The Current

Climate change is making flights more turbulent, meteorologist says. Here's what to do about it

More than three dozen people were injured when Air Canada Flight 33 suddenly hit clear air turbulence early this week. Paul Williams, an atmospheric science professor at the University of Reading, warns changes in the jet stream are 'completely invisible' and almost impossible to detect.

Severe turbulence is 'stronger than gravity' and 'completely invisible,' Paul Williams explains

Atmospheric scientist Paul Williams says clear air turbulence is 'completely invisible,' which makes abrupt changes in weather systems difficult to detect and poses a threat to aviation safety.  (Jim Watson/AFP/Getty Images)

Incidents of sudden and severe turbulence like passengers experienced earlier this week aboard an Air Canada flight from Vancouver to Sydney are hard to predict and are increasing due to climate change, a meteorologist warns. 

Thirty-seven passengers and crew members were injured Thursday when flight AC 33 hit "severe clear air" turbulence and was forced to divert to Honolulu's international airport, according to a spokesperson for the airline. Those on board told reporters they hit the ceiling of the cabin when the aircraft unexpectedly dropped.  

Paul Williams, a professor of atmospheric science at the University of Reading, says clear air turbulence is "completely invisible" and can "pop up" and within a few minutes be gone. This makes abrupt changes in weather systems difficult to detect and poses a threat to aviation safety. 

He told The Current's guest host Katie Simpson from the U.K. that radar — which forecasts changes in the jet stream — is only 75 per cent accurate and that an analog alternative comes with a steep price tag.

Here is part of their conversation.   

Dr. Williams, from what you know so far, what does it appear happened on this plane? 

The airline is saying that this is clear air turbulence. If that's true, then it would have been completely invisible — not only to the pilots through the cockpit window, but even to the radar in the cockpits. 

That's consistent with the passenger reports that say the pilot came on the radio after the turbulence encounter and said that in the cockpit, they had no warning that this event was about to happen. 

Pretty scary, especially if you're a nervous flyer — and fear of flying is actually quite a common phobia. 

Emergency workers assist passengers of Air Canada Flight 33, which was diverted to Honolulu on Thursday after hitting severe turbulence. (Australian band Hurricane Falls via Reuters)

What would it have felt like if you're a passenger sitting on this plane and all of a sudden the plane encounters this clear air turbulence? 

Judging from the passenger reports, this was definitely, at least, severe turbulence.

The definition of severe turbulence is that it's stronger than gravity. The plane will be dropping tens of feet ... more quickly than gravity can pin you to your seat. 

It follows logically that if you're not seatbelted, you become a catapult — rise up and potentially strike your head against the cabin ceiling. That seems to be what's happened here. 

Pilots and air traffic control bodies do their best to avoid turbulence by studying the weather patterns before each flight. (John Fraser/CBC)

Much of our audience is probably very familiar with normal turbulence. You notice it if you're flying through a cloud ... But what exactly is clear air turbulence? 

Yes, it's slightly mysterious, isn't it? Especially because we can't see it. I think we instinctively fear things we can't see. 

Flying through a cloud, when at least you can see it, you know it's there and you're going to expect some turbulence in the next few minutes. 

But this clear air turbulence is generated by instabilities in the jet stream because of very rapidly moving air currents up there at 35,000 feet. The wind speed increases with altitude. If that effect is too strong, then the atmosphere just can't contain the stresses and strains. It becomes unstable and breaks down. 

Air turbulence can be caused by a number of factors, including heat, jet streams and flying over mountain ranges. (John Fraser/CBC)

You keep describing this [as] something that's invisible and hard to detect. Is there research under way to try and find better ways to detect this? Why is it so difficult to see this coming?

A key source of information that pilots have is from forecasts of the turbulence. ... They're pretty good and they're getting more accurate every day, but they're not perfect. They're only about 75 per cent accurate.

I think a key lesson from this Air Canada encounter yesterday is that we really need to redouble our efforts to improve those forecasts. 

There's also technology that could help ... a bit similar to radar, called Lidar. It actually uses light instead of radio waves and that's just the right frequency of electromagnetic waves to detect the invisible turbulence.

This technology exists today. The reason it's not used is it's simply too expensive and it's too heavy. But ... that really could confine clearer turbulence encounters to the history bins. That would be a really transformative and game changing event if it happened. 

And while you say that there is less than one per cent chance at certain altitudes, your research so far has found a strong link between climate change and increased turbulence. Can you explain the link?

Yes it's a good point. Normally when someone mentions climate change, we think about how it's getting warmer here at ground level, but the climate is changing at 35000 feet...because of our CO2 emissions. It's modifying the jet stream and just increasing those instabilities in the jet stream. 

We really need to start to take this seriously.- Paul Williams

We are predicting a major increase in severe invisible clear air turbulence by several hundred per cent in the next few decades. We really need to start to take this seriously. 

What can we do? We can stop changing the climate, that might be a good idea. We could improve those clear air turbulence forecasts, or maybe we could invest in this Lidar technology. Those are the three things I think we could and should be doing to prevent events like the one we saw yesterday becoming two to three times more common in just a few decades time. 

Climate scientists point to air travel as a significant cause of CO2 emissions in the atmosphere. ... What do people need to think about around the concern that, here is a problem that is causing more challenges around climate change, but at the same time there are greater challenges to safety in the air?

Yeah that's a great point. People have called it poetic justice. That airplanes have put out all of this CO2 and now the atmosphere is fed up and getting its revenge, maybe would be one way to see it.

Aviation, of course, contributes to climate change ... the other sectors are decarbonizing increasingly rapidly. Aviation is somewhat struggling to do that. 

I think we will see electric planes increasingly coming into use even in just a decade or so for short haul flights. There are movements there to decarbonize the aviation sector, and, of course, we're all committed to that change as well. 


Written by Aruna Dutt, with files from CBC News. Produced by Allie Jaynes and Richard Raycraft. Q&A has been edited for length and clarity.