High-Resolution Image

Satellite instruments cannot directly measure the aerosol chemical composition which is needed to discriminate man-made or anthropogenic aerosols (smoke or air pollution) from natural aerosols (dust or sea salt). However the MODIS satellite's ability to distinguish fine (submicron) from coarse (supermicron) aerosols over the oceans, serves as a signature of the anthropogenic component and can be used to estimate it. The image shows the total aerosol optical thickness (a measure of the aerosol loading) (top figure) and the corresponding anthropogenic aerosol (bottom figure) for the period June-August and September-November.

Application of two years of global MODIS data shows that 21±7% of the aerosol optical thickness over the oceans has an anthropogenic origin. We found that three chemical transport models, used for global estimates of the aerosol forcing of climate, calculate a global average anthropogenic optical thickness over the ocean between 0.030 and 0.036, in line with the present MODIS assessment of 0.033. This increases our confidence in model assessments of the aerosol direct forcing of climate. The MODIS estimated aerosol forcing of climate over cloud free oceans is therefore -1.4±0.4 W/m2.

Click here to view a recent paper by Y. J. Kaufman, O. Boucher, D. Tanre, M. Chin, L. A. Remer, and T. Takemura, 2005: Aerosol anthropogenic component estimated from satellite data. Submitted to Geophys. Res. Lett.