Clear Air Turbulences, short CAT, which occur completely unexpectedly, increase. The tricky thing about it is that no pilot, radar, satellite or meteorologist can predict a CAT. The turbulence comes from nowhere. According to atmospheric scientist Paul Williams from the University of Reading (England), this phenomenon is likely to occur much more frequently in the future, because climate change not only affects the ground, but also the altitude in a special way.
11 July 2019: Air Canada’s Boeing 777 flew quietly over the Pacific. The night was cloudless. Many passengers slept, some stood in the corridors, others watched movies. The seat belt signs did not light up. Then it happened. As atmospheric scientist Paul Williams of the University of Reading now predicts, this phenomenon is likely to occur much more frequently in the future – because climate change not only affects the ground, but also the altitude in a special way.
Without any warning, the plane fell to a depth of several hundred metres. Books, laptops, drinks bottles flew through the air like projectiles – and passengers who were not strapped on slammed their heads against the cabin ceiling and immediately fell back down onto seats or other passengers. As suddenly the horror had begun, so suddenly it stopped again. The crew had to look after bleeding, crying and shocked people. Oxygen masks dangling from the ceiling. Of the 269 passengers, 37 were injured, some of them severely. To get them to the hospital quickly, the captain decided to cancel the flight from Vancouver to Sydney and instead land in Honolulu, Hawaii, after another two hours.
What had shaken the Canadian jet on 11 July in what appeared to be the best flying weather was a case of Clear Air Turbulence, or CAT for short. There are many reasons why airplanes sometimes shake and shake unpleasantly – but there is no other air turbulence as feared as the so-called clear air turbulence. The tricky thing about it is that no pilot, radar, satellite or meteorologist can predict a CAT. The turbulence comes from nowhere.
Before Air Canada, on that July day, the CAT had already inflicted turbulence on another aircraft – an Airbus A380 of the Emirates airline. The giant aircraft had taken off from New Zealand the day before. About three hours before landing in Dubai, the jet sank without warning. Passengers who were not strapped in were ripped from their seats; many of them also crashed their heads against the cabin ceiling and injured themselves. A video circulating on social networks shows a scenery of overturned trolleys in the galleys, the completely devastated business class bar.
In the future, atmospheric scientist Paul Williams of the University of Reading predicts, this phenomenon will probably occur much more frequently – because climate change not only affects the ground, but in a special way also the altitude. A CAT event, misleadingly known among passengers as an “air hole”, could occur when air masses pass each other above an altitude of 6000 meters at different speeds. This happens particularly often in the area of jet streams – those strong wind bands in the troposphere that move from west to east over mid-latitudes or subtropical areas. The polar front jet stream is actually a welcome flight attendant: especially in winter it gives the aircraft tail wind on many routes and thus sometimes shortens the flight time from Chicago to Frankfurt, for example, by two hours.
Jetstream tends to roll due to climate change
However, due to climate change, says Williams, the jet stream has been tending to wobble for some time now. For example, it often no longer moves weather systems across Europe as quickly as before, which is why there is an increase in persistent weather conditions, such as weeks of sunshine or weeks of rain.
Moreover, according to researcher Williams, the jet stream is becoming increasingly restless due to climate change: its wind speeds at different altitudes are becoming increasingly different. Since satellite data collection began in 1979, Williams writes in the scientific magazine “Nature”, vertical wind shear at the typical cruising altitude above the North Atlantic has increased by around 15 percent. The risk of turbulent transatlantic flights is already higher than before.
Risk increases if CO2 emissions are not massively limited
And this risk will continue to rise, especially if mankind does not massively limit CO2 emissions. Williams has calculated how flying weather will change if emissions continue unchecked. Result: In the period after 2050, the number of particularly strong CAT events will increase.
Source: Spiegel online