It was a terrifying and deadly experience. On May 21, a 73-year-old British man died and a hundred people were injured on a Singapore Airlines flight from London to Singapore. Severe turbulence caused the plane to plummet 1,800 meters in minutes, forcing the Boeing 777 to make an emergency landing in Bangkok, Thailand. On Sunday, 12 people were also injured on a Doha-Dublin flight due to turbulence over Turkey. These two events, for which investigations are underway, have rekindled questions about the impact of climate change on these unstable weather phenomena.
Turbulence is a sudden, irregular movement of air that occurs most frequently in three situations: during thunderstorms and storms, over mountains, and in clear air. The first two types are easily detected by pilots, either visually or by radar. Conversely, the latter are considered the most dangerous, as they are invisible and occur unexpectedly.
Clear-air turbulence is caused by vertical wind shear when two air masses overlap and move at different speeds or in different directions. "An airplane lifted upward over a distance can suddenly lose support and drop a few dozen meters," explained Nicolas Bellouin, a climate modeler at the University of Reading (UK) and researcher at Paris Sorbonne University's Aviation and Climate Chair. Wind shears most often occur in the vicinity of jet streams, powerful air currents moving around the globe at altitudes of 8 to 12 kilometers, where airplanes fly.
This is why most flights experience turbulence, whether light, moderate, severe, or extreme, the degree of intensity of which is defined by vertical wind speed. At this stage, it is not possible to determine what type of turbulence the Singapore Airlines Boeing encountered. "There were some fairly violent thunderstorms nearby, but conditions were also favorable for turbulence in clear air," noted Bellouin.
Whatever the cause of the incident, climate change, which is linked to the burning of fossil fuels and therefore in part to aviation, is set to worsen these situations. Clear-air turbulence has already become more frequent over the past 40 years, according to a landmark British study published in June 2023 in the journal Geophysical Research Letters. Severe turbulence has increased by 55% over the North Atlantic, from 17.7 hours per year in 1979 to 27.4 hours in 2020. This is one of the world's busiest air routes, with almost 2,000 flights a day between Europe and North America. Moderate turbulence has increased by 37% (reaching 96 hours per year) and light turbulence by 17% (547 hours). The study results show similar increases over the US.
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