Using Aerocom Results to Constrain Black Carbon, Sulphate and Total Direct Aerosol Radiative Forcing and Their Uncertainties

Abstract:

Aerosols affect the global radiative balance, and hence the climate, through a multitude of processes. However, even the direct interaction of aerosols with incoming sunlight is at present insufficiently constrained. Here we compare the output of 15 recent aerosol climate models (AeroCom Phase II), both column averaged and vertically resolved. Through a simple MonteCarlo approach, we show that the model based total anthropogenic aerosol direct radiative forcing (DRF) uncertainty may be underestimated. Constraining modelled vertical profiles of black carbon (BC) concentration to aircraft measurements in remote regions, we further show that recent BC DRF estimates may be biased high. A short modelled BC lifetime is indicated as a necessary, though not sufficient, requirement for reproducing measurements. Finally, modeled sulphate aerosol DRF is discussed in the context of differences in representation of humidity and hygroscopic growth in the models.