Forget the Doha climate jamboree that ended earlier this month. The theological discussions in Qatar of the arcana of climate treaties are irrelevant. By far the most important debate about climate change is taking place among scientists, on the issue of climate sensitivity: How much warming will a doubling of atmospheric carbon dioxide actually produce? The Intergovernmental Panel on Climate Change has to pronounce its answer to this question in its Fifth Assessment Report next year.

The general public is not privy to the...