tag:theconversation.com,2011:/institutions/uni-research-2558/articlesUni Research2024-03-11T10:04:45Ztag:theconversation.com,2011:article/2185452024-03-11T10:04:45Z2024-03-11T10:04:45ZEast Africa must prepare for more extreme rainfall during the short rainy season – new study<p>East Africa has recently had an <a href="https://earthobservatory.nasa.gov/images/150712/worst-drought-on-record-parches-horn-of-africa">unprecedented series of failed rains</a>. But some rainy seasons are bringing the opposite: huge amounts of rainfall. </p>
<p>In the last few months of 2023, the rainy season, known as the “short rains”, was much wetter than normal. It brought severe flooding to Kenya, Somalia and Tanzania. In Somalia, <a href="https://news.un.org/en/story/2023/11/1144202">more than</a> 2 million people were affected, with over 100 killed and 750,000 displaced from their homes. Tens of thousands of people in northern Kenya <a href="https://www.euronews.com/green/2023/12/15/floods-have-washed-away-entire-villages-kenyas-rains-made-twice-as-intense-by-climate-chan">lost</a> livestock, farmland and homes. </p>
<p>The very wet short rainy seasons are linked to a climate event known as a positive Indian Ocean Dipole (known as the “IOD”). And climate model projections <a href="https://www.nature.com/articles/s41558-020-00943-1">show an increasing trend</a> of extreme Indian Ocean dipoles. </p>
<p>In a <a href="https://doi.org/10.1029/2023GL105258">new research paper</a>, we set out to investigate what effect more frequent extreme Indian Ocean Dipole events would have on rainfall in east Africa. We did this using a large number of climate simulations and models.</p>
<p>Our results show that they increase the likelihood of very wet days – therefore making very wet seasons. </p>
<p>This could lead to extreme weather events, even more extreme than the floods of 1997, which led to <a href="https://www.fao.org/3/w7832e/w7832e00.htm">10 million people requiring emergency assistance</a>, or those of 2019, when <a href="https://fews.net/east-africa/special-report/january-2020">hundreds of thousands were displaced</a>.</p>
<p>We recommend that decision-makers plan for this kind of extreme rainfall, and the resulting devastating floods.</p>
<h2>How the Indian Ocean Dipole works</h2>
<p>Indian Ocean Dipole events tend to occur in the second half of the year, and can last for months. They have two phases: positive and negative. </p>
<p>Positive events occur when the temperature of the sea surface in the western Indian Ocean is warmer than normal and the temperature in the eastern Indian Ocean is cooler than normal. Put simply, this temperature difference <a href="https://www.nature.com/articles/43854">happens when</a> winds move warmer water away from the ocean surface in the eastern region, allowing cooler water to rise. </p>
<p>In the warmer western Indian Ocean, more heated air will rise, along with water vapour. This forms clouds, bringing rain. Meanwhile, the eastern part of the Indian Ocean will be cooler and drier. This is why flooding in east Africa can happen at the same time as <a href="https://theconversation.com/indian-ocean-linked-to-bushfires-and-drought-in-australia-20893">bushfires in Australia</a>.</p>
<p>The opposite is true for negative dipole events: drier in the western Indian Ocean and wetter in the east. </p>
<p>Under climate change we’re expecting to see more frequent and more extreme positive dipole events – bigger differences between east and west. This is <a href="https://www.carbonbrief.org/guest-post-why-climate-change-will-cause-more-strong-indian-ocean-dipole-events/">shown by climate model projections</a>. They are believed to be driven by different paces of warming across the tropical Indian Ocean – with western and northern regions projected to warm faster than eastern parts.</p>
<p>Often heavy rain seasons in east Africa are attributed to El Niño, but <a href="https://rmets.onlinelibrary.wiley.com/doi/10.1002/asl.1015">recent research</a> has shown that the direct impact of El Niño on east African rainfall is actually relatively modest. El Niño’s principal influence lies in its capacity to bring about positive dipole events. This occurs since El Niño events tend to cool the water in the western Pacific Ocean – around Indonesia – which also helps to cool down the water in the eastern Indian Ocean. These cooler temperatures then help kick-start a positive Indian Ocean Dipole.</p>
<h2>Examining unprecedented events</h2>
<p>Extreme positive Indian Ocean Dipole events are rare in the recent climate record. So to examine their potential impacts on rainfall extremes, we used a large set of climate simulations. The data allowed us to diagnose the sensitivity of rainfall to larger Indian Ocean Dipole events in a statistically robust way.</p>
<p>Our results show that as positive dipole events become more extreme, more wet days during the short rains season can be expected. This effect was found to be largest for the frequency of extremely wet days. Additionally, we found that as the dipole strength increases, the influence on the most extreme days becomes even larger. This means that dipole events which are even slightly “record-breaking” could lead to unprecedented levels of seasonal rainfall. </p>
<p>Ultimately, if positive Indian Ocean Dipole seasons increase in frequency, as predicted, regular seasons of flooding impacts will become a new normal.</p>
<p>One aspect not included in our analysis is the influence of a warmer atmosphere on rainfall extremes. A warmer atmosphere <a href="https://www.carbonbrief.org/explainer-what-climate-models-tell-us-about-future-rainfall/">holds more moisture</a>, allowing for the development of more intense rain storms. This effect could combine with the influence of extreme positive dipoles to bring unprecedented levels of rainfall to the Horn of Africa. </p>
<p>2023 was <a href="https://wmo.int/media/news/wmo-confirms-2023-smashes-global-temperature-record">a year of record-breaking temperatures driven both by El Niño and global warming</a>. We might expect that this warmer air could have intensified rain storms during the season. Indeed, evidence from <a href="https://www.worldweatherattribution.org/climate-change-indian-ocean-dipole-compounding-natural-hazards-and-high-vulnerability-increased-severity-of-flooding-in-the-horn-of-africa/">a recent assessment</a> suggests that climate change-driven warming is highly likely responsible for increased rainfall totals. </p>
<h2>Responding to an unprecedented future</h2>
<p>Policymakers need to plan for this. </p>
<p>In the long term it is crucial to ensure that any new infrastructure is robust to withstand more frequent and heavier rains, and that government, development and humanitarian actors have the capacity to respond to the challenges.</p>
<p>Better use of technology, such as innovations in <a href="https://fastaweather.com/">disseminating satellite rainfall monitoring via mobile phones</a>, can communicate immediate risk. <a href="https://www.science.org/content/article/ai-churns-out-lightning-fast-forecasts-good-weather-agencies">New frontiers in AI-based weather prediction</a> could improve the ability to anticipate localised rain storms, including <a href="https://www.wfp.org/publications/2023-machine-learning-early-warning-systems">initiatives focusing on eastern Africa</a> specifically. </p>
<p><a href="https://www.youtube.com/watch?v=9g_06jBU-ag">Linking rainfall information with hydrological models designed for dryland environments</a> is also essential. These will help to translate weather forecasts into impact forecasts, such as identifying risks of flash flooding down normally dry channels or bank overflow of key rivers in drylands.</p>
<p>These technological improvements are crucial. But better use of the forecast information we already have can also make a big difference. For instance, initiatives like <a href="https://www.climatecentre.org/priority_areas/fbf-ibf/">“forecast-based financing”</a>, pioneered by the Red Cross Red Crescent movement, link forecast triggers to pre-approved financing and predefined action plans, helping communities protect themselves before hazards have even started.</p>
<p>For these endeavours to succeed, there must be dialogue between the science and practitioner communities. The scientific community can work with practitioners to integrate key insights into decisions, while practitioners can help to ensure research efforts target critical needs. With this, we can effectively build resilience to natural hazards and resist the increasing risks of our changing climate.</p><img src="https://counter.theconversation.com/content/218545/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Erik W. Kolstad receives funding from the European Union’s Horizon 2020 programme through the CONFER project (grant 869730)</span></em></p><p class="fine-print"><em><span>Katerina Michaelides receives funding from EU H2020, the FCDO and the Leverhulme Trust. </span></em></p><p class="fine-print"><em><span>Michael Singer receives funding from the European Union's Horizon 2020 Programme. </span></em></p><p class="fine-print"><em><span>David MacLeod 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>Projections show that there’ll be Indian Ocean dipoles in the future – and that means more rainy days, and more extreme rainfall.David MacLeod, Lecturer in Climate Risk, Cardiff UniversityErik W. Kolstad, Research professor, Uni ResearchKaterina Michaelides, Professor of Dryland Hydrology, School of Geographical Sciences, University of BristolMichael Singer, Professor of Hydrology and Geomorphology, Cardiff UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/925902018-03-02T04:06:12Z2018-03-02T04:06:12ZThe freak warm Arctic weather is unusual, but getting less so<figure><img src="https://images.theconversation.com/files/208423/original/file-20180301-152590-1i2v0gk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Research Vessel Lance in the middle of broken Arctic sea ice after a large warm winter storm in February 2015.</span> <span class="attribution"><span class="source">Nick Cobbing</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The Arctic has been unusually warm since the beginning of 2018. In the past week air temperatures have hovered around 20°C above normal or even higher. On February 25, the Cape Morris Jesup weather station in northern Greenland recorded 6.1°C, despite the fact that at this time of year, when the sun is still below the horizon, temperatures are typically around -30°C. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208260/original/file-20180228-36683-8lx7xb.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">Daily Arctic temperatures in 2018 (thick red line), for 1958-2002 (thin lines) and the average for 1958-2002 (thick white line).</span>
<span class="attribution"><span class="source">Zack Labe</span></span>
</figcaption>
</figure>
<p>A surprising feature of this warming event was how far into (and beyond) the Arctic it has penetrated. Warm air migrated north from the Atlantic Ocean, over the North Pole and towards the Pacific Ocean, bringing above-freezing air temperatures to large areas of the Arctic Ocean for more than 24 hours. </p>
<p>We have not seen a warm intrusion from the Atlantic Ocean on this scale since at least 1980.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=544&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=544&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=544&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=684&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=684&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208461/original/file-20180301-152569-q8tv2h.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=684&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Air temperatures at 3pm on February 25, 2018, based on GFS forecast. The warm air incursion is clearly visible in green.</span>
<span class="attribution"><span class="source">ClimateReanalyzer.org/University of Maine</span></span>
</figcaption>
</figure>
<h2>Is this unprecedented?</h2>
<p>Warm events in the middle of the northern winter are not unheard of. Large winter storms can bring strong winds that pump warm air into the Arctic from lower latitudes. </p>
<p>For example, during the Norwegian explorer Fridtjof Nansen’s <a href="http://frammuseum.no/polar_history/expeditions/the_first_fram_expedition__1893-1896_/">1896 expedition aboard the icebreaker <em>Fram</em></a>, the crew <a href="http://doi.org/10.1002/2017GL073395">observed temperatures of -3°C</a> on one midwinter’s day. More recently, in December 2015, an <a href="http://doi.org/10.1038/srep39084">Arctic warming event</a> brought <a href="https://journals.ametsoc.org/doi/10.1175/MWR-D-16-0234.1">temperatures of 2°C to the North Pole</a>, and the warm weather <a href="https://www.nature.com/articles/srep40051">continued into early 2016</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=230&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=230&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=230&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=289&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=289&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208446/original/file-20180301-152569-1l3jaun.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=289&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Winter warming events at the North Pole. Number of days each winter when the air temperature exceeds a given threshold.</span>
<span class="attribution"><span class="source">Graham et al., 2017</span></span>
</figcaption>
</figure>
<p>But, crucially, this type of event is <a href="http://onlinelibrary.wiley.com/doi/10.1002/2017GL073395/abstract">becoming more common and longer in duration, with higher peak temperatures</a>.</p>
<h2>Record low sea ice extent</h2>
<p>February 26 brought a new record low for sea ice extent: maximum sea ice extent on that day was <a href="http://sites.uci.edu/zlabe/arctic-sea-ice-extentconcentration/">14.20 million square kilometres</a>, which is 1.29 million km<sup>2</sup> below the <a href="https://nsidc.org/data/seaice_index">1981-2010 average for that day</a>. This follows several years with record low winter maximum sea ice extents in <a href="http://nsidc.org/arcticseaicenews/2017/03/arctic-sea-ice-maximum-at-record-low/">2015, 2016 and 2017</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208419/original/file-20180301-152587-1fknqpg.png?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">Arctic sea ice extent for January and February 2018 (orange line), compared with the 1980s average (purple line), 1990s average (cyan line), and 2000s average (blue line).</span>
<span class="attribution"><span class="source">Zack Labe/JAXA AMSR2</span></span>
</figcaption>
</figure>
<p>The current warm conditions in the Arctic have implications for sea ice year-round. Sea ice grows in winter and melts in summer. The warm air temperatures will slow down sea ice growth, and strong winds will push it around, breaking it up in places – as happened <a href="https://twitter.com/seaice_de/status/968043600490717184">north of Greenland earlier this week</a>. </p>
<p>Open water where the ice is broken will release extra heat into the atmosphere. By the time the spring sun comes around, the sea ice pack is thinned and weakened, and <a href="https://journals.ametsoc.org/doi/10.1175/JCLI-D-15-0773.1">may melt more easily</a>.</p>
<h2>Cold weather in Europe</h2>
<p>While the Arctic has been hot, Europe has been bitterly cold this week: London recorded -6°C; Berlin reached -14°C; and the Alps plunged to -27°C. Rome received 5-15cm of snow on Monday, and up to 40cm of snow fell in Britain on Wednesday. </p>
<p>It might sound counter-intuitive, but this cold weather is directly linked to the recent warming event in the Arctic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=475&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=475&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=475&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=597&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=597&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208359/original/file-20180228-36706-y9onp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=597&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 for February 25, 2018, showing a warm Arctic and cold Europe and parts of Russia. Browns and reds indicate above-average temperatures; blues indicate below-average temperatures.</span>
<span class="attribution"><span class="source">Climate Re-analyzer/University of Maine</span></span>
</figcaption>
</figure>
<p>Normally, the cold air above the polar region is contained in the Arctic by a ring-like band of strong winds called the polar vortex. But in the middle of February this year, the polar vortex split into two vortices: one over Eurasia and the other over North America. </p>
<p>Between these two features, a strong high-pressure system gradually formed. As a result, warm air was pumped up into the Arctic on the west side of the high, while cold air was channelled southwards to the east of it. Hence the exceptionally warm air in the Arctic and the cold snap in Europe.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=501&fit=crop&dpr=1 600w, https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=501&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=501&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=629&fit=crop&dpr=1 754w, https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=629&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/208434/original/file-20180301-152559-1p5dzri.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=629&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Illustration of the Arctic polar vortex and northern hemisphere weather patterns.</span>
<span class="attribution"><span class="source">XNR Productions</span></span>
</figcaption>
</figure>
<h2>Is the polar vortex changing?</h2>
<p>The polar vortex is driven by the strong temperature differences between the warm mid-latitudes and the cold Arctic. With the Arctic warming more rapidly than the mid-latitudes, this temperature difference is decreasing and some scientists believe that the polar vortex is weakening. </p>
<p><a href="http://onlinelibrary.wiley.com/doi/10.1029/2012GL051000/abstract">Research</a> <a href="http://doi.org/10.1088/1748-9326/10/1/014005">suggests</a> that the polar vortex has become “wavier” as a result of this weakening. A wavier jet stream would lead to more frequent cold outbreaks of polar air at lower latitudes, and at the same time cause <a href="https://journals.ametsoc.org/doi/10.1175/JCLI-D-14-00822.1">warm air to intrude into the Arctic</a>. However, other researchers have argued that “<a href="https://www.nature.com/articles/ngeo2234">large uncertainties regarding the magnitude of such an influence remain</a>”. </p>
<p>Generally speaking, warming at every latitude makes <a href="https://www.nature.com/articles/nclimate2268">cold spells at low latitudes less likely, and warm intrusions at high latitudes more likely</a>, unless the Arctic warming leads to a fundamental change in the dynamics of the atmosphere.</p>
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Read more:
<a href="https://theconversation.com/climate-shenanigans-at-the-ends-of-the-earth-why-has-sea-ice-gone-haywire-69485">Climate shenanigans at the ends of the Earth: why has sea ice gone haywire?</a>
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<p>Since 1979, Arctic warming events have <a href="http://iopscience.iop.org/article/10.1088/1748-9326/aa7def/meta">grown more frequent</a>. However, climate projections indicate that there will be fewer Arctic storms in the latter part of this century, and thus <a href="https://link.springer.com/article/10.1007%2Fs00382-017-3767-x">fewer Arctic warming events</a>.</p>
<p>As scientists, we were startled by the extent of this week’s Arctic warming, and will be working hard to understand the short- and long-term implications. All eyes will be on the upcoming maximum winter Arctic sea ice extent, which is likely to happen in the next few weeks and could possibly set a new record low.</p><img src="https://counter.theconversation.com/content/92590/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amelie Meyer receives funding from Norwegian Polar Institutes Centre for Ice, Climate and Ecosystems (ICE) through the N-ICE project.</span></em></p><p class="fine-print"><em><span>Erik Kolstad receives funding from the European Commission and the Research Council of Norway. </span></em></p><p class="fine-print"><em><span>Mats Granskog receives funding from the Norwegian Polar Institutes Centre for Ice, Climate and Ecosystems (ICE). </span></em></p><p class="fine-print"><em><span><a href="mailto:robert.graham@npolar.no">robert.graham@npolar.no</a> receives funding from the Norwegian Polar Institutes Centre for Ice, Climate and Ecosystems. </span></em></p>The bizarre heatwave in the Arctic this week – with temperatures dozens of degrees above normal – is part of a growing trend of “warm air intrusions” that threaten to disrupt polar ice all year round.Amelie Meyer, Postdoctoral Researcher, Physical Oceanography, Norwegian Polar InstituteErik W. Kolstad, Research professor, Uni ResearchMats Granskog, Senior research scientist, Norwegian Polar InstituteRobert Graham, Postdoctoral Researcher, Climate Modelling, Norwegian Polar InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/569422016-04-14T03:24:39Z2016-04-14T03:24:39ZMarine sediments unlock secrets about climate change in South Africa<figure><img src="https://images.theconversation.com/files/118333/original/image-20160412-15861-16u3eog.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ocean sediments in South Africa provide evidence of climate variation going back 270,000 years.</span> <span class="attribution"><span class="source">Rogan Ward/Reuters</span></span></figcaption></figure><p>Climate change <a href="https://ipcc-wg2.gov/AR5/images/uploads/WGIIAR5-Chap22_FINAL.pdf">projections</a>
suggest that droughts will intensify in most parts of South Africa by the end of the 21st century. This is due to reduced precipitation and the loss of water through the combination of evaporation and plant transpiration. The majority of <a href="http://www.nature.com/nclimate/journal/v5/n9/pdf/nclimate2735.pdf">climate models predict</a> that most southern African countries will warm more than the global mean by 2-3°C. This warming will simulate stronger reductions in precipitation. </p>
<p>But these changes might not happen uniformly across South Africa. The southwestern Cape and Limpopo province seem to be the regions affected most from <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.1742/full">rainfall reductions</a>. On the other hand, wetter conditions are <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.1314/abstract">projected</a> in the southeast and along the Drakensberg mountain range.</p>
<p>While seasonal fluctuations in rainfall are normal, rainfall that is substantially below or above average can have serious negative effects. For example, during the 2007 El Niño-related drought in southern Africa, rainfall averaged 50mm-200mm below <a href="http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-89-7-StateoftheClimate">normal</a> rainfall season levels during the most critical period for crops. This caused significant crop damage. </p>
<p><a href="http://onlinelibrary.wiley.com/doi/10.1029/2008GL034180/abstract">Future precipitation projections</a> indicate that both these extremes – droughts as well as flooding – may become more frequent in the future. But do these climate predictions deviate from past natural climate variability? And is the projected change within the range of historical natural variability?</p>
<h2>A silent witness of climate change</h2>
<p>Marine sediments – solid, natural elements that are broken down by processes of weathering and erosion, and collect on the ocean floor – provide evidence of climate variation over time. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=464&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=464&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=464&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=583&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=583&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118527/original/image-20160413-23631-62w9lu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=583&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Studies show that the South African climate changed periodically between long-term droughts and
wet conditions approximately every 23,000 years.</span>
<span class="attribution"><span class="source">Margit Simon</span></span>
</figcaption>
</figure>
<p>These sediment cores offer a journey through time: the longer the sediment core, the longer you are able to go back in time. For example, analysis of sediments delivered into the southwest Indian Ocean from rivers flowing off eastern South Africa can provide evidence of climate variability going back as far as 270,000 years. </p>
<p>Several rivers make their way through KwaZulu-Natal and the Eastern Cape provinces in South Africa before entering the Indian Ocean. During the rainy season they transport more water – and hence more sediment – into the ocean. The composition of the sediment – for example, the amount of iron it carries – also differs between wet and dry periods. In tropical and subtropical humid regions, high precipitation promotes intense chemical weathering of bedrocks. This results in highly weathered soils whose geo-chemical signature, rich in iron, is transferred to marine sediments. </p>
<p>Our <a href="http://www.nature.com/ncomms/journal/v4/n5/full/ncomms2897.html">analysis of marine sediment cores</a> found that South Africa experienced rapid climate transitions toward wetter conditions at times when the Northern Hemisphere experienced extremely cold conditions during the last glacial cycle. These cold phases were associated with slow-downs of the global ocean circulation, which transports warm water from the tropics northwards in the Atlantic Ocean. </p>
<p>Warm tropical and subtropical waters remained longer in the Southern Hemisphere, allowing warm and wet conditions to prevail in South Africa for centuries to thousands of years at a time between 100,000 and 40,000 years ago. The <a href="http://www.sciencedirect.com/science/article/pii/S0012821X13005463">Agulhas Current</a> adjacent to South Africa warmed during that time. This potentially provided heat and moisture for additional rainfall on land. </p>
<p>In addition, our <a href="http://www.nature.com/articles/srep18153">most recent study</a> of a 10m-long sediment archive off the KwaZulu-Natal coast tells the story of climate variation over the past 270,000-odd years. The study, of sediment washed into the Indian Ocean via the Thukela River, reveals that climate changed periodically between long-term droughts and wet conditions approximately every 23,000 years. These cycles were caused by changes in the amount of solar radiation reaching subtropical South Africa. </p>
<p>The reason for this is that every 23,000 years the summer season in southern Africa occurs when the earth is closer to the sun during its orbit. So it receives slightly more solar radiation, warming the land more intensely. This creates changes in winds blowing over the Indian Ocean towards eastern South Africa, bringing more intense rainfall.</p>
<h2>Climate change and human evolution</h2>
<p>There is a striking correspondence between the archaeological record of South Africa and the timing of the abrupt climate change, as derived from <a href="http://www.nature.com/ncomms/journal/v4/n5/full/ncomms2897.html">marine sediments</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=493&fit=crop&dpr=1 600w, https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=493&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=493&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=619&fit=crop&dpr=1 754w, https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=619&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/118526/original/image-20160413-23631-13rpn6b.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=619&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bifacial points recovered from Blombos Cave, South Africa. The Middle Stone Age tools are made of silcrete and finished by pressure flaking.</span>
<span class="attribution"><span class="source">Christopher Henshilwood/University of the Witwatersrand</span></span>
</figcaption>
</figure>
<p>Modern humans, <em>Homo sapiens</em>, first evolved in Africa about 200,000 years ago. South Africa offers an unprecedented variety of archaeological sites that provide compelling evidence for the emergence of modern human behaviour. One example is the use of personal ornaments and the development of complex adaptive strategies during the Middle Stone Age, about 280,000 to 30,000 years ago.</p>
<p>What shaped human cultures during this time is an ongoing debate and the subject of many <a href="https://www.youtube.com/watch?v=Dd_hw4kBPg0">research activities</a>. </p>
<p>Comparing the history of hydrological changes in the region with artefacts from the Middle Stone Age <a href="http://www.nature.com/ncomms/journal/v4/n5/abs/ncomms2897.html">showed</a> a striking correspondence. Climate-driven pulses in southern Africa were probably fundamental to the origin of key elements of modern human behaviour in Africa. But also to the subsequent dispersal of <em>Homo sapiens</em>.</p>
<p>One of the reasons for this is that humans need water, plants need water and so, too, do the animals that humans hunt and eat. These conditions are favourable for population growth. As human population density increases, people are able to network more readily, share ideas and invent technologies. </p>
<p>Looking ahead, many of the projected changes in climate are within the range of historical natural variability. But there are also significant changes that exceed the range of natural climate variability. The main difference between the climate change happening now and that of the geological record is the timing in which these changes occur: climate changes today are occurring at an unprecedented rate.</p><img src="https://counter.theconversation.com/content/56942/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Margit Simon works for Uni Research Climate/Bjerknes Centre for Climate Research, Norway& Cardiff University, UK. She received funding from European Commission 7th Framework Marie Curie People programme FP7/2007-2013 through funding of the Initial Training Network “GATEWAYS” (<a href="http://www.gateways">www.gateways</a> itn.eu) under the grant number 238512, the Climate Change Consortium of Wales. </span></em></p>Marine sediments provide evidence of climate variability in South Africa going back 270,000 years. These changes correspond with changes in the archaeological record of the country.Margit Simon, Postdoctoral Fellow, Uni ResearchLicensed as Creative Commons – attribution, no derivatives.