Imported non-subsidised coal is the second-most cost-effective source of electricity in Europe.

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Coal is the dominant energy source for generating electricity in China, with Coal-fired power plants account for nearly three quarters of electricity produced in China, and the most intense demand is along the coast in Eastern Chinese provinces.

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Coal-fired power plants are a big source of particle pollution.

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Among them: an agreement for the United States to assist China in improving its "clean coal technology" at its growing number of coal-fired power plans, a major source of greenhouse gas emissions.

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But should he proceed with regulations to control pollution from existing coal-fired power plants, the single largest source of carbon pollution, those regulations probably will contribute to shuttering facilities already struggling to compete with cheap natural gas.

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Coal provides some 60% of its power output, and its second-cheapest source after hydropower (which is 10% of total output).

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Blending of local and imported coal would have increased costs for power producers which source the fuel from the state-run monopoly supplier.

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The New Source Review provision under the Clean Air Act, for example, is intended to prevent older coal-fired power plants from equipping their old units to produce more energy that release more pollutants.

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While methane is a cleaner source of energy than oil or coal when burnt, on its own it is an unusually powerful heat-trapping agent -- perhaps 20 times more potent than carbon dioxide.

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