Getting rid of air pollution might make droughts worse. Ruh-roh.

Air pollution could be masking the role of greenhouse gases on droughts.

The situation: Climate change is making some regions wetter and others drier. But it’s been hard to detect exactly what difference humanity has made. A new report in Naturesupports the theory that air pollution could be masking that role.

The study: Researchers analyzed tree ring records to document shifting soil-moisture conditions—a proxy for droughts. Human influence on drought levels was obvious in the first half of the last century, then there was a diverging trend between 1950 and 1975, and a return to a positive signal in the years since.

The dirty years: This 25-year period coincides with an increase in atmospheric aerosols, the tiny particles spewed from planes, cars, coal plants, farms. They can alter cloud formation, change rainfall patterns, trap heat, or reflect sunlight away from the planet. From the mid-70s onwards various clean air acts came into force around the globe, suggesting the pollution was mitigating our effect on droughts.

What it means: The authors said the connection needs more research. But if air pollution is a major force on droughts, it could really complicate things.

—James Temple