Over the past year, the United States and China forged a climate change partnership that would have been almost unthinkable not long ago. Not only have both countries committed to emissions reduction and sustainable energy goals of substantial ambition, they are pursuing those goals in concert.

This bilateral climate cooperation has been crucial to the UN climate summit in Paris and will continue to be so after any agreements are signed. Following years at loggerheads, the converging positions of the world’s two largest emitters are becoming invaluable components of future climate response actions.

So why is this happening?

A combination of domestic, bilateral and international forces help explain the transformation, and reveal its potential and continuing challenges.

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