Thanks to Linode Cloud Computing for  supporting this episode of SciShow.

You can go to linode.com/scishow  to learn more and get a $100 60-day credit on a new Linode account. [♪ INTRO] No one can argue that the COVID-19  pandemic hasn’t been extremely disruptive to our way of life. But the pandemic hasn’t just affected us.

It’s also affected the environment. For example, on the one hand, increased  demand for things like masks and gloves has unfortunately led to a lot of waste in the  form of single-use plastics and other materials. On the other, decreased commuting  led to a dip in emissions.

And there have been a few knock on effects. Like changing the weather. Which turns out to be a lucky natural  experiment to help us understand just how much humans are  affecting the world around us, up to and including lightning  storms – pandemic or no.

During the pandemic, especially its first  year, the amount of lightning strikes over some parts of the world, especially  Europe, Africa, and Asia, decreased. And several teams of researchers have chalked  that up to improvements in air quality. Previous studies had shown that air  quality improved over the course of the pandemic, especially in 2020, the year when  the greatest number of people stayed home.

And based on what we understand,  the amount of air pollution has direct consequences for lightning. That’s because most air pollutants are  aerosols, particles suspended in air. When water vapor encounters particles, it  condenses around them, forming water drops.

These drops in turn more readily form clouds. But the amount of aerosols in the  atmosphere is key, because it’s this amount that determines whether the water  will fall back down as rain. The atmosphere is a really complicated system, and we don't fully understand everything  that goes into making a raincloud.

However, we do know that aerosols in the  atmosphere give water a place to condense. More aerosols lead to smaller droplets, because there are more places for the water to go. This lends itself to a combination of  very cool droplets and ice crystals, which tends to generate a lot of static.

It is the perfect storm of  conditions to create lightning. So basically, the more aerosols are in the  atmosphere, the more lightning strikes occur. Researchers documented a correlation  between the two in real time in 2005, when a volcanic plume in the Philippines wafted a bunch of aerosols into  the atmosphere just off the coast.

Lightning strikes increased  in the area soon after. And in 2017, researchers  realized that lightning strikes happened more frequently over shipping lanes. These are areas of the ocean where  cargo ships often pass through, sort of like roads across the sea.

Ships pump out aerosols in their exhaust, and those aerosols linger in the  atmosphere over those shipping lanes. So the increase in lightning is probably  due to the increase in aerosols. Both of these studies looked at  lightning strikes over the ocean, which are easier to study  than lightning over land.

That’s because there are fewer factors to  consider when looking at ocean lightning. After all, the ocean is  mostly just featureless water, while land has other factors  that might affect the weather. Things like topography and  tree cover and seasonal changes can all affect the weather, and all  of these can muddle the connection between aerosols and lightning strikes.

For example, cities warm faster than rural areas, in what’s called the urban heat island effect. This is because cities tend  to be made up of materials that retain more heat, like asphalt and concrete. Since temperature changes can affect rainfall too, that means that rain over cities is  already different from nearby rural areas, and that’s even before  thinking about climate change.

That means we don’t fully understand  how much human-generated aerosols are affecting lightning strikes, because we  can’t filter out all those other variables. Events like the pandemic,  though, can bridge this gap, because we know that the only thing  that changed over highly populated areas during the pandemic was aerosol concentration. Temperature and all other things remained  the same, so that suggests that at least some of the decrease in lightning  strikes had to be due to aerosols.

That brings us one step closer to actually  being able to say that air pollution over land leads to more lightning,  and that reducing air pollution would mean fewer thunderstorms  and lightning strikes. And that means research like this plays  a vital part in helping us untangle all of the different ways that humans  are influencing the environment. This is still an open area of research,  which means we have a lot of questions we need to answer before we can  understand these effects fully.

We don’t know whether different pollutants  affect lightning differently, or how changing weather conditions can interact with  these aerosols to produce different effects. But learning more can help  inform air pollution policies, for reasons that go beyond just human health. And maybe could help  understand all the strange ways we influence the world we live in.

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Thank you for watching this episode of SciShow, and thank you to Linode for supporting this video. [♪ OUTRO]