Are floods effects of air pollution

Not only greenhouse gases but also aerosols have a lasting influence on regional climates.

Clouds over India

College Park (USA) - Greenhouse gases such as methane or carbon dioxide are not the only causes of future climate change. Air pollution with soot and sulfur particles, which are mainly released when coal and fuels are burned, can also have a strong regional impact on precipitation. Regions that are already dry would have to expect even less rain and droughts because of these so-called aerosols, according to a new study by climate researchers, while wet areas can expect significantly more rainfall and possible floods. The analysis, published in the journal "Nature Geoscience", reveals an aspect of climate change that has hitherto been neglected.

"For the first time, we have determined the long-term effects of aerosols on cloud height and thickness and the resulting changes in precipitation," says Zhanqing Li from the University of Maryland in College Park, USA. In a computer simulation, his team incorporated detailed data on the air-polluting aerosol particles that had been obtained over ten years over the vast prairie landscapes of the United States using both satellites and land-based measurements. The soot and sulfur particles act in the upper layers of the atmosphere as condensation nuclei for water molecules, which first form clouds and finally fall on the earth as raindrops, snowflakes or hailstones.

The influence of air pollution on cloud formation could already be determined beforehand, but the long-term effect on the climate remained largely unclear. Li and colleagues have now closed this gap with their new models. Steve Ghan from the Pacific Northwest National Laboratory in Richland is convinced that "this work proves that increasing amounts of aerosol will change the precipitation behavior." Rain will fall even more rarely in regions that are already dry and, on the other hand, much more intense in wetter areas. Since this effect has often not been taken into account in climate models so far, in order to improve it, air pollution must be determined more precisely in the future and taken into account in the calculations.