Weatherwatch: Tiny Particles in the Air Can Trigger Massive Storms

This article by Kate Ravilious was originally posted here.

Mankind has made the world warmer, but we’ve also made it stormier. In a study conducted over the Amazon rainforest, scientists have shown that tiny particles – smaller than one-thousandth of the width of a human hair – cause storms to intensify, and potentially have knock-on effects for weather around the world.

Jiwen Fan, from the US Department of Energy’s Pacific Northwest National Laboratory studied storm formation near the Brazilian city of Manaus. Its 2 million people make Manaus the largest city in the Amazon, and the busy streets and smokey chimneys produce a near permanent pollution plume. 

A heavily instrumented weather station downwind of Manaus meaures aerosols, clouds, and solar and thermal energy. Photograph: US Department of Energy ARM Climate Research Facility

Fan and her colleagues were able to show that the tiniest particles in this plume spawn massive droplets, leading to heat release, followed by powerful updrafts and super-charged storms. 

Previously, these tiny particles were thought to be too small to aid droplet formation. In pristine areas (such as the Amazon and over oceans) tiny particles could be having a significant effect. 

“The results suggest that, from pre-industrial to the present day, human activity may have changed storms in these regions in powerful ways,” says Fan, whose findings are published in Science.