London: An unusually prolonged period of extremely low temperatures in the stratosphere has resulted in an unprecedented depletion of Earth’s protective ozone layer above the Arctic last winter and spring, according to a new NASA-led study.
The study finds that 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 10 to 20 miles (15 to 35 kilometers) above the surface, protects life on Earth from the sun’s harmful ultraviolet rays.
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 processes occur each winter in the Arctic, the air temperature in the stratosphere is generally higher, limiting the time frame during which the chemical reactions occur, meaning there`s generally far less ozone loss than in the Antarctic.
NASA analysed daily global observations of trace gases and clouds from NASA’s Aura and CALIPSO spacecraft; ozone measured by instrumented balloons; meteorological data and atmospheric models.
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.
“Day-to-day temperatures in the 2010-11 Arctic winter did not reach lower values than in previous cold Arctic winters,” said lead author Gloria Manney of NASA’s Jet Propulsion Laboratory in Pasadena, California, and the New Mexico Institute of Mining and Technology in Socorro.
“The difference from previous winters is that temperatures were low enough to produce ozone-destroying forms of chlorine for a much longer time. This implies that if winter Arctic stratospheric temperatures drop just slightly in the future, for example as a result of climate change, then severe Arctic ozone loss may occur more frequently,” she added.
The Arctic ‘hole’ was considerably smaller than those over the Antarctic, because the Arctic polar vortex - a persistent large-scale cyclone within which the ozone loss takes place - was about 40 percent smaller than those typical in the Antarctic.
But while the Arctic vortex is smaller and shorter-lived than its Antarctic counterpart, it`s more mobile, often moving over densely populated northern regions.
Decreases in overhead ozone lead to increases in surface ultraviolet radiation, which are known to have adverse effects on humans and other life forms.
The study has been published in the journal Nature.