for National Geographic News
Radical, globe-spanning schemes—including giant space mirrors and high-tech "trees"—may someday be needed to prevent a global warming disaster, unless greenhouse gas emissions are cut considerably, a new study says.
This week the United Kingdom's Royal Society issued a report, the first from a major scientific body devoted to ranking the various proposals for "geoengineering."
"It is an unpalatable truth that unless we can succeed in greatly reducing [greenhouse gas] emissions we are headed for a very uncomfortable and challenging climate future," said study leader John Shepherd, an earth scientist at the University of Southampton in England, in a statement.
Should that future arrive, the society reluctantly recommends seriously considering the following five global-cooling ideas.
Even so, the scientists caution that such projects would likely cost many billions—or even trillions—of U.S. dollars and could spark fights over who would control the planet's thermostat.
"The greatest challenges to the successful deployment of geoengineering may be the social, ethical, legal and political issues," the report says, "rather than scientific and technical issues."
Volcanic eruptions can quickly cool the planet by spewing tiny droplets containing sulfur dioxide into the atmosphere, where they reflect some of the sun's rays back into space.
Researchers have proposed fighting global warming with their own "flying volcanoes"—jets or balloons that release similar droplets. (Related: "'Volcano Cure' for Warming? Not So Fast, Study Says.")
Millions of tons of these droplets would need to be sent into the air every year to cancel out current global warming, at a cost of tens of billions of U.S. dollars, the report estimates. Even so, the flying volcanoes would be one of the most cost-effective types of geoengineering.
Because of the droplets' rapid cooling effect, they "could be useful in an emergency, the reports says, for example to avoid reaching a global warming 'tipping point'," such as the thawing of the Arctic. Widespread thawing of permafrost could release huge amounts of methane—a powerful greenhouse gas—causing even more global warming.
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