Science News

Changing Climate Increases Turbulence

Wed, 10th Apr 2013

Ben Valsler

Increasing atmospheric carbon dioxide could lead to more “clear air turbulence”, leading to bumpier and more expensive transatlantic flights.

TurbulenceTurbulence may make a flight less comfortable for passengers, but the cost to airlines is far higher.  Injury to passengers and structural damage to planes resulting from turbulence is thought to cost at least tens of millions of pounds.  The biggest problem is clear-air turbulence, which cannot be seen by pilots or detected by satellites or on-board radar.

Now, publishing in the journal Nature: Climate Change, Paul Williams and Manoj Joshi argue that increasing atmospheric carbon dioxide concentration could significantly increase the incidence and strength of these turbulence events, making transatlantic flights bumpier, slower and more expensive.

Despite over half a century of powered flight, the mechanisms that cause aircraft turbulence are still not fully understood.  Convection causes up- and down-drafts around clouds, but clear air also contains instabilities that lead to local changes in wind speed and direction.  Spotting large clouds with radar and satellite technology allows pilots to navigate around the worst of the convention currents, but clear-air turbulence is only forecast on large scales, using algorithms similar to those used for forecasting the weather.

Anecdotal reports of increased turbulence since the turn of the century and a suggested increase in the prediction data since the 1950s prompted Willams and Joshi to use climate models to see if a changing climate could increase the amount of turbulence pilots may experience.

They modelled air flow and atmospheric jet streams for two different situations – comparing pre-industrial revolution CO2 levels with concentrations twice as high, which we are estimated to reach around the middle of this century.

Their models predict, at standard cruise altitudes, there will be an increase of 10–40% in the average strength of turbulence, and a 40–170% increase in the frequency of turbulence.

This is just one research project, possibly the first to look at the effect of climate change on aviation turbulence, and only looks at clear-air turbulence, one of many factors to affect the cost and comfort of transatlantic flight, but it looks like the “fasten your seatbelts” lights might need to be left on in future…

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I saw this proposed, but I'm not sure I understand the basis of the claim that CO2 will cause heterogeneous heating in the atmosphere, which will trigger the pressure differences that will cause the increased winds.

Is this just because more CO2 in the atmosphere means that illuminated parts of the Earth's surface will pass more heat into those parts of the atmosphere and so the pressure differential will be higher?

Chris

chris, Thu, 11th Apr 2013

That one is pretty interesting. Ever heard of 'gravity waves'? If you haven't you're excused because neither had I :) until I started to look into what you asked.

"New research by NCAR researchers and collaborators points to gravity waves, which ripple unseen through the atmosphere, as the culprit in many cases of clear-air turbulence. If those waves can be forecast, the research suggests that planes in many cases could be rerouted around them.

Gravity waves are a common atmospheric phenomenon. They are caused when air is forced upward, generally over mountains or in thunderstorms, and bumps up against the stable floor of the stratosphere. This sets off ripples that can travel hundreds of miles before breaking. (Gravity waves are unrelated to gravitational waves, which are perturbations in the gravitational field.)" From Triggering turbulence in clear air.

If that is correct one can assume that with more heat in a system you will find more and stronger turbulence, at least globally, even if locations may differ locally.  I found this table, although not the paper referred too, that relates to their predictions though, and it seems as they have taken a lot of possible parameters into consideration there. Northern North Atlantic flight-level winter clear-air turbulence in a changing climate.
yor_on, Sun, 14th Apr 2013

Gosh, thank you; I had not come across this phenomenon; the name is confusingly bad though isn't it?! chris, Tue, 16th Apr 2013

Yea :)

I was trying to see what connection it had to gravity as soon as I saw it, leaving me sorely confused.. yor_on, Tue, 23rd Apr 2013

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