In the future, hopping on a plane from LA to Honolulu might take a minute longer than it does today. You probably won't miss that lost moment, but the airline industry will: The tiny additional flight time could amount to thousands of extra hours and millions of dollars of additional jet fuel each year.
That, at least, is one takeaway from a new research paper published this week in Nature Climate Change, which examined US Department of Transportation data on 250,000 commercial flights between Honolulu to the West Coast. The study found that climate variability, rather than day-to-day weather, determines average flight times, and that stronger jet stream winds across the Pacific over the 21st century will, on average, make roundtrip flights slightly longer.
"Upper level wind circulation patterns are the major factor in influencing flight times," said lead study author Kris Karnauskas of the Woods Hole Oceanographic Institute in a statement. "Longer flight times mean increased fuel consumption by airliners. The consequent additional input of CO2 into the atmosphere can feed back and amplify emerging changes in atmospheric circulation."
As temperatures in the equatorial Pacific rise and fall, atmospheric waves are sent off toward higher latitudes of both the Northern and Southern hemisphere. A major factor influencing these air circulation patterns is the El Niño Southern Oscillation, a band of warm ocean water that develops ever 3 to 5 years off the west coast of South America and spreads across the tropical Pacific. The ENSO, Karnauskas found, is a strong predictor of high-altitude wind speed -- and therefore flight times -- across the Pacific as well.
Monthly flight time difference (shown in blue) for United flights between HNL -- LAX and average wind speed index (shown in black) are almost perfectly correlated. Image via of Karnauskas et al 2015
As we continue pumping heat-trapping CO2 into the air, the ENSO and air circulation patterns are changing. Analysing 30 different global climate models used by the Intergovernmental Panel on Climate Change, Karnauskas and his team found that a warming world may reposition the jet stream such that aeroplanes face stronger winds travelling from California to Hawaii, adding a little bit of time and fuel to the trip. By the same token, shorter flights going eastbound could burn less fuel. But Karnauskas finds that the fuel savings going east didn't cancel out the additional fuel on flights headed west.
You might wonder why an extra few minutes in the air really matters. Well, Karnauskas did some fast maths and showed that if an additional one minute were tacked onto each of 30,000 round trip US flights every day, it would amount to 300,000 additional air hours per year and a billion additional gallons of jet fuel. This, in turn, would cost the airline industry $US3 billion dollars annually, while adding an additional 10 billion kilos CO2 to our atmosphere.
Those numbers may sound staggering, but they shouldn't be taken as predictions: Karnauskas is merely showing us that small changes in flight times can amount to big economic and environmental costs. But even if a fiercer jet stream means longer trans-Pacific flights, it's not at all clear how climate change will impact flight times, jet fuel use, and aeroplane carbon emissions globally over the 21st century, because wind patterns are changing differently in different regions.
As Penn state geoscience professor told Scientific American, "This study is focused primarily on one part of the total picture, as you know, and so points the way to larger studies assessing something more like the whole (airline industry) route structure as currently flown and what might be flown in a changing world."
Which is to say, air travel is just another aspect of our world that Earth's changing climate is going to impact -- and in ways we're just beginning to understand.
Read the full scientific paper at Nature Climate Change.