|February 07, 2012|
Is Climate Change Bringing the Arctic to Europe?
|Less Summer Arctic Sea Ice Cover May Mean Some Colder, Snowier Winters in Central Europe [For Now]|
The probability of cold winters with much snow in Central Europe rises when the Arctic is covered by less sea ice in summer. Scientists of the Research Unit Potsdam of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association have decrypted a mechanism in which a shrinking summertime sea ice cover changes the air pressure zones in the Arctic atmosphere and impacts our European winter weather. These results of a global climate analysis were recently published in a study in the scientific journal Tellus A.
That's the news release for yet another new study examining what will inevitably be the huge implications for extreme weather from the massive amount of heat released by the declining Arctic sea ice cover.
Arctic sea ice in September 2007 reached its lowest extent on record, approximately 40% lower than when satellite records began in 1979. Sea ice loss in 2011 was virtually tied with the ice loss in 2007, despite weather conditions that were not as unusual in the Arctic. "Such a large area of open water is bound to cause significant impacts on weather patterns, due to the huge amount of heat and moisture that escapes from the exposed ocean into the atmosphere over a multi-month period following the summer melt."
"The question is not whether sea ice loss is affecting the large-scale atmospheric circulation.... It's how can it not?" That was the take-home message from Dr. Jennifer Francis of Rutgers University, in her talk "Does Arctic Amplification Fuel Extreme Weather in Mid-Latitudes?", presented at last week's American Geophysical Union meeting in San Francisco.
Dr. Francis presented new research in review for publication, which shows that Arctic sea ice loss may significantly affect the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. High-amplitude loops in the upper level wind pattern (and associated jet stream) increases the probability of persistent weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions.
The new German study looks at the specific case of winters in central Europe. The UK Independent story explains, "A growing number of experts believe complex wind patterns are being changed because melting Arctic sea ice has exposed huge swaths of normally frozen ocean to the atmosphere above."
As cold weather hit much of Europe, the story describes the findings this way:
In particular, the loss of Arctic sea ice could be influencing the development of high-pressure weather systems over northern Russia, which bring very cold winds from the Arctic and Siberia to Western Europe and the British Isles, the scientists believe. An intense anticyclone over north-west Russia is behind the bitterly cold easterly winds that have swept across Europe and some climate scientists say the lack of Arctic sea ice brought about by global warming is responsible.
"The current weather pattern fits earlier predictions of computer models for how the atmosphere responds to the loss of sea ice due to global warming," said Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research. "The ice-free areas of the ocean act like a heater as the water is warmer than the Arctic air above it. This favours the formation of a high-pressure system near the Barents Sea, which steers cold air into Europe."
Sea ice covering the Barents and Kara Seas has been exceptionally low this winter, according to the US National Snow and Ice Data Centre in Boulder, Colorado. But air temperatures above the Barents and Kara Seas have been higher than average. The relatively mild westerly winds that have kept Britain from freezing much of this winter have been blocked by fierce high pressure over north-west Russia, centred on an area just south of the Barents Sea.
Indeed, as the story makes clear, although the impacts are complicated, more and more climate experts have been making the connection:
Professor Rahmstorf said the Alfred Wegener study confirms earlier predictions from computer models by Vladimir Petoukhov of the Potsdam Institute, who forecast colder winters in western Europe as a result of melting sea ice.
Dr Petoukhov and his colleague Vladimir Semenov were among the first scientists to suggest a link between the loss of sea ice and colder winters in Europe. Their 2009 study simulated the effects of disappearing sea ice and found that for some years to come the loss will increase the chances of colder winters.
"Whoever thinks that the shrinking of some far-away sea ice won't bother him could be wrong. There are complex interconnections in the climate system, and in the Barents-Kara Sea we might have discovered a powerful feedback mechanism," Dr Petoukhov said.
You can read the original study online: "Impact of sea ice cover changes on the Northern Hemisphere atmospheric winter circulation." Here's more detail for non-scientists from the Alfred Wegener Institute for Polar and Marine Research news release:
If there is a particularly large-scale melt of Arctic sea ice in summer, as observed in recent years, two important effects are intensified. Firstly, the retreat of the light ice surface reveals the darker ocean, causing it to warm up more in summer from the solar radiation (ice-albedo feedback mechanism). Secondly, the diminished ice cover can no longer prevent the heat stored in the ocean being released into the atmosphere (lid effect). As a result of the decreased sea ice cover the air is warmed more greatly than it used to be particularly in autumn and winter because during this period the ocean is warmer than the atmosphere. "These higher temperatures can be proven by current measurements from the Arctic regions," reports Ralf Jaiser, lead author of the publication from the Research Unit Potsdam of the Alfred Wegener Institute.
The warming of the air near to the ground leads to rising movements and the atmosphere becomes less stable. "We have analysed the complex non-linear processes behind this destabilisation and have shown how these altered conditions in the Arctic influence the typical circulation and air pressure patterns," explains Jaiser. One of these patterns is the air pressure difference between the Arctic and mid-latitudes: the so-called Arctic oscillation with the Azores highs and Iceland lows known from the weather reports. If this difference is high, a strong westerly wind will result which in winter carries warm and humid Atlantic air masses right down to Europe. If the wind does not come, cold Arctic air can penetrate down through to Europe, as was the case in the last two winters. Model calculations show that the air pressure difference with decreased sea ice cover in the Arctic summer is weakened in the following winter, enabling Arctic cold to push down to mid-latitudes.
Despite the low sea ice cover in summer 2011, a cold winter with much snow has so far not occurred here in Germany. Jaiser explains this as follows: "Many other factors naturally play a role in the complex climate system of our Earth which overlap in part. Our results explain the mechanisms of how regional changes in the Arctic sea ice cover have a global impact and their effects over a period from late summer to winter. Other mechanisms are linked, for example, with the snow cover in Siberia or tropical influences. The interactions between these influential factors will be the subject matter of future research work and therefore represent a factor of uncertainty in forecasts."
I added "for now" to the subhed "Less Summer Arctic Sea Ice Cover Means Colder, Snowier Winters in Central Europe" because if we stay on our current emissions path, then the warming is going to be so great in the second half of the century it will generally overcome even these cold blasts.
In the worst case, we get both continuing high levels of emissions and high carbon-cycle feedbacks.