Using aviation biofuel continues to be difficult

Emissions from flying are comparatively low, but growing

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”.

That is not the same as carbon-free. The chemistry of what went into an aircraft’s fuel tank would change little, if at all. Rather, the idea would be to borrow the carbon in the fuel from the air, in the form of carbon dioxide. Then, add energy and hydrogen and remove the oxygen to turn it into appropriate hydrocarbons, and release the energy added in the same way that the energy in conventional fuel is released—by burning the fuel in a turbojet that then turns a turbofan or a propeller. As long as the added energy was not itself derived from fossil fuels, this would not add to the natural stock of atmospheric CO2.

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