Climate change should be humans' top priority

From a very responsible and reliable source come some very frightening words on climate change (or global warming).

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 optimistic¹.

The IPCC predicts that sea levels could rise by as much as 59cm this century². 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 temperature³.

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.

¹. James Hansen et al, 2007. Climate Change and Trace Gases. Philiosophical Transactions of the Royal Society – A. Vol 365, pp 1925-1954. doi: 10.1098/rsta.2007.2052. http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf

². Intergovernmental Panel on Climate Change, February 2007. Climate Change 2007: The Physical Science Basis – Summary for Policymakers. Table SPM-3. http://www.ipcc.ch/SPM2feb07.pdf

³. I am grateful to Marc Hudson for drawing my attention to this paper and giving me a copy.

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