Washington AFP | Thursday 11/13/2014
Lightning has the power to spark wildfires and kill, and scientists said Thursday that climate change may lead to 50 percent more of it by century's end.
The report in the US journal Science is based on measurements of precipitation and cloud buoyancy, applied to 11 different climate models that estimate how warm the planet may get by 2100.
"With warming, thunderstorms become more explosive," said climate scientist David Romps of the University of California, Berkeley.
"Warming causes there to be more water vapor in the atmosphere, and if you have more fuel lying around, when you get ignition, it can go big time."
Previous estimates of how lightning would be affected used indirect techniques that were not closely tied to precipitation.
The result was a range between five and 100 percent more lightning for every one degree Celsius of warming.
The current study is based on the energy available to make air in the atmosphere rise, combined with precipitation rates.
Convective available potential energy, or CAPE, is measured by radiosondes, balloon-borne instruments released around the United State twice daily.
"CAPE is a measure of how potentially explosive the atmosphere is," explained Romps.
"We hypothesized that the product of precipitation and CAPE would predict lightning."
Using data from the US National Weather Service, researchers found that 77 percent of variation in lightning strikes could be predicted by knowing CAPE and precipitation.
"We were blown away by how incredibly well that worked to predict lightning strikes," said Romps.
- More lightning -
When applying the parameters to climate models, the team found that each one degree Celsius rise in global average air temperature would mean about 12 percent more lightning strikes.
If temperatures warm four degrees Celsius by century's end, that would mean nearly 50 percent more lightning by then.
Lightning now strikes 25 million times a year around the world.
More lightning strikes could place people at higher risk of being hit and injured or killed, and may also have a devastating effect on wildlands and species.
An uptick in the rate of strikes could cause more fires in dry forested areas, killing off a host of birds and other woodland creatures and endangering people who live nearby.
Lightning begins as a static charge inside a rain cloud. Turbulent wind conditions inside the cloud can lead to a negatively charged bottom and positively charged top.
When these electrical fields get strong enough, the atmosphere is no longer able to insulate the electrical charge and it erupts into a lightning strike.
"Lightning is caused by charge separation within clouds, and to maximize charge separation, you have to loft more water vapor and heavy ice particles into the atmosphere," said Romps.
"We already know that the faster the updrafts, the more lightning, and the more precipitation, the more lightning."
Lightning strikes have killed 25 people in the United States so far this year, according to the National Weather Service.
Florida had six lightning fatalities, the highest for any state.