You're listening to Shortwave from NPR.

Sometimes when I'm driving through the mountains here in the Pacific Northwest,

I see small clouds rising above the trees like little puffs of breath.

And it's not just a metaphor, those trees are exhaling and it's forming clouds.

Plants emit gases that form aerosol particles and cloud seeds.

Dr. Lubna Dada studies these particles

is part of an international experiment named Cloud, all caps.

She and fellow atmospheric scientists are interested in, you guessed it, cloud formation.

There are several processes that lead to cloud formation and the most important thing to keep

in mind is that each cloud needs a cloud seed so that they can form something on top of it.

And this seed is usually an aerosol particle or a particle that is suspended in the atmosphere and it comes from

different sources such as sea spray or dust or combustion processes or

biomass burning.

So some aerosols are natural,

while others come from human pollution.

Just think about the process of water condensing

on your window when you cook.

So these aerosols are acting just like your window.

So they form and then they act like a surface which can take in more gases to grow to form this cloud.

In addition to producing rain and snow, clouds play a huge role in our climate.

Some types of clouds act as a layer of protection between incoming solar radiation and the Earth, and they cool the atmosphere.

Other types of clouds act like a blanket, and they trap heat.

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