Ultraviolet radiation at high latitudes and the risk of skin cancer.

Solar irradiance in the spectral region 280 to 800 nm was measured with a double monochromator at 2 locations in Norway, Tromsø (69.7 degrees N) and Longyearbyen (78.2 degrees N). During the observational (midnight sun) period in Longyearbyen, the maximum UVB irradiance recorded was less than 0.3 W/m2, and no radiation was detected for wavelengths below 300 nm. Such low levels are believed to be a consequence of the low solar elevation angle and the high ozone content of the Arctic ozone layer, which absorbs the incident UV light. With levels between 280 and 350 DU over the period of study, Tromsø and Longyearbyen recorded only one-ninth of the calculated UVB radiation at the equator. There is therefore a considerably higher risk of radiation damage to the skin in equatorial regions (controlling for skin type), a finding that agrees with the statistical evidence for a 7-8 times higher rate of skin cancer in the white population of equatorial countries.