Greenhouse gases could aggravate ozone loss and slow recovery, UN agency says

17 September 2007 – Increased atmospheric concentrations of global warming greenhouse gases (GHGs) could lead to more severe loss in the polar regions of ozone, the naturally occurring gas that filters out cancer- and cataract-causing ultraviolet (UV) rays from the sun, according to the United Nations meteorological agency.

While GHGs will lead to a warmer climate at the Earth’s surface, at the altitude the ozone layer is found the same increase is likely to lead to a cooling of the atmosphere, the UN World Meteorological Organization (WMO) said in a paper marking the 20th anniversary of the UN-backed Montreal Protocol on Substances that Deplete the Ozone Layer.

Lower temperatures enhance the chemical reactions that destroy ozone. At the same time, the amount of water vapour in the stratosphere has been increasing at the rate of about 1 per cent per year. A wetter and colder stratosphere means more polar stratospheric clouds, which is likely to lead to more severe ozone loss in both polar regions, WMO added.

A cooling of the winter stratosphere over the last decades has indeed been observed, both in the Arctic and in the Antarctic, the agency noted, adding that these changes could delay the expected recovery of the ozone layer.

WMO called on all nations with stratospheric measurement programmes to enhance them. It also urged funding agencies to support research on stratospheric ozone and harmful UV radiation.

In 2007, the ozone hole in the Antarctic appeared relatively early, and earlier than in 2006, when the largest and most severe Antarctic ozone hole on record occurred. During the last couple of weeks the growth of the hole has been quite similar to that observed in 2006, but it is still too early to determine how large it will be.

“Over the next 10 to 20 years, high quality global observations of ozone and ozone-depleting substances will be particularly critical in verifying the effectiveness of the actions taken under the Vienna Convention in 1985, the Montreal Protocol of 1987 and its amendments and adjustments,” WMO Secretary-General Michel Jarraud said.

The two pacts seek to phase chemicals such as chlorofluorocarbons and hydrochlorofluorocarbons which deplete the ozone.

“As ozone-depleting substances reach a broad peak and slowly begin to decline, the search for recovery of ozone requires vigilance,” Mr. Jarraud said. “The changes in [global climate] conditions may indeed have implications for ozone recovery.”

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