Climate change will increase the frequency and severity of 'clear-air turbulence', which means bumpier flights more often, with greater risk of injury.

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• What is clear-air turbulence?

  • Clear-air turbulence is sudden turbulence that occurs in clear skies at cruise altitude. It's hard to forecast and detect, and therefore difficult for pilots to avoid. 

• What will happen? 
  • Clear-air turbulence will become more common and severe as carbon dioxide levels increase. This will affect the busiest airspaces the most (North Atlantic, North America, North Pacific, Europe and Asia).
  • This includes the most severe type of clear-air turbulence, which is stronger than gravity and causes planes to move violently, and has in the past led to passenger hospitalisations and structural damage to planes. It's predicted that, by 2050-2080, severe clear-air turbulence will increase globally year-round, and occur twice as often over North America, the North Pacific and Europe.   

 

Where's the evidence?

• Williams, P. D. (2017) "Increased light, moderate, and severe clear-air turbulence in response to climate change", Advances in Atmospheric Sciences, 34(5), 576-586. Available at https://doi.org/10.1007/s00376-017-6268-2.

• Storer, L. N., Williams, P. D., Josh, M. M. (2017), "Global Response of Clear‐Air Turbulence to Climate Change", Geophysical Research Letters, 44(19), 9976–9984. Available at https://doi.org/10.1002/2017GL074618.

• Williams, P.D. and Joshi M. M.(2013) “Intensification of winter transatlantic aviation turbulence in response to climate change”, Nature Climate Change 3, 644–8. Available at http://www.met.reading.ac.uk/~williams/publications/nclimate1866.pdf.

Climate change will mean more weight restrictions on commercial planes flying from certain airports.

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• A plane's take-off conditions determine its speed and the weight it can carry. 

• This includes air density. Warmer air is thinner than cool air if it has warmed at constant pressure. As a result, warmer air gives planes less lift. Generally, pilots balance this out by increasing their take-off speed. 

• However, if a plane can't increase its take-off speed enough to compensate for the thinner air - which happens more often on shorter runways - then it will have to lighten its load. Airlines do this by removing passengers, cargo or fuel.

• A 2015 study of impacts on one of the most common short-to-medium range types of plane (the Boeing 737-800 aircraft) predicted that the number of weight-restricted days between May and September will increase by 50%-200% at four major airports in the US by 2050-70: Phoenix Sky Harbour International Airport, Denver International Airport, LaGuardia Airport in New York, and Reagan National Airport in Washington, D.C.. 

• A 2017 study expanded on this to look at impacts on five common commercial planes flying from 19 airports. This found that, on average, 10%-30% of annual flights departing at the hottest times of the day may require some weight restriction by mid-to-late century.  

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Where's the evidence?​

• Coffel, E.D., Thompson, T.R. 3 and Horton, R.M. (2017) "The impacts of rising temperatures on aircraft takeoff performance", Climatic Change 144(2), 381-388. Available at http://www.ethancoffel.com/papers/2017,%20Coffel,%20Thompson,%20Horton,%20CCL.pdf.

• Coffel, E.D. and Horton, R.M. (2015) "Climate Change and the Impact of Extreme Temperatures on Aviation", AMS Weather, Climate, and Society. Available at https://journals.ametsoc.org/doi/pdf/10.1175/WCAS-D-14-00026.1.

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• Expert commentary on the evidence:

  • Hane, F., (2015) "Comment on “Climate change and the impact of extreme temperatures on aviation” by Coffel and Horton", AMS Weather, Climate and Society. Available at https://doi.org/10.1175/WCAS-D-15-0030.1.

    • Author's response: Coffel, E.D. and Horton, R.M. (2016) "Reply to “Comment on ‘Climate Change and the Impact of Extreme Temperatures on Aviation’”, AMS Weather, Climate and Society. Available at https://doi.org/10.1175/WCAS-D-15-0063.1.

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Climate change will affect the routes and length of flights.

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Flight paths are influenced by wind patterns and the location and direction of air currents. Current flight paths are designed to take advantage of these to minimise flight time and fuel consumption. Carbon dioxide increases in the atmosphere, by changing wind patterns and currents, will affect these optimal flight paths.

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A study on the route between London's Heathrow Airport and New York's JFK Airport found that the doubling of carbon dioxide in the atmosphere - which is 'locked in' to happen later this century - will shorten the eastbound flight and lengthen the westbound flight, and slightly increase the average round-trip journey-time overall. The difference will be largest in Autumn and smallest in Spring and Summer. If this is applied to all transatlantic air traffic, then the overall increase in time will mean, each year:

• an extra 7.2 million US gallons of jet fuel burned at a cost of US$22 million

• an extra 70 million kilograms of carbon dioxide emitted into the atmosphere. This is equivalent to the annual emissions of 7100 average British homes.

This prediction is based on current levels of air traffic and doesn't take future growth into account. 

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Where's the evidence?

• Williams, P. D. (2016) "Transatlantic flight times and climate change", Environmental Research Letters, 11 (2). Available at http://centaur.reading.ac.uk/54734/.