An especially insidious form of turbulence has gotten worse because of climate change, according to new research. It’s turbulence that forms in cloudless skies that’s typically invisible to a plane’s radar, called clear-air turbulence. And it’s projected to become a bigger problem as the world warms.
Severe clear-air turbulence (CAT) has already become more common, according to a study published in the journal Geophysical Research Letters last week. On a typical flight route over the North Atlantic, there was a 55 percent increase in clear air turbulence between 1979 and 2020. While the increase in turbulence was the most pronounced over the US and North Atlantic, the study also found significantly more turbulence along popular routes over Europe, the Middle East, and South Atlantic, and Eastern Pacific.
“Following a decade of research showing that climate change will increase clear-air turbulence in the future, we now have evidence suggesting that the increase has already begun,” Paul Williams, co-author of the study and an atmospheric scientist at the University of Reading, said in a press release. “Airlines will need to start thinking about how they will manage the increased turbulence.”
Turbulence already costs US airlines hundreds of millions of dollars a year from injuries, flight delays, damage, and wear and tear to planes. And every extra minute of a flight spent in turbulence heightens those risks, Williams said.
Unfortunately, clear-air turbulence is particularly tricky to navigate. A plane’s radar can warn a pilot about turbulence from a nearby storm. But since that radar detects water droplets in clouds, it’s essentially blind to clear-air turbulence that forms when there’s not a cloud in sight.
This kind of turbulence forms because of differences in wind speed at different heights, called wind shear. Wind shear is increasing in fast-flowing bands of winds called jet streams. Jet streams are becoming more chaotic as greenhouse gas emissions from fossil fuels warm the lowest layer of Earth’s atmosphere, the troposphere. That chaos — stemming from the growing difference in temperatures between the troposphere and the stratosphere — is driving the rise in clear-air turbulence, says Isabel Smith, a meteorologist and PhD student at the University of Reading who was not involved in the study published last week.
While the study looks back on atmospheric data gathered over the past four decades, Smith’s own research estimates how much clear-air turbulence to expect in the future. She published another paper in March that found between a 9 to 14 percent average increase in CAT each season for every degree Celsius of global warming moving forward. Since the industrial revolution, the world has already warmed by more than a degree Celsius.
Summers, busy travel seasons when there’s typically less turbulence, are expected to see a bigger increase than winters, historically seasons with the most turbulence. But by 2050, summers could be as turbulent as winters were in the 1950s.
Even knowing that, Smith was still surprised to see how much of an increase there’s already been in clear-air turbulence since 1979. “We knew it was happening, but it is shocking seeing 55 percent — it is quite a large percentage value [increase]. It’s a bit scary when you see these large values.”