Container ships traveling the world's oceans could be to blame for an increase in lightning strikes at sea.
In a study published in Geophysical Research Letters this week, researchers said they had gone back through the records and found that two international shipping lanes in Asia experienced almost double the number of lightning strikes as identical strips of ocean a few hundred miles away.
The researchers, from the Department of Atmospheric Sciences at the University of Washington in Seattle, looked at lightning strikes in the Indian Ocean and the South China Sea for every year between 2005 and 2016.
They found much higher rates of lightning strikes in one shipping lane between Sri Lanka and Sumatra and another between Singapore and Vietnam.The team, led by Joel Thornton, ruled out weather conditions and other reasons for the differences and concluded it must be the ships themselves that were increasing the risk of lightning.
"We hypothesize that emissions of aerosol particles and precursors by maritime vessel traffic lead to a microphysical enhancement of convection and storm electrification in the region of the shipping lanes," said their report.
In laymen's terms, they concluded that soot and other particles in the ships' exhaust created ice particles which rub against each other to generate the lightning.
But they said that what was particularly strange was that although there were more lightning strikes in the shipping lanes there was no evidence of higher rainfall.
Ships occasionally get struck by lightning but larger vessels are fitted with lightning rods on their masts, which are designed to safely discharge the charge into the sea.