The Arctic region has suffered an ozone column loss of about 40 percent from the beginning of the winter to late March this year, but the unprecedented ozone destruction was rather expected, the World Meteorological Organization (WMO) said.

The unprecedented level of the depletion of the ozone layer was owing to the continuing presence of ozone-depleting substances in the atmosphere and a very cold winter in the stratosphere, the UN weather agency said in a press release.

Ozone scientists have foreseen that significant Arctic ozone loss is possible in the case of a cold and stable Arctic stratospheric winter, WMO said.

It also said that without the Montreal Protocol, this year’s ozone destruction would have been worse. Ozone depleting substances like chlorofluorocarbons (CFCs) and halons which were present in refrigerators, spray cans and fire extinguishers, have been phased out under the Montreal Protocol.

However, this has not fully translated into lower levels of ozone depletion. The slow recovery of the ozone layer is due to the fact that ozone-depleting substances stay in the atmosphere for several decades, WMO said.

The beneficial impact of the Montreal Protocol will be visible over a period of time. Thanks to this international agreement, the ozone layer outside the polar regions is projected to recover to its pre-1980 levels around 2030-2040 according to the WMO/UNEP Scientific Assessment of Ozone Depletion.

The agency also warned that increased ultraviolet (UV) radiation unusual for the season is possible if the ozone depleted area moves away from the pole and towards lower latitudes.

As the solar elevation at noon increases over the next weeks, regions affected by the ozone depletion will experience higher than normal UV radiation. The public is recommended to stay informed through national UV forecasts, WMO said.

ARCTIC VULNERABILITY

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

The ozone in the stratosphere is called the ozone layer. It is the shield that protects life on Earth from harmful levels of ultraviolet rays. About 90 percent of the ozone in the atmosphere is found in the stratosphere, while the remaining 10 percent is found in the troposphere. The stratosphere starts at about 10 km altitude and reaches up to an altitude of about 50 km.

Persisting cold temperatures at the stratosphere lead to the speeding up of ozone depletion, WMO says. In Antarctica such conditions prevail every winter/spring season, whereas in the Arctic the variability from one year to the next is much larger. Large ozone loss is therefore not an annually recurring phenomenon in the Arctic stratosphere. While increased amounts of longlived greenhouse gases, such as carbon dioxide and methane, are expected to cause some cooling of the stratosphere in the long term, it cannot explain the large variations in temperature that is observed from one year to the next in the Arctic stratosphere.

Satellite observations and the findings of ozonesondes have shown that almost two thirds of the ozone in a crucial region of the stratosphere has already been destroyed, WMO said. It says ozone loss takes place between 15 and 23 km above the ground with an ozone minimum around 19-20 km. It is in this region that most destruction has happened. The agency also says that this 'ozone poor region' has shifted away from the pole and covers Greenland and Scandinavia as of late March.

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