While the timing of this trend lines up with the planet’s rising temperatures, scientists are hesitant to definitively attribute tornadoes’ clustering behavior to human-caused climate change.

“The link between climate change and tornadoes is still pretty tenuous,” Dr. Fricker said. “It’s a really open and difficult question for us.” One difficulty is that tornadoes are too small on a planetary scale, and too ephemeral, to show up in the global mathematical models that scientists use to study climate change.