A study just out in the Proceedings of the National Academy of Sciences (PNAS) provides some reinforcement for the idea of a technology assessment of the environmental effects of fuel cell cars.

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 suggesting that water vapor emissions from fuel cell vehicles ought to be considered from the standpoint of a technology assessment, because water vapor can have effects upon the environment. We speculated:

“As fuel cell cars are suggested as a solution to global climate change caused by rising levels of greenhouse gas emissions, they are frequently misidentified as “zero-emissions vehicles.” Fuel cell vehicles emit water vapor. A global fleet could have the potential to emit amounts large enough to affect local or regional distribution of water vapor. Variation in water vapor affects local, regional, and global climates (1). Data on such effects are sparse because of complexities in the water vapor life cycle. 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. This increase could lead to shifts in local or regional precipitation or temperature patterns, with discernible effects on people and ecosystems The broad environmental effects of fuel cell vehicles are an issue worth addressing via a technology assessment before implementing a solution (4). Not all problems can be anticipated in this manner, but if some can, then the effort will have been well spent (5). In the case of hydrogen cars, the cure may indeed be better than the disease, but we should make sure before taking our medicine.”

Our point was not that the environmental effects of water vapor emissions would necessarily be significant (we haven’t done that research), but instead that research should be conducted to explore whether or not (and to what degree) such effects would be significant, even if such research leads to a dismissal of concerns. We received a number of dismissive replies to our letter suggesting that human emissions of water vapor were necessarily irrelevant in the climate system, because of its small contribution to he global water vapor cycle, and as a consequence, this aspect of a technology assessment would be unnecessary. (And ExxonMobil incorrectly states that fuel cells provide “zero vehicle emissions.”) While scientific claims of the irrelevance of water vapor emissions may prove correct, it would not preclude the importance of doing a comprehensive technology assessment. After all, CFCs were long thought to be a perfect industrial chemical because they had “no effect” on the environment. And a negative finding from a technology assessment can be just as important as a finding of harm.

A study just out in the PNAS (I don’t have a direct link yet) would seem to support our calls for a technology assessment, and was described by SciDev.net as follows:

“Line Gordon, of the University of Stockholm, Sweden, and her colleagues, looked at how much water vapour is being produced around the planet and compared this to estimates of what would have been produced if human activities hadn’t modified land-use and vegetation. Their study is the first to look at water vapour flows on a global scale. The researchers found that, worldwide, deforestation has decreased the evaporation of water by four per cent. Overall, this is almost exactly offset by the increase in the release of water vapour from irrigation. But the authors warn that the balance at the global level hides strong regional differences… The combined effect, say that authors, is a substantial difference in the distribution of vapour at a global scale compared to what the distribution would have been without human deforestation and irrigation. Studies in China have shown the changes to vapour flows within a region can affect the monsoon rains across the region. No one has yet studied the interaction between vapour flows and the climate on a global scale. The authors suggest the interaction could be large, and the implications for food security could be severe… [Gordon] underlines the need to start analysing the role of water vapour flows in the global climate. “We need to see how big an effect this can have on a global scale,” she says.”

Ultimately, water vapor emissions from a global fleet of fuel cell powered autos may indeed prove to be benign or irrelevant. It would certainly be wonderful to find a important energy technology with little downside. But given the low cost of exploring this topic, it would seem to make good sense to perform a comprehensive technology assessment (argued in the peer-reviewed literature) of fuel cell technologies, before committing to a particular technological or policy path. And any such assessment ought to consider water vapor as well.