WASHINGTON — It’s time to study and maybe even test the idea of cooling the 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. 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.”‘

This is the first time a government-associated science panel talked about the controlled small-scale outdoor tests of the artificial cloud concept, called solar radiation management or SRM. But panelists downplayed the idea and said it would require some kind of government or other oversight.

“Yes, small-scale outdoor tests might be allowed, but it wouldn’t just be in the hands of scientists to decide what’s allowable …” McNutt said. “Civil society needs to engage in these discussions where the line is to be drawn.”