Global warming to increase lightning strikes: Study

WASHINGTON: Global warming will lead to a 50 per cent increase in lightning strikes across the US during this century, according to a new study.

Researchers looked at predictions of precipitation and cloud buoyancy in 11 different climate models and concluded that their combined effect will generate more frequent electrical discharges to the ground.

"With warming, thunderstorms become more explosive," said Climate scientist David Romps, from the University of California, Berkeley.

"This has to do with water vapour, which is the fuel for explosive deep convection in the atmosphere. Warming causes there to be more water vapour in the atmosphere, and if you have more fuel lying around, when you get ignition, it can go big time," said Romps.

More lightning strikes mean more human injuries; estimates of people struck each year range from the hundreds to nearly a thousand, with scores of deaths.

But another significant impact of increased lightning strikes would be more wildfires, since half of all fires are ignited by lightning, Romps said.

Romps and graduate student Jacob Seeley hypothesised that two atmospheric properties -- precipitation and cloud buoyancy -- together might be a predictor of lightning, and looked at observations during 2011 to see if there was a correlation.

Precipitation -- the total amount of water hitting the ground in the form of rain, snow, hail or other forms -- is basically a measure of how convective the atmosphere is, he said, and convection generates lightning.

The ascent speeds of those convective clouds are determined by a factor called CAPE - convective available potential energy.

Researchers concluded that 77 per cent of the variations in lightning strikes could be predicted from knowing just these two parameters.

They then looked at 11 different climate models that predict precipitation and CAPE through this century and are archived in the most recent Coupled Model Inter-comparison Project (CMIP5).

On average, the models predicted an 11 per cent increase in CAPE in the US per degree Celsius rise in global average temperature by the end of the 21st century.

Because the models predict little average precipitation increase over this period, the product of CAPE and precipitation gives about a 12 per cent rise in cloud-to-ground lightning strikes per degree in the contiguous US, or a roughly 50 per cent increase by 2100 if Earth sees the expected 4 degrees Celsius increase in temperature.