Artificially cooling Earth may prove perilous: study

Yahoo News 24 Apr 08;

Radical proposals to inject sulfur particles into the Earth's stratosphere to cool it down and battle global warming could instead badly damage the ozone layer, a study warned Thursday.

"Our research indicates that trying to artificially cool off the planet could have perilous side effects," said researcher Simone Tilmes from the National Center for Atmospheric Research.

"While climate change is a major threat, more research is required before society attempts global geoengineering solutions."

The study, published Thursday in Science Express, warns that injecting sulfate particles into the air at an altitude of some 10 to 50 kilometers (six to 30 miles), could lead to a loss of ozone above the Arctic and delay the recovery of the hole in the ozone layer above Antarctica by decades.

In the past few years, scientists have been studying "geoengineering" ways to combat global warming rather than by just reducing emissions of greenhouse gases alone.

One of the ideas put forward and studied by Nobel Chemistry laureate Paul Crutzen draws on the lessons learnt from volcanic explosions, when vast amounts of sulfur particles are unleashed into the air.

The sulfur, which blocks the sun's rays, has in the past led to a cooling of surface temperatures around the volcano site.

Researchers, led by Tilmes, studied what would happen if regular, large amounts of sulfate particles were artificially injected into the atmosphere with the aim of cooling the surface temperatures.

But in fact the team found that over the next few decades, such large amounts of sulfates would likely destroy between about 25 to 75 percent of the ozone layer above the Arctic.

This could have a devastating effect on the northern hemisphere, computer simulations showed. The expected recovery of the hole over the Antarctic would also be delayed by 30 to 70 years.

Researchers found that such large amounts of sulfates would enable chlorine gases found in the cold layers of the stratosphere above the two Poles to become active, triggering a chemical reaction harmful to ozone.

Ozone is an unusual molecule. Ground-level ozone produced by pollution, mostly from cars, is harmful to the health. But in the stratosphere, where is it produced naturally, it screens out the sun's dangerous ultra-violet rays, which can cause such things as skin cancer.

"This study highlights another connection between global warming and ozone depletion," said co-author Ross Salawitch of the University of Maryland.

"These traditionally had been thought of as separate problems but are now increasingly recognized to be coupled in subtle, yet profoundly important, manners."

The damaging effects of such sulfate treatments would be lessened in the second half of the century, when international accords on banning the production of ozone-depleting chemicals are due to be fully felt, the study added.

Using chemicals to cut global warming may damage ozone layer
Randolph E. Schmid, Associated Press Yahoo News 24 Apr 08;

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.

Two Evils Compete: Global Warming vs. Ozone Hole
Andrea Thompson, LiveScience.com Yahoo News 24 Apr 08;

The evils of global warming and ozone depletion are competing problems, at least in Antarctica, the results of two new studies suggest.

Schemes to pump sulfur into the atmosphere to counteract global warming might help cool the Earth, but they could also cause problems at the poles, scientists warned today. Continuous injections could drastically deplete polar ozone, delaying the recovery of the current ozone hole over Antarctica by several decades.

And another study finds that if the southern ozone hole is patched, the heat would turn on in Antarctica.

Injecting sulfur into the atmosphere is one of the most talked about "geoengineering" schemes aimed at counteracting the warming caused by the carbon dioxide building up in Earth's atmosphere, largely due to industry and vehicles emissions.

Sulfur particles, along with some other aerosols, can have a cooling effect on Earth's surface because they scatter incoming sunlight back out to space. This effect can actually happen naturally when sulfur is spewed out in volcanic eruptions. After the 1991 Mt. Pinatubo eruption, which injected millions of tons of sulfur dioxide into the atmosphere, global temperatures dropped by about 1 degree Fahrenheit (0.5 degrees Celsius).

Not so simple

The artificial cooling idea proposed by Nobel laureate Paul Crutzen, among others, is to regularly inject large amounts of sulfate particles into the atmosphere to block the sun's rays and cool the Earth.

Unfortunately, it's not that simple, a new study suggests.

At very cold temperatures, sulfur particles provide a surface where chlorine gases in the atmosphere (from man-made chlorofluorocarbons, or CFCs, and other pollutants) can react and form molecules that destroy ozone. These cold temperatures can arise during polar winters, when sulfur helps form polar stratospheric clouds.

Simone Tilmes of the National Center for Atmospheric Research and her team used computer models to examine the effect yearly sulfur injections would have on ozone levels at both of the planet's poles.

The model showed that injecting sulfur in the amounts suggested by Crutzen and others would seriously impact Arctic and Antarctic ozone levels. Over the next few decades, these hypothetical injections would likely destroy between about one-fourth and three-fourths of the ozone layer above the Arctic. Because atmospheric circulation patterns over the Arctic tend to "wobble," this Arctic ozone hole even could sweep over populated areas, Tilmes said.

Lower ozone levels allow the sun's harmful ultraviolet rays to pierce through the atmosphere, which can cause severe problems for life on Earth's surface, from skin cancer in humans to DNA damage in many types of plants and animals.

Ozone wouldn't suffer the same depletion over Antarctica, "because it's already gone," Tilmes told LiveScience. But the sulfates would delay the expected recovery of the ozone hole by about 30 to 70 years, the model found.

"Our research indicates that trying to artificially cool off the planet could have perilous side effects," Tilmes said. "While climate change is a major threat, more research is required before society attempts global geoengineering solutions."

The results of the study, funded by the National Science Foundation, NASA and European funding agencies, are detailed in the April 25 issue of the journal Science.

Another problem

On the other hand, a full recovery of the ozone layer could lead to intensified warming over Antarctica, according to another new study, detailed in the April 26 issue of the journal Geophysical Research Letters.

Because ozone absorbs ultraviolet radiation, it warms the surrounding air. More warming high in the atmosphere over the Antarctic could change atmospheric circulation patterns there that have so far kept the southern continent isolated from the warming patterns affecting the rest of the world.

"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 lead author of the study, Judith Perlwitz of the University of Colorado at Boulder and the National Oceanic and Atmospheric Administration (NOAA).

Plan to reverse global warming could backfire
Julie Steenhuysen, Reuters 24 Apr 08;

CHICAGO (Reuters) - A proposed solution to reverse the effects of global warming by spraying sulfate particles into Earth's stratosphere could make matters much worse, climate researchers said on Thursday.

They said trying to cool off the planet by creating a kind of artificial sun block would delay the recovery of the Antarctic ozone hole by 30 to 70 years and create a new loss of Earth's protective ozone layer over the Arctic.

"What our study shows is if you actually put a lot of sulfur into the atmosphere we get a larger ozone depletion than we had before," said Simone Tilmes of the National Center for Atmospheric Research in Boulder, Colorado, whose research appears in the journal Science.

The sulfur injection idea has been proposed by a number of climate scientists as a potential solution to global warming.

Tilmes said the idea was intended to mimic the effects of a major volcanic eruption. Such eruptions in the past sent plumes of sun-blocking sulfur into an upper layer of the atmosphere known as the stratosphere that cooled temperatures on Earth.

Ozone in the stratosphere provides a protective layer high above Earth's surface that guards against harmful solar radiation.

Antarctica's ozone layer has been steadily thinning, resulting in a seasonal "hole" above the South Pole.

"We know that particles would result in the cooling of the planet," Tilmes said in a telephone interview.

But such cooling would come with unintended side effects. She said sulfate injections could react with chlorine gasses in cold polar regions, triggering a chemical reaction that would further deplete atmospheric ozone.

Tilmes and colleagues looked specifically at the impact of plans to repair holes in the ozone over the poles and concluded that regular injections of sulfates over the next few decades would destroy between one-fourth to three-fourths of the ozone layer above the Arctic.

That would affect a large part of the Northern Hemisphere because of atmospheric circulation patterns, they said. The impact would be less during the second half of the century because of international pacts to ban the production of ozone-depleting chemicals.

In the Antarctic, a sulfate-injection scheme would delay the recovery of the ozone hole by 30 to 70 years, or at least until the last decade of this century.

Tilmes and colleagues used different measurements and computer models to make their predictions.

She said her findings did not close the door on the idea of artificially cooling the planet in that way but raised a flag of caution.

"We need people to have atmospheric models to understand the process in more detail," she said in a telephone interview.

(Editing by Peter Cooney)