By Charlene Porter
Washington — The depletion of the ozone layer over the Arctic is more severe than scientists have ever seen it, with a 40 percent loss occurring from the beginning of winter to late March.
“This is pretty sudden and unusual,” said Bryan Johnson, a research chemist for the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado.
But depletion of the ozone that protects the Earth from the sun’s harmful rays is not a complete mystery. Scientists have previously predicted that significant Arctic ozone loss would occur in the event of an unusually cold winter in the Arctic stratosphere. And the depletion is a common winter-to-spring event in Antarctica, where extreme cold in the stratosphere and ozone-depleting chemicals create what’s come to be known as the ozone hole.
The stratosphere is the second layer of the Earth’s atmosphere, beginning about 10 kilometers above the surface. We live in the first layer of atmosphere, the troposphere. Most ozone resides in the stratosphere, and that ozone is called the ozone layer. Scientists have been watching its depletion for some time. Certain air pollutants eat away at ozone in conditions of very low temperatures and the increasing sunlight of springtime.
An international treaty, the Montreal Protocol, was adopted more than 30 years ago when nations of the world agreed that the ozone layer was diminishing and compounds called chlorofluorocarbons (CFCs) — widely used as refrigerants and solvents — were the cause. Since the 1987 protocol, CFC use and manufacture has been slowly phased out, but the ozone-depleting compounds are long-lived and will linger in the atmosphere for decades to come. The ozone layer is expected to recover to pre-1980 levels outside the polar regions by 2030 or 2040. A complete restoration of the ozone layer over the poles is expected to take as much as 20 years longer.
The World Meteorological Organization (WMO) has made the same observations about the Arctic ozone depletion this year. Secretary-General Michel Jarraud said, “The degree of ozone loss experienced in any particular winter depends on the meteorological conditions. The 2011 ozone loss shows that we have to remain vigilant and keep a close eye on the situation in the Arctic in the coming years.”
A WMO press release ventures that this year’s Arctic ozone depletion might have been worse had it not been for the phase-out of CFCs.
In Antarctica, the depletion of the ozone layer is an annual occurrence because of the extremely cold winter temperatures in the stratosphere. The Arctic winters, on the other hand, are usually not so severe and in some years, scientists detect no ozone losses in the northern regions. Before this year, the highest seasonal loss in the Arctic ozone layer was 30 percent.(This is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://iipdigital.usembassy.gov/iipdigital-en/index.html)