Ozone Depletion

Although ozone depletion is caused by chlorine and bromine released by the breakup of halocarbons in the stratosphere, climatic conditions have a strong influence on the rate and intensity of ozone depletion. It is climatic conditions peculiar to southern polar regions, for example, which have dramatically increased ozone depletion (the "ozone hole" ) over Antarctica and the Southern Ocean.

Recent research suggests that greenhouse gas - induced climate change is likely to accelerate ozone depletion over northern polar regions - even in the absence of increased sources of ozone depleting chemicals. Greenhouse gases trap heat in the troposphere, the lower atmosphere, and cool off the stratosphere. This promotes the formation of polar stratospheric clouds. It is chlorine and bromine attached to these chilly ice crystal clouds that is largely responsible for the southern ozone hole.

Continued climate change and development of northern polar stratospheric clouds is likely to create a northern ozone hole, which will appear on a regular basis during the winter and spring, but probably not every year. [31]

In fact, the 1995-6 winter and spring saw the worst northern ozone depletion yet recorded, with some monitoring stations reporting levels below 200 dobson units for the first time - "cracks" in the ozone layer. (Areas with this little ozone are considered to be part of the ozone hole in the southern hemisphere). Low ozone levels similar to those ordinarily found over Mexico and Africa were found over a wide area of the Arctic and Subarctic. [32]