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Published May 28, 2004 | public
Journal Article

Changes in Earth's Reflectance over the Past Two Decades


We correlate an overlapping period of earthshine measurements of Earth's reflectance (from 1999 through mid-2001) with satellite observations of global cloud properties to construct from the latter a proxy measure of Earth's global shortwave reflectance. This proxy shows a steady decrease in Earth's reflectance from 1984 to 2000, with a strong climatologically significant drop after 1995. From 2001 to 2003, only earthshine data are available, and they indicate a complete reversal of the decline. Understanding how the causes of these decadal changes are apportioned between natural variability, direct forcing, and feedbacks is fundamental to confidently assessing and predicting climate change.

Additional Information

© 2004 American Association for the Advancement of Science. 26 November 2003; accepted 21 April 2004. This research was supported in part by a grant from NASA (NAG5-11007). The cloud ISCCP D1 data sets were obtained from the NASA Langley Research Center Atmospheric Sciences Data Center. We are grateful to Y. Yung, B. Soden, T. Schneider, and five anonymous referees for their comments on drafts of this paper.

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