Bird droppings (guano) offer a small contribution to cooling in the Arctic by encouraging cloud formation, according to a study published in Nature Communications this week. These findings suggest a link between migratory seabird ammonia emissions from guano and clouds that has a previously unreported role in influencing the Arctic climate.

The Arctic has experienced considerable warming in recent years. Clouds have a key role in modulating surface temperature, and thus understanding the factors that influence their formation is essential. Central to the development of clouds is the availability of cloud condensation nuclei - small particles upon which water can condense - which are impacted by various interacting physical and biological reactions.

Betty Croft and colleagues determine how migratory seabird colonies influence cloud growth, using a combination of observations and computer modelling. They report the presence of summertime bursts of atmospheric particles linked to ammonia emissions from guano. Although concentrated around the colonies, these particles spread throughout the Arctic, encouraging cloud-droplet formation. As a consequence, more incoming sunlight is reflected back to space, resulting in a minor cooling signal in the Arctic.

The authors caution that this cloud cooling effect is relatively minor, and is not strong enough to offset the impacts of anthropogenic climate change.