| Vol. 9 | No. 1 | Winter 2006-2007 |
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Dialogue
Since hydrogen fuel cells emit water vapor (a heat-trapping gas), what impact would a hydrogen-based transportation system have on global warming? |
To compare the potential climate impact of a future transportation system dominated by hydrogen fuel cells rather than fossil fuels, we must consider all of the heat-trapping emissions produced by these two power sources. If gasoline, for example, fully combusts in a vehicle engine, the tailpipe exhaust will contain both carbon dioxide and water vapor. Tailpipe exhaust from fully combusted fuel cell hydrogen gas (H2), on the other hand, will contain primarily water vapor.
The impact these emissions have on our climate depends in large part on their atmospheric lifetimes. Water vapor remains in the atmosphere only a few days or weeks, and hydrogen gas about two years, but carbon dioxide lingers more than a century. Transitioning to a transportation system based on hydrogen would therefore have essentially no long-term impact on climate due to short-lived water vapor exhaust or minor hydrogen gas leaks, but would dramatically reduce our emissions of long-lasting carbon dioxide—the key factor driving global warming.
We must be sure, however, that the technology we use to produce hydrogen does not contribute to global warming. Fossil fuel-based production methods would release carbon dioxide (and heat-trapping methane) into the atmosphere, whereas production fueled by renewable energy would not.
Also in this issue of Earthwise:
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Citizen Jack's Climate Campaign
