Carbon emissions per kilometre travel by the average passenger have fallen by more than 80% over the past 50 years. Each new generation of aircraft generally consumes 50 to 20% less fuel than previous one, largely thanks to improved engine technology. There are several companies working on battery prototypes that could fly 200 kilometres on batteries alone or double that with hybrid power using sustainable aviation fuel. But these small planes won't be in the air till 2028 at the earliest. Using liquid hydrogen has been floated but this would take an awfully long time to get there.