Consistent estimates from satellites and models for the first aerosol indirect forcing

Satellite-based estimates for the aerosol indirect forcing are consistently smaller than those from models due, in part, to the use of present-day results that do not capture the temporal changes between present day and pre-industrial conditions. Here, we use results from a coupled aerosol-climate model to pick regions and seasons that are sufficiently pristine to represent pre-industrial conditions. Then we use results from MODIS and CERES to estimate the forcing between present and pre-industrial conditions. The estimated forcing in the North Pacific Ocean region ranges from -1.8 to -2.2 Wm^-2 from observations. This range is similar to our modeled forcing for this region, -2.65 Wm^-2, but is smaller than the modeled forcing using the same methodology as that used with the satellite observations, -3.6 W/m². Nevertheless, a previous estimate based on satellite observations was a factor of 10 smaller, -0.2 to -0.5 Wm^-2. Results demonstrate that while the estimated forcing from models may be somewhat larger than estimates based on satellite data, a judicious choice of analysis methods, yields results that are much closer than previous satellite and model-based comparisons.