September 23, 2011

Retreat of the Arctic Sea Ice

Arctic Sea Ice in September 2011 was only four percent shy of the minimum record set in 2007. This map from the Economist compares the average summer sea ice extent from 1979 to 2000 (the red-dotted line) with the recent September reading (the light blue line). It also shows the two shipping lines (one hugging the coast of Russia, the other through Canada’s northern waters) that will revolutionize sea transport if the melting continues. This very cool animation takes the map a step further, showing in rapid sequence the September readings over the last thirty-two years, enabling you to visualize how the red-dotted line got formed.

The Economist (“Beating a Retreat”) notes that the Arctic sea is melting far faster than climate models have predicted. Because “Arctic air is warming twice as fast as the atmosphere as a whole,” an ice free summer Arctic is likely to happen sometime between 2020 and 2050 rather than the end of 21st century—the date predicted by most climate models. Why that high rate of warming? Here is the explanation from The Economist:

Some of the causes of this are understood, but some are not. The darkness of land and water compared with the reflectiveness of snow and ice means that when the latter melt to reveal the former, the area exposed absorbs more heat from the sun and reflects less of it back into space. The result is a feedback loop that accelerates local warming. Such feedback, though, does not completely explain what is happening. Hence the search for other things that might assist the ice’s rapid disappearance.

One is physical change in the ice itself. Formerly a solid mass that melted and refroze at its edges, it is now thinner, more fractured, and so more liable to melt. But that is (literally and figuratively) a marginal effect. Filling the gap between model and reality may need something besides this.

The latest candidates are “short-term climate forcings”. These are pollutants, particularly ozone and soot, that do not hang around in the atmosphere as carbon dioxide does, but have to be renewed continually if they are to have a lasting effect. If they are so renewed, though, their impact may be as big as CO2’s.

At the moment, most eyes are on soot (or “black carbon”, as jargon-loving researchers refer to it). In the Arctic, soot is a double whammy. First, when released into the air as a result of incomplete combustion (from sources as varied as badly serviced diesel engines and forest fires), soot particles absorb sunlight, and so warm up the atmosphere. Then, when snow or rain wash them onto an ice floe, they darken its surface and thus cause it to melt faster.

Reducing soot (and also ozone, an industrial pollutant that acts as a greenhouse gas) would not stop the summer sea ice disappearing, but it might delay the process by a decade or two. According to a recent report by the United Nations Environment Programme, reducing black carbon and ozone in the lower part of the atmosphere, especially in the Arctic countries of America, Canada, Russia and Scandinavia, could cut warming in the Arctic by two-thirds over the next three decades. Indeed, the report suggests, if such measures—preventing crop burning and forest fires, cleaning up diesel engines and wood stoves, and so on—were adopted everywhere they could halve the wider rate of warming by 2050.

Without corresponding measures to cut CO2 emissions, this would be but a temporary fix. Nonetheless, it is an attractive idea because it would have other benefits (soot is bad for people’s lungs) and would not require the wholesale rejigging of energy production which reducing CO2 emissions implies. Not everyone agrees it would work, though. Gunnar Myhre of the Centre for International Climate and Environmental Research in Oslo, for example, notes that the amount of black carbon in the Arctic is small and has been falling in recent decades. He does not believe it is the missing factor in the models. Carbon dioxide, in his view, is the main culprit. Black carbon deposited on the Arctic snow and ice, he says, will have only a minimal effect on its reflectivity.

The rapid melting of the Arctic sea ice, then, illuminates the difficulty of modelling the climate—but not in a way that brings much comfort to those who hope that fears about the future climate might prove exaggerated. When reality is changing faster than theory suggests it should, a certain amount of nervousness is a reasonable response.

The direct consequences of changes in the Arctic are mixed. They should not bring much rise in the sea level, since floating ice obeys Archimedes’s principle and displaces its own mass of water. A darker—and so more heat-absorbent—Arctic, though, will surely accelerate global warming and may thus encourage melting of the land-bound Greenland ice sheet. That certainly would raise sea levels (though not as quickly as News Corporation’s cartographers suggest in the latest edition of the best-selling “Times Atlas”, which claims that 15% of the Greenland sheet has melted in the past 12 years; the true figure is more like 0.05%). Wildlife will also suffer. Polar bears, which hunt for seals along the ice’s edge, and walruses, which fish there, will both be hard-hit.

The effects on the wider climate are tricky to assess. Some meteorologists suspect unseasonal snow storms off the east coast of America in 2010 were partly caused by Arctic warming shifting wind patterns. One feedback loop that does seems certain, though, is that the melting Arctic will enable the extraction of more fossil fuel, with all that that implies for greenhouse-gas emissions. . . .

The strategic implications of the change in shipping routes is emphasized by Russian Prime Minister Vladimir Putin, who at a recent conference claimed that the northern route will soon rival the Suez Canal in importance. From Yale Environment 360:
"The shortest route between Europe’s largest markets and the Asia-Pacific region lies across the Arctic,” Putin told the Arctic Forum, a conference meeting in the White Sea port of Arkhangelsk. “I want to stress the importance of the Northern Sea Route as an international transport artery that will rival traditional trade lanes.” Putin noted that with the northern trade route now largely ice-free in summer, the number of test runs along the route is increasing. . . .  “I have no doubt this is just the beginning,” said Putin, noting that a voyage across the Northern Sea Route from Europe to Asia is a third shorter than traveling through the Suez Canal. But environmentalists warn that a shipping rush in pristine Arctic waters poses serious environmental threats, and that Russia and other Arctic nations must vastly upgrade their ability to react to oil spills and other maritime accidents.

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