Reading the IPCC Report

The reports are now in part out and webbed, and I started by looking over "Summary for Policymakers" from the Working Group II report. It makes an interesting contrast with the news stories. For instance:

"Globally, the potential for food production is expect to increase with increases in average temperature over a range of 1-3 degrees centigrade, but above this it is projected to decrease."

Or in other words, given the predicted temperature increase of .2 degrees/decade, global warming will tend to increase food production for at least the next fifty years, and perhaps as much as the next hundred and fifty. Has anyone noticed that prediction in news stories about the report?

"Globally, commercial timber productivity rises modestly with climate change in the short- to medium-term, ... "

I also like "Nearly all European regions are anticipated to be negatively affected by some future impacts of climate change, ... ." Note the "some." It's hard to imagine any substantial change in the world, good or bad, for which which the statement would not be true.

Also note, from Chapter 2, that the projections of sea level rise "are smaller than given in the TAR due mainly to improved estimates of ... " TAR appears to be the 2001 estimate, if I understand it correctly. Perhaps I missed it--did any news story report that fact?

As Tim points out, the IPCC is now hedging its sea level predictions--in part by pointing out the uncertainty, in part by saying what might happen over thousands of years and adding that they can't be certain it won't happen over mere centuries. But the six scenarios they provide numbers for give predictions ranging from a low of .18 meters to a high of .59 meters--about two feet. The bulk of that is from thermal expansion, so actual melting of continental ice would have to be several times as high as their estimate in order to substantially increase it.

I am, of course, selecting bits from the post that support my point--that the news stories are hype, selecting out negative predictions, often very uncertain ones, and ignoring positive predictions and ambiguity. There are other bits of the report that do indeed support a negative view of the consequences.

Another point that struck me was how much of the report depended not on climate science, however good or bad that may be, but on social science, especially economics. My guess, from a quick look over it, is that those results are very uncertain and might easily get the sign of the effects wrong.

People adjust to change--they vary the crops they grow, the areas under cultivation, where they live and the like in response to changing climate. If you assume no such adjustment--not, I think, what the IPCC is doing--then the net result is almost certainly negative. With enough adjustment, taking advantage of opportunities produced by, for example, longer growing seasons, the net result can be positive. It's not clear how they know, or how they can know, how much adjustment will actually take place. I am reminded, perhaps unfairly, of just how bad the predictions in _Limits to Growth_ turned out to be.