Scientists Warm Up to Idea on Cooling Down the Earth

Three and a half decades ago, British physicist John Latham raised the wild idea of injecting droplets of seawater into clouds to brighten them, increasing their reflection of solar radiation and thereby cooling the planet. He suggested 1,000 unmanned vessels could sail the oceans, spraying water into the air. "If we can increase the reflectivity by about 3%, the cooling will balance the global warming caused by increased C02 in the atmosphere," the late Latham said in 2007. For a long time, the response to this and other solar geoengineering ideas has been cool. But interest and funding opportunities have increased along with temperatures, per the Economist. And on Tuesday, the idea was put to the test as part of a research project from the University of Washington and nonprofit SRI International, per the New York Times.

Until recently, efforts to reduce pollution from ship exhaust using particles from that pollution brightened clouds enough to offset 5% of climate warming from greenhouse gases, atmospheric scientist Sarah Doherty, who manages the university's marine cloud brightening program, tells the Times. She adds the time is ripe to explore marine cloud brightening with sea salt aerosols, rather than pollution. She agrees with critics who say the process could alter climactic patterns in unknown ways, but she adds that's why it's important to study the effects now, before cloud brightening becomes a necessity. Indeed, it could take a decade of testing before scientists are "in a position to potentially use marine cloud brightening at the scale required to cool the Earth," per the Times.

Scientists need to figure out whether this could work in the real world, the right size of aerosols needed—too small particles are useless, too big reduce cloud reflectivity—and the right number to expel, among other factors. In the Solar Radiation Modification (SRM) experiment launched Tuesday with $10 million in funding over three years, researchers pushed water and highly pressurized air through a series of nozzles in an effort to create salt particles of less than a micron (1/25,000 of an inch), which appears about right in terms of effectiveness. Researchers hope the aerosols stay the desired size while moving through the air under varying wind and humidity conditions. Separately, a team from Australia's Southern Cross University has tested how clouds respond to aerosols sprayed from a ship, though the results haven't been released. (More geoengineering stories.)