Long-haul flights are getting longer due to stronger winds caused by global warming, according to a study. US scientists linked a small increase in return-journey times of long-haul flights with an increase in the variation of the jet stream, the high-altitude air that flows from west to east. Just one minute extra flight time meant jets spent about 300000 hours longer in the air per year, burning roughly a billion additional gallons of jet fuel.Kris Karnauskas, associate scientist at Woods Hole Oceanographic Institution in Massachusetts, said: "Upper-level wind-circulation patterns are the major factor in influencing flight times."Longer flight times mean increased fuel consumption by airliners. The consequent additional input of CO into the atmosphere can feed back and amplify emerging changes in atmospheric circulation. We already know that as you add CO to the atmosphere and the global mean temperature rises, the wind circulation changes as well - and in less obvious ways."The study, published in the journal Nature Climate Change, analysed about 250000 return flights from Hawaii to Los Angeles, San Francisco and Seattle by four airlines for the period 1995 to 2013.It found that when an eastbound flight became 10 minutes shorter, the corresponding westbound flight became 11 minutes longer.Karnauskas said : "We're talking about anomalies happening down at the equator that are affecting the atmosphere in such a spatially broad way, that it's probably influencing flights all around the world." ..