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Q & A: hot hydrogen baloney

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Most recent answer: 03/03/2011
Q:
http://www.newton.dep.anl.gov/askasci/phy00/phy00886.htm
Somebody asks about the waste heat from hydrogen-powered vehicles. The answer rambles all over the place but has a special warning: " But I am saving the best (or worst), and most neglected issue for last. One that has been neglected, like the proverbial elephant in the living room. WATER IS A POTENT GREENHOUSE GAS. I have searched in vain for climatological studies that have factored in the effect of the release of millions of tons of water vapor into the atmosphere. We may be trading smog for fog!" BALONEY!
- Mike W
A:
This "expert" response from, of all places, a Dept. of Energy site, misses one of the most basic points of climate science. Rain exists. Water vapor is indeed a potent greenhouse gas but  precipitates out rapidly. The amount in the atmosphere doesn't remember old values but quickly adjusts to a level set by ocean temperatures, etc. Therefore it's treated as part of the response of the climate system. Other greenhouse gases (CO2, methane...) persist far longer in the atmosphere and therefore are the main drivers of the system. The main challenge of all the climate models is to understand how water responds to temperature changes caused by those other drivers, since the water serves to amplify their effects by an amount that is hard to determine precisely. So there's a good physical reason why no one is worried about a little more water getting into the atmosphere.

Oddly, given this bogus scare, the same answer ignores the actual basic problem with the "hydrogen economy", just mentioning in passing some technical problems in producing the hydrogen. The technical problems are merely the laws of thermodynamics. Almost all the hydrogen around is in the form of water- it's already burned. It's already low-free-energy, so it's not a fuel. If you have some completely other energy source (coal, nuclear, solar,...) then you can make some H2 and use it as fuel. You will never get as much energy from that fuel as you took from your energy source. So the hydrogen in water is simply not an energy source at all. It's a material that might be of use to help carry energy around- like a car battery. The question of where we can get our energy without driving the greenhouse effect or causing other problems remains.

 If we get the energy to make H2 from burning coal (assuming we can't sequester the CO2) then we've got a problem, just the same as if we used that energy to charge batteries. The only thing we don't have to worry about is the water from burned hydrogen causing warming itself.

Mike W.

(published on 03/03/2011)

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