Lightning is a beautiful yet deadly phenomenon that our world is certainly not short of. As you read that sentence, around 200 bolts of lightning struck the ground across the Earth. With around 100 strikes per second, lightning bolts streak through the sky and hit the ground somewhere on our planet around 8 million times per day. But according to a new study, that number could be set to dramatically increase if the current rate of global warming continues, at least within the U.S. As reported in the journal Science, we could expect to see a 12% increase in lightning activity for every 1oC (1.8oF) of warming, meaning the U.S. could experience a 50% increase in strikes by the turn of the century.
Examining the potential impacts of global warming is not exactly a neglected field of study, but while scientists have spent years investigating how severe weather could be affected, much of the focus has been on hazards such as hurricanes.
Lightning is also hazardous; it can strike and kill people, and also trigger potentially devastating wildfires. Yet studies exploring how lightning could change with rising temperatures are few and far between, and those that have been conducted have produced wildly different results.
For the current study, scientists from the University of California, Berkeley, started off by examining the relationship between atmospheric variables and lightning rates. They hypothesized that two factors-- precipitation (the amount of water that hits the ground) and the amount of energy available to make atmospheric air rise-- could predict lightning flash rate. These variables can both be used as measures of storm convection (the vertical movement of air), a process that is known to generate lightning.
Lightning requires two key ingredients: water in all three states (liquid, solid and gas) and quickly rising clouds to keep the ice suspended. “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,” lead author David Romps said in a news-release. “We already know that the faster the updrafts, the more lightning, and the more precipitation, the more lightning.”
By comparing lightning strike data with precipitation and convection energy data, they found that their chosen variables were able to predict lightning strikes with remarkable accuracy. These two factors alone, they discovered, could predict 77% of the geographic and temporal (time) variations in lightning strikes in the US.
Next, they applied these variables to 11 different climate models, all of which assume that there will be no significant drops in greenhouse gas emissions, and found that lightning would likely increase by around 12% per 1oC. Since it is predicted that temperatures will be around 4oC higher at the end of the century, this means there could be a 50% increase in strikes in the US by 2100. This could potentially mean more human injuries and more wildfires, since around half of all wildfires are started by lightning.
Their findings make sense since heavy precipitation and storm energy are related to the availability of water vapor in the atmosphere, and warmer atmospheres can hold more moisture. What this work cannot predict, however, is when or where the lightning strikes may occur.
“It could be regions that get a lot of lightning strikes today will get even more in the future, or it could be that parts of the country that get very little lightning could get much in the future,” said Romps. “We just don’t know at this point.”