Ship exhaust makes oceanic thunderstorms more intense

Ship exhaust makes oceanic thunderstorms more intense, by Science Daily.

Thunderstorms directly above two of the world’s busiest shipping lanes are significantly more powerful than storms in areas of the ocean where ships don’t travel, according to new research.

A new study mapping lightning around the globe finds lightning strokes occur nearly twice as often directly above heavily-trafficked shipping lanes in the Indian Ocean and the South China Sea than they do in areas of the ocean adjacent to shipping lanes that have similar climates.

The difference in lightning activity can’t be explained by changes in the weather, according to the study’s authors, who conclude that aerosol particles emitted in ship exhaust are changing how storm clouds form over the ocean.

The new study is the first to show ship exhaust can alter thunderstorm intensity. The researchers conclude that particles from ship exhaust make cloud droplets smaller, lifting them higher in the atmosphere. This creates more ice particles and leads to more lightning.

The results provide some of the first evidence that humans are changing cloud formation on a nearly continual basis, rather than after a specific incident like a wildfire, according to the authors. Cloud formation can affect rainfall patterns and alter climate by changing how much sunlight clouds reflect to space.

“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,” said Joel Thornton, an atmospheric scientist at the University of Washington in Seattle and lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union.

“It is the first time we have, literally, a smoking gun, showing over pristine ocean areas that the lightning amount is more than doubling,” said Daniel Rosenfeld, an atmospheric scientist at the Hebrew University of Jerusalem who was not connected to the study. “The study shows, highly unambiguously, the relationship between anthropogenic emissions — in this case, from diesel engines — on deep convective clouds.”

It’s not unlikely this has a bigger effect on global warming than increasing carbon dioxide. (Book soon.)

The Earth’s albedo is the fraction of sunlight that is reflected back out to space without warming the planet, mainly by clouds and ice. Normally the albedo is about 30%, but if it fell to 29% there would be about three times as much global warming as observed in the last century. Small changes in the amount of clouds control the amount of sunlight that warms the Earth, like a tap controls the powerful gush of water through a fire hose.