Bird droppings are playing a previously unrecognized role in fighting climate change by helping keep the Arctic cool. The impact isn't enormous, but in the fight to save the planet, every bit helps.

Bird droppings, tactfully known as guano, are rich in nutrients like organic nitrogen and phosphate. Entire nations have been turned into mines where thousands of years of avian calling cards are dug up and exported. A paper in Nature Communications reports that guano has another value we were not aware of.

Fresh guano releases ammonia into the air. Like many other airborne molecules, ammonia provides nuclei around which water droplets can form, producing clouds. When PhD student Betty Croft of Dalhousie University, Canada, compared bird movements and cloud patterns across the Arctic, she found that the clouds followed the birds.

When migratory seabirds reach their northern breeding grounds, they feel the need to relieve themselves. Quite often really. The bird density in the Arctic and near Arctic in the short northern summer is so high that they drop millions of tonnes of guano each year. This releases an estimated 40,000 tonnes (44,000 tons) of atmospheric ammonia, contributing to cloud formation.

After further research, Croft showed that the ammonia increases the total cloud cover during summer, rather than just concentrating it in places where the birds congregate. Although high clouds can actually increase global warming, those at lower levels reflect sunlight back into space, cooling the planet. Moreover, as the paper notes, “more abundant particles form more numerous and smaller cloud droplets for a fixed cloud liquid-water content, that in turn increase reflection of solar radiation.”

The discovery was not entirely surprising, since penguin colonies on the other side of the world have been shown to also contribute to cloud formation. However, the penguins' influence on temperatures has yet to be calculated.

Croft, on the other hand, estimated that bird-induced clouds in the Northern Hemisphere have a net cooling effect of more than 1 watt per square meter near the largest bird colonies. Across a large area of the Arctic, the average contribution is 0.5 W/m^-2. For contrast, the warming effect from additional carbon dioxide humans are releasing is thought to be 1.6 W/m^-2, although unfortunately that extends over the entire planet, not just a section of the far North.

So next time you wonder whether you're doing enough to fight global warming, just remember: If you're like most people, millions of birds are probably beating you just by taking a crap.