Here's a conundrum: the same aerosol pollutants that harm human health also help cool the climate, says atmospheric scientist Sarah J. Doherty. Is there a way to clean up the air without warming the planet? Exploring the unintended consequences of reducing air pollution, she makes the case for a better understanding of marine cloud brightening — or intentionally adding sea salt aerosols to clouds over the ocean, which could reflect sunlight back into space and potentially reduce global warming.