There’s been a lot of talk in the past few decades about the kind of effect that mankind is having on the environment, becoming a global issue that’s worked its way into politics. Studies have shown some of the more obvious ways that excess emissions are having, which include raising the average global temperature on a yearly basis. Those emissions aren’t just limited to land, however, as it’s been found that cargo ships are causing the weather to change.

Joel Thornton led a team of researchers at the University of Washington have been studying weather patterns around the world, which included a record for lightning strikes on a global basis over the past decade. The team found that the regions with the most lightning strikes were found in the Indian Ocean and the South China Sea. Not only that, but the majority of the lightning strikes were in a straight path, which happened to be the lines of major shipping paths in the region.

Thornton’s team looked at several factors in these regions, which included air temperature and moisture, as well as wind. When it was determined that those ultimately weren’t factors that played into the increased lightning strikes, the team concluded that it was the high amount of cargo ships that travel in the area. “We were quite sure the ships had to be involved,” Thornton said. “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.” These trade routes transport trillions of dollars in world trade, with around 100,000 ships making the passes.

The study said that the cargo ships are creating massive amounts of toxic emissions, which rise into the air and “lead to a microphysical enhancement of convection and storm electrification in the region of the shipping lanes.” When this happens, the cloud particles become smaller, creating more ice that results in lightning strikes. Though scientists wouldn’t say what kind of long term impact increased lightning had, it’s still detrimental to have that many toxins reaching the atmosphere.

Thornton added that the ships causing the increase of lightning is “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.” In areas where the air is clean, there aren’t nearly as many lightning strikes, even if there are clouds that have formed. Aerosols allow for water vapor to condense to form lightning, which is why you won’t see as much lightning in these cleaner areas.

Directly from the study, it says that “We conclude that the lightning enhancement stems from aerosol particles emitted in the engine exhaust of ships traveling along these routes. These particles act as the nuclei on which cloud drops form and can change the vertical development of storms, allowing more cloud water to be transported to high altitudes, where electrification of the storm occurs to produce lightning. These shipping lanes are thus an ongoing experiment on how human activities that lead to airborne particulate matter pollution can perturb storm intensity and lightning.”

Another interesting aspect of the increased lightning is that there wasn’t an increase in rainfall. Thornton explained that it’s not likely that these emissions would cause natural disasters such as hurricanes, but that the lightning should be worrying. Unfortunately, it’s too difficult to prove how much lightning would strike over land as a result of emissions, since there are many different factors at play. What the team was able to take away, though, was that they feel more able to predict the climate in the future because of the effects from the cargo ship emissions.

Daniel Rosenfeld of the Hebrew University of Jerusalem chimed in, though he was not part of the study. He said that the results of the study became “the first time we have, literally, a smoking gun, showing over pristine ocean areas that the lightning amount is more than doubling.” He added that “The study shows, highly unambiguously, the relationship between anthropogenic emissions – in this case, from diesel engines – on deep convective clouds.”

Atmospheric scientist Steven Sherwood agreed, saying “We’re emitting a lot of stuff into the atmosphere, including a lot of air pollution, and we don’t know what it’s doing to clouds…That’s been a huge uncertainty for a long time…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.”