Extreme Global Warming Fix Proposed: Fill the Skies With Sulfur

Kate Ravilious
for National Geographic News

August 4, 2006

A Nobel Prize-winning scientist has proposed a controversial method for protecting Earth from global warming: seeding the atmosphere with sulfur to reflect the sun's rays.

In the current issue of the journal Climate Change, Paul Crutzen of Germany's Max Planck Institute for Chemistry suggests injecting particles of sulfur into the stratosphere—the upper layer of the atmosphere—to cool the planet and buy time for humans to reduce greenhouse gas emissions.

The sulfur particles would be dropped from high-altitude balloons or fired into the atmosphere with heavy artillery shells, he says. Once airborne the particles would act like tiny mirrors, bouncing the sun's light and heat back into space.

Crutzen's plan would imitate the cooling effects of volcanic eruptions, which send large sulfur-rich clouds into the atmosphere. When Mount Pinatubo in the Philippines erupted in 1991, he points out, the huge plume of sulfur cooled the Earth by 0.9 degree Fahrenheit (0.5 degree Celsius) the following year.

A relatively small amount of sulfate could produce a level of cooling similar to that caused by the Pinatubo eruption, according to Crutzen's calculations. Crutzen, who won the Nobel Prize in Chemistry in 1995 for his work on the ozone layer, stresses that it is still important for nations to cut back greenhouse gas emissions, but extreme measures like this may be necessary to provide more time. "I hope that my experiment will never have to take place," he said in an email.

Geo-Engineering

This isn't the first time that scientists have suggested meddling with Earth's climate in order to reduce the impact of global warming.  Two years ago John Latham, an atmospheric scientist from the U.S. National Center for Atmospheric Research in Boulder, Colorado, and his colleagues put forward a plan to whisk up seawater to encourage cloud formation in the lower atmosphere, thereby reflecting radiation back into space.

"All of us recognize that geo-engineering seems increasingly likely to be the only route to staving off a cataclysm in the short term before new, clean energy sources are developed sufficiently," Latham said.

He thinks that Crutzen's idea is feasible, but he says further investigation is needed.

"This idea could help to hold the temperature constant, but we need to examine some of the potential adverse ramifications," Latham said.

Crutzen admits that there is a risk of the sulfur becoming a health hazard if it rained back down on Earth.

In addition there could be an increase in damage to the ozone layer and a whitening of the sky.

"If things go wrong during the experiment, then [we would] stop," he said. "In a few years the atmosphere [will] return back to its earlier condition."

On the upside, sunsets and sunrises would become more spectacular.

Crutzen calculates that launching enough sulfate to have an effect for two years would cost between 25 billion and 50 billion U.S. dollars, about $25 to $50 per head in the developed world.

There may still be time for nations to reduce greenhouse emissions enough to make such extreme measures unnecessary, Crutzen concludes, but no one can know for certain.

"We don't know the future, so this question is impossible to answer," he said.

Source: http://news.nationalgeographic.com/news/2006/08/060804-global-warming.html