Global radiation climate changes: The world network

Changes in global radiation measured with thermoelectric pyranometers at stations of the World Radiation Network in 1958, 1965, 1975 and 1985 were found to be large and statistically significant in many cases. Comparison of the data from the 46 unmoved stations and from the spline-fitted latitudinal distributions of the more than one hundred measurements available for each year yielded the same mean reduction. This was 5.3% (9 W m^-2) for the difference in annual irradiation between 1958 and 1985 weighted for the land surfaces of the Earth. Causes of the substantial spatial and temporal variations found in the magnitude, significance and even sign of the changes could not be clearly identified because of the uneven distribution of the station network, the small number of years examined and the unknown accuracy of the measurements. Detailed studies at carefully selected individual pyranometer stations are needed to resolve these difficulties.Contribution from the Agricultural Research Organization, The Volcani Centre, Bet Dagan, Israel. No. 2991-E, 1990 series.