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.
In short: We can now estimate, based on observations, how sensitive the temperature is to carbon dioxide. We do not need to rely heavily on unproven models. Comparing the trend in global temperature over the past 100-150 years with the change in “radiative forcing” (heating or cooling power) from carbon dioxide, aerosols and other sources, minus ocean heat uptake, can now give a good estimate of climate sensitivity.
The conclusion—taking the best observational estimates of the change in decadal-average global temperature between 1871-80 and 2002-11, and of the corresponding changes in forcing and ocean heat uptake—is this: A doubling of CO2 will lead to a warming of 1.6°-1.7°C (2.9°-3.1°F). This is much lower than the IPCC’s current best estimate, 3°C (5.4°F).
Given what we know now, there is almost no way that the feared large temperature rise is going to happen. Mr. Lewis comments: “Taking the IPCC scenario that assumes a doubling of CO2, plus the equivalent of another 30% rise from other greenhouse gases by 2100, we are likely to experience a further rise of no more than 1°C.”
A cumulative change of less than 2°C by the end of this century will do no net harm. It will actually do net good—that much the IPCC scientists have already agreed upon in the last IPCC report. Rainfall will increase slightly, growing seasons will lengthen, Greenland’s ice cap will melt only very slowly, and so on.
The scientists at the IPCC next year have to choose whether they will admit—contrary to what complex, unverifiable computer models indicate—that the observational evidence now points toward lukewarm temperature change with no net harm. On behalf of all those poor people whose lives are being ruined by high food and energy prices caused by the diversion of corn to biofuel and the subsidizing of renewable energy driven by carboncrats and their crony-capitalist friends, one can only hope the scientists will do so.