PNNL

Abstract

Analysis of changes in the surface and atmospheric energy budgets in response to CO2 and solar forcings can be used to reveal changes in the hydrologic cycle, as well as mechanisms causing these changes. We apply for the first time this energetic perspective to output from 11 fully coupled atmosphere-ocean general circulation models simulating experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP), which balances an abrupt quadrupling of CO2 concentrations from preindustrial levels (abrupt4xCO2) with uniform solar irradiance reduction. We divide the climate system response into a rapid adjustment, in which climate response is due to adjustment of the atmosphere and land surface on short time scales, and a feedback response, in which the climate response is predominantly due to feedbacks related to global mean temperature changes. Global mean temperature change is small in G1, so the feedback response is also small. G1 shows a comparatively smaller magnitude of land sensible heat flux rapid adjustment than in abrupt4xCO2 and a comparatively larger magnitude of latent heat flux adjustment, indicating a greater reduction of evaporation and less land temperature increase than abrupt4xCO2. Unlike for abrupt4xCO2, the sum of the radiative and turbulent fluxes in G1 shows small changes, indicating little ocean heat uptake. Using an energetic perspective to assess precipitation changes, abrupt4xCO2 shows a decrease in mean evaporative moisture flux and an increase in moisture convergence, particularly over land. However, most changes in precipitation in G1 are due to changes in mean evaporative flux, suggesting changes in precipitation due to changes in mean circulation are small. In G1, these changes in precipitation are approximately equivalent in magnitude to changes in latent heat flux, indicating that changes in precipitation minus evaporation are small.