Do you see a fluffy white cloud in the sky?
Depending where you are, it could be made of bird poop—well...kind of.
I’m Anna and this is Gross Science.
To understand how bird poop could make clouds, you first need to know a little something
about how clouds form.
So, clouds form when water evaporates from ocean, lakes, and other reservoirs, or is
released from plants in a process called transpiration.
This water is in a gaseous form, called water vapor, and it floats up into the atmosphere.
Now, the vapor could just hang out in the air unseen.
But in order to become a cloud, the water has to cool and attach itself to something
we call a “condensation nucleus.”
Dust particles, ice crystals, specks of pollution, and even fungal spores can all serve as “condensation
nuclei.”
Water molecules glom onto them, becoming water droplets—and when this is repeated over
and over again, we can see these droplets in the form of clouds.
So, what does this have to do with bird poop?
Well, bird poop is really rich in nitrogen.
And we’ve known this for years.
Beginning centuries ago, people would actually mine guano—which is a fancy term for the
accumulated poop or seabirds or bats—and they’d use it as fertilizer, because nitrogen
helps plants grow.
But, humans aren’t the only creatures with an affection for guano.
Bacteria love it, too.
Bacteria chow down on the guano, and release another nitrogen-based molecule, called ammonia,
as a waste product.
And given that tens of millions of seabirds spend their summers in the Arctic, bacteria
there produce a ton of ammonia—about 40,000 metric tons each year, to be exact.
When the ammonia drifts up into the atmosphere, it reacts with sulfuric acid and water.
And when other molecules in the air latch on it becomes a condensation nucleus—adding
to the total number of these guys floating around above the Arctic.
Now, you know how clouds can either look bright or dark?
Well, that’s due to the size and number of droplets they’re made of.
Here are two clouds, each in an environment with the same amount of water vapor in the
atmosphere.
The bright one is made of a large number of small droplets, while the dark one is made
of a small number of large droplets.
In the bright cloud, the water’s just divided among more condensation nuclei.
Now, there’s still a lot we don’t understand about how clouds affect climate, but we do
know that bright clouds help reflect sunlight away from Earth, which means that they can
have a cooling effect on our planet.
And that means that all the additional droplets contributed by the ammonia from Arctic bird
poop could be helping to keep our planet a little bit cooler.
The effects are likely not huge.
But as Greg Wentworth, a scientist involved with the study, told me, the birds make a
“relatively small, yet smelly, contribution.”
For me, this study brings home the importance of basic research.
Both on clouds, but also on seabird biology.
Now that that we know bird poop may be part of our climate story, it’s more important
than ever for us to study and protect them.
So, all you future scientists out there—I hope you’re feeling inspired.
And maybe just a little grossed out.
Ew.