Environmentalists like me got something terribly wrong about climate change

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.

It wasn’t until three years ago that I came to see the gravity of my mistake: that methane is an urgent problem and that one source of it is a relatively low-hanging fruit in the fight against climate change. Methane traps about 80 times as much heat in the atmosphere as carbon dioxide over 20 years. And methane emissions, which are driving an estimated 45 percent of human-caused warming, are rising rapidly.

I now believe that cleaning up methane leaks from the production and shipping of oil and gas — one of the most significant sources of these emissions — is the best hope we have to avoid triggering some of the most consequential climate tipping points in the next decade. I think realistically it is our only hope.

The reason the next decade is so crucial is that several natural systems may be on the brink of irreversible change. For example, if warming causes an acceleration in permafrost melt, large swaths of Alaska and Canada could be rendered uninhabitable. If warming forces a large Antarctic ice shelf to break loose, then much of Florida and many other coastal regions could be flooded. We need to slow global warming in time to prevent such catastrophes, and cutting methane emissions is the best, quickest way to do so.