The variation in global climate sensitivity among GCMs is largely attributable to differences in cloud feedbacks, and feedbacks of low - level clouds in particular. (skepticalscience.com)
the figures in the above were based on: «Deriving global climate sensitivity from palaeoclimate reconstructions» Hoffert and Covey, Nature Vol 360, 10th December 1992. (illconsidered.blogspot.ru)
The total surface and atmospheric forcings led Hansen et al. (1993) to infer an equilibrium global climate sensitivity of 3 + / - 1C for doubled CO2 forcing, equivalent to 3/4 + / - 1/4 CW ^ -1 m ^ -2. (realclimate.org)