"Earth's global albedo, or reflectance, is a critical component of the global climate as this parameter, together with the solar constant, determines the amount of energy coming to Earth. Probably because of the lack of reliable data, traditionally the Earth's albedo has been considered to be roughly constant, or studied theoretically as a feedback mechanism in response to a change in climate. Recently, however, several studies have shown large decadal variability in the Earth’s reflectance. Variations in terrestrial reflectance derive primarily from changes in cloud amount, thickness and location, all of which seem to have changed over decadal and longer scales.
A global and absolutely calibrated albedo can be determined by measuring the amount of sunlight reflected from the Earth and, in turn, back to the Earth from the dark portion of the face of the Moon (the earthshine or ashen light). For more than a decade we have been measuring the Earth’s large-scale reflectance from Big Bear Solar Observatory (BBSO). To get full coverage of the Earth, we have installed a carefully calibrated copy of the BBSO earthshine telescope in El Teide Observatory (OT) in Tenerife."