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We’re reminded time and time again that turbulence is a normal part of flying and not usually any cause for concern. However, in recent years stories about in-flight injuries resulting from severe turbulence, or sudden and extreme altitude drops forcing emergency landings have hit the headlines, making it feel like incidences of extreme turbulence are on the rise. So is turbulence getting worse, and is climate change to blame?
👉 In this article we’ll explore what causes in-flight turbulence, why it’s becoming more frequent, and how climate change is driving this trend.
Turbulence can raise the hairs and flip the stomach of even the most seasoned air traveller. Whether it’s a sudden drop or a more prolonged and bumpy ride, turbulence is unfortunately a part of air travel. But what actually causes these turbulent moments?
Let’s take a closer look at some of the common causes of in-flight turbulence:
At lower altitudes (ie. when ascending and descending) turbulence tends to be related to heavy winds. It can be likened to steering a boat through stormy seas.
At lower altitudes the wind is more prone to friction as its flow is affected by the Earth’s surface, which can cause variations in wind direction and speed, something that increases the chance of experiencing turbulence.
When air encounters large forms such as a mountain it forms a sort of wave in the air (much like a wave you’d encounter in the sea). Some of these air waves will pass smoothly over and above the mountain, however, some air may also build up against the side of the mountain, breaking up into lots of tumultuous currents, which planes then experience as turbulence. This is why it’s common to experience turbulence when passing over a mountain range.
It’s also possible to experience this type of turbulence when flying over built up cities. Skyscrapers and tall buildings can have a similar effect to a mountain range.
Wake turbulence is caused by the passing of another aircraft in proximity. Much like the wake caused by boats, the general rule is that the larger the plane, the larger the wake. Smaller planes tend to be more vulnerable if they encounter wake turbulence which is why there are strict rules on how close aircraft can fly to one another.
Jet streams are extremely strong wind currents at high altitudes. Capable of reaching speeds of up to 300 km per hour, jet streams tend to flow from west to east in the northern hemisphere (this is why flying in an easterly direction can often be significantly faster than flying west).
Generally speaking airlines will try to avoid flying into a jetstream as it means flying into a headwind which can make the journey slower, but the jetstream can also be used to their advantage when flying in the same direction.
Jet streams can suddenly change direction when they encounter areas of low or high pressure, which creates lots of turbulence - think of the turbulence they create like the water in a fast flowing choppy river.
At high altitudes turbulence is often caused by air rising in an upwards direction. This is because when the sun warms the earth and the air above it, the hot air expands and rises, causing what's known as an updraft.
The temperature of the air will begin to drop as it rises, with moisture particles eventually forming, creating clouds. These clouds are helpful for pilots as they will be able to see areas of turbulence, and the weather radar is also able to detect it, allowing them to avoid these areas.
Vertical air movement usually stops at higher altitudes where the temperatures are lower. This is why planes fly at high altitudes - because they’re less likely to encounter turbulence.
Clear air turbulence is turbulence that takes the aircraft by surprise. Clear air turbulence is caused by different bodies of air moving at different speeds. It tends to occur at an altitude of around 7,000 to 12,00 metres and is more likely in the regions of jet streams or areas with significant wind changes in a vertical direction.
Planes will usually try to fly around storms or cumulonimbus clouds. This is because they contain powerful shafts of air and moisture. A combination of updrafts and downdrafts within these stormy clouds are what cause the turbulence.
Studies show that storms are capable of creating turbulence even when they are hundreds or thousands of miles away from the aircraft. This is because the growth of a storm cloud pushes air away, creating waves in the atmosphere.
Frontal turbulence is more commonly experienced in winter months. It occurs when a mass of cold air hits warm air. The friction between the two air masses causes the warm air to lift up and over, trapping the cold air closer to the ground. Turbulence can occur where these two fronts meet.
Scientists had already predicted that climate change would lead to an increase in turbulence experienced by flights, however, there is now evidence to suggest that we’re already seeing the effects.
Researchers recently reviewed data from over a four decade period (1979 to 2020) and found that on a typical flight route over the Atlantic ocean there was a 55% increase in clear air turbulence over this period. The study also found that routes over Europe, the Middle East, the South Atlantic, and Eastern Pacific also experienced more turbulence.
The type of turbulence that we’re seeing an increase in is what’s known as clear air turbulence. Clear air turbulence is the most difficult to predict or navigate because there’s no visible warning sign for pilots to observe and the plane’s systems can’t detect it either.
Clear air turbulence is erratic air currents that form due to differences in wind speed at different heights - something that’s referred to as wind shear. Wind shear is now reported to be around 15% stronger than it was in the 1970s, and even more worryingly it's expected to increase even further in the coming decades.
Researchers believe that the main reason for the uptick in bumpier flights is warmer air that is altering the jet stream and causing it to suddenly change wind speed or height. But how exactly is climate change causing this effect?
Greenhouse gases trapped in the Earth’s atmosphere are causing global temperatures to rise. And nowhere is feeling this effect more so than the polar regions. Polar regions are warming at a faster rate than mid-latitude regions, which means that the normal north-south temperature difference is reduced. This reduction in temperature difference is causing a slight drop in zonal winds, which leads to more meandering movement in the jet stream.
The jet stream is expected to get more unpredictable and chaotic as time goes on, shifting north and south, and fluctuating outside of its normal boundaries. The wind shear in the jet stream is also increasing as a result.
👉 Scientists predict that clear air turbulence could triple over the next three to six decades, unless greenhouse gas emissions can be limited.
Increased turbulence might be the most headline grabbing impact of climate change on the aviation industry, however there are a number of other impacts.
For example, rising temperatures are also affecting the maximum takeoff weight of an aircraft due to its effect on surface air density which affects the uplift of the aircraft. Warmer weather reduces the maximum weight limit, which means that aeroplanes may be restricted in terms of weight as global temperatures rise.
Additionally, climate change is increasing the speed of the jet stream blowing west to east across the Atlantic. These increased wind speeds mean that, on west-bound journeys, the journey will be longer. Reports suggest that this means global flights will be in the air for an extra 2,000 hours per year, and will produce an excess of 70 million extra kilograms of carbon dioxide.
Turbulence already costs airlines millions every year as a result of flight delays, injuries, aircraft damage, and extra wear and tear to planes.
👉 The aviation industry in the US loses between 150 and 500 million USD annually due to turbulence.
It is, however, possible to pick up the structure and shape of the jet stream on satellites. And so one way to avoid some incidences of clear air turbulence is to avoid the four main jet streams that encircle the Earth. However, airlines often take advantage of the jet streams in order to decrease flight times by making use of the tailwinds. So avoiding the jet streams all together will result in longer flight times and the burning of more fuel (something that results in more greenhouse gases).
Although there is no accurate onboard turbulence detection system capable of detecting clear air turbulence, detection systems are advancing and over the last few years there have been some promising developments. Companies deploying light detection and ranging systems (LIDAR) are in various stages of development and it’s hoped that in the near future, sensors can be installed on aircraft allowing them to accurately detect clear air sensors.
NASA is also working on a microphone that may be capable of detecting patches of clear air turbulence, allowing pilots to manoeuvre away from these areas in advance.
While research suggests that climate change is making the atmosphere more turbulent, it’s not all bad news. The systems that provide pilots with data on turbulence and storms are improving all the time, which means that pilots can plan smoother routes. Modern aircraft are also constantly improving and are designed to withstand even severe turbulence
Some experts predict that our ability to detect and avoid turbulence will improve quicker than any increase in turbulence linked to climate change, making air travel even safer in the future despite any predicted uptick in turbulence.
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