Toward a Solar Geoengineering Approach to Climate Change: A Brief History of Latham and Salter’s Marine Cloud Brightening Proposal

It is not compatible with technological fix to global warming, to shoot pollutant aerosols into clouds. The late British physicist John Latham had a proposal to use salt from evaporated seawater. Seawater is free and plentiful. His colleague Stephen Salter, emeritus professor of engineering design at the University of Edinburgh, then suggested deploying a fleet of some 1,500 remote-controlled ships that would sail the ocean, suck up water and spray a fine mist into clouds to make them brighter. As greenhouse gas emissions continued to rise, so did interest in Latham and Salter’s unusual proposal. The Marine Cloud Brightening Project is a collaboration between the University of Washington, the Palo Alto Research Center and other institutions. The project group is now researching whether the deliberate addition of sea salt to the low, puffy stratocumulus clouds over the ocean would have a cooling effect on the planet.

Clouds are a climate enigma, which makes them particularly tricky to manipulate. Some types of clouds block sunlight, while others can trap heat. The goal with marine cloud brightening, of course, is to have more of the former. It is possible that inadvertently causing rain and clouds to thin out will lead to more heating. The way a cloud forms or responds to human intervention will depend on a range of complex, shifting factors — from weather to how particles spread by humans interact with other aerosols already in the air.

Clouds bring more than rain or snow. During the day, like massive parasols, clouds reflect some of the sunlight away from the Earth and back into space. Marine stratocumulus clouds are particularly important: they lie at low altitudes, are thick and cover about 20 percent of the tropical ocean area, cooling the water beneath. Scientists are looking into whether they could change theirphysical properties to stop more sunlight. The hope is to provide some sort of relief to coral colonies during heat waves on the Great Barrier Reef. But there are also projects aimed at global cooling that are more controversial.

There have already been tussles over what, if any, role solar geoengineering should play as a climate solution and how to regulate it. So far, the drama has mostly surrounded a different strategy called stratospheric aerosol injection (SAI), which involves catapulting particles up into Earth’s stratosphere to reflect sunlight back into space.

Lynn Russell, co-author of the paper and a climate scientist at the University of California San Diego, said in a press release that non-ideal backup plans are needed to buy time.

Solar and Marine Cloud Brightening: What We Can Learn about Measuring Sulfur, Oxygen, and Carbon Monoxide

A startup caused a global uproar when it conducted its own SAI experiments, despite a global moratorium on large-scale geoengineering. You can watch the co-founders on YouTube grilling fungicide in a parking lot to create sulfur dioxide gas they then launch aboard a weather balloon. Even groups optimistic about solar geoengineering balked at the experiments, saying it undermined more serious research into how to mimic the way volcanoes have temporarily cooled the planet when spewing sulfur dioxide during eruptions.

Marine cloud brightening mimics the effects of volcanic eruptions. Unlike SAI, it involves sending particles into low-lying clouds instead of high up into the sky. Sulfur in pollution from ship stacks has also been shown to have a similar reflective effect, although recent research suggests this might have been overestimated in the past.

Policymakers do not have the information necessary to reach decisions about when and if MCB should be deployed, Feingold said. We have some questions about whether we can design a MCB research program using our current modeling and observational tools, and what needs to be done to position ourselves to do so on a global scale.