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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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