In the mid-twentieth century, NASA scientists launched the first satellites to view Earth.

When they looked at the photos, they saw mysterious stripes of clouds crossing the oceans.

On closer inspection, they realized these cloud trails followed the shipping lanes.

In the mid-nineteenth century, after collisions between ships, nations designated lanes across the seas that ships would follow to avoid accidents.

As traffic grew over the twentieth century, more and more ships plied these maritime highways. But what caused the clouds?

Scientists realized that the exhaust plumes of hundreds or thousands of diesel-fired ships carried streams of aerosols and fine particulates into the low atmosphere, along the shipping lanes.

Water vapor condensed on these to form the trails: the ships were making their own clouds.

Newer satellites discovered something more. They picked up magnetic pulses from lightning patterns across the ocean, and the lightning also followed the shipping lanes.

Scientists now understand that the tiny water droplets in the ships’ cloud trails, finer than in regular clouds, are more conducive to lightning formation.

The ships actually make their own lightning storms, and the weather in their wake is more severe than over open ocean.

So if you’re having one of those days when it feels like a storm cloud is following you around—if you’re the captain of a cargo ship, it just may be.