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By Carl Pope
Mr. Pope is a clean energy policy adviser to several foundations and was the executive director of the Sierra Club from 1992 to 2010.
In my 50 years in the environmental movement, the decision I most regret is one I made in 2005. As the executive director of the Sierra Club, I decided the organization should largely ignore methane, a potent greenhouse gas, and focus on carbon dioxide, the most prevalent heat-trapping gas in the atmosphere and a byproduct of burning fossil fuels like coal, oil and gas.
My colleagues and I understood that methane, which comes from man-made and natural sources, would eventually have to be curbed to slow climate change. But the data suggested that it was a relatively minor contributor to global warming and could wait. And so I neglected methane for decades, as did many climate regulators, activists and negotiators.
