GLOBAL RADIATION CLIMATE-CHANGE AT 7 SITES REMOTE FROM SURFACE SOURCES OF POLLUTION

Seven series of global radiation measurements, totaling 190 station-years, were analyzed from sites covering the world-wide range of insolation regimes. All were remote from any local surface sources of atmospheric pollution. Global radiation decreased linearly with year of measurement at all sites and at six of them the decreases were statistically significant, averaging annually 17.67 MJ m-2 yr-1 (0.56 W m-2). Observations of daytime cloud cover made at five of the sites showed no large or significant changes over the same periods. There was some indication that the rates of decline in global radiation were larger at sites and during years with greater-than-average cloud cover. The results confirm an earlier finding of a large-scale decline in insolation, derived from an analysis of data from the World Radiation Network and show that this cannot only be attributed to local sources of pollution. Temporal variations in the rate of insolation decline were small; spatial variations were large and unexplained.