How climate change is making air turbulence worse
Analysis: We should anticipate an increase in both the frequency and intensity of clear air turbulence as climate change progresses
Recent incidents with clear air turbulence underscore the unpredictable dangers inherent in modern air travel, even with advanced technology and meticulous planning. Singapore Airlines is renowned for its exemplary safety record and exceptional service. But the airline’s Flight SQ321 from London to Singapore on May 21st, with 211 passengers and 18 crew members onboard, encountered severe turbulence 10 hours into the flight, causing it to descend 6,000 feet (1828 meters) in about three minutes before the airplane diverted to Bangkok.
The sudden turbulence caught the airline off guard, leading to chaos onboard as unsecured items were thrown around the cabin. Tragically, a 73-year-old with a history of heart problems suffered a fatal cardiac arrest, and many others were seriously injured.
On May 26th, eight passengers were taken to hospital after Qatar Airways flight QR017 from Doha to Dublin landed. Their injuries occurred when the plane “experienced turbulence while airborne over Turkey”, around two hours into the flight.
Clear air turbulence (CAT) is particularly insidious because it is invisible and difficult to detect, occurring without warning in seemingly calm skies. CAT is a higher altitude turbulence (normally above 15,000 ft) particularly between the core of a jet stream and the surrounding air. Thunderstorms, low-altitude temperature inversions, thermals, strong surface winds, or local terrain features are not considered CATs. There are two types of clear air turbulence (CAT): mechanical, which occurs due to disruption in the smooth horizontal flow of air, and thermal, which is caused by vertical air currents in an unstable atmosphere.
What causes clear air turbulence?
Jet Stream: A narrow, fast-moving air current near the tropopause caused by temperature gradients between air masses. Significant vertical and horizontal wind shear at the edges can create severe CAT, especially on the cold side. CAT can occur from 7,000 feet below to 3,000 feet above the tropopause.
Terrain: High ground disturbs air flow, causing turbulence. Severity depends on air flow strength, terrain roughness, contour changes, and elevation.
Thunderstorm Complexes: Cumulonimbus (Cb) cells have strong vertical currents, and aircraft within 20 nautical miles horizontally or 5,000 feet vertically of a Cb may encounter CAT.
Encountering severe clear air turbulence can result in structural damage to aircraft, potentially leading to break-up in extreme cases. Even moderate turbulence can cause damage to fittings and items within the aircraft. Prolonged exposure to turbulence can also shorten the aircraft’s fatigue life. Additionally, passengers and crew moving around during turbulence can sustain physical injuries. While injuries are common, a fatality is extremely rare. Furthermore, turbulence can impair flight crew performance, making tasks like reading instruments difficult, particularly in moderate or severe turbulence.
And yes, climate change is to blame for clear air turbulence too. Human-induced climate change is projected to enhance vertical wind shears at aircraft cruising altitudes within atmospheric jet streams. This enhancement is likely to increase the occurrence of shear instabilities, which are responsible for generating clear air turbulence. Climate modelling studies have indicated that the amount of moderate-to-severe clear air turbulence on transatlantic flight routes during winter is expected to increase significantly in the future as the climate changes. There is evidence that eastbound transatlantic flights, positioned closer to the strong tailwinds in the core of the jet stream, experience more clear air turbulence compared to westbound transatlantic flights. As climate change progresses, we should anticipate an increase in both the frequency and intensity of clear air turbulence.
This incident calls for a renewed focus on several fronts. Firstly, it emphasizes the need for continuous advancements in turbulence detection technologies. While radar systems have improved significantly, there is still room for the development of more sophisticated instruments capable of detecting and alerting pilots to CAT with greater accuracy and advance notice.
Secondly, it brings to light the importance of passenger awareness and preparedness. Airlines must ensure that safety instructions are not merely perfunctory but are understood and taken seriously by passengers. Clear communication about the importance of keeping seat belts fastened while seated, even when the flight appears smooth, can mitigate the risk of injury.
This incident highlights the ongoing challenges airlines face in ensuring passenger safety despite significant advancements in meteorological forecasting and aviation technology, and the recent incidents highlight the urgent need to address the impact of climate change on air travel.
This article, written by Prof Marina Efthymiou, was first published on RTE Brainstorm on Monday, 10 Jun 2024
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