Researchers at the Pacific Northwest National Laboratory have discovered pollution makes storm clouds larger. Because storm clouds trap heat in the atmosphere, bigger ones could be helping warm the Earth, a recent study concluded in the journal Geophysical Research Letters on May 10. Just how much the taller anvil-shaped clouds are warming the air is difficult to measure. This is how it works:

“Inside a thunderstorm cloud, warm air rises in updrafts, pushing tiny aerosols from pollution or other particles upwards. Higher up, water vapor cools and condenses onto the aerosols to form droplets, building the cloud. At the same time, cold air falls, creating a convective cycle. Generally, the top of the cloud spreads out like an anvil.” That’s according to a PNNL press release.

Previous studies had concluded pollution creates larger clouds. The new research suggests larger storm clouds could be creating stronger storms. The study looked at storm clouds in China (where there is a large amount of pollution) and rural Oklahoma (where there is less).

The press release also stated:

"Those numbers for the warming are very big," said Fan, "but they are calculated only for the exact day when the thunderstorms occur. Over a longer time-scale such as a month or a season, the average amount of warming would be less because those clouds would not appear every day," said lead author and climate researcher Jiwen Fan at PNNL.

Next, the researchers will look into these effects on longer time scales, the report said.

The U.S. Department of Energy Office of Science funded the study. The data from China were gathered under a bilateral agreement with the China Ministry of Sciences and Technology.