Be warned: Flights are getting bumpier

The plane suddenly dropped several feet, flew up, then lurched back down. I held my breath, bracing for the inevitable bobbing to repeat. The flight attendant offered me a barf bag and a conciliatory smile. The turbulence wasn't her fault — it wasn't even the pilot's. Yet for 20 minutes on my flight from Denver to my home in Indianapolis, the plane jerked up and down, sometimes so violently passengers let out a collective gasp that rattled me — I'm frightened of both flying and heights — to my core. I wondered if it was the last flight I'd ever take.

My experience was not an outlier. Air turbulence is becoming more common and more intense. On this particular flight, we experienced mountain-wave turbulence — the bumpiness that sometimes happens when flying over mountainous regions. Other kinds of turbulence include the bumps caused by thunderstorms and clear-air turbulence. Researchers say this last one is on the rise, and it may have made my regular 'ol mountain-wave turbulence more fraught.

Clear-air turbulence happens without bad weather, mountains, or mechanical issues with a plane. It's caused by wind shear — sudden changes in wind speed often associated with the jet stream, a strong band of wind high up in the atmosphere, Isabel Smith, a meteorology Ph.D. student at the University of Reading in England, told me. Smith and her advisor, Paul Williams, a professor of atmospheric science, have found that since 1979 — when satellites first started observing the atmosphere — clear-air turbulence has jumped 15%.

That's caused flights around the world to get bumpier. This past March, a Lufthansa flight from Austin, Texas, to Frankfurt, Germany, was so bumpy that seven passengers were injured. The plane had to be diverted to Washington, DC.

The culprit behind the newly turbulent skies is climate change, Smith said. As greenhouse-gas emissions like carbon dioxide rise, so do global temperatures, making the jet stream carry more wind shear that translates to "speed bumps in the sky" — or turbulence. It's a problem that isn't going away. In 2017, Williams used climate model simulations to predict future turbulence. He found that clear-air turbulence in the Northern Hemisphere could triple in the next three to six decades. And as emissions increase, so will overall turbulence. It's a vicious cycle that's ushering in a new reality for air travel, which has already been plagued by problems since the pandemic hit. So next time you travel, be sure to pack your Ambien, because it's going to get bumpy.

Speed bumps in the sky

Here's how it works: As emissions from greenhouse gases spread through the atmosphere, the upper levels of the sky develop unpredictable patterns of warm and cold air spots, which make the air bumpier for planes. The rising temperatures caused by greenhouse gases also drive more extreme weather, which disrupts the jet stream further.

Bill Duncan, the aviation-forecast operations leader at The Weather Company, told me the jet stream has changed from what we saw 20 to 30 years ago. "The jet stream is now wobbling, so to speak," he said. "You've likely heard articles speak of polar vortex, for example. As the jet stream buckles a bit because it's not as strong as it was in the past, now you have all this energy associated with the jet stream up 30,000 feet or so. It's allowing colder air to spill south, so we're seeing major weather events happening more and more than we did in the past."

This increase in clear-air turbulence is supercharging other kinds of turbulence, such as the mountain-air turbulence that I experienced over Denver. "This type of turbulence is generated from air flow being forced over a mountainous terrain and becoming very unstable, leading to waves in the atmosphere that can break and become chaotic and dangerous to encounter," Smith, the Ph.D. student, said. Given its position downwind of the Rocky Mountains, Denver is a hot spot for mountain-wave turbulence. And any flight path that goes over a mountainous area or along a coast, where temperatures can shift unexpectedly, is prone to turbulence.

After my last flight, Denver may no longer be on my list of vacation spots. But no flight path or airport is really safe from increasing turbulence. "All types of aviation turbulence are likely to increase in the future, in all seasons in most places in the world," John K. Williams, the head of weather AI sciences at The Weather Company, explained. "Perhaps even doubling in some places." Weather conditions in the fall and spring are typically more stable, so flying conditions are generally calmer, Smith said, but those seasons could become increasingly erratic as the air pressure changes.

A turbulent future

It's possible airlines could decrease the chances of hitting clear-air turbulence by avoiding the Earth's four main jet streams altogether. Commercial airlines tend to rely on these strong wind corridors as a kind of boost to reduce flight times and fuel use — kind of like walking on a moving sidewalk. But changes to the atmosphere mean these corridors are getting bumpier, so avoiding them could result in smoother flights. However, the experts I spoke with didn't think this was a real solution. Without the jet streams, flights would be longer and require more fuel, making them more expensive and worse for the environment — not really an appealing option for airlines.

Even so, pilots will likely have to take different flight paths to avoid turbulence. Duncan explained that meteorologists, dispatchers, and pilots can adjust a flight path based on timely weather data. Right now, this information is often too delayed to make a difference, but as the weather-modeling tech improves, that could change. And that's what John K. Williams is betting on.

"In recent years, our ability to predict the location, timing and severity of turbulence have also improved, and those predictions can be used by airlines and pilots to select less bumpy routes, or at least prepare passengers and flight crews for flight segments into turbulent air," he said.

At the core of these improvements is AI. "Machine-learning algorithms are used to find relationships between historical weather and observations of turbulence, improving themselves as more data are collected," Williams explained. "Those algorithms can then be run using the latest weather forecast model data to pinpoint areas of potentially hazardous turbulence."

But while we can get better at avoiding air turbulence, we won't be able to avoid it altogether. That's why some companies are going back to the drawing board to design airplanes that can better adjust to turbulent air. The Swiss company Neural Concept, which uses AI-generated simulations to help industrial companies improve their engineering, is currently working with the airplane manufacturer Airbus to improve its aircraft design.

Designing an airplane that's more steady in turbulent air is tricky because there are so many variables to account for, Pierre Baqué, Neural Concept's cofounder and CEO, told me. "This is where AI becomes critical," he said. "By applying deep learning models to the database of simulations, aircraft manufacturers can gain real-time insights into the correlation between tens of statistically averaged variables that might impact turbulence."

The project is still in its early stages, so it could be years before we see the results of this work in commercial aircraft. And in the meantime, unpredictable air remains a problem. According to the National Transportation Safety Board, 163 serious injuries have been caused by turbulence since 2009. To keep flight attendants and passengers safe, some flights might have to cancel meal service, restrict passengers' ability to stand up or use the restroom, and limit the availability of flight attendants.

"I fly quite a bit, and I see people walk around all the time even when the seatbelt sign is on," Duncan said. "Turbulence is tricky — sometimes turbulence can come out of the blue. And you never know what kind of shear that aircraft will go through."

Alyson Smith, the managing director of emotional health and well-being programs at Delta, said passengers have a better chance of avoiding a turbulent flight if they fly very early in the morning or late at night. "Turbulence is generally the lowest during these time periods," she said.

Ultimately, the most important thing passengers can do is to listen to the flight crew and pay attention to the seatbelt sign. For me at least, I'll be staying buckled up while I'm in the sky.

Michelle Mastro is a writer who covers lifestyle, travel, architecture, and culture.