5.35*ln(386.59/341.44) = 0.66 W m-2 alleged CO2 forcing at the top of the atmosphere
which equates to only 0.66 * 1/3.7 = 0.18 W m-2 at the Earth's surfaceThe paper adds to several others showing that a decrease in cloudiness was largely responsible for warming in the latter 20th century, rather than man-made greenhouse gases.
Atmos. Chem. Phys., 12, 9581-9592, 2012
Atmospheric impacts on climatic variability of surface incident solar radiation
1State Key Laboratory of Earth Surface Processes and Resource Ecology, College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, Beijing, China
2Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA
3Institute for Atmospheric and Climate Science, ETH Zürich, 8092 Zürich, Switzerland
4Department of Geography, University of Maryland, College Park, MD 20742, USA
Abstract. The Earth's climate is driven by surface incident solar radiation (Rs). Direct measurements have shown that Rs has undergone significant decadal variations. However, a large fraction of the global land surface is not covered by these observations. Satellite-derived Rs has a good global coverage but is of low accuracy in its depiction of decadal variability. This paper shows that daily to decadal variations of Rs, from both aerosols and cloud properties, can be accurately estimated using globally available measurements of Sunshine Duration (SunDu). In particular, SunDu shows that since the late 1980's Rs has brightened over Europe due to decreases in aerosols but dimmed over China due to their increases. We found that variation of cloud cover determines Rs at a monthly scale but that aerosols determine the variability of Rs at a decadal time scale, in particular, over Europe and China. Because of its global availability and long-term history, SunDu can provide an accurate and continuous proxy record of Rs, filling in values for the blank areas that are not covered by direct measurements. Compared to its direct measurement, Rs from SunDu appears to be less sensitive to instrument replacement and calibration, and shows that the widely reported sharp increase in Rs during the early 1990s in China was a result of instrument replacement. By merging direct measurements collected by Global Energy Budget Archive with those derived from SunDu [Sunshine Duration], we obtained a good coverage of Rs [surface incident solar radiation] over the Northern Hemisphere. From this data, the average increase of Rs [surface incident solar radiation] from 1982 to 2008 is estimated to be 0.87 W m−2 per decade.