| Summary: | Solar UVB irradiance is measured worldwide with the Robertson-Berger sunburn meter whose spectral sensitivity is adapted to the action spectrum of human erythema. Thus, the Robertson-Berger sunburn meter measures the erythemal effective irradiance. In Alpine areas, on cloudless days in midsummer, the increase with altitude in global (direct and diffuse) erythemal effective irradiance is about 18 % per 1000 m, while the increase in total irradiance is about 8 % per 1000 m. The share of global erythemal effective irradiance in global total irradiance varies significantly in the seasonal course, with a maximal share occurring in midsummer. The share of diffuse irradiance in global irradiance is 35 % for erythemal effective and 8 % for total irradiance on cloudless days in midsummer. In high mountains and glaciated terrain, erythemal effective irradiance decreases to 61 % and total irradiance to 47 % at cloudiness 10/10 and the sun completely covered, compared with 100 % at 0/10 cloudiness. In the period 1981-91 a slight increase of erythemal effective irradiance was obtained at the high-mountain station Jungfraujoch (3576 m a.s.l., Switzerland), while a decrease was found in urban areas (USA, Russia). In the Alpine area, the enhanced ozone depletion observed in northern mid-latitudes in winter/spring 1992/93 caused an increase in instantaneous erythemal effective irradiance of up to 40 % measured on clear days at fixed solar elevations. However, daily totals irrespective of cloudiness, show no significant increase in erythemal effective irradiance. The mean daily totals over 7 days are within the range of standard deviation of the reference values for 1981-88. Consequently, there is no conclusive proof of an increased exposure of the ecosystem and humans. The health risks of ozone depletion are generally described by means of the Radiation Amplification Factor and the dose-response relationship. A 1 % decrease in ozone produces a 2.6 % increase in non-melanoma skin cancer and enhances cataract incidence by 0.6-0.8 %.
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