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

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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.

Meteorologists say the temperature topped out at 119 degrees in Phoenix on Tuesday as a stifling heat wave blanketing the Southwest U.S. brought some of the hottest weather in years.

The heat has caused flights to be canceled, strained the power grid and made life miserable for workers toiling outside.

As the global climate changes, air travel disruptions 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.

American Airlines Group was forced to cancel 50 flights so far this week — 43 of them Tuesday — from its Phoenix hub because of high temperatures. An additional seven flights to Phoenix were delayed Tuesday due to the heat. The 50- to 76-seat Bombardier jets flown by American Eagle are certified to operate at 118.

The Bombardier family of regional jets can become too hot to fly when the weather turns extreme.

Bigger jets like Boeing 737s and Airbus A320s have higher operating thresholds (126 and 127 degrees, respectively), he said. But even though bigger planes weren’t affected, Feinstein said, American decided to give passengers on any flight to or from Phoenix the option to change their trips.

Robert Mann, the president of airline industry analysis firm R.W. Mann & Co., said that although airlines were working to become more efficient, they were not doing much to prepare for the longer-term effects of climate change. “In a world where they’re focused on near-term issues, the glacial rate of environmental change is not within their fleet-planning horizon,” he said.

Feinstein of American Airlines referred questions about the effect of climate change on flying to an industry trade group, Airlines for America. The trade group provided its Earth Day statement describing its members’ efforts to become more environmentally friendly by using more fuel-efficient engines and modifying planes to be more aerodynamic.

Aviation is a major producer of carbon dioxide, responsible for about 2 percent of human-made emissions each year.

Researchers are just beginning to explore how climate change affects aviation and planes’ ability to fly. Because there is so little data available and so many factors at play — aircraft design, airport size and location, the weight of passengers and cargo, to name just a few — it can be hard to attribute any one service disruption to global warming.

Depending on their locations, airports may experience the effects differently. High-altitude airports like Denver have thinner air by nature, so lift is even more affected by higher temperatures.

La Guardia Airport in New York could also be affected, even though it is at sea level. La Guardia has a short runway relative to other major commercial airports, and on particularly hot days that can be a problem: Planes might not have enough distance to achieve the speed and lift needed to get airborne.

“Typically in the hotter days of the summer, you may have to bump payload, which includes cargo and/or passengers,” said David Wilhelm, a senior dispatch manager at Southwest Airlines. Reducing weight allows a plane to take off with less lift.

La Guardia, because of its short runway, already forces many planes to reduce their weight, regardless of the weather. A Boeing 737, for example, has to cut its maximum payload by a thousand pounds for a successful departure. That restriction increases on hotter days, up to 15,000 pounds when the temperature hits 91.4 degrees.

Restrictions like these are determined by individual airports and airlines, and not by a standardized industry regulation. American Airlines consults data from the National Weather Service to determine if conditions at their airports are suitable for takeoffs and landings.

In 2015, Radley Horton, a research scientist at Columbia University’s Earth Institute, published a joint study with a Ph.D. student, Ethan Coffel, on the effect of extreme heat on aviation. The conclusion: “We can say with confidence that there will be more weight-restricted days, and larger weight restrictions,” he said.

Already, since the 1980s, airports have seen an increasing number of weight-restricted summer days, their research found. “One thing that’s become abundantly clear,” Horton added, “is this is an underexplored area.”

The study examined conditions at four airports: La Guardia; Ronald Reagan Washington National Airport, which also has relatively shorter runways; Phoenix Sky Harbor International Airport; and Denver International Airport. Some airports, like Denver, could counteract rising temperatures by extending their runways. That option is less workable for a location like La Guardia, however, as it is hemmed in by New York City on one side and the East River on the other.

As global temperatures continue to rise, some of the heaviest planes on the longest flights may eventually be unable to depart during the hottest part of summer days, Horton said. Like an ocean liner waiting for the right tide to leave port, airplanes may be grounded until the air is cool and dense enough for takeoff at full capacity.

Extreme heat on the ground also affects airport workers; loading and unloading luggage and servicing planes between flights could become more onerous. In Phoenix this week, American Airlines set up cooling stations — air-conditioned tents on the tarmac — for its employees.

Places like Phoenix, already known for summer heat, are measurably warming up. Data from the National Centers for Environmental Information show that every year since 1976 has been hotter than the city’s historical average. Seven of the 10 hottest years on record there have been in the past decade.