Environment
SMOKE from wildfires now burning in North America may be seeding the formation of cirrus clouds over Europe. More clouds could affect the amount of solar radiation trapped close to Earth’s surface, in a potential new aspect of climate change.
Cirrus clouds are the wispy strands often visible high in the sky. They grow from accumulations of ice crystals in the frigid air near the stratosphere. Whether these ice crystals form depends on the temperature, humidity and the type and amount of particles floating in the air.
Particles like mineral dust blown up from deserts or soot from aeroplane exhaust can provide a nucleus that crystals form around. This also happens with particles containing sulphur from pollution and natural sources.
But until now, researchers didn’t think particles from wildfire smoke had an influence. That is because smoke from wildfires generally didn’t reach high enough, says Albert Ansmann at the Leibniz
Institute for Tropospheric Research in Germany. Lab tests have also shown that particles in fresh wildfire smoke aren’t well suited for ice crystals to form around.
In 2017, however, and during a later expedition to the Arctic, Ansmann and his colleagues observed instances in which cirrus clouds appeared to be forming in the same part of the atmosphere as smoke coming from huge fires burning in California and Canada.
Those observations made Ansmann rethink the link between smoke and clouds, especially with unprecedented megafires sending more smoke higher into the atmosphere. “There’s so much smoke close to the stratosphere,” says Ansmann. Not only is the air colder at those altitudes, he says, but the smoke particles transform as they waft to those heights. He thinks that over days or months,
