Jantimot, You have aced water vapour. Water vapour and hydrogen powered aircraft. Typically they fly about the earth's "weather zone'. So when aircraft burn hydrogen and spew water vapour out the back at 10,000 meters it is above the weather zone. How long will that gas H20, a far more a global warming agent than CO2, simply be ignored. At high altitude hydrogen may be an antagonist, not a solution. We need answers as to how long H2O produced by aircraft remains a global warming issue above the earth's weather zone. But, perhaps the elephant in the room is methane CH4, produced in huge quantities, rotting landfill, all ruminants and just rotting vegetation.
