Airplanes are becoming more and more bumpy. Is this really due to climate change?

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A few years ago, the most turbulent flight I experienced was on a flight to Yinchuan. The ups and downs were so severe and lasted so long that I could only describe the feeling as being terrified...

Current research generally agrees that global warming has led to an increase in clear air turbulence. The troposphere is the layer of the atmosphere closest to the Earth's surface in which we live. There are multiple layers within the atmosphere, and above the troposphere is the stratosphere. The increase in greenhouse gases causes heat to be trapped in the troposphere, which would normally be released into the stratosphere. As a result, the stratosphere cools at a rate similar to the warming of the troposphere. This creates significant temperature differences in the vertical direction of the atmosphere. This causes the airflow to become more chaotic and unstable, so the number of encounters with clear air turbulence will increase.

It's a sunny day with a clear blue sky. The captain has just announced that the plane has reached cruising altitude, so the seat belt sign has been removed. Passengers are walking around the cabin. Suddenly, the plane starts to shake. You instinctively grab the armrests of your chair. Passengers who have already stood up hold on tightly to their support. At the same time, a baby starts to cry.

A minute later, the all-clear sounds, and your body relaxes, letting out a deep breath. Then, the plane plummets like a rock. Your stomach drops into your throat—but there's no thunderstorm, not even a cloud outside. What the hell is going on?

© Gfycat

The phenomenon, called clear-air turbulence , is caused by eddies of high-speed air currents that swirl around the globe. These powerful currents circle the Earth from west to east, and we see them on weather maps as broad, wavy lines that curve as low and high pressure centers shift.

As long as these air currents are not too far from the flight path, airline aircraft will like to fly in these high-speed air currents, which can increase speed and shorten flight time.

These vortices are invisible to the naked eye, but they can impact the wings of an airplane. When the impacts are strong enough, they can cause the plane to suddenly pitch up and down. Passengers can get spooked, and crew members can stumble. Over the past 40 years, clear-air turbulence has increased by 55% around the world[1]. Climate models predict that clear-air turbulence could increase by 100% to 200% in the next 30 to 60 years. Each turbulence comes without warning.

© The Wall Street Journal

Pilots can detect turbulence relatively easily when it is in a storm or cloud layer. Aircraft radar can track rainfall patterns in the distance to reveal turbulent movement of the air. The captain can warn passengers and crew in advance, telling them to take their seats and fasten their seatbelts before turbulence arrives. However, radar cannot detect the presence of clear-air turbulence; the captain usually only knows about it when the aircraft encounters it.

Cloud turbulence is created by the heating effect of the sun. When daybreak arrives, the sun begins to heat the ground, which in turn heats the air near the surface. This warmer air is less dense than the cooler air above, so it rises. The replaced cooler air sinks, and the process repeats over and over, creating what is known as convection currents. These rising and sinking currents push against the wings of an airplane, and if the thrust is strong and sudden, the airplane will naturally shake.

© Gifer

Clear-air turbulence occurs almost exclusively in high-speed airflows. The fast airflow band within the high-speed airflow (think of it as a rectangular tube) exerts shear forces on the slower airflows above and below it, causing the upper and lower boundaries of the high-speed airflow to become unstable and fuzzy. However, at the same time, the density difference between the gas within the high-speed airflow and the gas above and below it stabilizes the boundary again.

© CN Traveller

By studying historical flight and weather data, Paul Williams of the University of Reading in the United Kingdom and his colleagues found[2] that the frequency of turbulence in the North Atlantic jet stream increased by 17% to 55% between 1979 and 2020. The largest increase was in the most severe category of turbulence (gravitational acceleration exceeding 1g).

© Giphy

Under this kind of gravity acceleration, any unsecured object on the plane, including your stomach, will temporarily float up, because turbulence causes the plane's downward acceleration to be faster than gravity. If you are not wearing a seat belt, you will rise from your seat as the plane rapidly descends dozens of meters.

So what does this increase mean for regular flights?

First, severe turbulence is a relatively rare occurrence. According to in-flight measurements, severe turbulence only occurs about 0.1% of the time in the atmosphere at cruising altitude. "That means that in an average eight-hour flight, there are only about 30 seconds of severe turbulence," explained Williams, a professor of atmospheric sciences. It is more likely that a person will take 10 flights and not encounter severe turbulence on nine of them, but only on one flight will they encounter severe turbulence for several minutes.

© Wattpad

Mild and moderate turbulence are more common and what most of us will experience. In moderate turbulence, aircraft jumps and drops in altitude are typically within a few meters. Williams says that today, an eight-hour flight might have 10 to 15 minutes of clear-air turbulence, but models predict that this level of turbulence could double or triple in the coming decades as wind shear increases in air currents due to global climate change.[3]

Airlines may face higher maintenance costs as planes age and wear out more quickly due to more frequent turbulence. Passengers may also encounter more anxious parents like me, struggling to keep their young children in their seats and nervous every time the seatbelt sign comes on — a buckle that’s too easy for a toddler to open.

References:

[1]agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL103814

[2]www.nature.com/articles/s41586-019-1465-z

[3]link.springer.com/article/10.1007/s00376-017-6268-2

By Katherine Wright

Translated by tim

Proofreading/Lean Bamboo and Bean Curd

Original article/www.scientificamerican.com/article/yes-airline-flights-are-getting-bumpier-heres-why/

This article is based on the Creative Commons License (BY-NC) and is published by tim on Leviathan

The article only reflects the author's views and does not necessarily represent the position of Leviathan