Chronos said:
I have to wonder how difficult it would be to reduce water vapor emissions to an acceptable level, whatever that might be. I suspect the technology already exists. It is true that nitrogen oxides are produced simply by heating air - no fuel required. But, it is also true they are easily reduced to negligible levels when you do not have the corequisite need to remove other hydrocarbon combustion byproducts. A variety of alternative energy sources for hydrogen production have already been noted in this thread. They all have various advantages and disadvantages, as do conventional fossil fuels. That does not mean they are unworkable, or even impractical. It is virtually certain costs would decline over time merely as a consequence of economies of scale. It is also probably safe to assume that technological advances would play a role. While I may have questions that have not been satisfactorily answered in my mind, that does not mean they cannot or will not be solved. It certainly does not mean there is no point in trying. I'm willing to concede I may have limitations that are not universally shared. The horseless carriage had its naysayers. It still turned out to be fairly practical and quite popular.
I'm not a chemist (at least not a good one) so I am not up on catalytic converters, but I am willing to believe that efficient suppression of nitrogen oxides could be possible if you don't have to worry about carbon by products as well, but I have no idea what the energy consequences of that are.
But I keep hearing complete disconects between methods of 'making hydrogen' and the concept of the conservation of energy. Making hydrogen from any of its common 'ores' will consume more energy than you get from either burning it or running it in your fuel cell. It is the source of THAT energy that everyone is looking for.
As for the water vapor GHG 'pollution', the global warming enthusiasts DO believe it is a problem. They cite heating of the atmosphere by CO2 trapping, as causing more oceanic evaporation, putting water vapor in the atmosphere which causes more warming; a POSITIVE feedback effect.
Of course I believe water vapor emission from vehicles is quite benign. The thermal efficiency of our engines would be higher if liquid water were emitted instead of hot vapors.
But why is everyone concerned about mechanisms that heat the air. The end goal is to cool the planet, and remove the solar energy that was absorbed in the oceans and the ground and ground cover. By far the most efficient mechanism of planetary cooling going on is evaporation of ocean water, into the atmosphere. About 590 calories per gram of energy is transported into the atmosphere, and the heated atmosphere rises (convection) until the water condenses out as raindrops at higher altitudes, thereby depositing that heat in the upper atmosphere, from whence it can be radiated to space. Even better if it can go higher to a colder region and form ice or snow crystals, and deposit another 80 calories per gram of latent heat of freezing. Water or ice clouds reflect sunlight back into space, and they alo absorb incoming sunlight at wavelengths longer than about 700 nanometers, in several water absorption bands from 0.7 out to around 4 microns. That direct absorption of sunlight by water LOWERS the ground level insolation cooling the planet..
If you take the two limit cases of zero water molecules in the atmosphere, and complete saturated water vapor and clouds from ground to 20 km or so all over the entire globe, it is quite apparent that you set in motion effects which will return naturally to the present status quo from either end. There is no evidence that there are multiple stable states in between those two extremes. There is one, that we have now.
Any mechanism that transfers heat energy from the ground/ocean to the atmosphere, whether it be by direct conduction due to contact with the ground, or radiation in the infrared, or evaporation of water, will lead to convective transport of that heat to the upper atmosphere, where it can finally exit to space. Evaporation is the most efficient by a long shot, so it is water vapor which regulates our planet's temperature; not CO2 or other trace gases.
Nonw of which helps us find another source of energy to make hydrogen energy storage medium.
