Klimaendring og flyging - Spenn deg fast! - Curt Lewis

Climate change could make flights longer and bumpier

As if flying wasn't already enough of a chore, there's an increasing number of studies showing climate change might make it worse.

Changes to the jet stream could make flights longer and more turbulent.

And higher temperatures could affect the maximum takeoff weight, meaning more weight restrictions and even flight cancellations.

The problems could have an effect on the profits of airlines, which are already operating on slim margins.

Bumpier journeys

Research from Reading University has found that flights could become lengthier and more turbulent because of climate change.

Climate change will make the jet stream stronger, and while tailwinds will help flights in one direction, headwinds will slow them down on the return leg.

This effect doesn't cancel itself out, and in fact on the transatlantic route, the costs could amount to $22m (£17m) in additional fuel every year.

The same researchers found that a more powerful and unpredictable jet stream could increase the number of incidents of severe turbulence by 149%.

This could increase the risk of injury and add to an airline's insurance costs.

Boeing says its planes can be equipped to counter the effects of turbulence as well as to avoid it altogether.

But flying around turbulence could lengthen the flight and add to fuel costs.

Taking off

A study in July looked at five different commonly-used planes, and found that 10-30% of flights could require some weight restriction by the middle of the century due to rising temperatures.

That could mean a reduction in passengers and cargo of between 0.5-2%.

The problem is that a wing's lift is directly related to the density of the air flowing past it: the denser the air, the greater the lift.

In extreme heat, the air becomes less dense, making take-off harder.

Engines are affected too, because they create less thrust.

As a result, a plane might have a lower maximum take-off weight, or it might need more space on a runway to get airborne.

Heat limits

For most major passenger jets, the maximum operating temperature is around the 49C, give or take a few degrees depending on the aircraft.

At the moment, those temperatures are mercifully rare.

Still, major airlines were forced to delay or cancel dozens of flights out of Las Vegas and Phoenix airports in June due to a heat wave.

The concern is that climate change will make it more common.

While deserts are obviously the most affected, the study's author Ethan Coffel says some Asian airports - Bangkok and Hong Kong, for example - could see a substantial fraction of long-haul flights requiring some takeoff weight restriction during the hottest parts of the day.

Slim margins

Mr Coffel thinks the problem could be a "non-trivial" addition to an airline's costs, which will come in the form of reduced payloads.

This is an industry with slim profit margins and on any given flight the difference between making a profit or a loss might boil down to just a few passengers. It's why airlines overbook flights.

This year, the International Air Transport Association (Iata) expects the airline industry globally to make a profit margin of 4.1% and to keep $7.54 for each passenger, but this is a good year and those figures are much lower outside the lucrative US market.

Some industry-watchers feel the research is extremely speculative, because it deals with conditions that are several decades away.

"It could be an issue very long term, but you've got to expect aircraft performance will improve, or maybe people will fly less," said FlightGlobal's Greg Waldron.

Fewer freezes

Canadian manufacturer Bombardier says airlines that operate in very hot cities tend to get around the problem by scheduling flights in the evening or early in the morning to operate in lower temperatures.

Boeing says its customers can order a "high and hot" package, which improves performance with slightly more thrust and slightly larger control devices on the wing.

But Ethan Coffel notes that those solutions aren't free.

"There is always an opportunity cost - performance would have been better without climate change," he said.

At the other end of the spectrum, flights are sometimes cancelled due to cold weather too.

For example, more than 6,000 flights were cancelled in the US because of a storm in March, mostly due to icy conditions on the runway.

So if the climate continues to get warmer, would a few flights cancellations in Phoenix be balanced out by fewer cancellations in Toronto because of less freezing weather?

"It is possible that cold weather impacts could be reduced - that would be a useful future research area," said Ethan Coffel.