Via a link from Eric Raymond, I've just been reading a presentation
by Richard Lindzen, an MIT climate scientist critical of current global warming arguments. His basic claims:
1. The direct effect of a doubling of atmospheric CO2 should be about a one degree C increase in global temperatures. The substantially larger effect projected in the IPCC reports depends on positive feedbacks in their models.
2. The atmosphere is a sufficiently complicated system so that predicting feedback effects on the basis of theory is difficult or impossible. Insofar as the feedbacks can be estimated empirically, they appear to be negative, not positive.
3. The historical evidence shows about a one degree increase from the past doubling. In order to make that consistent with the models it is necessary to include in the models additional features to explain a lower increase than would otherwise be predicted.
Interested readers should follow the link and look at the presentation themselves, both because my summary may not be entirely accurate--it's based on a single reading--and because there is a lot more there.
I do not know enough about climate science to judge the argument on its merits. Lindzen sounds convincing, but it would be nice to see what sort of rebuttals people who disagree with him can offer—perhaps some readers can offer links to such. As I have commented in earlier posts, my own criticism of current global warming arguments and policy is based on the economics not the climate science. I have yet to see any convincing reason to believe that an increase in temperature of the magnitude suggested by the IPCC reports would have net negative consequences, let alone catastrophic ones. Apropos of which ... .
Human settlement and agriculture are currently limited by cold not by heat—the equator is populated, the poles are not. If global temperatures go up, more land in the northern hemisphere should become warm enough for human purposes. How big is the effect—by how many miles does the temperature contour shift? I recently did a very rough back-of-the-envelope calculation in response to someone online suggesting that the effect was larger than I was assuming, and concluded he was correct.
I estimated the rate at which temperatures change as you move north from a page
showing that day's maximum temperatures in different parts of the world. Assuming the rate of change is uniform and about the same for maximum, minimum, and average, a three degree C increase in temperature represents a shift of climate contours by more than two hundred miles—enough to more than double the effective area of Canada. Hopefully some reader can point me at a more accurate estimate, but I think that's sufficient to suggest the scale of the effect.
Freeman Dyson, in The Scientist as Rebel, argues that increased CO2 should have a larger effect on temperatures in colder areas. The argument is fairly simple. Water vapor is a strong greenhouse gas. The more water vapor in the air, the less the effect of adding CO2. The colder the climate, the less water vapor in the air.
If he is right, then the effect on the northern limits of human habitation should be larger than my calculation shows. As far as I can see, the result is a large gain from the standpoint of human beings, via a large increase in the amount of usable land in North America and Eurasia. It would be interesting to compare the size of that increase to the size of the decrease in usable land from the sea level rise of a foot or two suggested by the IPCC models; my guess is that the decrease is much less than the increase, but I have not done the calculation.
One would also expect an increase in average temperatures to raise them at the equator—although by less, if Dyson is correct. I am not sure how large the resulting negative effects would be; people live and farm at the equator, but my guess is that temperatures are already above what would be optimal from their standpoint, hence an increase would be, for them, a loss not a gain.
Tim Lambert, in the comments, offers a link
to a page with criticisms of Lindzen's position.