The impacts of climate change are already being felt in communities around the world through extreme heat, more frequent and intense storms, and more. Solar geoengineering might be one way to reduce these impacts—but it comes with its own risks. Do the benefits, in the form of reduced climate impacts, outweigh solar geoengineering’s risks?
A new study, published in the Proceedings of the National Academy of Sciences, is an initial effort to answer that question. It finds the benefits—in the form of reduced heat-induced mortality—from using solar geoengineering are about ten times larger than the mortality costs that could come from the additional air pollution and ozone loss potentially caused by solar geoengineering.
“Benefit-cost analyses should not—and ours does not—mechanically determine policy outcomes but should be a crucial input to policy analysis and debate,” says study co-author David Keith, the director of the Climate Systems Engineering initiative at the University of Chicago. “This perspective is particularly relevant to solar geoengineering given its uncertainties, risks, and distributional effects.”
Keith and his co-authors—Anthony Harding from Georgia Tech and Gabriel Vecchi and Wenchang Yang from Princeton University—study sulfate aerosol injection, a type of solar geoengineering that involves spraying tiny reflective particles into the upper atmosphere. Those particles would then redirect some sunlight back to space and help cool Earth, reducing mortality from heat—one of the leading risks of climate change.
However, sulfate aerosols are themselves a form of air pollution—a leading contributor to mortality worldwide. They can also damage the ozone layer, causing an increase in mortality from skin cancers. The authors quantify the reduction in heat-induced deaths and compare that to the reduction in deaths attributed to the increased air pollution and ozone damage tied to the sulfate aerosols. They find the mortality benefits of injecting the sulfate aerosols outweigh the costs by a factor of ten.
The study also shows that the benefits from using sulfate aerosols are larger in hotter, poorer regions that experience the worst impacts from global warming and are least able to adapt. Cooling by solar geoengineering reduces heat-induced mortality in hotter regions. At the same time, it increases mortality in cooler regions due to both an increase in colder temperatures that increase mortality risk and the air pollution/ozone death risks.
“Our role as scientists is to expand the base of knowledge. Governments must decide if, when and how to put theory into practice,” says Keith. “Our paper is lightyears short of a comprehensive benefit-cost analysis, but we hope it’s a useful first step and that it will spur our colleagues to provide more and better quantitative comparisons between risks and benefits.”