Long-term variations of global radiation in Central Europe 1950–2020 and their impact on terrestrial surface air warming

Abstract

The variation of global radiation from 1950–2020 and its impact on the terrestrial surface air warming was investigated based on measurements of sunshine duration, global radiation and temperature from six measuring stations from the national weather services in Austria, Switzerland and Germany. A quantitative estimation of that impact was conducted with the help of a multiple linear regression model based on monthly values from the period 1950–2020. The applicability of this approach was ensured by a set of five statistical standard tests. The overall temperature increase from 1950–2020 (about +2.1 °C in the annual and summer semi-annual average at the six measuring stations) is dominated by the temporally continuous temperature increase (global warming). However, a fraction of the increase (+0.3 °C corresponding to about 14% and +0.5 °C corresponding to about 25% for the entire year and the summer half-year, respectively) is attributed to the increase of global radiation. With regard to the brightening period in the last four decades (ca. 1982–2020), the fraction of the increase of global radiation within the total temperature increase is substantial: about one third for the entire year (ca. +0.6 °C), even half for the summer half-year (ca. +1.1 °C). The model results are reasonable in view of the comparison with the temperature measurements at the six stations. Increased air pollution by aerosols led to a continuous weakening of global radiation at the earth’s surface (global dimming) in Europe from about 1950–1980, but with the subsequent improvement of air quality, an increase occurred again (global brightening). Global brightening, which has continued until today, has more than compensated for global dimming of 1950–1980. From 1982–2020, direct solar radiation increased by about one-third in both the summer and winter months. This increase is about twice as large as the decrease during the dimming phase, except for the case of nearly overcast sky. The phases of global dimming and brightening are mainly caused on one hand by increasing and decreasing opacity of the atmosphere by aerosols, the direct aerosol effect. On the other hand, indirect radiative aerosol effects of cloud droplets, including effects of cloud properties, have had an increasing impact on global radiation.