A significant amount of the climate change caused by greenhouse gas emissions in the past century has been hidden from us, scientists say — by another type of pollution that actually cools the climate and temporarily cancels out some of the warming. Two new studies, both released today in the journal Nature Geoscience, address the powerful influence of aerosols — fine particles or drops of liquid often released by industrial activity — on the climate, and suggest that as nations around the world work to reduce this type of air pollution, we will begin to see more rapid warming than expected. And that could hurt our ability to meet the climate goals set in last year’s Paris Agreement.

Scientists have long been aware that certain types of aerosol emissions — most notably, sulfate — can block solar radiation from getting through to the surface of the Earth, either by scattering sunlight directly or by helping to increase the extent and reflectivity of cloud cover over the planet. This results in a kind of cooling effect, especially in the areas where the pollution is heaviest, which can temporarily mask the ongoing warming effect caused by greenhouse gases in the atmosphere.

The important thing to remember about aerosols, though, is that they tend to have a rather short lifespan in the atmosphere — eventually, the rain brings them back out of the sky. If humans are continuously pouring pollution into the air, then the cooling effect will probably appear pretty constant. But as certain parts of the world start cutting down on their aerosol emissions, scientists have actually noticed a phenomenon known as “regional brightening,” in which the dimming effect on solar radiation begins to lift away.