Answer is still up in the air

It’s not that aircraft are inefficient in terms of carbon emissions per person-kilometre travelled, rather it is the distances travelled (“Flight risk”, November 4).

The book Time to Eat the Dog? examined this and found that the energy consumption of a full Boeing 747 was 1.25 megajoules per passenger-km, compared with 3.19MJ/passenger-km for a single-occupant compact car. So even if we said the plane’s effect on the climate was double its energy consumption, a jet aircraft is still less damaging per personkm than the car.

A transport mode that could have a role in a world of constrained carbon emissions is the solar-powered electric airship. In flight, these would have zero carbon cost, could stay aloft indefinitely, could take off and land vertically so wouldn’t need airports and could hover using zero energy.

Although much slower than other aircraft, if they could cruise at 135km/h, you could get to the UK in six days. You would be closer to the ground so would see more and, if designed like the Hindenburg, they would have a bunk bed, a lounge and a dining room. Peter Olorenshaw (Maitai Valley, Nelson)