Ultraviolet insolation and the tropical rainforest: Altitudinal variations, Quaternary and recent change, extinctions, and the evolution of biodiversity

Ultraviolet light occurs in three wavebands. UV-A is the longest waveband (>315 nm) which is close to visible light and is of limited biological significance. UV-B (280–315 nm) is damaging and mutagenic to living organisms. UV-C (<280 nm) is lethal to all life, but is fortunately absorbed in the stratosphere, so does not reach the surface of the Earth in sunlight. It is therefore toUV-B that we must turn our chief attention. This, like UV-C, is also partly absorbed by ozone in the stratosphere, but some reaches the Earth’s surface. Recent concerns about the ‘‘Ozone Hole’’ have focussed attention on polar regions, but in fact tropical regions have fairly low ozone concentrations in the stratosphere above them (Smith and Warr, 1991). The result is that, given their high overall insolation resulting from the low latitude, tropical regions have rather high UV-B levels.