Smug eco-warriors may think they’re curbing global warming with their vegan diets, charged-up Teslas, and rooftop solar panels. But according to Peter Wadhams, head of the Polar Ocean Physics Group at the University of Cambridge, we’re barely staving off disaster. He should know: The pessimistic professor has been studying sea ice for nearly 50 years. “Reducing our emissions is not going to be enough to prevent catastrophic consequences,” he says. In his scorching new book, A Farewell to Ice, he presents a slew of radical—and sometimes theoretical—ways to save civilization.

Carbon Vacuums

One way to reverse global warming would be to hoover up the greenhouse gases that are now making Earth all hot and bothered. “Direct air capture of CO₂ is something the whole world should be putting its research money into,” Wadhams says. “The problem is that the level of effort thus far has been much too small; the sense of urgency isn’t there.”

Salt-Spraying Ships

University of Edinburgh engineers designed a fleet of boats that would pipe ocean water hundreds of feet into the sky, spraying the clouds with salt crystals to make them reflect more sunlight. The ships would target areas with persistent marine cloud cover, like the Californian and Chilean coasts.

Sparkle-Blasting Balloons

Researchers in the US and UK have proposed shooting sulfuric acid or sulfur dioxide into the stratosphere using balloons, planes, or artillery shells, effectively filling the sky with sparkles to deflect sunlight. Such aerosol injections show promise, Wadhams says, but introduce environmental dilemmas: They might also deplete the ozone layer.

Supersized Space Mirror

Astrophysicists at the Lawrence Livermore National Laboratory have explored launching a giant mirror or vast expanse of reflective mesh into orbit to protect the planet from the sun. But Wadhams remains skeptical: “Nobody has come up with a feasible plan for assembling this that doesn’t carry a colossal cost.”