Ridley on climate sensitivity

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).
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The big question is this: Will the lead authors of the relevant chapter of the forthcoming IPCC scientific report acknowledge that the best observational evidence no longer supports the IPCC’s existing 2°-4.5°C “likely” range for climate sensitivity? Unfortunately, this seems unlikely—given the organization’s record of replacing evidence-based policy-making with policy-based evidence-making, as well as the reluctance of academic scientists to accept that what they have been maintaining for many years is wrong.

Source.