In recent days, American Airlines has been forced to cancel more than 40 flights in Phoenix. The reason: With daytime highs hovering around 120 degrees, it was simply too hot for some smaller jets to take off. Hotter air is thinner air, which makes it more difficult — and sometimes impossible — for planes to generate enough lift.

As the global climate changes, disruptions like these are likely to become more frequent, researchers say, potentially making air travel costlier and less predictable with a greater risk of injury to travelers from increased turbulence.

“We tend to ignore the atmosphere and just think that the plane is flying through empty space, but of course, it’s not,” said Paul D. Williams, a professor in the Department of Meteorology at the University of Reading in Britain who studies climate change and its effect on aviation. “Airplanes do not fly through a vacuum. The atmosphere is being modified by climate change.”

The problem in Phoenix primarily affected smaller jets operated by American’s regional partner airlines. “When you get in excess of 118 or higher, you’re not able to take off or land,” said Ross Feinstein, a spokesman for American Airlines, referring to the smaller aircraft.