Spring sees record loss of Arctic ozone

Friday 08th Apr 2011 by theWeatherclub

The depletion of the ozone layer - the atmospheric shield that protects life on Earth from harmful levels of ultraviolet rays - has reached an unprecedented level over the Arctic this spring. This was due to the continuing presence of ozone-depleting substances in the atmosphere and a very cold winter in the stratosphere layer of the atmosphere. The record loss comes despite an international agreement which has been very successful in cutting production and consumption of ozone destroying chemicals. Because of the long atmospheric lifetimes of these compounds it will take several decades before their concentrations are back down to pre-1980 levels, the target agreed in the Montreal Protocol on Substances that Deplete the Ozone Layer.

Observations by the World Meteorological Organisation' s 'Global Atmosphere Watch Network' show that the Arctic region has suffered an ozone column loss of about 40% from the beginning of the winter to late March. The highest ozone loss previously recorded was about 30% over the entire winter. Although unprecedented, the level of the decline is not unexpected. Ozone scientists know that significant Arctic ozone loss is possible in the case of a cold and stable Arctic stratospheric winter. Stratospheric ozone depletion occurs over the Polar Regions when temperatures drop below -78°C. At such low temperatures clouds form in the stratosphere. Chemical reactions that convert some harmless gases into active ozone depleting ones take place on the clouds particles. The result is rapid destruction of ozone during sunlight hours. This means, some Arctic winters experience almost no ozone loss, whereas cold stratospheric temperatures lasting beyond the polar night can occasionally lead to substantial ozone loss.

Thanks to the Montreal Protocol, the ozone layer outside the Polar Regions is projected to recover to its pre-1980 levels around 2030-2040. In contrast, the springtime ozone layer over the Antarctic is expected to recover around 2045-60, with the Arctic recovering one or two decades earlier.

"The Arctic stratosphere continues to be vulnerable to ozone destruction caused by ozone-depleting substances linked to human activities," said WMO Secretary-General Michel Jarraud. "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."