Using aviation biofuel continues to be difficult

COMPARED WITH electricity generation (44%), road transport (17%) and even cement-making (4%), aviation, at about 2%, is not a huge source of man-made greenhouse-gas emissions. But it is a source, and it is growing fast. The International Civil Aviation Organisation, an arm of the UN, forecasts that such emissions could rise between three- and seven-fold by 2050 if nothing substantial is done. More efficient engines (see chart) and the introduction of a certain amount of electrification will help, but will only cut into this growth rate, not reverse it. To do that would require the fuel itself to be made “carbon-neutral”.