Air pollution has suppressed the effect that natural airborne particles have on the climate, in particular how well clouds reflect Earth-warming sunlight.

Dominick Spracklen and Alexandru Rap of the University of Leeds, UK, used a computer model to test how the effects of natural aerosols, such as dust and sea spray, were altered by airborne particles from human sources, such as emissions from cars and power plants. In the Northern Hemisphere, artificial aerosols have halved the effect that natural aerosols have on cloud reflectivity. Such an effect has not yet occurred in the more pristine Southern Hemisphere.

Abundant artificial aerosols could complicate efforts to understand the feedback between natural aerosols and climate in the past.

Geophys. Res. Lett. 40, 1–4 (2013)