Biological particles, such as bacteria, fungal spores and plant material, trigger ice formation in clouds, suggests a study published online in Nature Geoscience. The finding could prove important because the effect of airborne particles on the formation of cloud ice is one of the largest remaining sources of uncertainty in climate change projections.

Kim Prather and colleagues loaded a newly developed mass spectrometer onto an aircraft and examined the chemical composition of atmospheric ice-forming particles in a cloud over Wyoming. They found that biological particles accounted for 33% of the ice-forming particles, and mineral dust accounted for 50%.

Using a global aerosol model the team suggest that biological particles can enhance the formation of cloud ice that forms in response to desert storms.