The Cloud Feedback Model Intercomparison Project (CFMIP)

23 The primary objective of CFMIP is to inform future assessments of cloud feedbacks through improved understanding of 24 cloud-climate feedback mechanisms and better evaluation of cloud processes and cloud feedbacks in climate models. 25 However, the CFMIP approach is also increasingly being used to understand other aspects of climate change, such as 26 nonlinear change and regional changes in atmospheric circulation and precipitation. CFMIP is supporting ongoing model 27 inter-comparison activities by coordinating a hierarchy of targeted experiments for CMIP6, along with a set of cloud related 28 output diagnostics. CFMIP contributes primarily to addressing the CMIP6 questions ”How does the Earth System respond to 29 forcing?” and ”What are the origins and consequences of systematic model biases?” and supports the activities of the WCRP 30 Grand Challenge on Clouds, Circulation and Climate Sensitivity. 31 A compact set of Tier 1 experiments is proposed for CMIP6 to address the question: “1) What are the physical mechanisms 32 underlying the range of cloud feedbacks and cloud adjustments predicted by climate models, and which models have the most 33 credible cloud feedbacks?” Additional Tier 2 experiments are proposed to address the following questions: 2) Are cloud 34 feedbacks consistent for climate cooling and warming, and if not, why? 3) How do cloud-radiative effects impact the 35 structure, the strength and the variability of the general atmospheric circulation in present and future climates? 4) How do 36 responses in the climate system due to changes in solar forcing differ from changes due to CO2, and is the response sensitive 37 to the sign of the forcing? 5) To what extent is regional climate change per CO2 doubling state-dependent (nonlinear), and 38 why? 6) Are climate feedbacks during the 20 th century different to those acting on long term climate change and climate 39 sensitivity? 7) How do regional climate responses (e.g. in precipitation) and their uncertainties in coupled models arise from 40 the combination of different aspects of CO2 forcing and sea surface warming? 41 CFMIP also proposes a number of additional model outputs in the CMIP DECK, CMIP6 Historical and CMIP6 CFMIP 42 experiments, including COSP simulator outputs and process diagnostics to address the following questions: 1) How well do 43 clouds and other relevant variables simulated by models agree with observations? 2) What physical processes and 44 mechanisms are important for a credible simulation of clouds, cloud feedbacks and cloud adjustments in climate models? 3) 45 Which models have the most credible representations of processes relevant to the simulation of clouds? 4) How do clouds 46 and their changes interact with other elements of the climate system? 47 Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-70, 2016 Manuscript under review for journal Geosci. Model Dev. Published: 12 May 2016 c © Author(s) 2016. CC-BY 3.0 License.

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