Well doesn't that sound like a paradox? It is however really one of the main reasons why warming in the Arctic region is happening 3-4 times as fast as the global average, a research team of the Royal Netherlands Meteorological Institute (KNMI) says. And it would help to explain the Arctic winter warming mystery...
In the High North there are several positive climate feedbacks, physical mechanisms that accelerate or at least amplify the atmospheric average temperature rise that climatologists measure at other latitudes around the world.
Summer is season of feedbacks
One of these is the albedo feedback. This recent NASA video does a good job explaining the principle: less ice and snow means a generally darker surface, which absorbs solar radiation, instead of reflecting it back to space. Therefore ice melting leads to further temperature rise.
Does this explain why Arctic melting is happening so much faster than elsewhere on Earth? Only to some extent. Models show the albedo feedback may not be as powerful as some have suggested. Besides, it only operates in the summer months, as in winter there is no Sun up North, so reflectivity is irrelevant.
The same applies to another important Arctic feedback, increased dynamics of the floating Arctic sea ice. As the ice thins and the stretches of open water increase in size, there is less friction to water currents and more calving. The Arctic Ocean is in fact one enormous counter-clockwise gyre, with a drain: the East Greenland Current. Here more and more ice debris flows into the warm Atlantic, a publication in the Journal of Geophysical Research warned earlier this month. Again however, this feedback explains only one half of the Arctic story, the summer half.
Arctic warming continues in the winter months
That is very helpful to explaining the graphs of for instance the 2007 and 2011 Arctic melting records; the summer feedbacks however do not offer sufficient explanation for the fact that measured annual temperature rise is now three to four times as high as the global average.
As for the ice, there seems to be some recovery [extent more than thickness] in winter, but not enough. The fact that the smallest winter sea ice maximum in the satellite record was reached earlier this year should at least serve to emphasize something is going on in the winter months too.
Somehow the Arctic climate system seems ill-equipped to shed the extra summer warmth - and now the researchers of KNMI think they know why. In fact they say during the long dark winter months the warming simply continues.
You have to use some 3D insight to understand why. When the Sun no longer shines over the Arctic, the icy surface rapidly cools down, creating what meteorologists call a thermal inversion, with a dense cold layer of air close to the ice - and milder temperatures somewhat higher up in the atmosphere.
Cold air forces Arctic to recycle energy
These layers prevent the Arctic system from radiating summer heat to the cosmos. The cold layer to the surface can't warm up the warmer air above it. More importantly also the warmer air higher in the atmosphere emits less infrared radiation to space than one might think. That's because it can just as well 'point' the energy down, to try and warm the colder air beneath it, the researchers write in their publication in Nature Geoscience. Much energy is therefore being recycled within the climate system.
"This winter thermal inversion increases the Arctic climate sensitivity," says KNMI climate researcher and lead author Richard Bintanja. "Without it the Arctic system would be much better capable of emitting infrared radiation to space - and cooling down after an initial warming."
According to Bintanja the cold air acts as a blanket, actually sabotaging an existing negative climate feedback: Theoretically the warmer the climate, the more energy it would emit to space, somewhat slowing down the process of warming. Diminishing a natural negative feedback has the same effect as adding another positive climate feedback - and that's one thing the Arctic could do without.
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