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ECS in Climate Models: Quantifying the Uncertainties due to Cloud Feedback Versus Ocean Heat Uptake Using a Modeling Hierarchy

Funding Program Area(s)
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University Grant
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Collaborative Institutional Lead

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Equilibrium Climate Sensitivity (ECS), which characterizes the Earth’s surface temperature response to increased atmospheric CO2 concentration, is an important property of the climate system. The range of ECS diagnosed in comprehensive climate models has not been narrowed with the progress made in these models, leading to large uncertainties in Earth’s temperature projection and associated social-economic impacts. Uncertainties in cloud feedbacks have been identified as the main cause of the large range of ECS, but oceanic adjustments, especially those associated with ocean heat uptake (OHU) and the Atlantic Meridional Overturning Circulation (AMOC), also play an important role. In this proposed work, we will focus on understanding the individual and combined roles of cloud feedbacks and ocean adjustments in modulating the ECS. The proposed research is motivated by our overarching hypothesis that oceanic adjustment is a key source of uncertainty, in addition to that associated with the cloud feedbacks; further, the ocean adjustment and the associated OHU work through the cloud feedbacks to modulate the ECS. Our strategy is to combine existing model output diagnoses with a modeling hierarchy in which we systematically enable and disable cloud feedbacks in conjunction with perturbations to OHU.