The ozone hole that appears over Antarctica fluctuates in size, normally reaching its widest in the polar spring as extreme cold temperatures in the stratosphere and the return of sunlight unleash chlorine radicals that destroy ozone.
Last year, the World Meteorological Organization said it detected the first sign of ozone recovery, largely thanks to a 1987 ban on gases that cause ozone depletion, but said it could be a decade before the hole starts shrinking. This year, a colder than usual stratosphere widened the hole to a peak of 28.2 million square kilometers on October 2, bigger than Canada and Russia put together.
It was a record for a hole recorded on October 2 of any year, and the hole has remained at daily record levels on every day since then, the WMO said, citing data from NASA. Over the 30 days around the peak, the hole averaged 26.9 million square km, making it the third largest, after 2000 and 2006.
"This shows us that the ozone hole problem is still with us and we need to remain vigilant. But there is no reason for undue alarm," WMO Atmospheric and Environment Research Division senior scientist Geir Braathen said in a statement. "Overall, however, this does not reverse the projected long-term recovery in the coming decades."
Ozone depleting chemicals, including the chlorofluorocarbons once used in refrigerators and spray cans, were banned under the 1987 Montreal Protocol. The UN has said the treaty will prevent 2 million cases of skin cancer annually by 2030.
"The Montreal Protocol is in place and is working well," Braathen said. "But we may continue to see large Antarctic ozone holes until about 2025 because of weather conditions in the stratosphere and because ozone depleting chemicals linger for several decades after they have been phased out."
Xinhua -china.org.cn
30/10/15
--
-
Related:
No comments:
Post a Comment
Only News