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Tipping points - those critical thresholds in a complex system where a small nudge can cause a catastrophic response - are perhaps the most fearsome threats to the Earth’s climate, but they also haunt ecosystems, financial markets, and even sufferers of medical conditions such as epilepsy and asthma. A fascinating review in Nature today (subscription) sketches out the mathematical patterns on which many of these instances seem to be based, and describes giveaway signs that might warn us to change course before the system tips.

One common warning sign, for example, is flickering between the pre-tipping point state and the post-tipping point state. In climatology, abrupt changes traced in records of the Earth’s past suggest the planet has regularly gone through tipping points, such as the sudden warm-ups that change glacial periods into deglaciations. Earlier this year researchers reported in Nature Geoscience that rapid flickering signaled the end of Earth’s most recent cold spell, the so-called Younger Dryas period. The authors of the new review, led by Marten Scheffer of Wageningen University in The Netherlands, say that in a similar way, debilitating epileptic seizures can be preceded by frequent small symptomless seizures - the ‘flickers’ of the epileptic brain.

Continue reading "Why a climate crisis is like an epileptic seizure" »

Posted by Anna Barnett on September 03, 2009
Categories: Anna Barnett, Climate prediction, Earth science, Extreme Events | Permalink | Comments (1) | TrackBacks (0)

At the AGU Chapman conference today, Yale archaeologist Harvey Weiss took the prize for an abrupt climate change picture worth a thousand words. Excavating an Akkadian palace in Tell Leilan, Syria, in 2006 and 2008, Weiss's team found one room with a grain storage vessel smashed on the floor. Lying next to it were a standard litre measure used for rationing grain, and the tablet on which a bureaucrat had been recording the rationing. The artifacts date from about 2190 B.C., when cities and towns of the Akkadian empire in Mesapotamia were being abandoned en masse as the region suffered crushing drought.

"This site is the Pompeii of ancient Mesapotamia," says Weiss. "They walked away."

Weiss reviewed evidence that a rapid change in storm tracks in the North Atlantic - yet to be satisfactorily explained - dried out the Tigris and Euphrates valley 4,200 years ago. And that valley wasn't alone. Around the same time, deflection of the Indian Monsoon hit the Nile with a drought, and Egypt's Old Kingdom went down. The extreme events are also mirrored in North America from New Jersey to the Yukon. In a separate talk today, glaciologist Lonnie Thompson showed a new ice core data* from Huascarán in Peru, the highest tropical mountain, with a huge spike in dust deposition around this time. The dust probably blew off an aridifying West Africa, Thompson says.

Continue reading "AGU Chapman Conference: "They walked away"" »

Posted by Anna Barnett on June 18, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Extreme Events, Palaeoclimate, Society | Permalink | Comments (0) | TrackBacks (0)

Today's theme at the AGU Chapman Conference on Abrupt Climate Change is that big baddie of climatic tipping points, the shutdown (and rebooting) of the Atlantic Meridional Overturning Circulation, or AMOC. Could this massive system go down again? Tom Delworth of NOAA took on that question and offered up some interesting new modelling evidence.

When running strong, AMOC carries heat from the Southern Hemisphere northward. It's thought that some of the past coolings under scrutiny here stem from slowing or stopping of this conveyor belt. AMOC's future change in response to greenhouse gas increases was recently considered in an assessment report on abrupt change by the US Climate Change Science Program, which Delworth helped author.

While some state-of-the-art models suggest the circulation could slow this century - a 25-30% decrease is the report's best estimate - not a single one forecasts another shutdown in that time. That led the US panel to evaluate AMOC shutdown as "very unlikely", in the parlance of the IPCC - meaning a less than 10% probability. The lack of support from models meant they couldn't set the likelihood any higher, says Delworth - but on the other hand, the possibility of flawed simulations kept them from setting it lower, at "extremely unlikely". But Delworth's new work validates the model results.

Continue reading "AGU Chapman: Meridional madness" »

Posted by Anna Barnett on June 16, 2009
Categories: AGU Chapman conference on Abrupt Climate Change, Anna Barnett, Climate prediction, Extreme Events, Palaeoclimate | Permalink | Comments (0) | TrackBacks (0)

Scientists have long debated how the global climate might be affected by thawing of the Arctic's permanently frozen soils, known as permafrost. As permafrost melts, bacteria break down the organic matter in the soil, releasing greenhouse gases. But at the same time, plants flourish with access to warmer, deeper soils, taking in carbon dioxide. The overall affect on the climate was assumed to be the balance between the gassing and greening.

A new study in this week’s Nature [subscription], suggests that initially, after 15 years of thaw, plants grow faster and take in more carbon than is released by the melting tundra, making the ecosystem an overall carbon sink. But after a few decades, the balance shifts and the ecosystem becomes a source of carbon.

"The plants are growing faster, but after a few decades the rate of carbon loss from the soils is so high the plants can't keep up," says Edward Schuur from the University of Florida in Gainesville, who led the research. When Schuur extrapolated the findings to the entire Arctic region, they suggested a release of around a billion tonnes of carbon every year — of the same order of magnitude as emissions from current deforestation of the tropics. Burning of fossil fuels releases about 8.5 billion tonnes of CO2 a year.

It's estimated that permafrost soils store about twice as much carbon than is currently present in the atmosphere, so the stores of carbon in permafrost are unlikely to run out any time soon. "It's a slow-motion time bomb," says Schuur.

Read the full story over on Nature News.

Anjali Nayar is an intern reporter with Nature News.

Posted by Olive Heffernan on May 28, 2009
Categories: Extreme Events, GHG emissions, In the News, Research | Permalink | Comments (2) | TrackBacks (0)

Today, at the AGU Joint Assembly, I looked into two kinds of risk: of drought leading to civil violence and of the odds that extreme weather events may cause other types of disruption.

It’s always encouraging to see undergraduates engaged in scientific research, the more so when it is interdisciplinary. That’s what surprised me about a poster with the intriguing title, “Climate Change and Civil Violence,” which turned out to be a class project at Princeton University, stretching over three semesters, with three successive classes of students involved in the research.

The students, led by their professor, Gregory van der Vink, focused on a swath of West Africa - 21 countries from Mauritania to the Central African Republic, including most of the semi-arid Sahel region, as well as coastal forests. They looked at the likelihood that climate change, especially increasingly severe drought, will lead to civil violence in each of the countries studied. It is obviously difficult to attribute specific environmental causes to social phenomena, but the students—majoring in politics, various sciences, pre-engineering, and other fields—gave it a good try.

The choice of drought as the key climatic factor was based on the expectation that the Sahel will further dry, shortening the growing season by at least 20% over the next 40 years. Nomadic herdsmen will, for example, have to move further south or adopt a more sedentary life, or both.

Another key factor is the resiliency of the population, its ability to cope with the coming climatic changes. This factor varies considerably from country to country, the researchers found, and is related to population size, political system, natural resources, and other variables. The relative significance of each of these is difficult to assess, of course.

Bottom line: after exhaustive analysis, the students concluded that the five countries in the study that are most vulnerable to drought-induced civil violence are Nigeria, Senegal, Mali, Côte d’Ivoire, and Gambia. Of these, three—Nigeria, Senegal, and Mali—have already experienced conflicts that included an environmental factor, they say. Of the five, only Gambia has not experienced any violent conflict during the past 10 years.

The study, as the students themselves note, was a preliminary effort to correlate environmental and socio-economic risk factors that could lead to civil violence. They are not predicting specific events in particular countries, but there seems little doubt that this topic is one that will assume increasing importance in coming years to policy makers and civilian populations alike, and not just in Africa.

Continue reading "AGU 2009 Joint Assembly: Climate risk research " »

Posted by Olive Heffernan on May 27, 2009
Categories: AGU 2009 Joint Assembly, Extreme Events, Harvey Leifert, Research, Society | Permalink | Comments (0) | TrackBacks (0)

Cross-posted from The Great Beyond

New Yorkers beware! A new study published in Nature Geoscience says the north-eastern US coast will be in more trouble from global warming than previously believed.

Looking at the predictions from a whole set of different climate models, researchers Jianjun Yin, Michael Schlesinger and Ronald Stouffer found that changes in ocean circulation will result in higher sea levels in the region, over and above expected global sea level changes. Depending on whether greenhouse gas emissions are low or high, an additional rise of between 15 and 21 cm can be expected by 2100, they say.

“Some parts of lower Manhattan are only 1.5 meters above sea level,” says Yin, a researcher at Florida State University (National Geographic). “Twenty centimetres of extra rise would pose a threat to this region.”

The graphic right shows dynamic sea level rises at coastal cities worldwide in the medium greenhouse-gas emission scenario, due to the knock on effects of changes in the Atlantic meridional overturning circulation.

“Our results show that the northeast coast of the United States is among the most vulnerable regions to future changes in sea level and ocean circulation, especially when considering its population density and the potential socioeconomic consequences of such changes,” write the researchers. “It should be noted that the impact of the melting of the Greenland ice sheet on the [Atlantic meridional overturning circulation] is not taken into account here.”

Continue reading "Will warming wash-away Wall Street?" »

Posted by Olive Heffernan on March 17, 2009
Categories: Daniel Cressey, Extreme Events, Features, In the News, Research | Permalink | Comments (0) | TrackBacks (0)

The loss of ice from Greenland ranks as one of the most troubling, and poorly understood, aspects of climate change. Melting of the colossal ice sheet, which is already undoubtedly underway, has the capacity to raise global sea levels by an astounding 7 meters.

Not only is Greenland losing mass from direct surface melting, its outlet glaciers (those that terminate in the sea) are spewing large icebergs directly into the ocean at an increasingly alarming speed as they retreat. Many have worried that these changes are a sign of what’s in store. But a new study published this week in Nature Geoscience [subscription] suggests that the recent rapid retreat of many of Greenland’s outlet glaciers will be short-lived.

A team led by Andreas Vieli at Durham University, UK, used a computer model to reconstruct the recent behaviour of the Helheim Glacier, one of Greenland’s largest outlet glaciers. Helheim retreated some 7 kilometers between 2002 and 2005, during which time it discharged considerable volumes of ice into the ocean.

View image

Vieli’s team looked at whether the recent changes observed in the Helheim Glacier could be explained by one of two hypotheses; the first was that increased surface meltwater reaching the base of the glacier was speeding its slide toward the sea. The second potential explanation was that changing conditions in the area where the glacier meets the sea would trigger a domino effect on the glacier itself, leading to even faster ice flow and thinning upstream.

Their model showed that only the second hypothesis could explain past changes in the Helheim Glacier. Though they only analysed changes in this one outlet glacier, the authors say it is representative of many outlet glaciers south of 70°N that have recently thinned and rapidly released ice to the ocean.

Continue reading "Rapid retreat of Greenland's outlet glaciers may be temporary " »

Posted by Olive Heffernan on January 13, 2009
Categories: Cryosphere, Extreme Events, Journal Club, Olive Heffernan | Permalink | Comments (1) | TrackBacks (0)

The year 2008 was likely the coolest year of the current decade, but it was still the tenth warmest year on record since instrumental climate records began in 1850.

The average global sea-surface and land-surface air temperature from December 2007 to November 2008 was 14.3 °C, the World Meteorological Organization (WMO) has announced. This is slightly lower than for all previous years of the ‘naughties’, but still some 0.3 °C above the 1961-1990 annual average. The warmest year on record is 1998, with an average global temperature just above 14.5 °C.

Left: Global map of surface temperature anomalies in degrees Celsius for the 2008 meteorological year. Right: Annual-mean global-mean anomalies, except 2008, which is the 11-month (Jan-Nov) mean anomaly. Credit: NASA Goddard Institute for Space Studies.

When calculating global average temperatures, climatologists prefer the meteorological year, from December through November, as it is easier to split it into actual seasons than is the calendar year.

The WMO temperature analysis is based on land-based weather stations in 188 countries, complemented by measurements from ships, buoys and satellites. NASA’s Goddard Institute for Space Studies and the UK Met Office, which both contributed their own datasets to the WMO analysis, independently arrive at very similar values.

Continue reading "2008 cooling, but the heat is on" »

Posted by Quirin Schiermeier on December 17, 2008
Categories: Climate prediction, Climate variability, Extreme Events, Quirin Schiermeier | Permalink | Comments (3) | TrackBacks (0)

I hadn’t anticipated quite so much rain during the AGU’s Fall conference in San Francisco, but apparently this exact week is, on average, the city’s wettest of the year. Or so I heard at today’s session on how the region is likely to be impacted by climate change.

California has been long recognized as a leader on climate policy, both on the home front and even internationally. It passed its first climate bill twenty years ago and just last week, the state adopted the nation's most sweeping climate action plan to date, pledging to cut its greenhouse gas emissions by 15% by 2020.

A close look at how the region is expected to fare under various warming scenarios makes its leadership in this arena look a lot like common sense. While temperatures in California are expected to increase in line with global averages, more worrying for the state is the projected water shortages, according to Dan Cayan of the Scripps Institution of Oceanography in La Jolla, San Diego, who spoke at AGU today. California faces the possibility of a 10% decrease in precipitation over the course of the century and could concurrently lose half of its late spring snowmelt. That's bad news for a region that is already heavily reliant on external water sources.

Sea-level rise will also be part of the equation, especially for the numerous coastal properties with little protection, said Peter Gleick, president of the Oakland, California –based Pacific Institute. Should those in the interior think they’re better off, though, climate models show that inland regions will warm more rapidly than the coast and will likely be more populated in the future owing to lack of available living space on the coast.

Continue reading "AGU 2008: On the home front" »

Posted by Olive Heffernan on December 17, 2008
Categories: AGU, Adaptation, Climate prediction, Extreme Events, Olive Heffernan | Permalink | Comments (0) | TrackBacks (1)

As residents of New Orleans prepare to return home and breathe a sigh of relief that Hurricane Gustav was less damaging than feared, new research published today in Nature [subscription] suggests that the strongest tropical cyclones will pick up speed in the coming decades.

Weighing in on the long-running and at times very stormy debate over whether and how warmer seas will affect the intensity and frequency of hurricanes is a team led by climatologist James Elsner of Florida State University.

Using a 25-year archive of satellite data, Elsner and colleagues derive wind speeds for tropical cyclones over the globe. They find that the maximum wind speeds reached by the strongest tropical cyclones increased from 1981-2006 in most ocean basins, with the greatest changes in the North Atlantic and Northern Indian Oceans.

There was no trend in the intensity of cyclones occuring over the South Pacific, however, and the upward trend observed over a couple of ocean regions was not statistically significant. The researchers also found no increase in either the frequency or average intensity of tropical cyclones over the globe.

The approach taken by Elsner and colleagues – looking at whether the most severe cyclones will hit a higher speed limit during their lifetime – is both novel and socially relevant, simply because the most severe storms do the most damage if they make landfall. Once tropical cyclones reach speeds of over 74mph, they are officially classified as hurricanes.

The real bone of contention within the scientific community has been whether hurricanes will become more intense and more frequent as a result of human-induced climate change. Elsner and colleagues steer well clear of linking the trend to global warming though - they can’t attribute cause as their study doesn’t investigate other factors such as cyclone origin and duration, proximity to land, El Niño conditions and solar activity.

Continue reading "As Gustav subsides, new study says strongest cyclones will pick up speed" »

Posted by Olive Heffernan on September 03, 2008
Categories: Atmospheric Science, Extreme Events, Features, In the News, Journal Club, Ocean science, Olive Heffernan, Society | Permalink | Comments (1) | TrackBacks (0)

Global warming has been expected to bring not only droughts, but also floods, because what rain you get comes hammering down harder. And the downpours of the future now look to be even more drenching than expected.

A new Nature Geoscience paper (subscription required) considers the intensity of precipitation measured hour by hour for a century in the Dutch town of De Bilt. Theoretically, it’s thought that the intensity of rainfall, including the biggest cloudbursts, should rise by 7% for each degree Celsius that the temperature goes up. That’s based on a thermodynamics equation called the Clausius-Clapeyron relation - and it’s what you see if you look at extreme rainfall on the scale of days.

But it's the rainiest hours, not the rainiest days, that interest the paper's authors, Geert Lenderink and Erik Van Meijgaard of the Royal Netherlands Meteorological Institute. That turns out to make a difference.

Continue reading "A precipitous rise in extreme rainfall " »

Posted by Anna Barnett on July 21, 2008
Categories: Anna Barnett, Climate variability, Extreme Events, Regional climate | Permalink | Comments (1) | TrackBacks (0)

Hurricanes may become rarer in the Atlantic throughout the 21st century if the world continues to warm, suggests a new study. The research is the latest to address the question of how – and whether - global warming will affect the intensity and frequency of hurricanes.

Globally, the number of major hurricanes has shot up by 75% since 1970. And although rising ocean temperatures are generally accepted as the key culprit – hurricanes can only form where sea surface temperatures exceed 26ºC - the link to global warming has remained a contentious issue.

In the new study, published online yesterday in Nature Geoscience [subscription], Thomas Knutson of the US National Oceanic and Atmospheric Administration and colleagues showed, using a regional climate model of the Atlantic basin, that the trend in increased hurricane activity in the Atlantic over the past 25 years will not continue into the future, though hurricanes in the area may become more intense and associated with heavier rainfall.

Though they use a different model, the results generally concur with the recent paper by hurricane specialist Kerry Emanuel, which shows that hurricanes are likely to decrease in frequency but increase in intensity in certain locations as temperatures rise.

I’ve written the full story here for Nature News.

Olive Heffernan

Image: NASA / Univ. Wisconsin-Madison

Posted by Olive Heffernan on May 19, 2008
Categories: Climate Science, Extreme Events, Features, Hurricanes, In the News, Journal Club, Olive Heffernan | Permalink | Comments (2) | TrackBacks (0)

One of the more irritating aspects, if you will, of global change is that air pollution has so far prevented the planet from warming more rapidly than it actually did. Clean air is of course a good thing. But reducing pollution might expose an as of yet ‘masked’ portion of global warming.

This could have a dramatic affect on the Amazon rainforest. A team led by Peter Cox of the University of Exeter, UK, reports in a paper in this week’s Nature that reductions in aerosol pollution will tremendously increase the risk of severe drought in the Amazon region. Here is an editor’s summary of the paper.

Although it accounts for nearly a quarter of the world's fresh water, drought is not unknown in Amazonia.

In the dry season, from July to October, rainfall in the region is linked to sea surface temperatures (SST) in the tropical Atlantic. In years with a pronounced temperature gradient - warming of the tropical Atlantic north of the equator relative to the south – the normal’ position of high and low atmospheric pressure systems can shift, delaying or suppressing the onset of the South American monsoon.

The effect has been observed in 2005, when large parts of the Amazon region were hit by the worst drought in decades. See a Nature news story by Mike Hopkin here (subscription required) and a New York Times story here about the devastating event.

Cox thinks that the 2005 drought was a harbinger of things to come. Their “simulations for the 21st century show a strong tendency for the SST conditions associated with the 2005 drought to become much more common, owing to continuing reductions in reflective aerosol pollution in the Northern Hemisphere.”

Droughts like in 2005 will happen every two years by 2025, and in nine out of ten years by 2060, the model suggests.

How robust is this dire prediction? The Amazonian climate, for reasons not quite understood, is notoriously difficult to simulate. But the Hadley Centre’s climate model which was used for this study has previously reproduced features of the regional climate with greater accuracy than other models.

In Mike Hopkin's words, “the ultimate fear is that the Amazon forest - often touted as an invaluable piece of armour against climate change - could become part of the problem rather than a key element of the solution. Droughts make it more likely that it will become a net source of greenhouse gases to the atmosphere, rather than mopping them up.”

Quirin Schiermeier

You can vote or comment on the importance of the new paper in the Journal Club of Nature Reports Climate Change.

Posted by Quirin Schiermeier on May 08, 2008
Categories: Biosphere feedbacks, Climate Science, Climate prediction, Extreme Events, Quirin Schiermeier, Topics | Permalink | Comments (5) | TrackBacks (0)

It’s been quite a while since the Gulf Stream was last on the Nature cover. This week the old highlight is back.

Now that’s a topic which has caused an awful lot of confusion before. “How global warming will cause the next ice age”, stuff like that. So just to be clear: the Gulf Stream is the mostly wind-driven upper limb of the Atlantic meridional overturning circulation, which ceaselessly transports warm surface water from the Caribbean to middle and high latitudes on the other side of the Atlantic. Yes, ceaselessly. As long as the Earth keeps rotating there’s really nothing in the world (not even global warming) that could bring it to a halt.

It is common knowledge - and true - that the British Isles and Scandinavia enjoy a much warmer climate than Newfoundland or Labrador thanks to the Gulf Stream. But its climatic influence goes far beyond that, a US-Japanese team report in a paper in Nature this week.

They detected the Gulf Stream’s signature in the entire lower atmosphere - namely in air and cloud temperatures, rain bands, pressure fields and wind convergence - above its meandering cross-Atlantic course, and far inland in Europe.

That the influence of the Gulf Stream might penetrate deeply into the atmosphere has been previously assumed. Firm evidence that this is indeed the case, and vehemently so, comes from the combination of satellite observations, operational weather analysis and atmospheric circulation models which the team utilised for their study.

Very likely the Gulf Stream’s direct local effects on the atmosphere are tele-connected, via planetary atmospheric waves, with weather conditions in far-away regions. How frequent and pronounced these remote responses might be is not at all clear. But it seems at least as if Gulf Stream-driven atmospheric dynamics over the North Atlantic have a marked influence on hemisphere-wide climatology.

This, you’ve guessed it, adds another piece to the climate change puzzle. Come what may, the Gulf Stream will not ‘run dry’. But its strength does vary, and a possible weakening of the Atlantic overturning circulation, to which it belongs, is unlikely to leave the Gulf Stream unaffected.

A new ice age will not come over Europe because of that, but storm tracks and rainfall patterns could be affected in rather unpredictable ways.

Quirin Schiermeier

You can vote or comment on the importance of the new Gulf Stream paper in the Journal Club of Nature Reports Climate Change.

Posted by Olive Heffernan on March 12, 2008
Categories: Extreme Events, Features, Journal Club, Ocean science, Quirin Schiermeier | Permalink | Comments (5) | TrackBacks (0)

Signs of a very different 21st-century climate are already showing up, and not just in the melting arctic. A new review in Nature Geoscience highlights reports that the boundaries of the tropics, defined by temperature, rainfall, wind, and ozone patterns, have shifted poleward by at least 2 degrees latitude in the last 25 years. According to climate models, that's as far as the tropical belt was supposed to creep by the end of this century. Five different methods used to measure the tropics all show more or less breakneck rates of expansion -- one gives as much as 4.8 degrees in 25 years.

Continue reading "Tropics expanding fast " »

Posted by Anna Barnett on December 04, 2007
Categories: Anna Barnett, Climate Science, Extreme Events | Permalink | Comments (2) | TrackBacks (0)

Olive Heffernan

This week on Nature Reports Climate Change, Amanda Leigh Haag looks at how climate change is increasingly becoming an issue of national security, raising the alarm on issues of border control and immigration policy globally.

The feature details how regions likely to bear the brunt of climate impacts are already beginning to look to neighbouring states for potential resettlement deals, while less vulnerable nations are considering the likely spillover of large-scale migration from areas impacted by severe drought or flooding.

This raises some interesting issues, such as whether adaptation should focus on protecting the rights of people to live in their home, rather than offering relocation programmes, and whether these scenarios are inevitable without drastic measures to prevent further warming….but more on that shortly.

Posted by Olive Heffernan on September 26, 2007
Categories: Adaptation, Extreme Events, Features, In the News, Olive Heffernan | Permalink | Comments (10) | TrackBacks (0)

Olive Heffernan

Much like the rest of Britain, I’m beginning to wonder if it’s ever going to stop raining. And despite feeling slightly miffed at an appalling excuse for a summer, I realise I'm lucky to be based in slightly soggy London, given that large areas of the country are currently besieged by some of the worst flooding in recent British history.

Calling it a ‘21st century catastrophe’, Michael McCarthy at the Independent writes that “Britain is suffering from a wholly new type of civil emergency: a disaster caused by 21st-century weather,” which has left more than a third of a million people without drinking water, nearly 50,000 people without power, thousands more people homeless and caused more than £2bn worth of damage so far.

Britain is not alone in experiencing extremely heavy rainfall. As reported on MSNBC, “parts of China had the heaviest rainfall since records began, killing more than 700 so far this year. Hundreds of thousands have been displaced by flash floods in southern Pakistan.”

While these single events cannot be attributed to climate change, many are questioning if the flash flooding is a sign of what is in store for the future. And scientists have some of the answers.

In a paper coming out in Nature this Thursday, Francis Zwiers of the Canadian Centre for Climate Modelling and Analysis in Toronto and colleagues present the first evidence that human-generated greenhouse gas emissions have altered rainfall patterns in the 20th Century. In the region between 40 and 70 degrees North, covering northern Europe, Russia and parts of North America, rainfall increased by 62 millimetres per century between 1925 and 1999. Zwiers and colleagues say that 50-85% of this increase can be attributed to human activity. For further discussion and comments on the paper, there’s a news story by my colleague Daniel Cressy on News@Nature. And it’s also been picked up by the BBC.

And a recent paper published in Science in June suggests that global warming may result in even more rainfall worldwide than is currently evident in climate model simulations. Frank J. Wentz of Remote Sensing Systems in Santa Rosa, California and co-workers compared global satellite data from 1987 to 2006 and found that rainfall increased at the same rate as atmospheric water vapour per degree Celsius of surface warming. Climate models had projected a dampened response of rainfall to global warming owing to a decrease in surface winds, but Wentz and colleagues found that surface winds have in fact become stronger, leading to heavier rainfall (more on this in Nature Reports Climate Change soon).

Coming back to Britain… the situation is likely to worsen over the next 24 hours. Eight severe warnings have been issued covering the rivers Thames, Severn and Ouse, in particular for towns such as Gloucester, Tewkesbury, Oxford, Abingdon, Reading and Bedford. Fifty other flood warnings are in place across England and Wales.

To see the areas generally most at risk of flooding in England and Wales, visit the Environment Agency’s flood map online, where you view flood risk by postcode. For an up to date interactive on the current situation, the Guardian has quite a snazzy interactive highlighting areas most at risk.

Olive Heffernan
News Editor
Nature Reports Climate Change

Posted by Olive Heffernan on July 24, 2007
Categories: Climate Science, Extreme Events, In the News, Olive Heffernan | Permalink | Comments (3) | TrackBacks (0)