Richard Muller, a physics professor at University of California-Berkeley, said Monday that the only way to prevent global warming was to stop using coal for power.

“I think there are two key things that we can do,” he told MSNBC host Rachel Maddow. “One of them is a global effort towards energy efficiency and conservation. I think that is realistic. But the biggest thing is — and this will be controversial — the biggest thing is a switch away from coal and to the one thing that can replace it in the poor countries that are going to produce most of the carbon dioxide, natural gas. We have to make fracking clean so that countries such as China and India can switch. Natural gas produces one third the carbon dioxide of coal for the same energy. If we don’t do this, I don’t think we have a chance.”

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