Comments on: Water Vapor and Technology Assessment

By: Martin Sams

Martin Sams — Mon, 23 Apr 2007 13:49:24 +0000

Has increased populations been considered in the effect of water vapor emissions. What if countries like India, Brazil, etc. develop a hydrogen infrastructure? Has this potentialy large contributer to global warming been looked at?

I dont know how much water vapor a hydrogen car will release, but it seems that if we replace all cars on the road now plus the growth of developing countries that is a fairly large amount of water vapor being released.

By: Julia Shepherd

Julia Shepherd — Tue, 21 Jun 2005 14:18:43 +0000

I agree that a review of the outcome of a switch to fuel cells should be undertaken. Unless the hydrogen is sourced entirely without the use of fossil fuels, there will still be CO2 emissions somewhere along the line, and with the growth in the global vehicle fleet increasing at current rates, the amounts of water produced may have consequences.

By: Tind Shepper Ryen

Tind Shepper Ryen — Wed, 18 May 2005 06:37:39 +0000

Eli, we currently do not allow any html tags within comments as part of our ongoing (and thankfully mostly behind the scenes) battle against comment spam. However, line breaks in comments are kept, to allow rudimentary paragraphs, and URLs are auto-linked in comments. If you ever need more than this feel free to email me and we can find something more convenient.

By: Roger Pielke, Jr.

Roger Pielke, Jr. — Wed, 18 May 2005 03:55:25 +0000

Eli- Thanks for these additional comments. Please note that our letter was not in any way a statement against fuel cells, but a call for technology assessment with respect to any proposed new technology. Your views on fuel cells being no worse than ICEs may certainly be correct (however, water vapor may be an issue worth thinking about in either case). But it is worth making such arguments explicitly (i.e., in the peer reviewed scientific literature) and in the context of decisions about adoption of any new technology, fuel cells included. We have enough experience with technologies long thought benign based on simple analyses (or no analyses) that turn out to present problems that it seems to me that we dismiss concerns, however apparently trivial, at our own peril. Given the low (relative) costs of technology assessment, it seems that we might err on the side of being obsessively comprehenisve in our assessments. Thanks again.

By: Eli Rabett

Eli Rabett — Wed, 18 May 2005 03:08:10 +0000

Prof. Pielke: Even if you do not accept the responses to your letter, water vapor emission from fuel cells will be at worst comparable to that from an internal combustion engine without the many other problems associated with other ICE emissions. In the cells, higher efficiency compensates for the heat of combustion being completely associated with oxidation of hydrogen rather than both carbon and hydrogen. Thus your argument expands to a more powerful one against ICEs.

Still, it is intrinsically simpler to condense water vapor emissions from operating fuel cells. This is done in some proton exchange membrane fuel cells to improve their performance. For higher temperature systems the waste heat in the vapor stream can be used to pre-heat input gas increasing efficiency and condensing the water. This alternative is not available to ICEs.

While I am far from a fan of fuel cells, your argument is not an argument against fuel cells, but one against oxidation of hydrogen to the dreaded dihydrogen oxide, and to raise it as a possible objection to the introduction of fuel cells is misleading.

PS: How do you insert paragraph marks in this blog’s comments?

By: Roger Pielke, Jr.

Roger Pielke, Jr. — Wed, 18 May 2005 00:57:26 +0000

Eli- Thanks for your comment. Here is what we wrote on that point in the letter to Science: “However, our preliminary calculations indicate that a complete shift to fuel cell vehicles would do little to slow water vapor emissions, which presumably have increased perceptibly in some metropolitan locations through the growth in use of internal combustion engines. In some locations, changes in relative humidity related to human activity have arguably affected local and regional climate (2, 3). Depending on the fuel cell technologies actually employed, relative humidity in some locales might conceivably increase by an amount greater than with internal combustion engines.”

H20 emissions from internal combustion engines already have obvious societal and environmental impacts in some places, such as Alaska, e.g., see http://www.gi.alaska.edu/ScienceForum/ASF4/497.html.

By: Eli Rabett

Eli Rabett — Tue, 17 May 2005 23:57:38 +0000

Perhaps you have noticed that combustion of hydrocarbons also produces water vapor? or perhaps not?

By: Crumb Trail

Crumb Trail — Wed, 11 May 2005 22:42:14 +0000

Wet Elephant

Prometheus advocates paying attention to a neglected climate consideration. Last year a few of us (myself, Bobbie Klein, Genevieve Maricle, Tom Chase) here at the Center for Science and Technology Policy Research wrote a letter (PDF) to Science sugges…