In Europe, where the threats of global warming and air pollution are taken much more seriously than in some other parts of the world, the contributions of aviation to rising carbon-dioxide levels are coming under scrutiny. The U.K. aims to cut its carbon emissions 60 percent by 2050, but a new report released this week says that can't happen without including aviation, which is not addressed under current schemes. About 5.5 percent of U.K. carbon emissions are from aircraft, but that percentage will rise to about 25 percent by 2050. Richard Branson, of Virgin Airlines, has said that airlines could cut their emissions by 25 percent right now by implementing new procedures, such as taxiing less and carrying less fuel. Branson also recently pledged to spend $3 billion to develop alternative fuels.