By George Monbiot
Published in the Guardian 3 July 2007
Reading a scientific paper on the train this weekend, I found, to my amazement, that my hands were shaking. This has never happened to me before, but nor have I ever read anything like it. Published by a team led by James Hansen at Nasa, it suggests that the grim reports issued by the Intergovernmental Panel on Climate Change could be absurdly optimistic(1).
The IPCC predicts that sea levels could rise by as much as 59cm this century(2). Hansen’s paper argues that the slow melting of ice sheets the panel expects doesn’t fit the data. The geological record suggests that ice at the poles does not melt in a gradual and linear fashion, but flips suddenly from one state to another. When temperatures increased to 2-3 degrees above today’s level 3.5 million years ago, sea levels rose not by 59 centimetres but by 25 metres. The ice responded immediately to changes in temperature(3).
We now have a pretty good idea of why ice sheets collapse. The buttresses that prevent them from sliding into the sea break up; meltwater trickles down to their base, causing them suddenly to slip; and pools of water form on the surface, making the ice darker so that it absorbs more heat. These processes are already taking place in Greenland and West Antarctica.
Rather than taking thousands of years to melt, as the IPCC predicts, Hansen and his team find it “implausible” that the expected warming before 2100 “would permit a West Antarctic ice sheet of present size to survive even for a century.” As well as drowning most of the world’s centres of population, a sudden disintegration could lead to much higher rises in global temperature, because less ice means less heat reflected back into space. The new paper suggests that the temperature could therefore be twice as sensitive to rising greenhouse gases than the IPCC assumes. “Civilization developed,” Hansen writes, “during a period of unusual climate stability, the Holocene, now almost 12,000 years in duration. That period is about to end.”(4)