In a finding with implications for everything from climate change to the future of wildfires, researchers from the US and India have found an unexpected knock-on effect of COVID-19: a significant reduction in the number of lightning bolts worldwide.
It happened because COVID-19 produced lockdowns which, in turn, caused people to use less fossil fuel, says Earle Williams, a physical meteorologist at Massachusetts Institute of Technology, US, who has presented his findings at a meeting of the American Geophysical Union in New Orleans, Louisiana.
“People stopped flying, people stopped using public transportation, people stopped driving,” he says. “So, there was less pollution.”
That’s important because fossil fuel burning produces aerosols that play a role in thunderstorm build-up by acting as tiny particles around which moisture can condense.
When they are few in number, they produce big droplets that quickly fall out as rain. When there are more of them, the droplets are more numerous, but smaller. This allows them to rise high enough to freeze into ice crystals. Turbulence among these ice crystals and small, hail-like particles called graupel produces the static electricity that powers lightning bolts.
The effect, Williams says, showed up most strongly during the height of COVID-19 lockdown, in March, April and May of 2020.
Satellite images at the time showed a substantial reduction in the amount of aerosol pollution, particularly in China, Southeast Asia, Europe, sub-Saharan Africa, and the Maritime Continent of Indonesia, the Philippines and neighbouring island nations.
Meanwhile, two different networks for monitoring global lightning strikes showed 10-20% reductions, depending on whether they were counting cloud-to-ground strikes or all lightning bolts, including those that ran cloud-to-cloud.
These, too, found that the places with the biggest reductions were China, Southeast Asia, Europe, sub-Saharan Africa, and the Maritime Continent – exactly the places where COVID-19 lockdowns had produced the biggest improvements in air quality.
Even in the Americas, where the effects of the pandemic were less consistent (with some areas seeing better air quality and others seeing worse), the pattern held, with areas where pollution was reduced also seeing reduced lightning. “In a broad brush there is a consistency,” Williams says.
It’s an important finding not just for meteorologists, but for trying to predict the effect of climate change on lightning – and, by extension, on bushfires.
On the one hand, Williams says, it appears that temperature plays a major role in thunderstorm formation. “There is every indication you will have more lightning in a warmer world,” he says. But temperature isn’t the only factor. Overall, Williams says, “it depends on whether the future is cleaner or dirtier.” And since efforts to reduce climate change should also reduce pollution, he adds, “that alone should reduce lightning activity.”
Richard A Lovett
Richard A Lovett is a Portland, Oregon-based science writer and science fiction author. He is a frequent contributor to Cosmos.
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