Should geoengineering be used to address global warming?

To counter the ill effects of such rapid warming, political leaders are trying to forge agreements to cut the emissions of greenhouse gases, often called "climate mitigation."

Governments are also beginning to look at ways to adapt to living in a warmer world, with its other possible effects such as changes in rainfall patterns (droughts and floods), more intense storms, and rising sea levels.

Geoengineering presents a third way to try to alleviate the problems.

But when discussing modifying Earth's climate, most scientists strongly emphasize two points: Such schemes should be attempted only after careful consideration and only as a last resort if disastrous climate changes begin to be felt. And they should never be a substitute for reducing emissions. At best, geoengineering represents a "thumb in the dike" – a temporary and partial solution. As Cascio puts it: "It's a stay of execution, not a pardon."

Even considering those reservations, some environmentalists remain far from persuaded. Geoengineering amounts to "an act of geopiracy," says the Swedish Society for Nature Conservation. "There is no reason for the governments or peoples of most of Africa, Asia, and Latin America to trust that the governments, industries, or scientists of the biggest carbon-emitting states will protect their interests."

Plans to modify the world's climate fall into two basic categories: One approach would reduce the amount of sunlight taken in by Earth and its atmosphere – sometimes called Solar Radiation Management (SRM). About 70 percent of sunlight is absorbed by Earth and its atmosphere, while the remaining 30 percent is reflected back into space. If just 1 percent more sunlight were reflected, Earth would cool by a measurable amount.

Other ideas concern removing carbon dioxide from the atmosphere, directly offsetting carbon dioxide emissions. (See sidebar at left.)

Perhaps the best-known sun-blocking concept involves lacing the upper atmosphere with particles of sulfur to make it more reflective. Real-world experience suggests that such a technique could work.

In 1991, for example, Mt. Pinatubo in the Philippines erupted, sending plumes of sulfates and other particles high into the atmosphere, which reflected more sunlight back into space. The resulting condition cooled Earth by about 1 degree F. for the next year. A little more than a century earlier, an even more massive eruption of the Krakatoa volcano in Indonesia probably had an even larger effect on world temperatures. Depending on how long it continues, the volcanic eruption in Iceland will doubtless have a similar effect.

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