Published online by Cambridge University Press: 05 October 2012
Introduction
Anthropogenic ozone depletion in the stratosphere causes enhanced ultraviolet-B (UV-B) radiation on the Earth's surface (Taalas et al. 2000; ACIA 2005). Ozone layer thickness and ozone depletion vary with season and latitude. At present, the ozone layer has had measurable reductions at mid-latitudes, and is most vulnerable near the poles. The ozone hole over Antarctica has occurred consistently since the early 1980s; over the years, it has varied in depth and size. Harmful UV-B radiation is partly absorbed by the stratospheric ozone layer, but the ozone layer has no attenuating effect on UV-A radiation.
The intensity of solar UV radiation incident on organisms and ecosystems is influenced by a range of factors, making it a highly dynamic component of the environment. Solar elevation contributes to latitudinal, seasonal, and diurnal variations in UV; these variations are more pronounced for UV-B than for UV-A. The increase in UV-A penetration with altitude might be little more than that for total irradiance, but penetration of UV-B is higher (Paul & Gwynn-Jones 2003). Clouds, albedo, and aerosols also influence the diurnal, seasonal, and interannual variation of UV radiation (Taalas et al. 2000). The largest relative increase in UV-B caused by ozone depletion has occurred at high latitudes. In the Northern Hemisphere, Arctic areas of Scandinavia are expected to be affected by the largest UV changes and steepest ozone depletion (Björn et al. 1998; Taalas et al. 2000). The greatest increase in UV-B radiation at high latitudes occurs in the spring.
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