I double checked. The co2 effect seems to be around 1.3 compared to the effect on the ground, but there are other factors that increase the greenhouse effect be

I double checked. The co2 effect seems to be around 1.3 compared to the effect on the ground, but there are other factors that increase the greenhouse effect beyond that. There seems to be a fair bit of uncertainty on the numbers: https://en.wikipedia.org/wiki/Environmental_effects_of_aviation#Factors https://en.wikipedia.org/wiki/Environmental_effects_of_aviat... The 10% combined efficiency of the three energy conversions matter because energy itself isn't 100% green. With the current energy mix, there are more emissions from synthetic fuels than fossil ones.