Scientists Forecast a Big Increase of Clear-Air Turbulence That Could Lead to Bumpier Flights
Global warming is making high-altitude winds more volatile. Scientists say there are ways to help prevent serious incidents.
Scientists at the European Geosciences Union conference last week said there is growing scientific evidence that global warming is driving a big increase in dangerous clear-air turbulence, which is invisible from the cockpit and can surprise pilots and damage aircraft.
Along some busy flight routes, turbulence is projected to “double or treble or quadruple over the next few decades,” said Paul Williams, a professor of atmospheric science and head of the weather research division at the University of Reading in the United Kingdom. “What we find … is that the jet stream regions in both the Northern and the Southern hemispheres are affected.”
As its name implies, clear-air turbulence can happen when there are no visible signs of a weather disturbance, often at or near the boundary of contrasting air masses, moving in different directions and at varying speeds. It can unexpectedly toss large airplanes up and down by several hundred feet, potentially damaging the airframe and injuring passengers and crew.
The increase of clear-air turbulence has been documented for a few years. Researchers are now starting to understand how and why it happens, which could help develop new ways to forecast and avoid it, especially when it involves the jet stream, strong rivers of air in the Northern and Southern hemisphere that steer weather systems and air masses from west to east.
But looking at how climate change affects wind speeds in the upper atmosphere hasn’t proven very helpful in understanding clear-air turbulence, Williams said. Vertical wind shear—the difference in the speed and direction of winds at different altitudes—is a much more useful variable for the researchers.
“When we look in the same three re-analysis data sets of what the vertical wind shear has been doing, there’s been a clear increase by around 15 percent over the past four decades,” he said.
Vertical wind shear in the jet streams can be compared to what happens when a smooth river starts flowing more steeply downhill and speeds up, said Davide Faranda, research director of climate physics in the Laboratoire de Science du Climat et de l’Environnement, part of the French National Center for Scientific Research.
“It can become turbulent,” he said. “So if you have a small boat and you put it in this river, you will see shaking a lot, and it’s the same for planes when they fly in the turbulent jet streams.”
Faranda’s interest in clear-air turbulence stems from a childhood fascination with both planes and weather, as well as a personal experience with a very bumpy ride on the way home from a science conference in 2023.
“It was LA to Charlotte, after the AGU conference in San Francisco,” he said. “We basically had clear-air turbulence for over three hours, with extreme things like the luggages storage opening, luggage flying away. So that traumatized me.”
Rough Spots in the Jet Stream
The waves in the jet streams can start on the land surface, Faranda said.
“You don’t have rocks or slopes in the atmosphere, but in fact, it can feel the slopes of the continental shelves, the Rocky Mountains, or the Alps or Greenland,” he said. “Where you have these strong changes in elevation that perturb the atmosphere, it can propagate up to the level where planes are flying.”
But the exact location of each rough patch changes constantly because the jet streams shift in wavy patterns, sometimes with big loops north and south, driven mainly by regional temperature contrasts between polar regions and the mid-latitudes, he said.
“Global warming is faster at the poles,” Faranda said, “and it’s melting ice and it’s also warming differently in oceans and on continents.”
As global warming jars climatic patterns, it affects the jet streams, he said.
Williams, the University of Reading scientist, was “the first to understand that if the jet stream is affected, then turbulence in the jet stream is affected, and therefore flight operations are affected,” Faranda said.
In his EGU presentation, Williams said it’s important to look at vertical wind shear because the signal in the data is much stronger compared to the noise.
“Why do we care about stronger wind shear? Well, of course, it’s because we fly through it,” he said, showing a photo of a grounded jet plane that lost an engine in severe clear-air turbulence. The data shows there has been a 55 percent increase of severe air turbulence since the 1970s, he added.
Climate models show that, under the most realistic greenhouse gas emissions scenarios, a “hotspot in the tropical upper troposphere will continue to grow, which means an even stronger midlatitude temperature gradient,” he said.
That hotspot in the upper troposphere is an area of amplified warming resulting partly from water vapor feedbacks, as moist, hot air steams off the tropical oceans. That heat bulge is increasing the temperature gradient in areas near some of the busiest flight paths, including transatlantic routes.
If rapid warming continues, Williams said, studies show vertical wind shear could increase 29 percent by 2100, or 17 percent if global emissions are halved by mid-century and keep dropping.
“This, of course, means a lot more turbulence in not that many years from now,” he said.
Faranda added that his own experiences and research on clear-air turbulence won’t keep him from flying. New measurements by weather instruments and greater awareness of the potential for such turbulence will help keep most flights safe, and changes to wing design and plane construction could make them less vulnerable, he added.
“In principle, you can fly through these areas without consequences in most cases,” Faranda said. But with projections for more intense and frequent turbulence, it’s important to maintain observation programs, he added.
“With the new global political situation, there is a lot of talk of reducing instruments for monitoring the weather and the climate, and this would produce worse weather forecasts,” he said. And fewer weather observations will likely lead to shakier flights.
Cover photo: A passenger jet takes off at Ronald Reagan Washington National Airport on Aug. 12, 2024, in Arlington, Va. Credit: J. David Ake/Getty Images
