And when you burn it, it's better for the environment in terms of greenhouse gases than carbon dioxide by a factor of about 18-to-1.

FORBES: Mark A. Moser

They show that warming spells very like that of the past 100 years occurred repeatedly, long before the large-scale use of fossil fuels and the associated emissions of carbon dioxide gas were a possible factor.

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Carbon dioxide emissions come from energy use, and energy is the key factor that makes modern economies so much more productive than pre-industrial societies.

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Another factor is climate change - livestock rearing produces methane, which is 23 times more powerful than carbon dioxide in global warming terms, according to Lord Stern.

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