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It's time to study and maybe even test the idea of cooling Earth by injecting sulfur pollution high in the air to reflect the sun's heat, a first-of-its-kind federal science report said Tuesday.

The idea was once considered fringe — to purposely re-engineer the planet's climate as a last-ditch effort to battle global warming with an artificial cloud. No longer. In a nuanced, two-volume report, the National Academy of Sciences said that the concept should not be acted upon immediately because it is too risky, but it should be studied and perhaps tested outdoors in small projects.

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It could be a relatively cheap, effective and quick way to cool the planet by mimicking the natural effects on climate of large volcanic eruptions, but scientists concede there could be dramatic and dangerous side effects that they don't know about. Because warming has worsened and some countries might act unilaterally, scientists said research is needed to calculate the consequences.

Panel chairwoman Marcia McNutt, editor of the journal Science and former director of the U.S. Geological Survey, said in an interview that the public should read this report "and say, 'This is downright scary.' And they should say, 'If this is our Hail Mary, what a scary, scary place we are in.'"

The panel said that once the geoengineering process begins, it would be difficult to stop because warming would come back with such a force. So a decision to spray particles into the air would have to continue for more than 1,000 years.

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Scientists are pretty terrified about these last-minute fixes to global warming http://t.co/3k1FviY2s1 pic.twitter.com/Jy8cvUuodE — Tim McDonnell (@timmcdonnell) February 10, 2015

— The Associated Press