United Press International: U.S. and European Union researchers say airline emissions of carbon dioxide are 20 percent higher than previously estimated. An unpublished study by the U.S. Transportation Department, European air traffic manager Eurocontrol, Manchester Metropolitan University and the technology firm QinetiQnet said total emissions are set to reach between 1.2 billion and 1.5 billion tons annually by 2025, The Independent reported Tuesday. The report, presented at a conference last year in …