Authors: E. Palle; P. Montanes-Rodriguez; P.R. Goode; S.E. Koonin
Affiliation: Big Bear Solar Observatory; New Jersey Institute of Technology;
Kellogg Radiation Laboratory; California Institute of Technology
The net sun light reaching the Earth is the main driver of the climate system.
This net radiation depends both on the solar constant and the earth's albedo.
Several mechanisms have been proposed in the literature to affect the earth's
clouds/albedo perhaps providing an indirect amplification mechanism of the solar
signal.
Since 1998, earthshine measurements of the Earth's reflectance have been routinely
carried out at Big Bear Solar Observatory. We correlate the overlapping period
(1999 through mid-2001) of these observations with satellite observations of
global cloud properties to construct from the latter a proxy measure of the
Earth's global shortwave reflectance. This proxy shows a steady decrease in
the earth's reflectance from 1984 to 2000, with a strong drop during the 1990's.
During 2001-2003 only earthshine data are available, and they indicate a complete
reversal of the decline. The radiative forcing implied by either of these decadal
changes in reflectance is climatologically significant. Understanding how these
changes are apportioned between natural variability, direct forcing, and feedbacks,
is fundamental to confidently assessing and predicting climate change.