We’ll only know years from now, but the climate summit opening today in Paris could prove to be transformative. It could set in motion a new dynamic among nations that, over time, will progressively strengthen the global climate effort.

Any agreement coming out of Paris will, by some measures, fall short. Countries’ nationally determined contributions move us closer, but not close enough, to the goal of keeping global warming below 2 degrees Celsius. And for those who believe legally binding emission targets are essential, the outcome will likely be disappointing.

But relying solely on those yardsticks would undervalue the potential of the deal taking shape.

For the first time in more than two decades of climate diplomacy, we are on the verge of a binding agreement that commits all countries to contribute their best efforts, holds them accountable for their promises, and works to build ambition over time.

For too long, countries have used the inaction of others as an excuse for their own. A new agreement can move us beyond this standoff mentality of “we won’t unless you will.” It can build confidence that all are contributing their fair share, and in so doing, it can enable each to do more.

There are two reasons to feel confident that Paris can produce such an outcome. The first is a striking convergence among governments on the broad contours of a deal. The second is the unprecedented level of political will countries are bringing to the talks; today’s opening is the largest gathering of world leaders ever.

The substantive convergence reflects a new paradigm drawing on the hard lessons of the past 20 years. Neither fully binding nor simply do-as-you-please, it is instead a hybrid approach blending bottom-up flexibility, to achieve broad participation, with top-down discipline, to promote accountability and ambition.

This pragmatic middle ground surfaced in C2ES’s Toward 2015 dialogue, a series of formative discussions among senior negotiators from two dozen countries, and has since taken hold in political talks among governments, reflected most recently in the aide-mémoire issued by France following discussions among ministers from 60 countries.

In a new brief, C2ES outlines the essential elements of an agreement that would put this new hybrid paradigm into practice.

As negotiators have scoped out the substance, a deepening sense globally of both the impacts of climate change and the opportunities of a clean energy economy has spurred rising political will. A new climate alliance between the United States and China has helped lead the way, but more than 170 countries have now offered their own contributions to the Paris accord.

This wave of “nationally determined” contributions demonstrates already how bottom-up flexibility helps bring countries in. But Paris must do more than simply stitch countries’ targets together. Flexibility must be complemented by top-down discipline in the form of binding procedural commitments that help ensure accountability and drive ambition.

First, countries must commit in Paris to report regularly on their emissions and steps to reduce them, followed by rigorous international review. That’s how we will know if they are keeping their promises.

Second, the agreement must work to strengthen efforts over time, by bringing countries back to the table every few years to take stock of collective progress and offer new, stronger contributions.

Through this kind of cycle – tell us what you’ll do, show us whether you’re doing it, tell us what you’ll do next – the agreement can instill confidence that all countries are doing their fair share. This can, in turn, alter the political dynamic within countries, undercutting old excuses for inaction, and making it easier to do more. That would be the true value of the Paris agreement.

There’s no pretending Paris will deliver the solution to climate change – we’ve learned by now that no one summit or agreement can.

But the kind of agreement within reach in Paris can transform the political equation among nations. It can capture the rising will of the moment in a way that serves to continually strengthen our will going forward. That would, in our estimation, be a success.