Are There Observational Proxies in the Presentday Climate for Future Cloud Perturbations

Climate sensitivity, defined as the equilibrium change in global mean temperature in response to a doubling in the atmospheric CO2 concentration, is still a very uncertain quantity (e.g., Randall et al. 2007). The primary reason for the spread in climate sensitivities, as simulated by different global climate models, is the difference in the representation of cloud processes and cloud-climate feedbacks (Soden and Held 2006; Dufresne and Bony 2008). Cloud processes determine the amount and distribution of precipitation, which is a key parameter for land-atmosphere interactions, for carbon-climate feedbacks, and for climate impact studies (e.g., water resources). Moreover, the representation of cloud microphysical properties is critical for the simulation of interactions between clouds and aerosols. Improving how cloud processes are represented in global climate models is thus of paramount importance, not only for estimates of climate sensitivity but also for projections of future climate change and their use in impact studies.

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