Rising humidity has boosted storm potential in northern hemisphere

Grand Canyon lightning storm

The conditions that trigger severe storms are becoming more common

John Sirlin / Alamy

Unstable atmospheric conditions that are ripe for thunderstorms and sometimes tornadoes have increased across the northern hemisphere in the past 40 years. The finding is one of the best indications yet that strong storms are getting more frequent, as climate models predict – but this might not necessarily mean there will be more tornadoes.

“It favours more occurrence of severe storms such as tornadoes,” says study author Aiguo Dai of the University at Albany in New York. “But the actual formation …