TRANSPORTATION: Climate change may lengthen some airline flights, worsen jet emissions -- study

ClimateWire | by Malavika Vyawahare, E&E reporter | Tuesday, July 14, 2015

It started off as a hunch and then the idea "took off," is how Kristopher Karnauskas, a geophysicist at the Woods Hole Oceanographic Institution, described his latest research on the impact of climate change on flight times.

One of Karnauskas' students noticed that her flight from Honolulu, Hawaii, to Newark, N.J., seemed to take less time than usual. That occurrence led him to examine flight data for the past 20 years for the route from Hawaii to the West Coast.

The resulting research -- published in Nature Climate Change -- suggests that climate phenomena like El Niņo-induced changes in wind circulation and the Arctic Oscillation, a wind circulation pattern, have a significant relationship with flight times. And it appears that climate change may also change air circulation patterns and lengthen some flight times, leading to the release of more carbon dioxide from the aviation industry.

Specifically, the study reported that changes in the climate could lengthen round-trip flight times on three flight paths from Hawaii to the West Coast by 1 minute in the next 100 years, releasing almost 4.6 million kilograms of CO2 emissions annually because of the rise in fuel consumption.

"If climate change causes a change in the atmospheric circulation and that changes the amount of time airplanes spend in the air," Karnauskas said, "that would modify the amount of fuel they are burning."

While the time by which the duration of flights would change may seem relatively small, if the number of trips made every day around the world is considered, there is a potential for a large feedback between climate change and air travel, because of increased fuel use, Karnauskas said.

Karnauskas and his team estimated that if such an increase were to occur, emissions from commercial flights across the world could grow by as much as 0.03 percent of the total CO2 emissions caused by human activities.

The contribution that jet fuel makes to emissions is well-documented, but the way climate change affects air travel has only emerged as a field of research in recent years, and the possible feedback effects on climate change are even less understood.

However, without looking at data from more routes, it's not fully clear what the change in flight times might be, Karnauskas cautioned, or even what the net effect would be.

What is more certain, Karnauskas asserted, is that in the next 100 years, in response to climate change, we can expect a systematic change in the jet stream.

A jet stream is a massive gush of fast winds in the upper atmosphere that can run thousands of miles long and span hundreds of miles in width, forming a channel that can both carry a plane along or hinder its path. In the Northern Hemisphere, the jet stream generally flows from west to east with the Earth's rotation, and flights heading in that direction benefit from them. In response to growing greenhouse emissions, this jet stream is expected to shift northward and extend eastward, Karnauskas said.

Study met with some skepticism

However, not everybody is convinced about the significance of the results of the current study. "It is well-known that atmospheric circulation patterns affect trans-Atlantic journey times. This paper finds that the same is true of flights between Hawaii and the continental USA," said Paul Williams of the Department of Meteorology at the University of Reading, U.K., who has studied the impact of climate change-induced turbulence on air travel. Williams emphasized that "the major factor that is increasing overall aircraft emissions is the massive expansion of global air traffic, with passenger-kilometers currently growing at about 60 percent per decade. The increases estimated by the authors are interesting but small by comparison."

Industry groups struck a similar note of caution. A statement from Airlines for America, an industry trade group, said its members "employ sophisticated flight planning and weather forecasting systems to generate domestic routes and optimal oceanic tracks in response to current weather and near-term weather forecasts." Major domestic airlines like Delta, JetBlue and United are members of the group. "These modeling processes take into account the best state of the science. Whether the specific study would impact such modeling would depend on its corroboration and determinations as to whether assumptions in the already established models need to be adjusted," the statement added.

Though their estimates are based on a number of assumptions, Karnauskas said that current climate change models do not take this effect into account at all. Airlines that carefully model for fuel efficiency will need to pay attention, he suggested.

Williams echoed the view that this was a ripe area for further research and its impacts could not be discounted. "The two-way influence between aviation and climate has only recently been recognized and certainly warrants further investigation," he said.