A NASA-led study has documented an unprecedented depletion of the Earth's protective ozone layer above the Arctic last winter and spring that was caused by an unusually prolonged period of extremely low temperatures in the stratosphere. University of Toronto physicist Kaley Walker was part of the international team behind the study to be published online Sunday, October 2 in Nature.
The researchers found the amount of ozone destroyed in the Arctic in 2011 was comparable to that seen in some years in the Antarctic, where an ozone "hole" has formed each spring since the mid 1980s. The stratospheric ozone layer, extending from about 15 to 35 kilometres above the surface, protects life on Earth from the sun's harmful ultraviolet rays.
The scientists found that at some altitudes, the cold period in the Arctic lasted more than 30 days longer in 2011 than in any previously studied Arctic winter, leading to the unprecedented ozone loss. Further studies are needed to determine what factors caused the cold period to last so long.
The Antarctic ozone hole forms when extremely cold conditions, common in the winter Antarctic stratosphere, trigger reactions that convert atmospheric chlorine from human-produced chemicals into forms that destroy ozone. While the same ozone-loss processes occur each winter in the Arctic, the generally warmer stratospheric conditions there limit the area affected and the time frame during which the chemical reactions occur. This means there is generally far less ozone loss in most years in the Arctic than in the Antarctic.
To investigate the 2011 Arctic ozone loss, Walker and scientists from 18 other institutions in nine countries (United States, Germany, The Netherlands, Russia, Finland, Denmark, Japan and Spain) analyzed a comprehensive set of measurements. These included daily global observations of trace gases and clouds from NASA's Aura and CALIPSO spacecraft; ozone measured by instrumented ba
|Contact: Kim Luke|
University of Toronto