A host of factors converged to produce a landmark climate agreement in Paris.

The most important was unprecedented political will, reflecting the deepening awareness worldwide of the real and rising risks posed by climate change, and of the economic rewards of a clean-energy transition.

Another was the impressive diplomatic force and finesse of the French, who masterfully managed a process prone to division and disorder, earning precious trust from parties that paid off in the end.

But in the run-up to Paris, one of the reasons I was confident of a good outcome was the growing convergence I’d seen in informal discussions among negotiators and ministers on the broad contours of a deal.

That emerging consensus was clearest to me in nearly 100 hours of intense closed-door discussions we held with senior negotiators from two dozen developed and developing countries.

With generous support from a number of governments, C2ES organized Toward 2015, a series of eight sessions in Germany, Switzerland and the United States that gave negotiators a chance to talk informally and to collectively envision the “landing zones” for Paris. The talks were off-the-record, but the thinking that emerged was captured in a report in July from the dialogue co-chairs, former South African environment minister Valli Moosa and former lead Norwegian negotiator Harald Dovland.

Looking back now at Valli and Harald’s report, I am surprised and gratified to see how closely it forecast the final outcome here in Paris. From broad structure to fine details, it was very much on the mark.

The report, for instance, said the agreement should:

• Be a legal agreement under the Vienna Convention on the Law of Treaties (i.e., a treaty). It is.
• Reaffirm the goal of keeping warming below 2 degrees Celsius (see Article 2.1).
• Reflect the principle of common but differentiated responsibilities and respective capabilities in light of different national circumstances (see Article 2.2), but do so differently across different elements of the agreement (see throughout), and rely less on differentiation via fixed categories of countries (e.g., no mention in the agreement of “Annex I”).
• Establish binding commitments by all parties to submit and maintain nationally determined contributions (NDCs), report on progress in implementing them, and participate in procedures holding parties accountable (see Articles 4.2, 13.7(b), and 15).
• Commit all parties to put forward their best efforts, and strengthen them over time (see Article 4.3).
• Establish processes for parties to take stock of collective progress every five years (see Article 14), and then update their NDCs (see Article 4.9).
• Encourage parties to map out their long-term mitigation strategies (see Article 4.19).
• Transition to a non-bifurcated transparency system covering all parties with built-in flexibility for varying national capacities, and a facilitative review process, to track parties’ implementation of their NDCs (see Article 13).
• Establish a new body to facilitate implementation (see Article 15).
• Set a collective aim of reducing climate vulnerability and strengthening resilience; commit parties to implement adaptation efforts; and periodically assess adaptation progress (see Articles 7.1, 7.9, and 7.14).
• Help enlarge the circle of contributors supporting developing countries (see Article 9.2), and
• Require parties relying on international transfers of emissions units to meet their NDCs to ensure no double counting (see Articles 4.13 and 6.2).

In one area in particular, the Toward 2015 report was slightly off. While it called for “progressive decarbonization of the global economy to the point of carbon neutrality,” the agreement expresses it differently: achieving a “balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century.”

And in some important respects, the Paris Agreement goes further than the Toward 2015 report:

• It calls on parties to “pursue efforts” to limit average warming to 1.5 degrees C;
• It establishes a mechanism (a successor to the Kyoto Protocol’s Clean Development Mechanism) to facilitate international emissions trading; and
• It establishes a mechanism to address “loss and damage” (an issue the dialogue report highlighted but didn’t directly address).

In recent months — indeed, until the final days in Paris — many of us were frustrated to see the formal talks move so slowly toward “landing zones” that in informal discussions had emerged so clearly.

Now that the deal’s sealed, I’d like to think that one ingredient of success here in Paris was the fact that a core group of negotiators had a chance to collectively visualize where they were headed. It underscores to me the value of giving negotiators a safe space to talk freely and find common ground.

It took the whole world to deliver the Paris agreement. At C2ES, we feel privileged to have played a part.