Harsher Winters Not Inconsistent with Global Warming
Biting winters driven by global warming: scientists
Agence France-Presse, Dec 22, 2010
PARIS (AFP) – Counter-intuitive but true, say scientists: a string of freezing European winters scattered over the last decade has been driven in large part by global warming.
The culprit, according to a new study, is the Arctic's receding surface ice, which at current rates of decline could to disappear entirely during summer months by century's end.
The mechanism uncovered triples the chances that future winters in Europe and north Asia will be similarly inclement, the study reports.
Bitingly cold weather wreaked havoc across Europe in the winter months of 2005-2006, dumping snow in southern Spain and plunging eastern Europe and Russia into an unusually -- and deadly -- deep freeze.
Another sustained cold streak in 2009-2010, gave Britain its coldest winter in 14 years, and wreaked transportation havoc across the continent. This year seems poised to deliver a repeat performance.
At first glance, this flurry of frostiness would seem to be at odds with standard climate change scenarios in which Earth's temperature steadily rises, possibly by as much as five or six degrees Celsius (9.0 to 10.8 degrees Fahrenheit) by 2100.
Climate sceptics who question the gravity of global warming or that humans are to blame point to the deep chills as confirmation of their doubts.
Such assertions, counter scientists, mistakenly conflate the long-term patterns of climate with the short-term vagaries of weather, and ignore regional variation in climate change impacts.
New research, however, goes further, showing that global warming has actually contributed to Europe's winter blues.
Rising temperatures in the Arctic -- increasing at two to three times the global average -- have peeled back the region's floating ice cover by 20 percent over the last three decades.
This has allowed more of the Sun's radiative force to be absorbed by dark-blue sea rather than bounced back into space by reflective ice and snow, accelerating the warming process.
More critically for weather patterns, it has also created a massive source of heat during the winter months.
"Say the ocean is at zero degrees Celsius (32 degrees Fahrenheit)," said Stefan Rahmstorf, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany.
"That is a lot warmer than the overlying air in the polar area in winter, so you get a major heat flow heating up the atmosphere from below which you don't have when it is covered by ice. That's a massive change," he told AFP in an interview.
The result, according to a modelling study published earlier this month the Journal of Geophysical Research, is a strong high-pressure system over the newly-exposed sea which brings cold polar air, swirling counter-clockwise, into Europe.
"Recent severe winters like last year's or the one of 2005-2006 do not conflict with the global warming picture, but rather supplement it," explained Vladimir Petoukhov, lead author of the study and a physicist at the Potsdam Institute.
"These anomalies could triple the probability of cold winter extremes in Europe and north Asia," he said.
The researchers created a computer model simulating the impact on weather patterns of a gradual reduction of winter ice cover in the Barents-Kara Sea, north of Scandinavia.
Other possible explanations for uncommonly cold winters -- reduced Sun activity or changes in the Gulf Stream -- "tend to exaggerate their effect," Petoukhov said.
He also points out that during the freezing 2005-2006 winter, when temperatures averaged 10 C below normal in Siberia, there were no unusual variations in the north Atlantic oscillation, another putative cause.
Colder European winters do not indicate a slowing of global warming trends, only an uneven distribution, researchers say.
"As I look out my window is see about 30 centimetres of snow and the thermostat reads -14.0 C," said Rahmstorf, speaking by phone from Potsdam.
"At the same time, in Greenland we have above zero temperatures -- in December."
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Global warming linked to harsh winters
Irishtimes.com, Dec. 20, 2010
The cold spell Ireland and the rest of northern Europe has been experiencing may, paradoxically, be the result of global warming, rather than evidence it is not happening, according to the most recent scientific research.
The Journal of Geophysical Research suggested a link between diminishing levels of sea ice in the Arctic and an increased probability of harsh winters across Europe, saying these “do not conflict the global warming picture, but rather supplement it”.
As HSBC Global Research noted in its latest report, If the World is Warming, Why is it so Cold?, “climate change involves profound disruptions in global average temperatures. But as individuals we only experience local weather.” And “coming on the back of the unusual cold winters of 2009-2010, this cold spell has caused some commentary that global warming is over”. The explanation they offer is that the “warming trend is not uniform, and northern Europe has shown considerable cooling this winter”.
Despite the cold spell here, “almost all the areas of the world have shown considerable warming . . .”
According to the British Met Office, “although La Niña has stabilised, it is still expected to affect global temperature through the coming year. This effect is small compared to the total accrued global warming to date, but it does mean that 2011 is unlikely to be a record year.”
Last week, the US National Aeronautics and Space Administration (Nasa) published the global temperature figures for January to November 2010, showing that this 11-month period has been the warmest since instrumental records began 131 years ago.
“High temperatures in 2010 have also been matched by a series of extreme weather events across the world, including droughts and floods in China, India, Pakistan, Russia, and the US,” the HSBC report noted. “But are these driven by man-made global warming?
“Nasa’s James Hansen is clear: ‘Would these events have happened if atmospheric carbon dioxide had remained at its pre-industrial level of 280 parts per million?’ His answer is ‘almost certainly not’.”
Essentially, the sequence of events this year matches the projections of the Intergovernmental Panel on Climate Change of “more frequent and more intense extreme weather events due to global warming”, according to the World Meteorological Organisation.
Global warming 'will give Britain longer, colder winters' as melting sea ice plays havoc with weather patterns
Melting ice will cause blasts of cold air to be funnelled over Britain during winter months
The Daily Mail (U.K.), Dec. 25, 2010
Britain will be hit by longer and colder winters in coming years because of global warming, scientists have said.
Melting Arctic Sea ice has changed wind patterns in the northern hemisphere - bringing blasts of colder air across the UK.
Scientists believe the changes could be why we have been experiencing such a bitterly cold December.
In the future we are three times as likely to be hit by bitterly cold winter months because of the changing climate.
Vladimir Petoukhov, who conducted the study at the Potsdam Institute for Climate Impact in Germany, said the disappearing sea ice will have an unpredictable impact on the climate.
'This is not what one would expect. Whoever thinks that the shrinking of some far away sea-ice won't bother him could be wrong,' he said.
'There are complex interconnections in the climate system, and in the Barents-Kara Sea we have discovered a powerful feedback mechanism.
'Our results imply that several recent severe winters do not conflict with the global warming picture but rather supplement it.'
Rising temperatures in the Arctic - increasing at two to three times the global average - have peeled back the region's floating ice cover by 20 percent over the last three decades.
As the Arctic ice cap has melted the heat from the relatively-warm seawater escapes into the colder atmosphere above, creating an area of high pressure.
That creates clockwise winds that sweep south over the UK and northern Europe.
The study was completed last year - before Britain was hit by a freezing winter and heavy snowfall.
Scientists said it was too early to say if the freezing conditions this year and last year were caused by changes in the Arctic.
But as the ice continues to melt, Britain will begin to have warmer than average winters - but not for another half a century.
Stefan Rahmstorf, professor of physics of the ocean at the Potsdam Institute, said: 'If you look ahead 40 or 50 years, these cold winters will be getting warmer because, even though you are getting an inflow of cold polar air, that air mass is getting warmer because of the greenhouse effect.
'So it's a transient phenomenon. In the long run, global warming wins out.'
The paper was published in the Journal of Geophysical Research last month.