evidence: In a more systematic evaluation of the sensitivity of a model to cloud parameterization, Mitchell et al. (1987) and later Senior and Mitchell (1993) examined the response of a GCM model to a doubling of CO2 when different versions of a cloud parameterization were employed in the same model. The results of their studies are summarized in Fig. 13 showing a sequence of global warming predictions as different feedbacks are systematically introduced. The first estimate corresponds to the warming in the absence of feedback, the next with water vapor feedback added, the third with snow/ice albedo feedbacks added to water vapor feedback and finally the case when cloud feedback is added. Senior and Mitchell (1993) found that the presence and absence of microphysical and optical thickness feedbacks, which were permitted in different versions of the parameterizations, produce a range in warming between 1.9° and 5.4°C. Yao and Del Genio (2002) also reported that the 2 × CO2 sensitivity of the Goddard Institute for Space Studies (GISS) GCM was similarly dependent on the details of the moist convection and large-scale cloud parameterizations. [...] The sensitivity of coupled ocean–atmospheric models to cloud feedbacks differs from the sensitivity of models with fixed SSTs (e.g., Ma et al. 1994; Williams et al. 2003; and also acknowledged in Cess and Potter 1988). CMIP (Meehl et al. 2000), under the auspices of the World Climate Research Program (WCRP) Working Group on Coupled Models (WGCM) was created specifically to examine and compare coupled models forced by 1% yr−1 increases in CO2.