Climate researcher Ken Caldeira was skeptical when he first heard about the idea of shading the Earth a decade ago in a talk by nuclear weapons scientist Lowell Wood.Caldeira conducts research on climate and carbon cycles at the Carnegie Institution at Stanford University. During the past decade, he said, talk about this idea has moved from cocktail parties to very sober meetings, like the workshop this week put on by the National Academy of Sciences.

But when Caldeira sat down to study this, he was surprised to discover that, yes, it would work, and for the very same reasons that big volcanoes cool the Earth when they erupt. Fine particles in the stratosphere reflect sunlight back into space. And doing it would be cheap, to boot. …

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