Winter 201112    #15
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First Time Ozone Hole
Formed in the Arctic

      In 2011, for the first time, ozone was destroyed over the Arctic regions to an extent comparable to yearly losses in Antarctica. Although Arctic temperatures are milder than the severe cold of the Antarctic stratosphere, a comparable percentage of ozone was destroyed in both polar regions this year. Writing in Nature,1 Gloria L. Manney and 28 co-authors claim that a true “ozone hole” formed over the Northern Hemisphere this year.

Picture above depicts the Ozone Hole over Antarctica. From 1979 to 1997, total ozone levels in the atmosphere declined 40% or more in the blue-toned region.

      In the 1980s, scientists were stunned to discover that a “hole” formed in the ozone layer of the stratosphere every spring over Antarctica. They were quickly convinced that the newfound ozone disappearance was real. Chlorine compounds were destroying the natural ozone, and the only known source of chlorine was a class of man-made chemicals called chlorofluorocarbons (CFCs), which were manufactured as refrigerants and as propellants in aerosol spray cans.

      In the Antarctic stratosphere, temperatures routinely plummet to an extremely frigid –80°C by the end of winter. When that happens, water vapor and nitric acid condense into polar stratospheric clouds from 15 to 30 km above the ground. The cloud particles offer surfaces on which chemical reactions, involving chlorine, can be catalyzed. These reactions decompose ozone in the atmosphere.

      Scientists were not sure that an ozone hole would form in the Arctic, since the Arctic stratosphere rarely gets cold enough for these clouds to form, although they did observe that some ozone was lost every year. Manney’s team reports that the whirl of air around the Arctic known as the “polar vortex” was unusually cold and isolated from surrounding regions for four months ending in March 2011. That isolation was enough to destroy most of the ozone there by March—which was unprecedented in the Northern Hemisphere.

      While the greenhouse effect warms the lower atmosphere, it actually cools the stratosphere. That is because greenhouse gases intercept some of the heat radiation that Earth emits to outer space. That energy warms the lower layers, but what the low layers gain, the upper layers lose. So the stratosphere has been steadily cooling for several decades precisely because the greenhouse effect has become stronger.

      Thus, with ever more global warming at the surface, a very cold stratosphere like the one in 2011 may occur more often, which would favor future Arctic ozone holes. With some concern, the authors conclude that an ozone hole in the north “could exacerbate biological risks from increased exposure” to ultraviolet radiation, especially when the polar vortex shifts over populated middle latitudes, as it did last April.

1. “Unprecedented Arctic ozone loss in 2011” by Gloria L. Manney and 28 others (2011). Nature, vol. 478, 469–475, 27 Oct. 2011, doi:10.1038/nature10556.

Copyright 2011

 Chief Editor:

Michael A Fortune, Ph.D.


 Email:  editor (@) climate-science dot org

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