Efficiency, when talking about mature markets, is rarely about emissions, it is about cost. We could have zero net emissions today by using pure hydrogen or bio

Efficiency, when talking about mature markets, is rarely about emissions, it is about cost. We could have zero net emissions today by using pure hydrogen or biofuels in existing turbofans with little modification. It does, however, matter quite a bit for emerging technologies which may be aimed at lowering emissions. Higher efficiency, for example, can overcome a lot of drawbacks that come with new technologies, like power to weight ratios. Electric cars, for example, have nowhere near the amount of energy storage that gas fueled cars do, but they are now getting similar ranges because they convert it to kinetic energy much more efficiently.