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Kaufman, Y., O. Boucher, D. Tanre, M. Chin, L. Remer, and T. Takemura, 2005:
Aerosol anthropogenic component estimated from satellite data.
Geophys.
Res. Lett, 32, L17804, doi:10.1029/2005GL023125, 2005.
Satellite instruments do not measure the aerosol chemical
composition needed to discriminate anthropogenic from
natural aerosol components. However the ability of new
satellite instruments 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 the fraction of anthropogenic aerosols with an
uncertainty of ±30%. Application to 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 over
cloud free oceans is therefore 1.4 ± 0.4 W/m2.
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