More To Explore

The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs. National Research Council and the National Academy of Engineering. National Academies Press, 2004. Available online at

The Hydrogen Energy Transition: Cutting Carbon from Transportation. Edited by Daniel Sperling and James S. Cannon. Elsevier, 2004.

The Hype about Hydrogen: Fact and Fiction in the Race to Save the Climate. Joseph J. Romm. Island Press, 2005. More information about hydrogen fuel-cell technologies and demons tration programs can be found online at, hydrogenandfuelcells/, and


□ Ambitious new technologies could help quench the world's thirst for energy without worsening global climate change.

□ Technologies such as these will eventu ally be called on to slash carbon dioxide production rates, but they may be needed even sooner if conventional approaches restrain CO2 emissions less than

for Energy is hoped.

If efficiency improvements and incremental advances in today's technologies fail to halt global warming, could revolutionary new carbon-free energy sources save the day? Don't count on it—but don't count it out, either BY W. WAYT GIBBS

To keep this world tolerable for life as we like it, humanity must complete a marathon of technological change whose finish line lies far over the horizon. Robert H. Socolow and Stephen W. Pacala of Princeton University have compared the feat to a multigenerational relay race [see their article "A Plan to Keep Carbon in Check," on page 50]. They outline a strategy to win the first 50-year leg by reining back carbon dioxide emissions from a century of unbridled acceleration. Existing technologies, applied both wisely and promptly, should carry us to this first milestone without trampling the global economy. That is a sound plan A.

The plan is far from foolproof, however. It depends on societies ramping up an array of carbon-reducing practices to form seven "wedges," each of which keeps 25 billion tons of carbon in the ground and out of the air. Any slow starts or early plateaus will pull us off track. And some scientists worry that stabilizing greenhouse gas emissions will require up to 18 wedges by 2056, not the seven that Socolow and Pacala

▲ Late 21st-century energy sources might include nuclear fusion reactors, hydrogen emitted from ponds of genetically engineered microbes, high-altitude wind farms, orbiting solar arrays, and wave and tidal generatorsall linked to a worldwide superconducting grid.

forecast in their most widely cited model [see box on next page].

It is a mistake to assume that carbon releases will rise more slowly than will economic output and energy use, argues Martin I. Hoffert, a physicist at New York University. As oil and gas prices rise, he notes, the energy industry is "re-


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Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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