But it's tough who gets to decide whether to re-engineer the earth's atmosphere or not.
"We would all hope it was done by some global consensus, but it's cheap enough that it's plausible to imagine some country going ahead and doing it themselves," he says. "It's hard to imagine what the international reaction would be if someone were to go ahead and do it themselves."
There's also the risk of going too far: If someone were to "turn down" the sun too much, it could have dire impacts on earth's global climate. That conjures images of movie villains and freeze machines — and to someone motivated enough, maybe they could do it.
"You can imagine some James Bond scenario where an evil scientist says, 'If you don't do what I demand, I'll freeze the planet,'" MacMartin says. "Technically, yes, it's possible to do that. But I guess it's just not something I worry about."
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Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at firstname.lastname@example.org.