The latest research suggests that climate change will increase air turbulence. But it’s impossible to say what role, if any, global warming has played in a spate of recent turbulence incidents that resulted in injuries on commercial flights.

“I wouldn’t draw anything from it,” said Paul Williams, an atmospheric scientist at the University of Reading in England who has studied the connection between atmospheric carbon dioxide levels and air turbulence. “Certainly there needs to be some [scientific] work done.”

In the past five weeks, news reports and social media sites have been filled with stories and videos of screaming passengers being violently rocked by turbulence.

“All of a sudden, out of nowhere — out of nowhere! — I thought this was the end,” passenger Gisela Arrow told WPLG in Miami after an Allegiant Air flight encountered heavy turbulence en route from Punta Cana, Dominican Republic, to Pittsburgh.

That May 5 flight had to be diverted to Fort Lauderdale, where seven people were taken to a hospital.

The Allegiant flight is just one of six that have made headlines since the second half of April due to violent air turbulence. Internationally, six people were injured on an April 18 Thai Airways flight from Jakarta to Bangkok.

Worse was an Etihad flight from Abu Dhabi, United Arab Emirates to Jakarta, Indonesia, on May 4 in which 31 people were injured and 10 were hospitalized when the Airbus A330-200 ran into violent turbulence about 45 minutes before landing. 

On U.S. flights, the May 5 Allegiant incident was followed on May 8 by a Delta flight from Atlanta to Chicago that had to make an emergency landing in Nashville after turbulence caused an engine cover to come off. No one was hurt.

A day later, severe turbulence on a JetBlue flight from San Juan to Orlando sent eight people to the hospital. And on May 16, four passengers were injured and two were hospitalized when a Southwest flight en route to Chicago Midway was forced to return to Boston after encountering heavy turbulence.

Despite this recent spate of incidents, FAA data shows that in recent years turbulence-related injuries have dropped over U.S. skies. Just 65 people sustained what the National Transportation Safety Board (NTSB) defines as a “serious injury” due to in-flight turbulence from 2013 to 2015, compared with 230 between 2008 and 2010.

But because airlines are only required to report serious injuries, such data is limited in scope. An older but more thorough FAA data set shows that turbulence-related accidents and injuries roughly doubled between 1982 and 2003 on a per-departure basis.

Though the report stated that higher passenger loads could account for the difference, Williams said he thinks climate change played a role, as well.

“I think it’s because the atmosphere has gotten more turbulent; that’s part of the explanation,” he said.

Williams’ views are based on his 2013 peer-reviewed study that was published in the journal Nature Climate Change. In conducting the study, he and co-author Manoj Joshi zeroed in on what is known as clear-air turbulence, which is the type of turbulence that causes most major incidents for commercial airliners.

Unlike turbulence caused by clouds and storm systems, which is easily visible, clear-air turbulence can’t be seen by pilots through the cockpit window and cannot be detected by radar. It typically occurs at altitudes above the clouds, where jetliners like to fly, and it’s often caused by sudden changes in atmospheric pressure or by the convergence of counter-moving jet streams.

Because it is invisible, incidents of clear-air turbulence often occur while the seat belt signs are off, increasing the chances that a passenger or crew member will get injured.

Jet streams are expected to strengthen due to climate change. But Williams sought to determine how that strengthening would affect turbulence. He focused his study on the North Atlantic corridor, which some 600 flights traverse each day. Through the use of climate model simulations, he looked at how the frequency and intensity of clear-air turbulence changes as atmospheric carbon dioxide is doubled from its pre-industrial baseline of an estimated 280 parts per million.

At present, carbon dioxide levels have already increased from the baseline to 400 parts per million. Scientists project the doubled figure of 560 parts per million will be reached this century, perhaps even by the middle of the century.

What Williams’ models showed is that in a world with carbon dioxide levels of double the pre-industrial level, the amount of air space that would contain significant clear-air turbulence increases by between 40% and 170%, with a cluster of results showing an increase of around 100%. In addition, the average strength of the turbulence would increase by 10% to 40%.

“It seems reasonable that if the volume of turbulence in the atmosphere is going to double, then the number of injuries is going to double as well, unless we can improve these forecasts,” Williams said.

If the amount of invisible air turbulence is on the rise, the ways to counter it would be through improved forecasts or the development of new detection techniques.

The latter of those is already underway. Between 2009 and 2014, a team of European scientists tested a system in which ultraviolet lasers are pointed in the direction a flight is headed. The lasers detect changes in air density, giving pilots a warning of turbulence.

The tests suggested that the laser-based system could detect moderate turbulence at a distance of up to 30 kilometers. However, author Herve Barny noted that conclusion is not definitive because they ran into only light turbulence during the test flights. Thus far, airlines have not begun using the technology.

Meanwhile, effective use of big data could provide a way to improve the turbulence forecasts that are issued every six hours by the World Area Forecast Centers in Washington and London. Airlines keep detailed records of turbulence incidents, Williams said, but as of yet there’s no central archive in which scientists can access that information to build turbulence models.  

He called such data a “treasure trove.” 

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