As I was walking outside tonight, I suddently thought about something which got me questionning. If some hydrogen propulsion produce water vapor, could it be a way to cool down the surface? I mean, arent the clouds in low atmosphere reflecting the ray from the sun? If we would all be using hydrogen car within the next decades, would the use in mass of such thing be huge enough to produce clouds in low atmosphere, so a negate effect on the temperature on the surface level? I might be all wrong however, im not a scientist and I didnt study in anything that could make me informed enough to know that I am right. I was just wondering if someone could enlight me on this.
Thanks

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Hydrogen has mainly been proposed for use in fuel cells, these produce water not water vapor.

Water vapor is a strong greenhouse gas and so would tend to lead to warming, only if the water vapor went on to form clouds of the right type may it produce some cooling.

Most current methods of producing Hydrogen (and all the currently economic ones) lead to the production of CO2, in fact more CO2 than burning the equivalent energy value of the Hydrogen as hydrocarbons. At present the overall efficiency of hydrogen cars, from a renewable energy source, is much worse than batteries or using biodiesel in a hybrid vehicle. I am sceptical that hydrogen cars will ever be the most efficient.

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<a href="http://www.boincforum.info/boinc/">boinc forum</a> and <a href="http://www.uk4cp.co.uk/">United Kindom</a> team, my climate change <a href="http://www.livejournal.com/users/mike_atkinson/">blog</a>.

There are three buses in Reykjavik which use hydrogen. Electric power in Reykjavik comes from waterfalls and hotsprings. Hot water comes from the underground and heat up the houses. So there is no production of CO2. If every cars and buses in Reykjavik would use hydrogen there would be no production of CO2. But another hydro electric power station would be necessary for all the hydrogen cars and trawlers.

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Does a coolant gaz exist?

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Batteries are being used now in real commercial transport applications, for example a <a href="http://www.solectria.com/products/buses.html">school bus</a>. However most of the action seems to be in hybrid vehicles which combine batteries with a conventional IC engine.

I suspect that a hybrid with slightly larger battery allowing 5-10 miles with the engine off would be the ideal solution. Most journeys are short and can be done on battery alone (with a batter top-up between journeys). Longer journeys would need to use the engine, but that is ideal, hydrogen has much worse energy density than hydrocarbons (it stores more energy per unit mass, but is much less dense) and is much more difficult to transfer.

Hydrogen powered vehicles <i>may</i> work, but major breakthroughs are required in hydrogen storage and distribution. The <a href="http://www.fas.org/faspir/2004/v57n3/hydrogen.htm">Journal of the Federation of American Scientists</a> puts it much better than me.

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____________________________<br>
<a href="http://www.boincforum.info/boinc/">boinc forum</a> and <a href="http://www.uk4cp.co.uk/">United Kindom</a> team, my climate change <a href="http://www.livejournal.com/users/mike_atkinson/">blog</a>.