Dyson’s early geo-engineering vision addressed a central, and still daunting, problem: neither sulfur-aerosol injection nor an armada of cloud whiteners nor an array of space-shades would do much to reduce carbon-dioxide levels. As long as carbon emissions remain constant, the atmosphere will fill with more and more greenhouse gases. Blocking the sun does nothing to stop the buildup. It is not even like fighting obesity with liposuction: it’s like fighting obesity with a corset, and a diet of lard and doughnuts. Should the corset ever come off, the flab would burst out as if the corset had never been there at all. For this reason, nearly every climate scientist who spoke with me unhesitatingly advocated cutting carbon emissions over geo-engineering.
Ken Caldeira, of the Carnegie Institution for Science, thinks we ought to test the technology gradually. He suggests that we imagine the suite of geo-engineering projects like a knob that we can turn. “You can turn it gently or violently. The more gently it gets turned, the less disruptive the changes will be. Environmentally, the least risky thing to do is to slowly scale up small field experiments,” he says. “But politically that’s the riskiest thing to do.”