“Hot air is less dense than cold air, its molecules zipping around at higher speeds, meaning planes have less lift when the mercury rises,” writes Mark Gongloff of Bloomberg Opinion. “That makes it harder for them to take off and stay aloft. Airlines and pilots will often choose to delay flights or unload passengers and luggage to shed weight from planes when the temperature climbs too high. This leads to cascading schedule disruptions across the entire system, along with passengers occasionally being trapped for hours on runways inside roasting aircraft.” (Michael Probst, Associated Press/The Minnesota Star Tribune)

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Lest you think air travel couldn't possibly get more miserable, climate change is here to prove you wrong.

Just as extreme heat makes people sluggish and unproductive at best, and threatens human life at worst, it also makes flying airplanes much more difficult. Hot air is less dense than cold air, its molecules zipping around at higher speeds, meaning planes have less lift when the mercury rises. That makes it harder for them to take off and stay aloft.

Airlines and pilots will often choose to delay flights or unload passengers and luggage to shed weight from planes when the temperature climbs too high. This leads to cascading schedule disruptions across the entire system, along with passengers occasionally being trapped for hours on runways inside roasting aircraft.

It's a problem that will only get worse as the planet warms and extreme heat of the sort blanketing the southern U.S. this summer becomes more routine. Up to 30% of all U.S. flights, on average, may be subject to weight restrictions during periods of high heat by mid-century, according to a 2017 Columbia University study. And barring a miraculous technological breakthrough, the aerospace industry has no real solution to overcome the harsh laws of physics.

"This is a physical restriction related to air density, and there are not a whole lot of direct technological fixes for it," said Ethan Coffel, an assistant professor at Syracuse University, who was an author of the 2017 study.

Most of us probably think of snow and ice as the biggest threat to on-time flights, but heat causes far more delays, Bloomberg News reported recently. Chicago's O'Hare International Airport, for example, suffered roughly twice as many weather delays in the summer of 2022 than it did last winter.

The high-heat problem is especially hard to overcome for airports with short runways, which give planes less room to gain the momentum they need to take off. New York's LaGuardia Airport has a particularly short runway and no space to expand, constrained as it is by Flushing Bay and dense Queens neighborhoods.

Unfortunately for America's mental health, LaGuardia is also what the Federal Aviation Administration calls a "pacing airport," or, as I see it, one that:

• Has a high volume of traffic.

• Is routinely unable to handle that volume of traffic.

• Ruins air schedules around the country as a result.

"Scheduling is a disaster every day as it is," said independent aviation consultant Robert Mann, "and heat just makes it worse."

Airports at high altitudes, such as Denver, are also uniquely vulnerable to high heat, as are the ever-warming cities of the Sun Belt. Surprisingly, the hottest of those cities, Phoenix, suffers relatively few weight-restriction days thanks to its longer-than-usual runways, which are also made of specially reinforced concrete. Of course, not every airport can afford the expense and delay of tearing up old runways and building new, stronger ones. And cancellations still happen, even in Phoenix. Workers on sun-baked taxiways and runways — which are usually much hotter than the atmosphere around the airport — are also especially vulnerable to the "heat island" effect. Workers in extreme conditions will need longer breaks or risk falling ill and causing airports to be short-staffed.

Aerospace manufacturers are always working on ways to make planes lighter and more efficient, but most of that progress has already been made. Barring revolutionary new materials, any further gains will be incremental at best. So until we figure out how to make airplanes out of gossamer, we'll have to rely on old-fashioned solutions to heat: moving flights to cooler times, lengthening and strengthening runways and ditching weight.

The net effect is that flight delays will probably keep rising, adding to climate change's growing impact on air travel. It's already making turbulence more dangerous, lengthening flights because of changing wind patterns, and fueling the extreme weather that leads to more delays. As with every other effect of rising heat, the most effective solution would be to stop burning the fossil fuels that contribute to warming — including the fuels burned by airplanes. Air travel isn't much fun these days anyway.

Mark Gongloff is a Bloomberg Opinion editor and columnist covering climate change. A former managing editor of Fortune.com, he ran the HuffPost's business and technology coverage and was a reporter and editor for the Wall Street Journal.