PNNL

Abstract

By examining the historical temperature record during the industrial era, we can infer the climate’s sensitivity to radiative perturbations, given knowledge of historical forcings. Energy conservation enforces a negative correlation between the climate feedback and historical forcing for a given change in global-mean temperature. Here, we examine the negative correlation between the radiative forcing due to aerosol-cloud interactions and the shortwave cloud feedback to warming that appears in a perturbed parameter ensemble (PPE). The PPE is not tuned with the intention of matching the historical record, but we show that a negative correlation emerges due to the combined effects of liquid cloud precipitation efficiency and radiative saturation in the shortwave. Using an energy balance model, we argue that these processes combine to push Earth System Models to yield a temperature record in keeping with observations but also limit our ability to constrain future warming posterior with the temperature record.