WASHINGTON -- None of the known alternate energy sources are technically ready to take the place of fossil fuels, suggesting the need for a crash energy development program if the world is to avoid the threat of global warming, experts say in a new study.
The study by 18 scientists and engineers in university, government and private labs evaluated technologies that would make energy without burning oil, coal or natural gas and found that no single system or combination of systems could replace these fossil fuels, based on the present level of development. The study appears today in the journal Science.
A few centuries from now society will have to wean itself from fossil fuels because the supply will run out, said Martin I. Hoffert, a professor of physics at New York University. But because burning the fuels at an increasing rate is putting enough carbon dioxide into the atmosphere to cause global warming, the nations of the world must confront the issue of developing clean, renewable energy sources in this century or face a climate disaster, he said.
''What our research clearly shows is that scientific innovation can only reverse this trend if we adopt an aggressive, global strategy for developing alternative fuel sources that can produce up to three times the amount of power we use today,'' said Hoffert, first author of the study. ''Currently, these technologies simply don't exist.''
Hoffert said U.S. government policy favors increased domestic oil production and shortchanges energy technology research that might lead ultimately and economically to replacing fossil fuels.
He said a combination of renewable energy sources -- such as wind and solar power generation, or electrical power beamed from orbiting solar satellites, and nuclear fusion power plants -- ''are theoretically capable of keeping our civilization going into the future, but the problem is that we haven't taken the challenge seriously enough to do research in it. We are putting practically nothing into really, seriously studying the problem.''
Joel Darmstadter, an energy researcher at Resources for the Future, an energy think tank, said the study by Hoffert and others is a useful review of the technical status of the world's alternate energy systems. The study, he said, could prompt policy discussions because it gives an evaluation of what is possible to replace fossil fuels.
But Darmstadter said the study failed to draw a clear picture of which of the alternative systems should have the highest priority and bases some of the discussion on ''far out and highly speculative'' technologies, such as the power satellite.
Currently, the world's power consumption is about 12 trillion watts, with 85 percent of it produced by burning fossil fuels.
To stabilize the amount of carbon dioxide emitted to the atmosphere by the middle of the century while still permitting the current level of global economic expansion would require production of about 30 trillion watts of power worldwide using power systems that do not emit carbon dioxide, the study found.
For that to happen, said Hoffert, the United States and other countries need a crash program of alternate energy technology development.
The study surveyed the entire field of alternate energy and found most systems have serious technical problems still unsolved. Among them:
n Nuclear fission: It is not the final answer because of a shortage of uranium fuel. The proven reserves of uranium would last less than 30 years if nuclear fission was used to make 10 trillion watts of power, about a third of what will be needed by the end of the century, the study found.
n Solar power: To meet the current U.S. needs with solar power would require sun collectors covering some 1,000 square miles. To make the equivalent of 10 trillion watts of added power would require surface arrays covering almost 85,000 square miles, an area larger than the state of Kansas, the study found.
n Wind power: These systems must operate from remote areas and the current power grids could not manage the load, the study found. New grids, perhaps using cooled superconducting cables, might be needed to harvest power from wind and solar systems.
n Solar power satellites: Orbiting solar arrays could make electricity, convert it to microwaves and then beam that energy to a ground antenna where it would be converted back to electricity.
But to make 10 trillion watts of power would require about 660 space solar power arrays, each about the size of Manhattan, in orbit about 22,000 miles above the Earth.
n Hydrogen energy: Hydrogen does not exist in pure, natural reservoirs and has to be extracted from natural gas or water. The study found that more carbon dioxide and less energy is produced by the extraction of hydrogen than by burning natural gas directly. Extracting hydrogen from water using solar or wind power is not now ''cost effective,'' the study found.
n Nuclear fusion: After decades of study, science still has not learned how to extract power from the fusion of atoms.
The study said additional research could lead to breakthroughs, but it would require political resolve and heavy investment.
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