Climate Change will increase Turbulence on Flights

11 April 2017

Interview with

Dr Paul Williams, University of Reading

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We’ve seen many recent extreme weather events - from mudslides in Columbia to flooding in Australia - which scientists say are a consequence of climate change; but it’s not just the weather that is affected. The Earth’s atmosphere is made up of several layers of air which all flow around each other in patterns known as jet streams and an increase in temperature will cause these to speed up. This is bad news for air passengers, including the 1 million people currently airborne at this very instant, because an increase in the speed of the jet streams will cause more turbulence making flying less comfortable and potentially more dangerous. Tom Crawford heard how it’s happening from atmospheric scientist Paul Williams…

Paul - We’ve been looking at turbulence over the Atlantic Ocean, and specifically severe turbulence which is strong enough to hospitalise people and, indeed, it does cause many serious injuries every year. What we’ve been interested in specifically is the impact that climate change might be having on severe turbulence. We can expect a 59% in light turbulence, 94% increase in moderate turbulence, and 140%  increase in severe turbulence and that, of course, means we’re looking at twice or maybe up to three times as much severe turbulence as there has been historically.

Tom - So you gave us an example of severe turbulence saying this can injure people, but most of us will have only experienced, I imagine, light or moderate turbulence - the shaking feeling when you flight starts bobbing around a bit. What do you mean, is there a turbulence scale?

Paul - There is. Scientists have developed a scale much in the same way that we have the Richter scale for measuring the strength of earthquakes. We do have a scale for measuring the strength of turbulence; it doesn’t have a name but it’s a 7 point scale in which 1 means light turbulence, 3 means moderate, 5 means severe, and 7 means extreme.

So just to put some definitions there; in light turbulence which anyone virtually whose flown will have experienced, there’s just a slight strain against the seat belts. Certainly food service would be able to continue and people would be able to walk around the cabin without difficulty in light turbulence.

Let’s turn the notch up to moderate turbulence. Now there’s a definite strain against seat belts, unsecured objects certainly being dislodged, walking difficult, flight attendants instructed to take their seats.

Now let's move up to severe turbulence; this by definition is stronger than gravity. So passengers would be forced violently against their seat belts, food service and walking are certainly impossible, and because it’s stronger than gravity any unbuckled passengers and crew will be potentially catapulted  around inside the cabin. So it’s this severe turbulence that really hospitalises people and it’s the kind of turbulence that’s not just an issue about comfort but about safety.

Tom - Okay. We’ve talked a lot about turbulence and how, as you’ve said, it’s going to increase in the atmosphere because of climate change. So how is that going to happen, how does turbulence form?

Paul - Yes, that’s the million dollar question! What it all boils down to is something that meteorologists refer to as a wind shear. That’s a complicated term but it means something very simple, which is simply the fact that the higher up you go in the atmosphere the windier it gets. So, for example, anyone who’s ever climbed up the Eiffel Tower will know that when you’re at ground level it’s usually not very windy, and by the time you’re about halfway up usually it’s getting quite windy by that stage. But, certainly, by the time you reach the top of the Eiffel Tower, usually the wind is blowing very strongly and that’s a wind shear. In fact, we know that this effect, the increase of wind speed with altitude, takes place from ground level not only up to the top of the Eiffel Tower, but beyond. All the way up to many kilometers; maybe ten kilometers high to form the jet stream. It’s the instabilities within those wind shears that generate turbulence.

In simple term, what climate change is doing is that it’s not warming the atmosphere uniformly. The different parts of the atmosphere are warming by different amounts. And specifically at 30 to 40 thousand feet where planes tend to have their cruising altitudes, the low latitude tropical regions are warming more than the high latitude arctic regions. So the north/south temperature difference across the Atlantic Ocean is becoming stronger because of climate change. It’s that temperature difference that drives the jet stream and as it becomes stronger, the jet stream is becoming stronger, the wind shears are becoming stronger and that’s the physical mechanism by which climate change is driving stronger and more frequent turbulence

Tom - And just with everything we’ve discussed, it almost seems to me like this could be the first real life experience of climate change affecting people now?

Paul - Yes. For some people, maybe focussed in the developed world, this might be one of the most obvious early signs of climate change. Of course that’s not true for people in the developing world where the impacts are much more serious in many ways about heat stress, and crop failure, and flooding etc., and sea level rise. But for some people in the developed world, especially frequent flyers, who of course make a contribution to climate change through aviation emissions, this effect might be one of the early signs of climate change. And, of course, for some people it might even be the thing that pushes them into actually caring about climate change in the first place, and maybe taking actions to minimise their carbon footprint.

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