Smoke from wildfires now burning in North America may be seeding the formation of more cirrus clouds over Europe. More clouds could affect the amount of solar radiation trapped close to the earth鈥檚 surface, in what researchers say may be a new aspect of climate change.
Cirrus clouds are the wispy strands often visible high in the sky. They form from accumulations of ice crystals in the frigid air near the stratosphere. Whether or not 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 ice crystals form around; this is also known to happen with particles containing sulphur from pollution and natural sources. But until now, researchers didn鈥檛 think particles from wildfire smoke had an influence on cirrus clouds.
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That is because smoke from wildfires generally didn鈥檛 reach high enough, says at the Leibniz Institute for Tropospheric Research in Germany. Laboratory tests also found the were not well suited for ice crystals to form around.
In 2017 and then during a later , however, Ansmann and his colleagues observed many instances in which cirrus clouds appeared to be forming in the same part of the atmosphere as smoke coming from record-breaking fires then burning in California and Canada. They used the reflected light, or backscatter, from lasers aimed at the sky to distinguish the wildfire smoke from other particles, and to distinguish the clouds from the smoke.
Those observations made Ansmann rethink the link between smoke and clouds, especially with unprecedented megafires sending more smoke higher into the atmosphere. 鈥淲ow, there鈥檚 so much smoke close to the stratosphere,鈥� says Ansmann. 鈥淭hen we have another situation.鈥�
Not only is the air colder at those altitudes, Ansmann says, but the smoke particles themselves transform as they waft to those heights over a period of days or months. He thinks that the aged smoke particles form into perfect spheres with a core of black carbon soot and a shell of organic carbon, which could make them better suited than fresh smoke for nucleating ice particles in clouds.
Since the Arctic expedition, Ansmann and his colleagues have observed cirrus clouds forming in conjunction with wildfire smoke in other parts of the world, including in Chile following the Black Summer fires in Australia, as well as in Cyprus in the eastern Mediterranean following fires in North America in 2020. They have also observed the same thing happening over Germany due to smoke from the wildfires now burning in Canada.
鈥淭his is the beginning of a new research field,鈥� says Ansmann. 鈥淚鈥檓 sure.鈥�
However, at the US National Oceanic and Atmospheric Administration (NOAA) is not convinced by these observations. 鈥淎ll they鈥檙e showing here is a few anecdotes,鈥� he says. Until physical samples of particles in clouds or statistical methods establish a more direct link, he says the influence of smoke on cirrus remains 鈥渃ontroversial and unresolved鈥�.
at the University of California, Merced, agrees the evidence is thin, but is open to the idea. If smoke does influence clouds, he would next want to know how much it happens, and how it might affect Earth鈥檚 radiation budget.
Depending on their thickness, cirrus clouds can reflect or absorb solar radiation and have a substantial cooling or warming influence on the climate. If smoke from wildfires driven by climate change increases cloud cover in ways that add to warming, it could theoretically be a new climate feedback loop, says Adebiyi. Given the increasing amount of wildfire smoke entering the atmosphere, 鈥渢his could really be important鈥�.
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