Co-Authors:
Cohen, S., Department of Environmental Physics and Irrigation, Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Centre, P.O. Box 6, Bet Dagan 50250, Israel
Abstract:
This chapter provides some background material on solar radiation and reviews some of the work done on the changing global radiation (Eg↓) and its influences on earth's climate. The flux density and wavelength of electro-magnetic radiation depend on its temperature. On the earth's surface the wavebands that contain the most energy, are therefore of prime interest in the context of climate influences, and are those emitted by the sun and the earth. Eg↓ is the total solar radiation falling on a horizontal surface of the earth, that is, at the bottom of the atmosphere (BOA). Precise wide-spread measurements of Eg↓ began in the early twentieth century and although it was first assumed that no multi-annual trends in this quantity occurred, by the 1970s there was evidence of significant decreases at some sites. As the evidence for large multi-decadal trends in Eg↓ grew, the relationship between decreasing solar radiation (or global dimming) and wide spread decreasing pan evaporation was noticed. The energetic similarity of these changes led to scientific recognition that changes in Eg↓ play a significant role in climate change. Previous assumptions that other parts of the earth's radiation balance were unchanging have subsequently come under scrutiny. © 2009 Copyright © 2009 Elsevier B.V. All rights reserved..
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