High-flown scheme to fend off warming

Boulder scientist refloats far-out idea to reflect sunlight back into space

Jim Erickson, Rocky Mountain News

Published September 15, 2006 at midnight

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Using high-flying jets to spray a sun-reflecting mist into the upper atmosphere could halt global warming when combined with drastic worldwide cutbacks in greenhouse gas emissions, a Boulder scientist has concluded.

But the techno-fix could be very costly and is fraught with uncertainty, admits Tom Wigley of the National Center for Atmospheric Research.

According to Wigley, a fleet of jets pumping sulfur high in the atmosphere could mimic the 1991 eruption of Mount Pinatubo, which blasted 10 million tons of sulfur into the stratosphere and cooled the Earth's surface by nearly 1 degree Fahrenheit for about a year.

Wigley is not the first to float the idea - it's been around since the 1970s.

But he is one of a growing number of mainstream scientists - including Nobel Prize winner Paul Crutzen of Germany - now pushing far-out solutions long dismissed as flaky and unworkable.

Many of the schemes fall within the boundaries of a discipline called geoengineering, which involves the intentional, large-scale manipulation of the environment.

The term is usually applied to proposals to alter global climate to reduce the effects of human-caused warming.

"Until recently, when we realized that the consequences of climate change were rather more severe than we had anticipated, these radical ideas had been dismissed - and probably rightly so," said Wigley, author of a paper on the sulfur-pumping idea that appears in today's edition of the journal Science.

"But now it's come to the point where I think we have to consider these things seriously," he said.

Under the plan outlined by Wigley, planes would pump 5 million tons of sulfur into the upper atmosphere each year for decades, reflecting sunlight back to space.

The injections could provide a grace period of perhaps 20 years while humanity reduces its reliance on fossil fuels that emit heat-trapping greenhouse gases such as carbon dioxide.

Under this two-pronged approach, Wigley says, it may be possible to stabilize the world's climate before global temperatures rise another 3.6 degrees Fahrenheit - a level often cited as the boundary of dangerous, irreversible climate change.

However, a lot of additional work is needed to determine if the sun blocker idea is technically and economically feasible, he says.

In the August edition of the journal Climatic Change, Crutzen estimated it could cost $25 billion to $50 billion to pump enough sulfur to last two years.

The environmental effects of such a program also require more study, Wigley says.

Sulfur released as sulfur dioxide gas combines with water vapor to form particles known as sulfate aerosols. Those aerosols reflect sunlight, but they also allow chlorine in the atmosphere to more effectively destroy the protective ozone layer, said Ken Caldeira, a global ecologist at the Carnegie Institution.

"I think geoengineering is a terrible idea, but one that needs to be studied," Caldeira said.

"To go tinkering with the only planet we have and hope we won't screw it up seems optimistic and naive," he said.

"But I think we are at the point where we need to explore all our options," he added.

Stephen Schwartz, of New York's Brookhaven National Laboratory, said that relying on geoengineering until greenhouse gas emissions can be curtailed "could buy some time, but in some sense it digs you into a deeper hole."

"I'd be very leery of using it to allow us to buy time and to continue emitting carbon dioxide, because it would allow us to keep delaying the day of reckoning," he said.

ericksonj@RockyMountainNews.com or 303-954-5129

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