Thursday, April 10, 2008

The Peril of Global Cooling

I recently heard a talk in which the speaker mentioned that during a period of mildly falling global temperatures in the middle of the twentieth century a number of people, including at least one prominent scientist, speculated that the earth was about to go into another ice age and argued that something should be done to warm it.

The speaker took it for granted that they were wrong, but I'm not so sure. The pattern of warming and cooling associated with ice ages and interglacials is complicated and not very well understood. We are currently in an interglacial, have been in one for a fair while, and it would not be surprising if it ended--five thousand years from now, one thousand years from now, or starting next Friday. The global cooling event that started one such episode about 13,000 years ago, the younger Dryas, seems have occurred over less than a century.

Global temperature over the past century or so have been trending up and that pattern may continue, but given how little we know about the complexity of climate science it is not something we can count on.

Assume, for the sake of argument, that global warming along the lines projected by the IPCC is ten times as likely as global cooling in the form of another ice age. Current projections suggest that global warming may be a serious inconvenience, but with a predicted temperature rise of about two degrees centigrade and a sea level rise of a foot or so over the next century there is little reason to expect it to be a catastrophe.

Not, at least, as contrasted to what we know happened during past ice ages—large parts of North America and northern Europe covered by glaciers, a mile of ice over Chicago. Even if the probability is only a tenth as high, the expected loss—probability times damage—is larger.

So perhaps it is global cooling, not global warming, that we should be worrying about.


At 9:45 PM, April 10, 2008, Blogger Ranjit Mathoda said...

You may find the climate change thoughts of Michael Crichton ( and Freeman Dyson ( of interest.


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