A terrifying and deadly experience. On May 21, a 73-year-old British man lost his life and around a hundred people were injured during a Singapore Airlines flight from London to Singapore. The cause: major turbulence, which caused the aircraft to plunge 1,800 meters in a few minutes, pushing the Boeing 777 to make an emergency landing in Bangkok. On Sunday, twelve people were also slightly injured on a plane traveling from Doha to Dublin due to turbulence over Turkey. The two events, for which investigations are underway, have rekindled questions around the impact of climate change in these unstable weather phenomena.
Turbulence is sudden and irregular movements of the air, which occur most often in three situations: during thunderstorms and storms; above the mountains; in a cloudless sky, what we call “clear air”. The first two types are easily detected by pilots, with the naked eye and using radar. Conversely, the latter are considered the most dangerous, because they turn out to be invisible and therefore occur unexpectedly.
This clear air turbulence is caused by vertical wind shear phenomena, when two air masses overlap and move with different speeds or in different directions. “A plane carried upwards over a distance may no longer be supported a little further, and therefore fall a few tens of meters”, explains Nicolas Bellouin, climate modeler at the University of Reading (United Kingdom) and researcher at the aviation and climate chair at Sorbonne University. Shears occur most often near jet streams (jet streams in English), powerful air currents that move around the globe at an altitude of 8 kilometers to 12 kilometers, where planes fly.
Increase in moderate and severe turbulence
This is why most flights experience turbulence, whether mild, moderate, severe or extreme, a degree of intensity defined according to the vertical wind speed. It is not possible at this stage to determine what types of turbulence the Singapore Airlines Boeing encountered. “There were some fairly violent thunderstorms nearby, but conditions were also favorable for clear air turbulence”indicates Nicolas Bellouin.
Whatever the cause of this accident, climate change – linked to the combustion of fossil fuels and therefore, in part, to aviation – will worsen this type of situation. Clear air turbulence has already become more frequent over the last forty years, according to a reference British study, published in June 2023 in the journal Geophysical Research Letters. The most severe of them increased by 55% over the North Atlantic, going from 17.7 hours per year in 1979 to 27.4 hours in 2020. This is one of the routes busiest airlines in the world, with nearly 2,000 flights per day between Europe and North America. Moderate turbulence increased by 37% (to reach 96 hours per year), and light turbulence by 17% (547 hours). The study results show similar increases over the United States.
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