A team of international legal scholars recently presented their analysis of the core principles guiding international climate change law. Their findings, particularly on the sensitive issue of equity, should be helpful to negotiators working toward a new global climate agreement next year in Paris.

The analysis by the Committee on the Legal Principles Relating to Climate Change comes as countries gear up for the final 18 months of a four-year round of climate negotiations under the U.N. Framework Convention on Climate Change (UNFCCC). The Durban Platform decision that launched the talks in 2011 calls for an agreement that will apply post-2020, have “legal force,” and “be applicable to all Parties.”

That final phrase is an oblique nod to an issue at the core of the climate negotiations from the start – the appropriate distribution of effort among developed and developing countries. While not speaking directly to the Paris talks, the Committee makes a clear case for a more nuanced, evolutionary approach to this thorny issue of “differentiation.”

The UNFCCC speaks to the broad issue of equity primarily through the core principle of “common but differentiated responsibilities and respective capabilities.”  While the principle has universal support, how it’s applied is a frequent dividing point.

The Kyoto Protocol took a strict binary approach to differentiation – establishing legally binding emission targets for developed countries, and no new commitments for developing countries.

The more recent Copenhagen Accord and Cancun Agreements include pledges from both developed and developing countries, but of different forms. Developed countries have absolute economy-wide targets, while developing countries can put forward any type of pledge.

Last year in Warsaw, at the midpoint in the current round of negotiations, parties agreed to communicate their “intended nationally determined contributions” to the 2015 agreement well ahead of the Paris conference. (Those countries “ready to do so” are encouraged to communicate their contributions in the first quarter of 2015).

But like the Durban Platform itself, the Warsaw decision was silent on whether or how parties’ contributions should be differentiated. Some developing countries, emphasizing industrialized nations’ “historical responsibility” for climate change, want to maintain a strict divide between developed and developing country obligations. However, the United States and some other parties reject the notion of fixed categories, and instead favor “self-differentiation” – as each country defines its own contribution, they will naturally fall along a spectrum.

The committee, which includes prominent legal experts from Europe, India, the United States, Brazil, Canada, South Africa, Australia, and Japan, offers a dynamic view that appears to favor the latter position.  The “applicable to all” in the Durban Platform “signals a shift away” from a binary division of responsibilities, in the committee’s view.

While noting the continued importance of “historical responsibility,” the legal scholars cite other principles of international law to support the idea that current and future emissions are also relevant when it comes to defining countries’ climate obligations. They further emphasize the often-overlooked phrase – “respective capabilities.” This suggests that a country’s obligations should reflect not only its “responsibility” for climate change, but also its financial and technological capacity to address it.

The implication is that the way the principle of “common but differentiated responsibilities and respective capabilities” is applied in practice should evolve over time as emissions patterns shift and as countries’ capacities grow.

It will fall to parties to figure out how the evolving principle will apply concretely in the Paris agreement – the committee doesn’t offer specific guidance. But if taken to heart, the committee’s broad message should help deliver an agreement that’s flexible, durable, universal – and equitable.