tag:theconversation.com,2011:/id/topics/nature-climate-change-journal-9013/articlesNature Climate Change (journal) – The Conversation2014-06-16T15:36:16Ztag:theconversation.com,2011:article/280172014-06-16T15:36:16Z2014-06-16T15:36:16ZArctic warming will bring fewer cold weather extremes<figure><img src="https://images.theconversation.com/files/51214/original/fqs6n5yt-1402930085.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In the deep freeze.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/akasped/11808898455/">akasped</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The climate is warming, and so basic logic would suggest we should expect fewer bouts of cold weather. Yet severe winter weather, such as the cold wave over the US this year, and the chilly winter of 2009/10 in the UK have left people questioning this assumption. </p>
<p>In early January 2014, across North America <a href="http://www.pmel.noaa.gov/arctic/atmosphere/polar_vortex_2014.html">record minimum temperatures</a> for the date were set at many weather stations, including at Chicago O’Hare Airport (-26.7°C, January 6), New York Central Park, (-15.6°C/4°F, January 7) and Washington DC Dulles Airport (-17.2°C, January 7). Daily maximum snowfall records were also broken at several stations. The cold temperatures and heavy snowfall caused widespread disruption to transport and power supply, closure of work places and public services, and damage to crops.</p>
<p>Unsurprisingly given the disruption, the national and global media extensively reported the cold wave, including debate on whether or not human-induced climate change was partly responsible. One particular hypothesis garnered a lot of attention: the suggestion that rapid Arctic warming and associated sea ice loss may be increasing the risk of cold extremes. </p>
<p>The theory goes something like this: as the Arctic has warmed more rapidly than places further south, a phenomenon known as <a href="http://www.skepticalscience.com/What-causes-Arctic-amplification.html">Arctic amplification</a>, the north-south temperature gradient has weakened. This temperature gradient powers the <a href="http://www.metoffice.gov.uk/learning/wind/what-is-the-jet-stream">jetstream</a>, a strong wind, high in the atmosphere that marks the boundary between cold Arctic air and warmer air to the south. A weaker north-south temperature gradient may cause a weaker jetstream. It’s also argued that a weaker jetstream will meander more, a bit like a river meanders more when the current is slower. When large southward meanders develop, Arctic air pushes south leading to cold conditions. This hypothesis has led to recent claims that Arctic warming will lead to more cold weather.</p>
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<img alt="" src="https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=460&fit=crop&dpr=1 754w, https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=460&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/51211/original/qmjktn2y-1402927967.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=460&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><a class="source" href="http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml">UIUC</a></span>
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<p>My <a href="http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2268.html">latest research</a> published in the Nature Climate Change journal, analyses thousands of weather records and suggest a more important – and remarkably simple – connection between Arctic warming and our weather. This link implies the opposite, that rapid Arctic warming will lead to fewer, not more, cold extremes.</p>
<p>Generally speaking (in the northern hemisphere), when the wind blows from the north temperatures tend to be colder than average. Conversely, when the wind blows from the south temperatures tend to be warmer than average. Cold extremes, those really cold days, occur most frequently when the wind is from the north. This is no real surprise, as the poles are cold and the tropics and equator to our south are warm.</p>
<p></p>
<p>What the data shows, however, is that days in autumn and winter with northerly winds (blowing from the north) have warmed significantly more than days with southerly winds. The result is a levelling off of temperatures at a new, warmer average as cold days’ temperatures rise towards the temperatures of warm days faster than the warm days themselves increase in temperature. Scientists call this a decrease in temperature variance, and it implies fewer temperature extremes, in this case notably fewer cold extremes.</p>
<p>Again, this makes perfect sense if you consider that the Arctic has warmed more rapidly than places further south. Cold northerly winds are not as cold as they were in the past, because the Arctic air they bring is, like the rest of the Arctic, <a href="https://nsidc.org/cryosphere/arctic-meteorology/climate_change.html">considerably warmer than it once was</a>.</p>
<p>The latest climate models suggest that these changes will continue and become more widespread in the future. I examined simulations from 34 different climate models, each run with projected increases in greenhouse gas concentrations. The models all agree that temperatures will warm in all seasons. Towards the pole beyond 40 degrees north, which includes large parts of US, Europe and Asia, temperatures are anticipated to become less variable in all seasons <a href="https://theconversation.com/batten-the-hatches-as-summers-to-have-more-heavy-downpours-27408">except summer</a>. A warmer and less variable climate has fewer cold extremes. </p>
<p>There is still a lot to understand about how the dramatic changes occurring in the Arctic will affect weather patterns further south – in particular, if and how the jetstream might be affected will be vital. But there is strong evidence that Arctic warming is taking the edge off those cold northerly winds, meaning the risk of extreme cold waves like that experienced in the US becomes rarer still. </p><img src="https://counter.theconversation.com/content/28017/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>The climate is warming, and so basic logic would suggest we should expect fewer bouts of cold weather. Yet severe winter weather, such as the cold wave over the US this year, and the chilly winter of 2009/10…James Screen, Research Fellow, Exeter Climate Systems Group, University of ExeterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/274082014-06-02T04:56:45Z2014-06-02T04:56:45ZBatten the hatches as summers to have more heavy downpours<p>The state of the British summer has always been a constant source of fascination and irritation, if only for its fickle nature. Now the latest prediction is for more heavy summer downpours.</p>
<p>Our <a href="http://dx.doi.org/10.1038/nclimate2258">study</a>, published in the journal Nature Climate Change, shows the first evidence that summer downpours in the UK could become heavier with climate change. We used a very high-resolution model more typically used for weather forecasting to study changes in hourly rainfall. Unlike current climate models, this has a fine resolution and is able to realistically represent hourly rainfall, so this allows us to make these future projections with some confidence. </p>
<p>What we found was that summers are likely to become drier overall by 2100, in a warming climate. But our results suggest that when it does rain, it will be heavier in short outbreaks. In particular, intense rainfall with the potential to cause serious flash flooding (more than 30mm in an hour) could become a more common occurrence, increasing in frequency by several times.</p>
<p>What the study provides is a much more complete picture of how UK rainfall may change in the future. Climate models generally work at coarse resolutions, using grids of around 12km square or larger. These have been able to accurately simulate winter rainfall, which generally comes from sustained, long-lasting periods of rain from large-scale weather systems. These models point toward wetter winters, with the potential for greater daily rainfall in the future.</p>
<p>But summer weather is harder to predict using such coarse models. It is changes on an hourly basis that are important, as rainfall tends to come in short but intense bursts during the summer – as seen during the <a href="http://www.metoffice.gov.uk/education/teens/case-studies/boscastle">Boscastle flooding of 2004</a> and “Toon Flood” in <a href="http://www.bbc.co.uk/news/uk-england-tyne-19714379">Newcastle in 2012</a>. So far climate models have lacked the resolution to accurately simulate the smaller-scale convective storms (intense showers formed by rising air) which cause this type of rain. To deal with this issue, our study uses the most high-resolution model ever used before in long climate simulations to examine rainfall change, based on a 1.5km square grid (the same as the UK Met Office Weather Forecast model), leading to much higher accuracy.</p>
<p>We ran this model to simulate two 13-year periods, one based on the current climate and one based on the climate at the end of the century under a high-emissions scenario (the <a href="http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/aug/30/climate-change-rcp-handy-summary">IPCC’s RCP8.5 scenario</a>). The simulations were so computationally intensive that it took the Met Office’s supercomputer – one of the world’s most powerful – about nine months to run the simulations, and even then we could only run the model for the southern half of the UK, about as far north as Manchester.</p>
<p>The simulation showed increased hourly rainfall intensity during winter, consistent with the simulations for the future provided by coarser resolution models and previous studies looking at changes on daily timescales. However the finely grained model also revealed that short-duration rain will become more intense during summer, something that the coarser model was unable to simulate. This finding is of major importance due to the potential for flooding: a threshold of 30mm per hour is used by the <a href="http://www.ffc-environment-agency.metoffice.gov.uk/">Met Office and Environment Agency Flood Forecasting Centre</a> as guidance to indicate likely flash flooding, and our results suggest this may be exceeded more often (up to five times) and over a wider area in the future.</p>
<p>Our findings are only the results of one climate model and we need to wait for other centres to run similarly detailed simulations to see whether their results support these findings. However, an increase in summer storms in a warmer, moister environment is consistent with theoretical expectations, and with the limited observational studies we have of hourly rainfall to date.</p>
<p>This work is part of the joint Met Office and NERC-funded <a href="https://research.ncl.ac.uk/convex/aboutourresearch/">CONVEX</a> project. The next steps are to see if the results are consistent with observations and predictions of hourly rainfall from climate models in other parts of the world, to be undertaken by the European Research Council-funded INTENSE project jointly run by Newcastle University academics in collaboration with the UK Met Office and other leading international scientists.</p><img src="https://counter.theconversation.com/content/27408/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Elizabeth Kendon gratefully acknowledges funding from the Joint DECC/Defra Met Office Hadley Centre programme (GA01101). This work forms part of a joint Met Office NERC funded project CONVEX (NE/1006680/1).</span></em></p><p class="fine-print"><em><span>Prof Hayley J. Fowler receives funding from the Natural Environment Research Council, the European Research Council and the Leverhulme Trust.</span></em></p>The state of the British summer has always been a constant source of fascination and irritation, if only for its fickle nature. Now the latest prediction is for more heavy summer downpours. Our study…Elizabeth Kendon, Senior Climate Scientist, Met Office Hadley CentreHayley J. Fowler, Professor of Climate Change Impacts, Newcastle UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/231102014-02-17T14:55:46Z2014-02-17T14:55:46ZAfter the flood: finding ways to insure the uninsurable without breaking the bank<figure><img src="https://images.theconversation.com/files/41616/original/w9g8x6bb-1392567651.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How to insure the uninsurable?</span> <span class="attribution"><span class="source">Matt Alexander/PA </span></span></figcaption></figure><p>More wet and windy weather arrives week after week, with the inundated areas of the south and southwest of Britain still at the mercy of the elements. Even while politicians begin <a href="http://www.theguardian.com/environment/2014/feb/10/uk-floods-cameron-ministers-flooding">the blame game</a>, we should look further ahead to when the floodwaters recede, the clean-up begins – and talk turns to who will pay.</p>
<p>In most countries, the government plays a role in covering flood losses. The UK is unusual because the government does not award compensation directly to individuals. Money is provided to local authorities through the <a href="https://www.gov.uk/government/publications/bellwin-scheme-2013-to-2014-guidance">Bellwin Scheme</a> to reimburse the costs of emergency measures taken to safeguard life or property. But this is only intended to cover uninsurable risk.</p>
<p>Damage to private property is considered insurable and is not covered, which means compensation is drawn from the insurance industry, or charitable aid. The <a href="http://www.princescountrysidefund.org.uk/news-events/news/prince%E2%80%99s-countryside-fund-gives-emergency-funding-flood-devastated-rural-communitie">Prince’s Countryside Fund</a> and the Duke of Westminster were among the first to make donations to help the flood victims, donating £50,000 each. As the floods continue, other <a href="https://www.gov.uk/government/news/pm-welcomes-action-from-businesses-in-support-of-flood-victims">businesses have pledged support</a>. The government has also announced new measures, including a <a href="https://www.gov.uk/government/news/new-measures-to-help-communities-hit-by-flooding#repair-renew">£5,000 grant to households and businesses</a> to pay for repairs which improve a property’s ability to withstand future flooding. But most of those with property underwater will have to rely on insurance.</p>
<h2>Unchartered waters</h2>
<p>Big changes have swept through Britain’s flood insurance landscape. Until last July, flood insurance cover was available to households and small businesses as a standard feature of buildings and contents insurance under the <a href="https://www.abi.org.uk/Insurance-and-savings/Topics-and-issues/Flooding/Government-and-insurance-industry-flood-agreement">Statement of Principles</a>. Under this agreement, members of the Association of British Insurers (ABI) agreed to cover properties at risk of flooding in return for government commitment to manage flood risk.</p>
<p>Following extensive negotiations a new flood insurance scheme, <a href="https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/265445/water-bill-flood-insurance-finance-accountablity.pdf">Flood Re</a>, was announced last June. This establishes a stand-alone, industry-run, not-for-profit insurance fund due to begin in 2015. Flood Re will provide cover for about 500,000 properties deemed at risk by the Environment Agency that might otherwise be uninsurable, or whose premiums are unaffordable. But the limitations of the Flood Re scheme need to be recognised.</p>
<p>While ABI members will continue to meet their commitments to existing customers, there’s no guarantee prices won’t rise between now and the implementation of Flood Re. In fact <a href="http://www.telegraph.co.uk/finance/personalfinance/insurance/buildingsandcontent/10623864/Flood-victims-abandoned-by-the-insurance-lifeboat.html">stories are already emerging</a> about dramatic premium hikes, and the expectation is that these will <a href="http://www.telegraph.co.uk/topics/weather/10630154/UK-weather-homeowners-will-not-be-covered-by-flood-insurance-scheme-amid-loophole.html">rise further</a>.</p>
<h2>Policy recommendations</h2>
<p>The government needs to take responsibility in the event of a catastrophic flood, but Flood Re’s liability will be capped at an expected limit of about £2.5 billion per year, equivalent to a 1:200 year flood loss scenario. As to who will bear the costs beyond this, the government has made no commitment. But this is a question that needs an answer. PricewaterhouseCoopers have estimated the insurance losses for December and January at £630 million, and while it’s too early to count the costs of the current floods, insurance industry forecasts suggest losses <a href="http://www.theguardian.com/business/2014/feb/10/flooding-costs-one-billion-pounds-insurance-expert-warns-rising-premiums">could reach £1 billion</a> if the rains continue.</p>
<p>What is also needed from the government and insurers are incentives to reduce flood risk. Planning controls need to restrict development in flood risk areas, set higher standards for buildings on floodplains, and require that the best techniques to improve resilience against flooding are used when rebuilding and refitting after flood damage. As we argued in a paper published in <a href="http://www.nature.com/nclimate/journal/v3/n11/full/nclimate2025.html?WT.ec_id=NCLIMATE-201311">Nature Climate Change</a>, using the flood insurance market to drive better adaptation to flood risk and the effects of climate change needs to be part of a wider strategy that includes land-use planning, building regulations and water management.</p>
<p>The Flood Re scheme needs to be clear whose insurance it will subsidise, and the effects on those not insured under the scheme. In fact many properties at risk will be excluded from the scheme. When Flood Re was first proposed, three categories of property owners were excluded from participation: small businesses, properties built after 1 January 2009, and properties in the highest council tax band.</p>
<p>It has since emerged that Flood Re will exclude many more properties than originally thought, with any policy classed as “non-domestic” unable to participate in the scheme, regardless of the risk. This will include housing association and council properties, many leasehold or private rented sector properties where homes are not insured individually, and properties which are both a residence and a business.</p>
<p>As it is, Flood Re does not reduce flood loss, but only spreads the risk, and therefore the costs, by protecting some policyholders at the expense of others. High-risk properties will be subsidised for decades by payments from low-risk households, with the financial risk still covered by the insurance industry, and government carrying no liability. Policyholders are unlikely to accept this situation without protest, and here the US experience may prove instructive.</p>
<h2>Lessons from the US</h2>
<p>In the US, flood coverage is excluded from property policies provided by private insurers, and is only available through the <a href="http://www.washingtonpost.com/blogs/post-politics/wp/2014/01/30/senate-approves-delay-in-higher-flood-insurance-premiums/">National Flood Insurance Program</a> (NFIP), with the federal government acting as insurer of last resort. Following massive payments for flood claims related to Hurricanes Katrina and Sandy, the NFIP is approximately US$26 billion in debt. This led to legislation to reform the program, phasing out subsidies over five years, and increasing the annual rate until premiums reflect the true risk.</p>
<p>But as rates rose and <a href="http://www.tampabay.com/news/business/banking/battling-flood-insurance-rate-hikes-without-government-help/2160697">homeowners faced huge bills</a>, sometimes <a href="http://www.bradenton.com/2014/01/09/4926356/washington-interest-group-says.html">hikes of 600-1000%</a>, they pressured congress to delay these rate hikes. Republicans and Democrats found common cause for once, with the proposal sailing through the normally divided senate <a href="http://www.washingtonpost.com/blogs/post-politics/wp/2014/01/30/senate-approves-delay-in-higher-flood-insurance-premiums/">in a matter of weeks</a>. Less than two years after the flood insurance reform legislation was passed, the senate voted to delay premium increases for up to four years while the <a href="http://www.fema.gov/">Federal Emergency Management Agency</a> drafts a plan to make flood insurance premiums more affordable and re-evaluates the accuracy of its <a href="http://www.fema.gov/floodplain-management/flood-insurance-rate-map-firm">Flood Insurance Rate Maps</a>.</p>
<p>Flood insurance reform efforts in the US have shown the political implications of angry voters. With flooding in some parts of Britain about to enter a third month and costs spiralling, it is something the UK government is also learning the hard way, with Flood Re facing its first test before it even has come into operation.</p><img src="https://counter.theconversation.com/content/23110/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Diane Horn receives funding from the ESPRC for an industrial CASE studentship with the Willis Research Network as industrial partner titled 'Future Flood - modelling the impact of planning policy on flood vulnerability and insurance risk in the Thames Gateway'. She has also received funding as part of a visiting scholarship from the Climate Change and Sea Level Rise Initiative at Old Dominion University, Norfolk, Virginia.</span></em></p>More wet and windy weather arrives week after week, with the inundated areas of the south and southwest of Britain still at the mercy of the elements. Even while politicians begin the blame game, we should…Diane Horn, Reader in coastal geomorphology , Birkbeck, University of LondonLicensed as Creative Commons – attribution, no derivatives.