"Results from a Low-Sensitivity Model"
at Climate Audit | 7/21/2013
"Anti-lukewarmers/anti-skeptics have a longstanding challenge to lukewarmers and skeptics to demonstrate that low-sensitivity models can account for 20th century temperature history as well as high-sensitivity models. (Though it seems to me that, examined closely, the supposed hindcast excellence of high-sensitivity models is salesmanship, rather than performance.)
Unfortunately, it’s an enormous undertaking to build a low-sensitivity model from scratch and the challenge has essentially remained unanswered.
Recently a CA reader, who has chosen not to identify himself at CA, drew my attention to an older generation low-sensitivity (1.65 deg C/doubling) model. . .
Climate Change 2001:Working Group I: The Scientific Basis
"Climate sensitivity is likely to be in the range of 1.5 to 4.5°C.
"This estimate is unchanged from the first IPCC Assessment Report in 1990 and the SAR. The climate sensitivity is the equilibrium response of global surface temperature to a doubling of equivalent CO2 concentration.
"The range of estimates arises from uncertainties in the climate models and their internal feedbacks, particularly those related to clouds and related processes.
"Used for the first time in this IPCC report is the Transient Climate Response (TCR). The TCR is defined as the globally averaged surface air temperature change, at the time of doubling of CO2, in a 1%/yr CO2-increase experiment.
"This rate of CO2 increase is assumed to represent the radiative forcing from all greenhouse gases. The TCR combines elements of model sensitivity and factors that affect response (e.g., ocean heat uptake). The range of the TCR for current AOGCMs is 1.1 to 3.1°C. ..."
Figure 22: Simple model results: (a) global mean temperature projections for the six illustrative SRES scenarios using a simple climate model tuned to a number of complex models with a range of climate sensitivities. Also for comparison, following the same method, results are shown for IS92a. The darker shading represents the envelope of the full set of thirty-five SRES scenarios using the average of the model results (mean climate sensitivity is 2.8°C). The lighter shading is the envelope based on all seven model projections (with climate sensitivity in the range 1.7 to 4.2°C). The bars show, for each of the six illustrative SRES scenarios, the range of simple model results in 2100 for the seven AOGCM model tunings.
(b) Same as (a) but results using estimated historical anthropogenic forcing are also used. [Based on Figures 9.14 and 9.13b]