How Big Smells Help Cool the Earth

If you’ve ever wondered how one gets into the climate change denial game, it’s actually pretty simple and has to do with how vast and complex the whole climate system is. There are just so many influences, feedbacks, and potential feedbacks, the whole picture is infinitely crop-able. This vastness enables relatively easy selective viewing. Which brings me to today’s study, brought to you by researchers at the University of Manchester and the journal Nature Geoscience, suggesting that man-made pollutants can actually have a cooling effect on the climate. Note that it isn’t an overall cooling effect, but anti-science arguments don’t tend to be very interested in holism to begin with.

The mechanism’s idea is simple enough. Organic vapors, either natural emissions or man-made pollutants, make clouds brighter. And brighter clouds reflect more sunlight back into space. Specifically, vapors (or stinks, if you will) under the right conditions act as “seed” particles that help the water droplets (water vapor) that make up clouds become cloud droplets, which you might think of as pre-rain, or rain drops small enough that they fall so slowly that they evaporate before reaching Earth. Cloud droplets are part of what makes a cloud a cloud and, crucially, the more of them there are in a cloud, the more reflective the topside of that cloud is.

What happens is that tiny amounts of condensed vapor from the Earth (salty sea spray, exhaust, even pine smell) enter a cloud, becoming the nuclei for water vapor to gather ‘round and form cloud droplets. And more cloud droplets means less sunlight reaching and warming Earth.

"We developed a model and made predictions of a substantially enhanced number of cloud droplets from an atmospherically reasonable amount of organic gases,” says study author Professor Gordon McFiggans. "More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds."

In the real world, it’s another piece of the enormous and super-dynamic puzzle that is Earth’s climate. It’s obviously something pretty important to note as we deal with mitigation strategies in the future. And indeed, one, if so desperately inclined, could dig up a yay pollution something or other from this, but let’s avoid strawmanning anything more than necessary and just say that, while manmade junk helps form cloud droplets, it is vastly inefficient compared to, say, the smell of a pine forest. Needless to say, one of those things does not require combustion and the forever destruction of finite resources.

Reach this writer at michaelb@motherboard.tv.