Geoengineering Is an Option. Just Read the Fine Print

Let’s be clear: time is getting short. Even as we race to build roads from carbon-sequestering concrete, breed drought-resistant crops, and perfect our battery tech, emissions keep rising. To avert the worst, we may need to turn to geoengineering—the deliberate, large-scale manipulation of the environment to counteract climate change.

Technically, planting a lot of trees is a form of geoengineering. So is fertilizing the ocean with iron filings to stimulate plankton growth. So is using massive CO₂ scrubbers to pull carbon directly from the air. (In theory, anyway—that particular technology is still in alpha.)

But what if the planet could just put on a sun hat for a while? That way, at least, we could sop up the carbon mess in relative comfort. Scientists have proposed a range of techniques—some commonsense, some harebrained, some downright scary. Then again, isn’t climate change pretty scary too?

Surface Radiation Management

How It Works
To reflect sunlight back into space, countries paint their roofs, roads, and sidewalks white and cover desert regions in bright polyethylene tarps.

Upside
The tarps and paint buckets could be deployed tomorrow.

Downside
To have any real effect, you’d need to whiten 10 percent of all the land on Earth—the equivalent of taking a paint brush to most of Russia. That’s a lot of rubles.

Marine Cloud Brightening

How It Works
Drone ships spray sea salt into the sky, causing the clouds above to thicken and become more reflective.

Upside
The tool is fairly precise. You could, for instance, deploy it over a dying coral reef.

Downside
Unknown effects on ocean currents, weather patterns, and the creatures that depend on them (including us).

Stratospheric Aerosol Injection

How It Works
Planes, rockets, artillery shells, or balloons loft millions of tons of sulfates into the atmosphere, creating a layer of particles that scatters sunlight.

Upside
Lower temperatures on land and sea; gorgeous yellow-red sunsets.

Downside
The sky might stop being blue; the stars might fade; monsoon disruptions might cause drought in Asia and Africa. And if you try to quit cold turkey, the warming will come back five times faster than before.

Cirrus Cloud Thinning

How It Works
Drones fly up where heat-trapping cirrus clouds form and spritz them with dust or pollen. The clouds curdle, leaving gaps where heat can escape.

Upside
The cooling effect may be strongest near the poles, where glaciers and sea ice need it most.

Downside
Overseed the clouds and they trap more heat. Whoops!

Space Sunshade

How It Works
Rockets carry loads of light-scattering material into orbit (mirrors, dust, metal mesh) and build a planetary parasol that shields Earth from the sun.

Upside
Blocking 2 percent of solar rays would cancel out all the warming caused by humans so far.

Downside
The cost and complexity are extreme. One proposal would require launching a million small mirrors every minute for 30 years. Possible side effects: accidental global cooling, droughts.

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