Hydrogen as Fuel for Civil Aviation

The stampede to make commercial aviation “carbon neutral” is a quintessential example of ignoring the low-hanging fruit while literally reaching for the sky. Here is a chart of greenhouse gas emissions by industry sector.

Suppose aviation were to eliminated entirely, as proposed for 2050 and described in the post here on 2022-06-01, “Here Is Your “Absolute Zero” Future, Serf”. Well, that would reduce emissions by 1.9%. And how much greenhouse gas emission will be created by the construction required to entirely replace the fuel production and transport infrastructure for aviation with a fuel that must be maintained at a temperature below 20.3° K and has a volumetric density (70.85 g/L) around 1/10 that of Jet-A fuel (820 g/L)? Oh, and go read up on the spin isomers of hydrogen—once you liquefy the stuff, the orthohydrogen in it goes on emitting heat for the next few days as it relaxes into the lower energy state of parahydrogen, which means it requires additional refrigeration beyond that needed to keep it below the boiling point, regardless of how well insulated the storage vessel may be.