Sailors are not big fans of thunderstorms or lightning. With good reason: lightning can turn deadly if you are caught unawares. But it turns out that cargo ships and lightning may go hand in hand. As Kendra Pierre-Louis at Popular Science reports, emissions from the diesel-powered ships could double the number of lightning that strikes along some of the world's busiest shipping lanes.
Researchers examined lightning strikes around the world from 2005 to 2016 using data from the Worldwide Lightning Location Network, a web of sensors around the globe that work together to track lightning strikes. “There’s a disturbance in radio waves in the atmosphere whenever there’s a lightning flash,” University of Washington in Seattle atmospheric scientist and study co-author Joel Thornton tells Pierre-Louis. “If you just have sensors located in different parts of the world where you can detect the disturbance, when sensors have detected it at different times you can triangulate the disturbance and locate where that flash occurred.”
By creating a global map of all those strikes, the researchers noticed a line of above normal lightning activity that paralleled the shipping routes in the Indian Ocean and South China Sea. However, areas adjacent to the lanes with the exact same climate only experienced half the number of strikes.
The researchers think that particulates from the ships’ diesel engines are impacting cloud formation above the shipping lanes. These bits of pollution seed the clouds, allowing more clouds to form with tinier water droplets. These small droplets are lofted higher into the atmosphere than the larger water droplets that more commonly form without cloud seeding. This means more ice particles form, which collide and rub against one another, causing electrical charges to build into lightning strikes. They published their results in the journal Geophysical Research Letters.
As Sid Perkins at Science reports, the researchers were able to rule out other causes, like the giant metal ships attracting lightning strikes since the ships aren’t often struck themselves. They also looked at weather patterns over the shipping lanes and were able to rule out any weather anomalies.
“It is the first time we have, literally, a smoking gun, showing over pristine ocean areas that the lightning amount is more than doubling,” Daniel Rosenfeld, atmospheric scientist at the Hebrew University of Jerusalem not involved in the study says in the release. “The study shows, highly unambiguously, the relationship between anthropogenic emissions—in this case, from diesel engines—on deep convective clouds.”
There may be other impacts that pollution and human emissions are causing that we have yet to find. “We're emitting a lot of stuff into the atmosphere, including a lot of air pollution, particulate matter, and we don't know what it's doing to clouds,” Steven Sherwood, atmospheric scientist at the University of New South Wales in Sydney, who was not involved in the study, says in the release. “That’s been a huge uncertainty for a long time. This study doesn’t resolve that, but it gives us a foot in the door to be able to test our understanding in a way that will move us a step closer to resolving some of those bigger questions about what some of the general impacts are of our emissions on clouds.”
We may get better answers soon. Earlier this year NASA switched on the Geostationary Lightning Mapper aboard the GOES-16 weather satellite, which will constantly record all the lightning strikes and cloud-to-cloud lightning that occurs in the Western Hemisphere, providing even more precise data of where and when the strikes take place.