Researchers have found that pollen influences cloud formation and precipitation

Ground-based and satellite observations in the United States show that increased pollen concentrations in spring lead to more ice in clouds and more precipitation, even at temperatures between minus 15 and minus 25 degrees Celsius.

“This is confirmed by laboratory results showing that pollen acts as an ice nucleus, influencing the freezing temperature of water in clouds and promoting precipitation,” says meteorologist Dr. Jan Kretzschmar, lead author of the study. Without these ice nucleating particles (INPs), water in clouds only freezes at temperatures below -38 degrees Celsius. The results were published in Environmental Research Letters.

“As part of the Breathing Nature Cluster of Excellence project, we therefore investigated whether this effect could be detected outside the laboratory and how climate change and biodiversity loss affect it,” explains co-author Professor Johannes Quaas, Professor of Theoretical Meteorology in Leipzig and spokesperson for the Breathing Nature consortium.

Globally, the effect of pollen on ice formation is relatively small compared to that of dust, for example, but it is significant on a regional and seasonal scale. In spring in particular, large quantities of pollen are released, rising into the atmosphere and penetrating cold air layers.

“Due to its size, pollen only stays in the atmosphere for a short time,” says Kretzschmar. “Our study highlights the importance of smaller pollen fragments, which are formed when pollen breaks apart in humid conditions. These smaller particles stay in the air longer and, in sufficient quantities, can penetrate into cold atmospheric layers, where they trigger the formation of ice,” he explains.

Climate change intensifies pollen impact – biodiversity a key factor

Anthropogenic climate change is leading to a shift in the start of the pollen season, a lengthening of the season, and an increase in airborne pollen concentrations. These trends are expected to intensify by the end of the century, potentially leading to more frequent and intense local precipitation events.

Another aspect of the study concerns the importance of biodiversity. Many plant species release large amounts of pollen at the same time each spring, which affects cloud formation and the amount of ice particles in the atmosphere. These interactions require further research to better understand the role of pollen in climate change and to incorporate it into future climate models.

“If we can properly simulate the effect of pollen and how it interacts with climate, we will be able to make more accurate predictions,” Kretzschmar says.

The Institute of Meteorology of the University of Leipzig, the Leibniz Institute for Tropospheric Research (TROPOS), the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig and the Max Planck Institute for Biogeochemistry participated in the study.