Satellite‐based assessment of top of atmosphere anthropogenic aerosol radiative forcing over cloud‐free oceans

Abstract

Most assessments of the direct climate forcing (DCF) of anthropogenic aerosols are from numerical simulations. However, recent advances in remote sensing techniques allow the separation of fine mode aerosols (anthropogenic aerosol is mostly fine aerosol) from coarse mode aerosols (largely marine and dust, which are mostly natural) from satellite data such as the Moderate Resolution Imaging SpectroRadiometer (MODIS). Here, by combining MODIS narrowband measurements with broadband radiative flux data sets from the Clouds and the Earth's Radiant Energy System (CERES), we provide a measurement‐based assessment of the global direct climate forcing (DCF) of anthropogenic aerosols at the top of atmosphere (TOA) only for cloud free oceans. The mean TOA DCF of anthropogenic aerosols over cloud‐freeoceans [60N–60S] is −1.4 ± 0.9 Wm−2, which is in excellent agreement (mean value of −1.4 Wm−2) with a recent observational study by Kaufman et al. [2005].