By Gernot Wagner and Martin Weitzman
Seriously addressing climate change means cutting carbon emissions and, ultimately, reducing the carbon already in the atmosphere. There’s no way around it. Another type of intervention, however, is increasingly garnering attention: solar geoengineering, that is, cooling the planet by making it reflect back more of the sun’s rays. It’s not a permanent solution to climate change, and it carries worrisome environmental and political risks of its own, but it’s an idea worth exploring.
The principle underlying solar geoengineering is simple enough: Brighter colors reflect more light and cool what’s underneath. That’s why houses in Mediterranean villages are often painted white. It’s also why scientists are so worried about the loss of polar sea ice, whose brilliant surfaces reflect solar radiation. Open water is darker and absorbs more sun and heat. In 1965, in the first report to a U.S. president on the effects of global warming, the one solution suggested to President Lyndon Johnson was solar geoengineering: attempting to brighten ocean surfaces on a grand scale.
Since then, scientists have largely shifted their attention from the oceans to the skies. The most prominent and widely discussed basic scheme would involve spreading tiny reflective particles in the upper atmosphere.
How do we know this could work? Nature provides ample precedent. Major volcanic eruptions have often dramatically reduced global average temperatures. The eruption of Mt. Pinatubo in the Philippines in 1991 catapulted almost 20 million tons of sulfur dioxide into the stratosphere. As a result, global average temperatures in 1992 were almost a degree Fahrenheit lower.
But volcanic eruptions are typically massive one-off events, providing a rapid and temporary global cooling. Temperatures soon return to previous levels. Solar geoengineering would require a more deliberate and long-term approach.