The amount of ultraviolet radiation reaching a particular spot on Earth depends on several factors including the position of the Sun, amount of cloud cover and pollution and ozone levels. This table shows the relationship between ozone loss and UV(B) increase for different positions of the Sun (i.e. seasonal and hemisphere changes) assuming that cloud cover and pollution are the same. (From: WMO, UNEP, NOAA, NASA and EC (1998).)