It would have been hard to imagine just a few short years ago that the United States and China would – together – be the ones driving a stronger global response to climate change.

For years, each claimed inaction by the other as an excuse for not doing more. But with their simultaneous acceptance today of the Paris Agreement, the world’s two largest economies and emitters committed themselves to a low-carbon future, and solidified a new global framework that will keep pressure on all countries to keep doing more.

The precise mix of motivations varies between the two. But fundamentally, the heads of both the United States and China have assessed the risks and opportunities presented by climate change, and they have decided it is in their nations’ interests – and is their responsibility as global leaders – to do more.

How faithfully the two countries now follow through on their commitments will depend in part on a host of shifting political and economic currents, and who assumes the reins in the years ahead.

But with their leadership up to and since last year’s Paris conference, the United States and China have helped establish new mechanisms and unleash new energies that ensure a staying power beyond the comings and goings of individual governments.

With the Paris Agreement, countries have applied the lessons of a quarter-century of fitful climate diplomacy to create a new framework that offers the best hope ever of an effective international response.

The agreement binds countries to a set of processes requiring them to: tell the world how they’re going to fight climate change; report regularly on how well they’re doing; undergo review by experts and by other countries; and, every five years, say what they’ll do next.

It is, in essence, institutionalized peer (and public) pressure. And if it works as designed, the agreement will over time strengthen confidence that countries are doing their fair share, making it easier for all to do more.

Beyond the agreement itself, and the role of national governments, Paris also will keep nurturing stronger action through its powerful “signaling” effect. For many mayors, governors, CEOs and other real-world decision makers, Paris was a catalytic moment, and its signals continue to resound.

From Warren Buffett, who cited Paris in his annual letter to shareholders as further impetus for Berkshire Hathaway’s multibillion-dollar investments in renewable power, to Moody’s, which is now taking countries’ Paris pledges into account in rating future investments, mainstream business is internalizing the Paris goals.

Mayors, too, are reading Paris as a cue for stronger action. In a new Global Covenant of Mayors for Climate & Energy, more than 7,000 mayors in 119 countries pledged to set climate goals beyond those of their national governments. C2ES recently joined with The U.S. Conference of Mayors to form the Alliance for a Sustainable Future, bringing mayors and business leaders together to forge collaborative approaches to cutting emissions.

In the long run, this activation of mayors, CEOs and other “non-state actors” could prove as decisive as the actions of national governments in determining the success of Paris.

No one moment and no one agreement can ensure the long-term transformation needed to keep climate change in check. But today’s U.S.-China announcement is the latest in a series of breakthrough moments that could mean the difference between a successful low-carbon transition and a future of climate calamity.