I just reviewed the “atmosfair Airline Index” for 2018, which is published by the non-profit “atmosfair” organization. I found the results dismal and disappointing. Perhaps my expectations were too optimistic and unrealistic. An average flight spews hundreds of kilograms of CO2 into the atmosphere, although the longer the flight, the more climate efficient the flights can be. The latest survey can be downloaded at: https://www.atmosfair.de/wp-content/uploads/aai2018-englischfarbe_final_mn.pdf
Airlines have been experimenting with Sustainable Aviation Fuels (SAF) since 2008 with 100,000 flights now operated on SAF, according to IATA. SAF is a lower emission fuel, but it is still “fossil-derived” and thus emitting CO2, albeit lower than conventional fuel. And unlike the latter, the fuel can be derived from sources such as cooking oil, plant oils, municipal waste, waste gases, and agricultural waste. A step in the right direction, but still more work left to be done!