In November, a plane powered by 100% ‘sustainable’ jet fuel took off from London to New York. It was hailed by some as a milestone in reducing the carbon footprint of air travel, which accounts for about 2.5% of global CO2 emissions. Could this be the start of a greener way to fly? Madeleine Finlay speaks to Guy Gratton, associate professor of aviation and the environment at Cranfield University, to find out if the future of aviation can ever truly be guilt-free.. Help support our independent journalism at theguardian.com/sciencepod