The term geo-engineering—direct technological interventions to reshape the planet—calls to mind the dark laughter of a science-fiction villain. But researchers are pondering ways to use geo-engineering to counter the effects of global warming. This past year, three European institutions released reports on the benefits and risks of “climate engineering.” Recommendations vary, but the reports each conclude that the most promising technologies should be tested on small scales. Scientists worry that some nation’s future unilateral geo-engineering project could cause frightening side effects that cross national boundaries. “If a country’s leaders feel some existential threat, they might resort to desperate measures,” says Ken Caldeira, a senior scientist at the Carnegie Institution at Stanford University. “What if Greenland is sliding into the ocean? And what if you could stop it?” 

Is the Earth Ready for these Global Warming Fixes?

Dim the Sky

Objective: Block solar radiation to drop Earth’s surface temperature.

Proposal: Unmanned airships or air-bursting artillery rounds inject sulfur-dioxide particles into the stratosphere. A former Microsoft executive proposes lofting a hose with helium balloons to pump liquefied sulfur dioxide into the sky.

Blowback: Global temperatures could spike as soon as treatments stop. Seeded areas may see redder, hazier skies.

Proposed by: Copenhagen Consensus Center 

Soak the Clouds

Objective: Decrease the amount of sunlight—and heat—absorbed by cloud cover.

Proposal: Funnel salt water into the air with robotic ships, brightening clouds to cool specific areas, such as the Arctic.

Blowback: The tactic is likely to alter weather patterns, nudging rainfall from one region to another in unpredictable ways. The good news is that seawater droplets cycle out of clouds within a few days.

Proposed by: Copenhagen Consensus Center 

Grow Algae Everywhere

Objective: Suck carbon dioxide out of the atmosphere, reducing greenhouse gases that contribute to warming.

Proposal: Deploy vast algae farms on land and at sea. Strips of algae could be built onto buildings, and miles of algae-filled plastic bags could stretch across an ocean’s surface. 

Blowback: To work well, a continent of algae is needed, and that’s more pricey than other carbon-capture schemes. 

Proposed by: NASA (algae farms); Institution of Mechanical Engineers, U.K. (buildings) 

Whitewash Everything

Objective: Deflect solar radiation to cool the surface of the planet.

Proposal: Installing white or otherwise reflective roofs on buildings and replacing less reflective crops with ones engineered to be glossier could lower summer temperatures in the U.S. by nearly 2 F.

Blowback: Large-scale genetic modification of crops could face stiff resistance, and there might not be enough rooftops to make a difference.

Proposed by: University of Bristol, U.K. (crops); U.S. Secretary of Energy Steven Chu (roofs)