Cargo ships that chug across our oceans in their millions may be having an astonishing impact on the planet, creating lightning storms wherever they go. It seems that the pollution they spew seed clouds in the atmosphere, causing more intense storms along the world’s major shipping lanes.
“It's one of the clearest examples of how humans are actually changing the intensity of storm processes on Earth through the emission of particulates from combustion,” explains Joel Thornton, who led the research published in Geophysical Research Letters, in a statement.
It turns out that the particulates that cargo ships emit may well be influencing the intensity of storms directly above the shipping lanes. As the soot and compounds of nitrogen and sulfur are emitted, they “seed” cloud formation, as water droplets form around them. Usually in the oceans, there are fewer particles in the air to condense around, so the water droplets that form are quite large.
But as hundreds of thousands of ships travel the same routes, the number of particles above the lanes is much greater, meaning that the water droplets formed as a result are much smaller, and this is critical. The smaller, lighter droplets are more likely to travel higher into the atmosphere, and thus more likely to freeze. As these particles collide and mix with other unfrozen droplets, the clouds become charged and electrified, and lightning storms develop.
How the researchers discovered the link between the ships and lightning was devastatingly simple. When study co-author Katrina Virts looked at data from the World Wide Lightning Location Network, which tracks the position of lightning strikes all around the globe, she noticed a curiously straight line cutting across the Indian Ocean. Along with her colleagues, Virts then compared this distribution with data from a global database of ship emissions.
“All we had to do was make a map of where the lightning was enhanced and a map of where the ships are travelling and it was pretty obvious just from the co-location of both of those that the ships were somehow involved in enhancing lightning,” says Thornton.
They then looked at the frequency of 1.5 billion lightning strikes occurring above the shipping lanes and on either side of them between the years 2005 and 2016. They found that despite the weather conditions being effectively the same both within the shipping channel and surrounding them, there were close to two times as many lightning strikes occurring over the major shipping routes across the India Ocean, the South China Sea, and through the Strait of Malacca.
This is some of the most solid evidence to date that particulate emissions can and do have profound effects on clouds and the storms they create.