An airplane takes off from Reagan National Airport as Glen Briscoe holds a large umbrella while watching boats come and go at Gravelly Point on July 9 in Arlington, Va. (Matt McClain/The Washington Post)

Nearly half of long-haul flights at some of world’s busiest airports could face disruptions on the hottest days because of extreme heat under climate change toward the end of the century, a study said Thursday.

On hot days, flights experience weight restrictions. Focusing on five major aircraft at 19 of the world’s busiest airports, researchers at Columbia University concluded that 10 to 30 percent of flights scheduled for takeoff in the heat of the day will have to reduce their weight by an average of about 700 pounds — or three passengers and their luggage.

For most airports, weight restriction days may increase to between 10 and 50 days a year by 2080. Airports in hot regions, at high elevations and with short runways will see the biggest changes. These include airports in Bangkok, Dubai, Miami, Los Angeles, Phoenix, Denver, Washington, D.C., and New York’s LaGuardia.

Researchers predict that flights leaving Dubai and LaGuardia in the peak of the summer may be unable to take off at full capacity half of the time or more. Airports in cooler regions with longer runways such as New York’s JFK, London’s Heathrow and Paris’s Charles de Gaulle will see lesser effects. Across all airports, restricted flights are predicted to increase by as much as 50 percent for large planes.

There are two ways rising temperatures can shut down flights. Under extreme temperatures of 120 degrees Fahrenheit, as in Phoenix the last week of June, regional planes can’t take off at all. That’s because regional aircraft are tested only up to 118 degrees, said a representative from American Airlines. Larger aircraft are tested up to 127 degrees.

For a plane to get off the ground, the lift force pushing up on the plane has to be greater than the force of the weight of the plane. Warmer air has less lift force, because there are “less molecules of air for the plane to push off of,” explained Radley Horton, the principle investigator of the study.

So the warmer the air, the lighter the plane has to be for takeoff. There are only three ways for a plane to lose weight: fuel, cargo and passengers.

“You can normally accommodate weight issues by adjusting fuel levels,” Billy Nolen of Airlines for America, the airline trade association said in an interview last month.

But for longer flights where a full tank of fuel is necessary, airlines “start to bump off passengers and their luggage,” said Paul Williams, who was not involved with the study but helped to prepare a report on climate change for the International Civil Aviation Organization last year.

“With increasing temperatures, we see pretty significant increases in weight restrictions,” said Ethan Coffel, a doctoral student involved with the study.

Climate scientists expect average temperatures to increase as much as 3 degrees Celsius by the end of the century. For every 3 degree increase, the weight of the aircraft has to be reduced by 1 percent, Williams said. That’s about 1,500 pounds for a standard Boeing 737.

From your brain to your skin pores, this is what goes into your body keeping you cool when the heat turns up. (Claritza Jimenez/The Washington Post)

Rising temperatures are just one way that climate change could affect air travel. Rising sea levels threaten coastal airports, extreme weather events lead to cancellations, and changes in wind patterns increase turbulence or alter fuel efficiency, according to researchers. While the carbon footprint of the airline industry has been given a lot of attention, this study joins only a half-dozen or so others examining the potential “reverse impact” of climate change on flights.

As for airlines, “climate change is seen as a very distant threat,” Williams said. But the researchers predict that removing even a few passengers can have big effects on airline costs. It’s possible these increases could be reflected in ticket prices.

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