Global Warming Forecast to Delay Ozone Layer Recovery
BALTIMORE, Maryland, February 6, 2009 (ENS)
Increasing greenhouse gases could stall the recovery of stratospheric
ozone in some regions of the Earth, according to new research by a team from
Johns Hopkins University. The scientists warn that increased rates of skin
cancer in those regions might result.
Darryn Waugh, a professor in the Department of Earth and Planetary Sciences
at Johns Hopkins University, and his colleagues reported Thursday that
climate change could provoke variations in the circulation of air in the
lower stratosphere in tropical and southern mid-latitudes, including
Australia and South America.
The circulation changes would cause ozone levels in these areas never to
return to levels that were present before decline began, even after
ozone-depleting substances have been wiped out from the atmosphere.
In tropical and southern mid-latitudes, Waugh says, "Global warming causes
changes in the speed that the air is transported into and through the lower
stratosphere. You're moving the air through it quicker, so less ozone gets
formed."
Researchers at NASA Goddard Space Flight Center in Greenbelt, Maryland
collaborated with Waugh in the study. The team forecast effects on ozone
recovery by means of simulations using a computer model known as the Goddard
Earth Observing System Chemistry - Climate Model.
On September 12, 2008, the Antarctic ozone hole reached its maximum size for
the year. Though larger than it was in 2007, the 2008 ozone hole was still
smaller than the record set in 2006. (Image courtesy NASA)
Waugh says this research will help scientists attribute ozone variations to
the right agent.
"Ozone is going to change in response to both ozone-depleting substances and
greenhouse gases," he says, "If you don't consider climate change when
studying the ozone recovery data, you may get pretty confused."
The research is published in the current issue of "Geophysical Research
Letters," a publication of the American Geophysical Union.
Dan Lubin, an atmospheric scientist who has studied the relationship between
ozone depletion and variations in the ultraviolet radiation that reaches the
Earth, says Waugh's findings could cause health problems for people living
in the tropics and southern mid-latitudes if ozone levels never return to
pre-1960 levels in those regions.
"The risk of skin cancer for fair-skinned populations living in countries
like Australia and New Zealand, and probably in Chile and Argentina too,
will be greater in the 21st century than it was during the 20th century,"
says Lubin, who is at Scripps Institution of Oceanography in La Jolla,
California and did not participate in the research.
Ozone is a gas which is naturally present in the atmosphere and absorbs
harmful ultraviolet radiation from the Sun. In the stratosphere, ozone
blocks ultraviolet light that can cause skin cancers, cataracts, and other
damage to animals and plants if it reached the surface.
This protective ozone layer has been in decline in the stratosphere since
the 1970s due to an increase in atmospheric concentrations of human-made
substances such as chlorofluorocarbon and bromofluorocarbon compounds such
as refrigerants, solvents, and foam blowing agents.
Since the late 1980s, most countries have adhered to the Montreal Protocol,
an international treaty to phase out production of such ozone-depleting
substances.
The ozone layer has not grown thinner since 1998 over most of the world, and
it appears to be recovering because of reduced emissions of ozone-depleting
substances. Antarctic ozone is projected to return to pre-1980 levels by
2060 to 2075.
Not all regions face worse prospects for ozone recovery as a result of
climate change, the Johns Hopkins scientists found.
In polar regions and northern mid-latitudes, restoration of ozone in the
lower stratosphere will suffer little impact from increasing greenhouse
gases, their projections indicate.
In the upper stratosphere, climate change causes a drop in temperatures that
slows down some of the chemical reactions that destroy ozone. So, the Johns
Hopkins team concludes, recovery might be reached in those parts of the
atmosphere earlier than forecast, even decades before the removal of
ozone-depleting substances.
While scientists have long suspected that climate change might be altering
the dynamics of stratospheric ozone recovery, Waugh's team is the first to
estimate the effects of increasing greenhouse gases on the recovery of ozone
by region.
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