Arctic Sea Ice is melting much, much faster than even the best climate models had projected. The reason is most likely unmodeled amplifying feedbacks. Image via Arctic Sea Ice Blog.
We’ve known for a long time about basic polar amplification. 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.
More recently another insidious feedback has become obvious — as the Arctic ice retreats, big oil companies can drill for more fossil fuels whose combustion will accelerate warming and ice retreat. You might call this the “brainless frog” feedback.
Now Reuters reports on yet another feedback:
Local pollution in the Arctic from shipping and oil and gas industries, which have expanded in the region due to a thawing of sea ice caused by global warming, could further accelerate that thaw, experts say.
The United Nations Environment Program (UNEP) said there was an urgent need to calculate risks of local pollutants such as soot, or “black carbon”, in the Arctic. Soot darkens ice, making it soak up more of the sun’s heat and quickening a melt….
“There is a grim irony here that as the ice melts … humanity is going for more of the natural resources fuelling this meltdown,” he said. Large amounts of soot in the Arctic come from more distant sources such as forest fires or industry.
So the direct pollution from shipping and fossil fuel extraction could speed up Arctic melt.
All of these feedbacks combined are likely to have dire consequences (see How The Arctic Death Spiral Favors Extreme, Prolonged Weather Events “Such As Drought, Flooding, Cold Spells And Heat Waves” and Why The Arctic Sea Ice Death Spiral Matters).
For the sake of completeness, Arctic warming is amplified for several additional synergistic reasons, beyond the change in reflectivity. As the International Arctic Science Committee (IASC) explains in their 2004 report, Impacts of a Warming Arctic (see figure here and below):
- 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 noted, 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, coupled with the climate-carbon-cycle feedbacks that the IPCC models, would make the task of averting the unmitigated catastrophe of 800 to 1000 ppm even more challenging.
We are headed into uncharted waters.