northern and central Europe — which brought cold air, originating over Russia, across the continent.</p>
<h2>Weather in the northern hemisphere</h2>
<p>The result of the unusual pressure pattern was an extremely cold month in northern and central Europe. Monthly average temperatures were 5-7°C below normal in western Russia, much of Finland and the Baltic countries, and parts of Germany and Poland, and at least 3°C below normal over most remaining parts of the region.</p>
<p>March in the UK was the coldest since 1962 (and colder than any winter month between 1997 and 2009), and Germany had its fifth-coldest March since 1881. With the cold came unusual snowfalls in many regions, perhaps the most notable being falls of up to 25cm on the islands of Jersey and Guernsey on 11-12 March — an exceptional event for any time of year. Further south, temperatures were near normal, but under the influence of low pressure it was very wet. Large parts of Spain had their wettest March on record, with rainfall totals more than four times normal.</p>
<p>It was also a rather cold month in the eastern and central United States and adjacent parts of Canada, generally ranking between the 5th and 20th coldest of the last p00 years, although warm conditions in the west meant that the overall American average for the month came in at 0.5°C below normal. Notably, this followed another warmer than-average winter for the United States.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=365&fit=crop&dpr=1 600w, https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=365&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=365&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=459&fit=crop&dpr=1 754w, https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=459&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/23400/original/33drpvjp-1368067331.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=459&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Temperature anomalies (departures from average) for the entire globe showing cold areas of the northern hemisphere in March counterbalanced by warm conditions in the Arctic, and across northern Africa and most of Asia.</span>
<span class="attribution"><span class="source">NASA GISS</span></span>
</figcaption>
</figure>
<p>In the US, the month stood out for its contrast with the exceptionally warm March of 2012 — one example was in Chicago, where the maximum of −4°C on 20 March compared with a week of high 20s and low 30s at the same time last year.</p>
<p>In 2013, the contrast between cold air to the north and much warmer air further south has led to some wild fluctuations in temperature in some areas — one example being at Amarillo in west Texas, which had maximum temperatures of 32°C on 22 April and 2°C on the 23rd (even the cold fronts are bigger in Texas).</p>
<p>On the other side of the coin, it was much warmer than normal in many other parts of the northern hemisphere. Temperatures were well above average through most of central and eastern Asia outside of Russia, as well as in the northern half of Africa.</p>
<p>China had its second-warmest March on record, and monthly average temperatures were more than 7°C above normal in parts of Mongolia and eastern Kazakhstan. Large parts of the Arctic also experienced unusually high temperatures.</p>
<p>In the third week of March several days near 12°C, about 25°C above normal, occurred on the west coast of Greenland as far north as the Arctic Circle, and it was also much warmer (relatively speaking) than normal in much of the Canadian Arctic. Arctic sea-ice continued to be below average for March, following a record low at the end of the 2012 summer melt</p>
<p>As previously noted, and shown in the figure above, warmer than average conditions were more widespread across the Northern Hemisphere — and indeed the entire globe — during the month.</p>
<h2>Is there a link to climate change?</h2>
<p>One way of assessing how unusual the atmospheric conditions were in March is to make use of an index of atmospheric circulation, known as the Arctic Oscillation (AO) index.</p>
<p>This is an indicator of pressure patterns in the middle and high latitudes of the northern hemisphere. If pressure is above normal in the Arctic and below normal in the central North Atlantic and North Pacific, the <a href="http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/JFM_season_ao_index.shtml">AO index will be negative</a>. It will be positive if the Azores high and Icelandic low are both stronger than normal. </p>
<p>The monthly average value of the Arctic Oscillation index for March was −3.18, meaning very-much-higher pressure over the Arctic and lower pressure further south.</p>
<p>This easily broke the previous record low for March, −2.82 in 1962, and was the sixth-lowest value on record for any month. Three of the six lowest monthly AO values on record have now occurred in the last four years, including the lowest of all, −4.27 in February 2010. You may recall that winter 2010 was exceptionally cold and snowy in the UK, much like March 2013.</p>
<p>As March 2013 has demonstrated, extreme phases of the Arctic Oscillation redistribute warmth from one region to another — and this is significant for seasonal weather.</p>
<p>In terms of climate change, there is no clear long-term trend in average values of the Arctic Oscillation index. However, a <a href="https://doi.org/10.3402/tellusa.v64i0.11595">number</a> of <a href="https://doi.org/10.1073/pnas.1114910109">recent</a> model-based <a href="https://doi.org/10.1029/2009jd013568">studies</a> have suggested a possible link between decreased Arctic Ocean sea-ice cover, driven by global warming, and extreme phases of the Arctic Oscillation.</p>
<p>This is still a new and active area of research, and it is too early to draw firm conclusions. The possibility will need to be monitored closely over the coming years.</p>
<p>This highlights a very interesting aspect of weather and climate at the poles, and particularly in the Arctic. Powerful “feedback mechanisms” operate in this part of the world — that can transiently accelerate or slow the pace of global warming. The prime example is the loss of Arctic sea-ice, which tends to accelerate the rate of warming in the Arctic Ocean.</p>
<p>Extreme weather in any given season in the Arctic — such as a record summer melt or particularly warm winter — can actually have lasting impacts in a climate system that is being changed by greenhouse warming.</p><img src="https://counter.theconversation.com/content/14083/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>James Screen receives funding from the Natural Environment Research Council, UK.</span></em></p><p class="fine-print"><em><span>The Bureau of Meteorology provides Australians with environmental intelligence for their safety, sustainability, well-being and prosperity. Our weather, climate and water services include observations, alerts, warnings and forecasts for extreme events. Blair Trewin does not consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
</span></em></p><p class="fine-print"><em><span>The Bureau of Meteorology provides Australians with environmental intelligence for their safety, sustainability, well-being and prosperity. Our weather, climate and water services include observations, alerts, warnings and forecasts for extreme events. Karl Braganza does not consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.
</span></em></p>If you are one of the many people with a larger than normal heating bill for recent months, you would probably be under the impression that it has been exceptionally cold in the northern hemisphere. We’ve…James Screen, Research Fellow, Exeter Climate Systems Group, University of ExeterBlair Trewin, Climatologist, National Climate Centre, Australian Bureau of MeteorologyKarl Braganza, Manager, Climate Monitoring Section, Australian Bureau of MeteorologyLicensed as Creative Commons – attribution, no derivatives.