Abstract

Aerosol radiative forcing from direct and indirect effects of aerosols is examined over the recent past (last 10-15 years) using updated sulfate aerosol emissions in two Earth System Models with very different surface temperature responses to aerosol forcing. The hypothesis is that aerosol forcin... Show moreAerosol radiative forcing from direct and indirect effects of aerosols is examined over the recent past (last 10-15 years) using updated sulfate aerosol emissions in two Earth System Models with very different surface temperature responses to aerosol forcing. The hypothesis is that aerosol forcing and in particular, the impact of indirect effects of aerosols on clouds (Aerosol-Cloud Interactions, or ACI), explains the recent ‘hiatus’ in global mean surface temperature increases. Sulfate aerosol emissions increase globally from 2000 to 2005, and then decrease slightly to 2010. Thus the change in anthropogenic sulfate induced net global radiative forcing is small over the period. Regionally, there are statistically significant forcings that are similar in both models, and consistent with changes in simulated emissions and aerosol optical depth. Coupled model simulations are performed to look at impacts of the forcing on recent surface temperatures. Temperature response patterns in the models are similar, and reflect the regional radiative forcing. Pattern correlations indicate significant correlations between observed decadal surface temperature changes and simulated surface temperature changes from recent sulfate aerosol forcing in an equilibrium framework. Sulfate ACI might be a contributor to the spatial patterns of recent temperature forcing, but not to the global mean 'hiatus' itself. Show less