Enhancement of cloud glaciation and rain frequency by airborne pollen

Pollen belong to a subset of atmospheric aerosol particles that enable the glaciation of supercooled liquid water, which is present in clouds down to an ambient temperature of -38°C. While the ice nucleating properties of pollen are widely researched in laboratory studies, it is challenging to evaluate their effect on clouds in observations at a large scale. Using a combination of ground-based measurements of pollen concentration and satellite observations of cloud properties during springtime, we show that the ice nucleating properties of pollen promote the glaciation of supercooled liquid water. We further establish the link between the pollen-induced increase in cloud ice to a higher precipitation frequency. In light of anthropogenic climate change, the extended and strengthened pollen season and alterations in biodiversity can, therefore, introduce a localized climate forcing and a modification of the precipitation frequency and intensity, especially during springtime.