How bird poo makes clouds that help cool the Arctic


Ammonia produced by guano-munching bacteria triggers a chemical cascade in the atmosphere. Evelyn Fetterplace reports.


Some migratory seabirds, such as red knots (Calidris canutus), breed in the Arctic in summer. But a series of chemical reactions stemming from their dropping can result in cloud coverage which helps cool the entire area.
Steve Leach / Getty Images

Each summer, tens of millions of seabirds descend on a pristine Arctic – and spray it with piles of poo. But this stinky onslaught can actually help cool the local area by triggering cloud formation, new research shows.

Betty Croft from Dalhousie University in Canada and colleagues used a combination of observations and computer modelling to explain the link between ammonia emissions from the poo, or guano, and formation of cloud droplets which reflect sunlight off the Earth.

The study, the first to examine the effect of ammonia emissions from Arctic seabird guano, was published in Nature Communications.

Clouds have a key role in regulating Earth’s surface temperature. More clouds mean more incoming sunlight is reflected towards space.

But cloud formation requires small particles in the air on which water can condense. These are called cloud condensation nuclei.

When masses of migratory seabirds arrive in the Arctic for summer, they bring with them big bursts of atmospheric particles.

The birds form huge colonies that produce a lot of droppings. And as bacteria breaks down guano, they emit ammonia.

Ammonia combines with sulfuric acid and water in the atmosphere to create new, bigger particles on which cloud droplets can form.

More particles produce smaller droplets. This increases the cooling effect, as masses of small droplets reflect more sunlight than big droplets.

The researchers found close to seabird colonies, the number of cloud droplets in the air can increase by more than 50%. They also found the particles spread over the Arctic and are able to generate clouds over the vast region.

One worry is that with the rapid rate of Arctic warming, seabird migratory patterns may change. Many birds are already changing the timing and courses of their migration.

The study shows that previously unrecognised seabird-particle-cloud connections are relevant to the climate system, Croft says.

But she also notes that the dynamics of atmospheric particles, clouds and climate are complicated. More research on other types of particle effects, and the way clouds interact with energy, needs to be done before we could predict how changes in Arctic seabird migrations might affect the Arctic climate.

The authors also caution that the cooling effect is fairly small – it won’t offset anthropogenic climate change on its own – but it does help us grasp the complex systems that affect global climate.

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Evelyn Fetterplace completed a Bachelor of Arts/Bachelor of Science at the University of Wollongong, with Honours researching shark attack mitigation technologies.
  1. http://nature.com/articles/doi:10.1038/NCOMMS13444
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