Unprecedented Ozone Loss In The Arctic
By Mike Mitchell
October 3, 2011 - A NASA-led study has documented an
unprecedented depletion of Earth's protective ozone
layer above the Arctic last winter and spring caused by
an unusually prolonged period of extremely low
temperatures in the stratosphere.
The discovery of a hole in the ozone layer above
Antarctica was announced by a team of British scientists
in 1985. The cause of the hole was attributed to
ozone-depleting chemicals like chlorofluorocarbons
(CFCs), which were primarily used in cooling units and
The study, published online Sunday in the journal Nature, finds 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.
ozone-loss processes occur each winter in the Arctic. However,
the generally warmer stratospheric conditions there limit the
area affected and the time frame during which the chemical
reactions occur, resulting in far less ozone loss in most years
in the Arctic than in the Antarctic. To investigate the 2011
Arctic ozone loss, scientists from 19 institutions in nine
countries (United States, Germany, The Netherlands, Canada,
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 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, Calif., 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."
The 2011 Arctic
ozone loss occurred over an area considerably smaller than that of the
Antarctic ozone holes. This is because the Arctic polar vortex, a
persistent large-scale cyclone within which the ozone loss takes place,
was about 40 percent smaller than a typical Antarctic vortex. While
smaller and shorter-lived than its Antarctic counterpart, the Arctic
polar vortex is 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.
Although the total
amount of Arctic ozone measured was much more than twice that typically
seen in an Antarctic spring, the amount destroyed was comparable to that
in some previous Antarctic ozone holes. This is because ozone levels at
the beginning of Arctic winter are typically much greater than those at
the beginning of Antarctic winter.
Manney said that
without the 1989 Montreal Protocol, an international treaty limiting
production of ozone-depleting substances, chlorine levels already would
be so high that an Arctic ozone hole would form every spring. The long
atmospheric lifetimes of ozone-depleting chemicals already in the
atmosphere mean that Antarctic ozone holes, and the possibility of
future severe Arctic ozone loss, will continue for decades.
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