As climate science predicts, the Arctic is warming faster than the rest of the globe (see NSIDC: Arctic melt passes the point of no return, “We hate to say we told you so, but we did”). This is often called polar amplification (PA).
I wanted to do a post on PA for two reasons. First, “there are no permanent weather stations in the Arctic Ocean, the place on Earth that has been warming fastest,” as New Scientist explained (see here and here). “The UK’s Hadley Centre record simply excludes this area, whereas the NASA version assumes its surface temperature is the same as that of the nearest land-based stations.”
Thus contrary to what the global warming deniers say about the recent temperature record, it is almost certainly the case that the planet has warmed up more this decade than NASA says, and especially more than the UK’s Hadley Center says.
So that’s why I see the NASA temperature record as more accurate, which puts 2005 as the warmest year on record, with a rough tie for second between 2007 and 1998. Sorry, deniers, not bloody much evidence for recent “global cooling.”
Second, PA is a tad more complicated — and more interesting — than the popular explanation has it.
As RealClimate notes in their useful discussion, “Polar amplification is thought to result primarily from positive feedbacks from the retreat of ice and snow.” Indeed, the popular explanation is that warming melts highly reflective white ice and snow, which is replaced by the dark blue sea or dark land, both of which absorb far more sunlight and hence far more solar energy.
But in fact Arctic warming is amplified for several additional synergistic reasons, which are worth knowing. As the International Arctic Science Committee (IASC) explains in their 2004 report, Impacts of a Warming Arctic (see figure here):
- In the Arctic, compared to lower latitudes, “more of the extra trapped energy goes into warming rather than evaporation.”
- In the Arctic, “the atmospheric layer that has to warm in order to warm the surface is shallower.”
- So, when the sea ice retreats, the “solar heat absorbed by the oceans in summer is more easily transferred to the atmosphere in winter.”
[And as one climate scientist explained to me, it can get incredibly cold above thick ice, but it can't get much colder than freezing above open water.]
All this leads to more snow and ice melting, further decreasing Earth’s reflectivity (albedo), causing more heating, which the thinner arctic atmosphere spreads more quickly over the entire polar region, and so on and on.
And that in turn threatens a cascade of effects. As the scientists at The International Polar Year note, this could “speed up melting of the Greenland ice sheet, accelerating the rise in sea levels,” and “Permafrost melting could also accelerate during rapid Arctic sea-ice loss due to an amplification of Arctic land warming 3.5 times greater than secular 21st century climate trends” (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“).
Yet the destruction of a significant fraction of the permafrost must be avoided at all cost, since the tundra feedback, coupled with the climate-carbon-cycle feedbacks that the IPCC models, could easily take us to the unmitigated catastrophe of 1000 ppm (see Tundra, Part 2: The point of no return).
That’s why polar amplification is important.