Assumptions?
I wonder what assumptions about electricity generation were used, and whether any predictions about the effects of improvements in same were made (eg current generation = all fossil-fuel/carbon/GHG-producing = very very bad, future generation = renewables/nuclear, minimal carbon/GHG = very very good).
I suspect it's going to prove to be easier to upgrade electricity generation than change airliner fuels radically, so the ground-based choice probably has greater potential to be "greenified".