Speaker: Riovie Ramos (William Paterson Univ.)
Topic: Can past climates constrain cloud and convective parameterizations?

Cloud and convective parameterizations strongly influence uncertainties in equilibrium climate sensitivity (ECS). We provide a proof-of-concept study to constrain these parameterizations in a perturbed parameter ensemble of the atmosphere-only version of the Goddard Institute for Space Studies (GISS) Model E2.1 simulations by evaluating model biases in the present-day runs using multiple satellite climatologies and by comparing simulated delta18O of precipitation (delta18Op), known to be sensitive to parameterization schemes, with a global database of speleothem delta18O records covering the Last Glacial Maximum (LGM), mid-Holocene (MH) and pre-industrial (PI) periods. Relative to modern, paleoclimate simulations show greater sensitivity to parameter changes, allowing for an evaluation of model uncertainties over a broader range of climate forcing and the identification of parts of the world that are parameter sensitive. Certain simulations reproduced absolute delta18Op values across all time periods and LGM and MH delta18Op anomalies relative to the PI better than the default parameterization. Not a single set of parameterizations worked well in all climate states, likely due to the non-stationarity of cloud feedbacks under varying boundary conditions.