![]() The Earth's albedo (or reflectance) is the fraction of shortwave solar radiation that it reflects back to space. The recent drop in albedo is attributed to a warming of the eastern pacific, which is measured to reduce low-lying cloud cover and, thereby, the albedo. The evolutionary changes in albedo motivate continuing earthshine observations as a complement to absolute satellite measurements, especially since earthshine and CERES measurements are sensitive to distinctly different parts of the angular reflectivity. CERES global albedo data (2001-) show a decrease in forcing that is about twice that of earthshine measurements. The first precise satellite measures of terrestrial albedo came with CERES. We find no correlation between measures of solar cycle variations and the albedo variations. The albedo shows a decline corresponding to a net climate forcing of about 0.5. ![]() We report here reflectance data (monthly, seasonal and annual) covering two decades, 1998–2017. In these relative measurements, we also observe the sunlit, bright part of the lunar face. For earthshine we measure the sunlight reflected from Earth to the dark part of the lunar face and back to the nighttime observer, yielding an instantaneous large-scale reflectance of the Earth. We have observed earthshine from Big Bear Solar Observatory to measure the terrestrial albedo. The net sunlight reaching the Earth's climate system depends on the solar irradiance and the Earth's reflectance (albedo). The CERES decline is about twice that of earthshine. The inter-annual pattern of earthshine fluctuations are in good agreement with those measured by CERES (data began in 2001) even though the satellite observations are sensitive to retroflected light while earthshine is sensitive to wide-angle reflectivity. We found no correlation between the changes in the terrestrial albedo and measures of solar activity. We measure a gradual, but climatologically significant 0.5 decline in the global albedo over the two decades of data. We find the inter-annual fluctuations in albedo to be global, while the large variations in albedo within individual nights and seasonal wanderings tend to average out over each year. ![]() ![]() The reflectance of the Earth is a fundamental climate parameter that we measured from Big Bear Solar Observatory between 19 by observing the earthshine using modern photometric techniques to precisely determine daily, monthly, seasonal, yearly and decadal changes in terrestrial albedo from earthshine. ![]()
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