Numerical Climate Modeling and Water Vapor Feedback

Yale University, New Haven CT

Investigators

Abstract

The problem being studied is how a changing climate will affect and be affected in turn by water vapor feedbacks. The main questions the PI will try to answer are: (1) why do global climate models (GCMs) produce water vapor feedback in accord with thermodynamic arguments, while some other models fail to do so; what types of models are trustworthy in addressing this issue, and for what physical reasons; and, will relative humidity in the upper troposphere stay constant as climate changes, or decrease with warming as suggested by some recent studies? These questions will be addressed through atmospheric GCMs (AGCM) climate-change experiments with microphysical and macrophysical alterations to the model. The Community Climate System Model (CCSM) atmospheric component (CAM) will be adapted for this use. The modeling capabilities initiated through this project will also be used for collaborative research with other Yale faculty on paleoclimate questions, and will be made available for student and educational use to the Yale community. A global modeling component to such projects has become increasingly feasible owing to the steadily declining costs of computing. This research aims to resolve some longstanding and controversial questions surrounding the importance of small vs. large-scale processes in determining global humidity, and the transport of water species near the tropical tropopause at convective outflow levels. Broader Impacts: Results should lead either to improved confidence in model forecasts of climate change, or else a more focused idea of where work is most needed. Either result would ultimately improve the usefulness of climate forecasts for societal and policy consideration. Also, this effort should facilitate greater use of quantitative and rigorous climate calculations in related research areas (ecological and societal impacts, paleoclimate, etc.).