  The ability of pollen to enable the glaciation of supercooled liquid water
has been demonstrated in laboratory studies; however, the potential large-scale
effect of trees and pollen on clouds, precipitation and climate is pressing
knowledge to better understand and project clouds in the current and future
climate. Combining ground-based measurements of pollen concentrations and
satellite observations of cloud properties within the United States, we show
that enhanced pollen concentrations during springtime lead to a higher cloud
ice fraction. We further establish the link from 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 future
alterations in biodiversity can introduce a localized climate forcing and a
modification of the precipitation frequency and intensity.
