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Fumes of ammonia rising from piles of droppings in Antarctica’s crowded penguin colonies help boost the formation of clouds, which have a cooling effect by reflecting sunlight away from the surface.

“This demonstrates a deep connection between the ecosystem and atmospheric processes,” says at the University of Helsinki in Finland.

The link comes down to the way ammonia affects the number of particles in the atmosphere. In order to form a cloud, water vapour must condense around a sizeable particle of some kind. But those are hard to come by in Antarctica’s cold, clean air.

Without much dust, vegetation or air pollution around, most of the particles available for a would-be cloud are clusters of sulphuric acid molecules generated as a result of natural emissions from phytoplankton in waters around the continent. High concentrations of ammonia were already known to accelerate the formation of these clusters a thousand-fold. But where would ammonia come from in Antarctica? Penguin droppings should be a rich source.

To check this, Boyer and his colleagues measured concentrations of ammonia, sulphuric acid and larger particles in the air several kilometres downwind of a 60,000-strong colony of Adélie penguins (Pygoscelis adeliae) on the Antarctic Peninsula. “They smell terrible,” says Boyer. “They’re dirty birds.”

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When wind was blowing from the direction of the colony, they found ammonia concentrations rose far above the levels found in air arriving from other directions. This rise in ammonia also boosted the formation of particles of sulphuric acid large enough for water to condense around them, and presumably to form clouds. This effect persisted for weeks after the penguins had moved on from the colony.

More clouds, especially over the ocean, would have a cooling effect by reflecting sunlight away from Earth’s surface. Boyer says this also implies that a decline in penguin populations – for instance, due to sea ice loss driven by climate change – could have a warming effect across Antarctica by reducing cloud cover. However, the measurements taken in the current work aren’t enough to estimate the size of the effect.

Other research suggests it could be significant. For instance, at Colorado State University and his colleagues found ammonia from puffin excretions in the Arctic similarly . They estimated this resulted in a cooling effect that cancelled as much as a third of the warming due to carbon dioxide in the air across the region. “I’m sure it makes some impact,” says Pierce.