DJ. wrote:I can't understand why we don't just convert internal combustion engines to run on hydrogen. Several companies are working on fuel cells that convert hydrogen to electricity, but a V12 running on it with water as the only emissions would be much more fun

I think the problem is the "WHUMP" & fireball the size of a football pitch when you crash one

. But yes, passenger jets are far more polluting & inject the pollution directly into the upper atmosphere where it does most damage - ever wondered how CO2 causes such a problem in the upper atmosphere when it's heavier than air? But I guess airlines, engine & airframe makers, holiday companies & airports have better lobbyists than kitcar drivers,