Until now, the logic went as follows: pollution particles help seed more clouds with more water, and more water-rich clouds, scientists theorized, would help reflect the sun's rays and slow global warming.
New research carried out at the University of Reading in England suggests the story is more complicated. Pollution, it turns out, affects different types of clouds in different ways. According to the new study, published this week in the journal Nature, pollution makes some clouds thicker but makes other clouds thinner.
"Until now, it was assumed that thicker clouds form when water droplets condense around the particles in polluted air, delaying rainfall, and allowing clouds to reflect more sunlight back into space," meteorologist Velle Toll, former Reading researcher, now at the University of Tartu in Estonia, said in a news release.
Scientists used infrared satellite to find and analyze hundreds of polluted clouds across the globe. In infrared images, polluted clouds appear brighter. Researchers compared observations made via satellite surveys to simulations designed to predict the effects of pollution on clouds. The analysis showed clouds aren't behaving as traditional models predict.
"There was little change in average water content across all the polluted clouds we found, showing that pollution makes little difference overall to many types of clouds. Some clouds got thicker, but other areas thinned out."
Climate modeling is all about reducing uncertainty, so the idea is to narrow the range of predicted outcomes and hone on in -- and prepare for -- the most likely scenarios.
"This reduces a big area of uncertainty for future forecasts of the climate," Toll said. "Our study provides more evidence that cutting emissions of greenhouse gases and air pollution is a win-win situation for the health of people's lungs and for preventing the worst impacts of climate change."