By RANDOLPH E. SCHMID
AP Science Writer
WASHINGTON (AP) -- The rule of unintended consequences threatens to strike again.
Some researchers have suggested that injecting sulfur compounds into the atmosphere might help ease global warming by increasing clouds and haze that would reflect sunlight.
After all, they reason, when volcanoes spew lots of sulfur, months or more of cooling often follows.
But a new study warns that injecting enough sulfur to reduce warming would wipe out the Arctic ozone layer and delay recovery of the Antarctic ozone hole by as much as 70 years.
"Our research indicates that trying to artificially cool off the planet could have perilous side effects," said Simone Tilmes of the National Center for Atmospheric Research in Boulder, Colo.
"While climate change is a major threat, more research is required before society attempts global geoengineering solutions," said Tilmes, lead author of a paper appearing in Thursday's online edition of the journal Science.
And while one study worries that fixing climate will destroy ozone, another raises the possibility that recovery of the ozone hole over Antarctica will worsen warming in that region.
A full recovery of the ozone hole could modify climate in the Southern Hemisphere and even amplify Antarctic warming, scientists from the University of Colorado at Boulder, the National Oceanic and Atmospheric Administration and NASA report in a paper scheduled for Geophysical Research Letters.
Although temperatures have been rising worldwide, there has been cooling in the interior of Antarctica in summer, which researchers attribute to the depletion of ozone overhead.
"If the successful control of ozone-depleting substances allows for a full recovery of the ozone hole over Antarctica, we may finally see the interior of Antarctica begin to warm with the rest of the world," said Judith Perlwitz of the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and NOAA.
The authors used a NASA supercomputer to model interactions between the climate and stratospheric ozone chemistry. A return to pre-1969 ozone levels would mean atmospheric circulation patterns now shielding the Antarctic interior from warmer air to the north will begin to break down during the summer, they concluded.
The idea of reversing global warming by injecting sulfates into the air was suggested by eruptions such as the 1991 blast by Mount Pinatubo in the Philippines, which produced a brief cooling.
The massive 1815 eruption of Tambora in what is now Indonesia produced such a strong cooling that 1816 became known as the "year without a summer" in New England, where snow fell in every month of the year.
But Tilmes knew that volcanic eruptions also temporarily thin the ozone layer, which protects people, plants and animals from the most dangerous ultraviolet rays from the sun.
So she and colleagues calculated the effect of suggested sulfate injections and concluded that the result, over the next few decades, would be to destroy between one-fourth to three-fourths of the ozone layer above the Arctic. This would affect a large part of the Northern Hemisphere because of atmospheric circulation patterns.
The sulfates would also delay the expected recovery of the ozone hole over the Antarctic by about 30 to 70 years, or until at least the last decade of this century, they said.
The research was supported by the United Kingdom Meteorological Office, University Corporation for Atmospheric Research and NASA.
The study comes just a day after the National Oceanic and Atmospheric Administration reported that despite efforts to reduce greenhouse gases, the rate of increase of carbon dioxide in the atmosphere is accelerating.
Concern has grown in recent years about such gases, with most atmospheric scientists concerned that the accumulation is causing increases in the earth's temperature, potentially disrupting climate and changing patterns of rainfall, drought and other storms.
The Intergovernmental Panel on Climate Change has worked to detail the scientific bases of this problem and the Kyoto agreement sought to encourage countries to take steps to reduce their greenhouse emissions. Some countries, particularly in Europe, have taken steps to reduce emissions.
But carbon dioxide emissions, primarily from burning fossil fuels such as coal, oil and gas have continued to increase. Since 2000, annual increases of two parts per million or more have been common, compared with 1.5 ppm per year in the 1980s and less than one ppm per year during the 1960s, NOAA's Earth System Research Laboratory said. Last year the increase was 2.4 parts per million.
Meanwhile, in a separate paper in Science, researchers said human activities are at least partly responsible for the Arctic having become a wetter place over the last half century.
Seung-Ki Min of Environment Canada, and colleagues, studied rain and snowfall patterns in the arctic and the factors affecting them.
They concluded that human-induced greenhouse gases have contributed to the increased precipitation rates observed in the Arctic region over the past 60 years.
They warned that this "Arctic moistening" could occur more quickly than current climate simulations indicate.
Their work was supported by the U.S. Department of Energy and the Canadian International Polar Year Program.
(Copyright 2008 by The Associated Press. All Rights Reserved.)