Australians ever since have enjoyed cheap power from this dirty source of carbon-dioxide, the main culprit of global warming.

自此澳大利亚人就利用这种产生大量二氧化碳的燃料获取廉价能源，而二氧化碳恰恰是全球变暖的罪魁祸首。

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Petroleum coke can be used as a cheap and readily available carbon source in many engineering applications.

石油焦是一种廉价的石油副产品，主要成分为碳。

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But corn kernels are a cheap and eco-friendly source of sugar--which is also a source of carbon.

FORBES: Shucking Petroleum

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.

NPR: PROMISES, PROMISES: Climate Change