Hydrogen cars and water vapor

LETTERS Letters to the Editor Letters (~300 words) discuss material published in Science in the previous 6 months or issues of general interest. They can be submitted by e-mail (science_letters@aaas.org), the Web (www.letter2science.org), or regular mail (1200 New York Ave., NW, Washington, DC 20005, USA). Letters are not acknowledged upon receipt, nor are authors generally consulted before publication. Whether published in full or in part, letters are subject to editing for clarity and space. Hydrogen Cars and Water Vapor ably 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. D.W. KEITH AND A. E. FARRELL’S POLICY FORUM “Rethinking hydrogen cars” (18 July, p. 315) draws attention to the need for broad technology assessment of a popular policy ROGER A. PIELKE JR.,* ROBERTA KLEIN, GENEVIEVE alternative. In the pursuit of this new techMARICLE, THOMAS CHASE nology, the focus on the problem to be Cooperative Institute for Research in Environmental solved can lead to insufficient attention Sciences, University of Colorado, Boulder, CO being paid to new environmental problems 80309–0216, USA. that might follow from its adoption. These *To whom correspondence should be addressed. new problems become tomorrow’s unantic- E-mail: pielke@colorado.edu ipated consequences, and the cycle begins References 1. J. P. Piexoto, A. H. Oort, Physics of Climate (American again. This cycle could be dampened, Institute of Physics, College Park, MD, 1992). however, with a thorough assessment of the 2. T. N. Chase, R. A. Pielke Sr., T. G. F. Kittel, J. S. Baron, T. new technology before it has completed J. Stohlgren, J. Geophys. Res. 104, 16673 (1999). 3. N. Moore, S. Rojstaczer, Geophys. Res. Lett. 29, development. 10.1029/2002GL014940 (2002). This cycle is currently under way with 4. T. K. Tromp et al., Science 300, 1740 (2003). hydrogen fuel cells. As fuel cell cars are 5. D. Guston, D. Sarewitz, Technol. Culture 24, 93 (2002). suggested as a solution to global climate change caused by rising levels of greenhouse gas emissions, they are frequently Response misidentified as “zero-emissions vehicles.” WE AGREE WITH PIELKE ET AL. ON THE IMPORFuel cell vehicles emit water vapor. A tance of examining the environmental and global fleet could have the potential to emit other implications of new technology early amounts large enough to affect local or in its development cycle. We are skeptical, regional distribution of water vapor. however, that water vapor produced by Variation in water vapor affects local, combustion can have any important effect regional, and global climates (1). Data on except when it is emitted in the stratosuch effects are sphere. The global sparse because of emission of water due In the case of hydrogen to oxidation of fossil complexities in cars, the cure may indeed fuels is of order 105 the water vapor life cycle. Howbe better than the disease, times smaller than the ever, our prenatural hydrological but we should make sure cycle, and even in liminary calculabefore taking our medicine.” cities, the humidity tions indicate that a complete shift perturbation due to –PIELKE ET AL. to fuel cell vehioxidation of fuels is cles would do likely to be small little to slow water vapor emissions, which compared with other human impacts on presumably have increased perceptibly in near-surface water vapor, such as the land some metropolitan locations through the use changes described in Pielke et al.’s growth in use of internal combustion reference (2). engines. In some locations, changes in DAVID W. KEITH1 AND ALEXANDER E. FARRELL2 relative humidity related to human activity 1Department of Engineering and Public Policy, have arguably affected local and regional Carnegie Mellon University, 129 Baker Hall, Pittsburgh climate (2, 3). Depending on the fuel cell PA, 15213–3890, USA. E-mail: keith@cmu.edu. technologies actually employed, relative 2Energy and Resources Group, University of California, humidity in some locales might conceiv- Berkeley, CA 94720–3050, USA. “ www.sciencemag.org View publication stats SCIENCE VOL 302 What About the Shortcuts? IN THEIR POLICY FORUM “RETHINKING hydrogen cars” (18 July, p. 315), D. W. Keith and A. E. Farrell overlook many shortcuts to early deployment of attractive and profitable hydrogen cars. Their over-$5000-per-car cost estimate for hydrogen fueling infrastructure is an order of magnitude above authoritative engineering-economic calculations for filling-station–scale methane reformers (1) now being commercialized, using off-peak distribution capacity for natural gas and not materially increasing net natural-gas demand (2). Their claim of needed “breakthroughs in hydrogen storage” ignores a 2000 design for a manufacturable, production-costed, costcompetitive, uncompromised, quintupledefficiency midsize SUV (3, 4) using currently commercial compressed-hydrogen tanks. The marginal cost of reducing NOx emissions with hydrogen is zero, not ~$1 million/ton, if reducing NOx is a free byproduct of a hydrogen transition that is profitable for other reasons (2). And while ultimately eliminating automotive CO2 will require either carbon sequestration or a climate-safe source of cheap electricity, carbon-releasing gas-reformation hydrogen in an efficient hydrogenready car (3, 4), as part of an integrated vehicles-and-buildings hydrogen transition strategy (5), would reduce CO2 emissions per kilometer by ~2 to 5 times at negative cost (3, 4), or officially by 2.5 times (6)—surely an important interim step worth pursuing with due deliberate speed. MICHAEL P. TOTTEN Center for Environmental Leadership in Business, Conservation International, 1919 M Street, NW, 5th floor, Washington, DC 20036, USA. References 1. C. E. Thomas, “Hydrogen and fuel cells: pathway to a sustainable energy future,” H2Gen Corp., 2 Feb. 2002 (available at http://66.160.67.66/PDF_Documents/ whitepaper.pdf). 2. A. B. Lovins,“Twenty hydrogen myths” (Rocky Mountain Institute, Snowmass, CO, 2003) (available at www.rmi.org/images/other/E-20HydrogenMyths.pdf). 3. A. B. Lovins, D. R. Cramer, Intl. J.Vehicle Design, in press. 4. D. R. Cramer, D. F. Taggart, in Proceedings of The 19th International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium and Exhibition (EVS-19) (available at www.hypercar.com/pdf/Hypercar_EVS19.pdf; see also www.hypercar.com/pages/casestudies.php). 5. A. B. Lovins, B. T. Williams, paper presented at the Proceedings of the National Hydrogen Association Annual Conference, April 1999 (available at www.rmi.org/images/other/HC-StrategyHCTrans.pdf). 6. D. Garman, “Freedom car: ‘free ride’ or fuel economy savior? An e-FFIENCY NEWS Point-Counterpoint,” Alliance to Save Energy newsletter, 21 May 2003 (available at www.ase.org/e-FFICIENCY/archives/ 2003_05.htm). 21 NOVEMBER 2003 1329