Not So Simple

Abstract

### Contents #### News The Hydrogen Backlash The Carbon Conundrum Choosing a CO2 Separation Techology Fire and ICE: Revving Up for H2 Will the Future Dawn in the North? Can the Developing World Skip Petroleum? #### Review Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Techologies S. Pacala and R. Socolow #### Viewpoints Sustainable Hydrogen Production J. A. Turner Hybrid Cars Now, Fuel Cell Cars Later N. Demirdoven and J. Deutch See related Editorial. S een up close, hydrogen looks like a recipe for success. Small and simple—one proton and one electron in its most common atomic form—hydrogen was the first element to assemble as the universe cooled off after the big bang, and it is still the most widespread. It accounts for 90% of the atoms in the universe, two-thirds of the atoms in water, and a fair proportion of the atoms in living organisms and their geologic legacy, fossil fuels. To scientists and engineers, those atoms offer both promise and frustration. Highly electronegative, they are eager to bond, and they release energy generously when they do. That makes them potentially useful, if you can find them. On Earth, however, unattached hydrogen is vanishingly rare. It must be liberated by breaking chemical bonds, which requires energy. Once released, the atoms pair up into two-atom molecules, whose dumbbell-shaped electron clouds are so well balanced that fleeting charge differences can pull them into a liquid only at a frigid −252.89° Celsius, 20 kelvin above absolute zero. The result, at normal human-scale temperatures, is an invisible gas: light, jittery, and slippery; hard to store, transport, liquefy, and handle safely; and capable of releasing only as much energy as human beings first pump into it. All of which indicates that using hydrogen as a common currency for an energy economy will be far from simple. The papers and News stories in this special section explore some of its many facets. Consider hydrogen's green image. As a manufactured product, hydrogen is only as clean or dirty as the processes that produce it in the first place. Turner (p. 972) describes various options for large-scale hydrogen production in his Viewpoint. Furthermore, as News writer Service points out (p. [958][1]), production is just one of many technologies that must mature and mesh for hydrogen power to become a reality, a fact that leads many experts to urge policymakers to cast as wide a net as possible. In some places, the transition to hydrogen may be relatively straightforward. For her News story (p. 966), Vogel visited Iceland, whose abundant natural energy resources have given it a clear head start. Elsewhere, though, various technological detours and bridges may lie ahead. The Viewpoint by Demirdoven and Deutch (p. [974][2]) and Cho's News story (p. 964) describe different intermediate technologies that may shape the next generation of automobiles. Meanwhile, the fires of the fossil fuel-based “carbon economy” seem sure to burn intensely for at least another half-century or so [see the Editorial by Kennedy (p. [917][3])]. Service's News story on carbon sequestration (p. 962) and Pacala and Socolow's Review (p. [968][4]) explore strategies—including using hydrogen—for mitigating their effects. Two generations down the line, the world may end up with a hydrogen economy completely different from the one it expected to develop. Perhaps the intermediate steps on the road to hydrogen will turn out to be the destination. The title we chose for this issue—Toward a Hydrogen Economy— reflects that basic uncertainty and the complexity of what is sure to be a long, scientifically engaging journey. [1]: /lookup/doi/10.1126/science.305.5686.958 [2]: /lookup/doi/10.1126/science.1093965 [3]: /lookup/doi/10.1126/science.305.5686.917 [4]: /lookup/doi/10.1126/science.1100103