Climate change linked to abnormally cold temperatures in the Arctic stratosphere; those conditions result in regional ozone loss
These clouds composed of frozen nitric acid and sulphuric acid form when temperatures in the stratosphere at an altitude of about 20 km fall below –78 degrees Celsius. This is currently the case in vast sections of the Arctic. Although these clouds are of natural origin – in isolated cases they have been substantiated by paintings from the 18th century – they have in the meantime become a portent of imminent ozone loss due to human activity. Chemical processes on the surface of the cloud particles transform the initially harmless degradation products of anthropogenically produced chlorofluorocarbons (CFCs) into aggressive ozone-depleting substances. Consequently the ozone-depleting impact of CFCs unfolds with full force whenever it is extremely cold in the stratosphere – like at the moment over the Arctic. Photo: Markus Rex, Alfred Wegener Institute.
By Summit Voice
SUMMIT COUNTY — While ozone hole over Antarctica has slowly started to heal — thanks to concerted global action to ban chlorofluorocarbons — unusually low temperatures in the Arctic ozone layer have recently initiated massive ozone depletion at the other end of the Earth.
The Arctic appears to be heading for a record loss of this trace gas that protects the Earth’s surface against ultraviolet radiation from the sun, according to measurements from an international network of more than 30 ozone sounding stations spread all over the Arctic and Subarctic and coordinated by the Potsdam Research Unit of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association in Germany.
“Our measurements show that at the relevant altitudes about half of the ozone that was present above the Arctic has been destroyed over the past weeks,” AWI researcher Markus Rex said in a press release. “Since the conditions leading to this unusually rapid ozone depletion continue to prevail, we expect further depletion to occur.”
The changes observed at present may also have an impact outside the thinly populated Arctic. Air masses exposed to ozone loss above the Arctic tend to drift southwards later. Hence, due to reduced UV protection by the severely thinned ozone layer, episodes of high UV intensity may also occur in middle latitudes.
“Special attention should thus be devoted to sufficient UV protection in spring this year,” Rex recommended.
Ozone is lost when breakdown products of anthropogenic chlorofluorocarbons are turned into aggressive, ozone-destroying substances during exposure to extremely cold conditions. For several years now scientists have pointed to a connection between ozone loss and climate change, and particularly to the fact that in the Arctic stratosphere at about 20km altitude, where the ozone layer is, the coldest winters seem to have been getting colder and leading to larger ozone losses.
“The current winter is a continuation of this development, which may indeed be connected to global warming,” atmosphere researcher Rex explains the connection that appears paradoxical only at first glance. “To put it in a simplified manner, increasing greenhouse gas concentrations retain the Earth’s thermal radiation at lower layers of the atmosphere, thus heating up these layers. Less of the heat radiation reaches the stratosphere, intensifying the cooling effect there.”
This cooling takes place in the ozone layer and can contribute to larger ozone depletion.
“However, the complicated details of the interactions between the ozone layer and climate change haven’t been completely understood yet and are the subject of current research projects,” Rex said. The European Union finances this work in the RECONCILE project, a €3.5 million research program including 16 research institutions from eight European countries working towards improved understanding of the Arctic ozone layer.
In the long term the ozone layer will recover thanks to extensive environmental policy measures enacted for its protection. This winter’s likely record-breaking ozone loss does not alter this expectation.
“By virtue of the long-term effect of the Montreal Protocol, significant ozone destruction will no longer occur during the second half of this century,” Rex explained.
The Montreal Protocol is an international treaty adopted under the UN umbrella in 1987 to protect the ozone layer and for all practical purposes bans the production of ozone-depleting chlorofluorocarbons (CFCs) worldwide today. CFCs released during prior decades however, will not vanish from the atmosphere until many decades from now. Until that time the fate of the Arctic ozone layer essentially depends on the temperature in the stratosphere at an altitude of around 20 km and is thus linked to the development of earth’s climate.
