Pollution aerosols may not offset climate warming

Abstract

Not all air pollution contributes to warming our planet. For example, sulfate aerosols, which form from industrial emissions, generally have a significant cooling effect. In some climate models, sulfate and other aerosols offset up to half of the heating from greenhouse gas emissions.Aerosol cooling effects occur both directly, by scattering incoming solar radiation, and indirectly, by affecting cloud properties such as water-droplet size and water content that cause the clouds to reflect more sunlight away from the earth. Still, the effect of aerosols on clouds remains one of the biggest sources of uncertainty when it comes to predicting future climate. A new paper suggests that these tiny, airborne particles are not cooling the earth through cloud effects as much as climate scientists had previously thought (Nature 2019, DOI: 10.1038/s41586-019-1423-9). The Twomey effect—an aerosol-triggered decrease in the size of water droplets in clouds—is known to increase cloud reflectivity. But the pollution