Lightning more frequent as world warms: study

Lightning strikes will increase by about 12 percent in the United States for every one degree Celsius rise in global average air temperature, US researchers who studied the effect of global warming on lightning activity said Thursday.

Observations have shown that lightning occurs more frequently when it is hotter than when it is colder, but it is difficult to know how much more lightning we should expect as global temperatures continue to increase.

Previous estimates have predicted lightning strikes could increase anywhere between 5 percent and 100 percent for every one degree Celsius rise in global average air temperature.

In the new study, David Romps of the University of California, Berkeley, and his colleague hypothesized that two atmospheric properties, known as precipitation and cloud buoyancy, together might be a predictor of lightning.

The researchers validated their hypothesis against observations, and then applied it in 11 global climate models to predict future increases in lightning strikes across the continental US, a region where lightning strikes frequently, and is well-recorded.

Their results suggested lightning strikes will increase by about 12 percent, from the current annual number of around 25 million, for every one degree Celsius rise in global average air temperature.

More lightning strikes mean more human injuries, said Romps, estimating that the number of people struck each year ranges from the hundreds to nearly a thousand, with scores of deaths.

Another significant impact of increased lightning strikes, he said, would be more wildfires, since half of all fires -- and often the hardest to fight -- are ignited by lightning.

More lightning also would likely generate more nitrogen oxides in the atmosphere, which exert a strong control on atmospheric chemistry.

The researchers said their method could also be used to assess future changes in lightning rates in other parts of the world.

The study was published in the US journal Science.