Precisely why you go for the largest polluters, like agriculture and ground transport. Air travel is the opposite of low hanging fruit because it's difficult to

Precisely why you go for the largest polluters, like agriculture and ground transport. Air travel is the opposite of low hanging fruit because it's difficult to make jets more fuel efficient—the air travel industry is already incentivized to do this to cut costs, so most of the low hanging fruit has been picked. You end up striving for incremental improvement on 2.5% of the problem.