Changes in solar energy availability for south-eastern Europe with respect to global warming

The aim of this study is to estimate projected changes of global radiation parallel to the global warming in south-eastern Europe. As a first step, statistical dependence of global radiation from local cloud indicators is analysed for a short period (1992–1996). Global radiation is derived from METEOSAT visual images, whereas cloud coverage is described in two parallel ways: surface-based visual cloudiness from 171 stations of the region and satellite based Outgoing Long-wave Radiation (OLR). In the second step regression coefficients of these cloud indicators against the hemispherical mean temperature are determined using an adaptation of the method of instrumental variables in recent monotonously warming periods: i.e. 1973–1996 for cloudiness, and 1979–2000 for the OLR. The local variables are used as independent variables of the first step and as dependent variables of the second one. As the last step of the whole computation the regression coefficients derived in the first and second step are combined to calculate expected change of global radiation. The product of the two regression coefficients typically yields a few percent of relative changes in global radiation considering 0.5 K hemispherical warming. The signs of the changes are overwhelmingly positive, indicating more solar energy expected to be available for agricultural and industrial purposes.