Clouds, solar irradiance and mean surface temperature over the last century

The inter-relation of clouds, solar irradiance and surface temperature is complex and subject to different interpretations. Here, we continue our recent work, which related mainly to the period from 1960 to the present, back to 1900 with further, but less detailed, analysis of the last 1000 years. The last 20 years is examined especially. Attention is given to the mean surface temperature, solar irradiance correlation, which appears to be present (with decadal smoothing) with a 22-year period; it is stronger than the 11-year cycle correlation with one year resolution. UV in the solar radiation is a likely cause. Cloud data are taken from synoptic observations back to 1952 and, again, there appears to be a correlation—with opposite phase for high and low clouds—at the 20–30 y level. Particular attention is devoted to answering the question, ‘what fraction of the observed increase in mean Global temperature (∼0.7∘C) can be attributed to solar, as distinct from man-made, effects?’We conclude that a best estimate is ‘essentially’ all from 1900 to 1956 and <14%<14% from 1956 to the present.