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Stratospheric Sulfur Could Stall Global Warming

September 15, 2006 — By Deborah Zabarenko, Reuters
WASHINGTON — To stall global warming for 20 years, one climate scientist Thursday proposed lobbing sulfur dioxide into the stratosphere, which would work in concert with cuts in greenhouse gas emissions.

The sulfur dioxide, a pollutant on Earth, would form sulfate aerosol particles to shade the planet, much as the ash clouds from a major volcanic eruption do, said Tom Wigley of the National Center for Atmospheric Research.

Wigley used computer models to determine that injecting sulfate particles at intervals from one to four years would have about the same cooling power as the 1991 eruption on Mount Pinatubo in the Philippines.

His research, published in the journal Science, indicates this approach would work together with cutting emissions of greenhouse gases, which are produced by the burning of fossil fuels.

The idea of injecting sulfates into the stratosphere, some 10 miles above the Earth's surface, was first proposed and quickly rejected three decades ago as a dangerous tinkering with natural processes.

But Wigley said he was prompted to pursue this angle when Paul Crutzen, a Nobel-winning atmospheric chemist, recently suggested a new look at the notion of geoengineering, as this notion is known.

COST-EFFECTIVE?

"I'm not suggesting we don't reduce our dependence on fossil fuels for energy," Wigley said in a telephone interview. "I think that that's the only long-term solution to the problem of global warming, we definitely have to do that.

"But ... can we make it economically and technologically easier by doing something that's also technology, which may be cost-effective?"

It would not be cheap, according to Wigley's estimates.

The most sensible way to get sulfur dioxide into the stratosphere would be to send numerous planes -- more than the world's current commercial airline fleet -- to take it there. This might cost hundreds of millions of dollars, he said.

The sulfur dioxide would form small sulfuric acid aerosol droplets. Another method to get these aerosols into the air is the possible addition of sulfur compounds to airplane fuel, which would then form sulfur dioxide, Wigley said.

On Earth, sulfur dioxide contributes to respiratory illness, aggravates heart and lung disease and contributes to acid rain. Power plants and other factories are the biggest producers.

But Wigley said the amount of sulfur dioxide needed for the geoengineering project would probably cause negligible pollution down on Earth's surface, because his model called for less than 10 percent additional sulfur dioxide than is emitted by the burning of fossil fuels.

The technology exists now to put this plan into effect, but studies of economic feasibility are needed, he said. It has the potential to stall global warming for 20 years, to buy time for solutions to the problem, according to Wigley.

"We've got to consider it very seriously because otherwise we might be in for much worse things just due to emission of carbon dioxide and other greenhouse gases," he said.

Source: Reuters