Lightning strikes are set to become more frequent if global warming resumes, according to a new study by climate scientists. In an extreme scenario where temperatures climb by 4 degrees Celsius, the increase could be as much as 50 per cent.
"With warming, thunderstorms become more explosive," explains David Romps, climatology professor at 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 vapor in the atmosphere, and if you have more fuel lying around, when you get ignition, it can go big time."
Romps and his colleagues have made their prediction on the future of lightning by looking into a factor known as CAPE - convective available potential energy - which is measured by the radiosonde balloons routinely released above the USA to monitor weather.
"CAPE is a measure of how potentially explosive the atmosphere is, that is, how buoyant a parcel of air would be if you got it convecting, if you got it to punch through overlying air into the free troposphere," says Romps. "We hypothesized that the product of precipitation and CAPE would predict lightning ... We were blown away by how incredibly well that worked."
Using these methods produced the following results:
On average, the models predicted an 11 percent increase in CAPE in the U.S. per degree Celsius rise in global average temperature by the end of the 21st century. Because the models predict little average precipitation increase nationwide over this period, the product of CAPE and precipitation gives about a 12 percent rise in cloud-to-ground lightning strikes per degree in the contiguous US, or a roughly 50 percent increase by 2100 if Earth sees the expected 4-degree Celsius increase (7 degrees Fahrenheit) in temperature.
Many people believe that global temperatures can and should be prevented from increasing any more than 2 degrees Celsius, in which scenario there would only be a quarter increase in lightning strikes. Others would point out that actually there has been no warming for the last fifteen years and more, so it could be that there won't be much of it this century and lightning strikes will remain at their current level.
But, assuming Romps and his colleagues are right and there will be fifty per cent more lightning in the year 2100, what will that mean?
Well, the current chance of a person being struck by lightning in the USA is 1 in 700,000 over a year: that is 0.0000014. Increasing this by fifty per cent brings it up to approximately 0.000002.
Romps and his colleagues' paper is published in major boffinry mag Science. ®