Every once in a while, unlucky passengers get bumped because an overbooked aeroplane is too heavy. It's maddening, and it makes you question the airline's ability to do arithmetic. But there is a method to weight restrictions, and Earth's rising temperatures could make it increasingly hard for planes to take off without shedding extra weight.
As air gets hotter, it gets less dense, and this can spell trouble for aircraft. Thin air can't generate enough lift and thrust to get a plane safely airborne within the fixed length of a runway. If it's too hot, aeroplanes will have to shed pounds, in the form of passengers and cargo, according to a study from Columbia University.
"This happens now," says study author Ethan Coffel, "Temperature is one of the primary factors that goes into calculations for every flight."
Coffel and his co-author Radley Horton looked at how rising temperatures would affect a common commercial aircraft, the Boeing 737-800, at four airports especially prone to weight restrictions during heat waves: Phoenix (for its high summer temperatures), Denver (for its high elevation), and LaGuardia and DC's Reagan (for their relatively short runways).
If maximum temperatures rise by the projected 3C to 4C 2050-2070, the number of days when weight restrictions apply would jump from 50 to 200 per cent.
These projections are for several decades from now, but it does mean airlines will have to start thinking about adapting to climate change. Sure, we'll have new planes by then, but technology may not solve everything.
"Aeroplane wings are designed to be effective in cruise where it spends most of its time," says Coffel. That means the shape of a wing can only be changed so much to optimise it for takeoff.
Airports might have to put in longer runways, or flights may have to be shifted to cooler parts of the day. The study, which was published in the journal Weather Climate Society and presented at the American Geophysical Union meeting this week, forces us to reckon with yet another niggling consequence of climate change.