The United Nations-backed conference taking place in Paris later this year presents a significant opportunity for governments to negotiate a new international climate agreement. A question of central importance to negotiators and observers is: what kind of policy architecture—including policy, legal, and institutional structures—is likely to be most effective in generating sufficient emissions reductions to restrain global climate change to within relatively safe levels?

By cooperating with one another, states can create incentives to reduce emissions, coordinate policies, foster new norms, and exchange useful knowledge. However, as there is no world government, they can choose whether or not to participate in, and be legally bound by, international agreements. Domestic factors—political, economic, technical and otherwise—tend to have a much greater influence on countries than international agreements and institutions, which is certainly the case with climate policies.

A highly centralized, more binding policy architecture like the Kyoto Protocol has the advantage of increasing the likelihood that participating countries will meet their commitments. However, this effect is modest and outweighed by a bigger, negative effect of deterring the participation, or depressing the ambition, of large, systemically important emitters, particularly the United States and China. Thus there is a trade-off between “broad but shallow” and “deep but narrow” agreements.

The emerging policy architecture for agreement in Paris 2015 suggests that negotiators and key observers have heeded this important insight. States’ emissions reduction contributions will be nationally determined and achieving them is unlikely to be a legally binding obligation under international law. This will enable the participation of the US and China and increase the collective ambition embodied in the agreement.

However, there will still be a large gap between the aggregate emissions reductions to 2030 implied in countries’ Paris pledges, and a reasonable benchmark of where they ought to be to stay on track to restrain the global average temperature rise to within 2°C above pre-industrial levels.

In a recent paper, three of my colleagues projected likely emissions in 2030 based on recent pledges of the US, European Union, and China, using for the remaining countries the International Energy Agency’s projections based on countries’ existing and planned policies and measures, under its New Policies Scenario. They concluded that global emissions would be 57–59 gigatons (GT) of carbon dioxide equivalent in 2030. A reasonable benchmark for 2030 would be more like 35GT, implying a gap of 22–24GT (equivalent to nearly half of current global emissions).

The reality of this gap does not mean Paris will be a failure; it is unrealistic to expect climate change to be “solved” in one big conference. It does, however, mean that countries will need to focus on how to build greater and greater ambition over time so that the gap is progressively reduced.

International cooperation can help with this, but it is primarily a matter of bringing down the barriers to domestic action that will increasingly be in countries’ national self-interests. When the full costs and benefits of mitigation actions are considered, it is clear that a large amount of emissions in most countries could already be reduced in ways that would bring local net-benefits to that country, even putting aside the long-term climate benefits.

This is due to the rapidly falling costs of many low/zero-carbon substitutes and the many “co-benefits” they tend to bring, like reduced local air pollution, more efficient buildings, and local knowledge spillovers from innovation in clean technologies. International cooperation could help to reduce the many barriers to the realization of these nationally net-beneficial emissions reductions, for example by improving countries’ institutional capacity to attract low-cost finance for renewable energy infrastructure.

Inevitably, some mitigation options will remain a net cost for countries to implement. But these are likely to be concentrated in particular sectors like highly traded energy-intensive goods, international shipping, and aviation. International cooperation could therefore be better targeted sectorally, focusing on the more difficult sectors.

Indeed, through coordinating the policies and measures countries use to reduce emissions, states can reduce over time the relative costs of low/zero-carbon goods and services and thus increase the pool of nationally net-beneficial mitigation options, while reducing the net costs of more expensive options. This is especially the case in areas like the application of carbon taxes and regulatory standards, and the provision of financial support for low/zero-carbon innovation.

This dynamic aspect of the transition to a zero carbon world is immensely important to bear in mind, for it means countries will find it increasingly feasible and desirable to increase their ambition. This effect, moreover, is likely to be self-reinforcing, leading to “tipping points” that result in the sustained use of new technologies and the entrenchment of new institutions, political-economy patterns and social norms. But the more these patterns can be reinforced at the international level, the better. For example, a provision in the Paris agreement that provides for regular, perhaps five-yearly, reviews and revisions of countries’ mitigation ambitions, to facilitate a regular upwards readjustment of expectations, would be very valuable.

Another aspect of the Paris conference that would help to channel political attention in the right direction is a clearer articulation of the long-term emissions reduction goal, and of associated medium-term and short-term shared global goals. These should include agreement on a goal of achieving “net zero” global emissions within the second half of this century, and decarbonizing the global electricity sector before 2050.

To further these objectives, countries could agree to phase out the consumption and production of coal, and to scale-up and better coordinate low/zero-carbon energy innovation. These cooperative measures could be integrated into the formal UN process in various ways. In the near term they may need to be advanced by willing countries, in Paris or otherwise, on the margins of the formal negotiations.

Ultimately, international cooperation can at best accelerate countries’ domestic transition to a zero-carbon economy. Paris 2015 looks like it will help. But the hardest work will remain, as each country and its citizens must find its own way to achieve a deep, timely, and just transition.

Fergus Green is a Policy Analyst and Research Advisor to Professor Nicholas Stern at the Grantham Research Institute on Climate Change and the Environment, and the Centre for Climate Change Economics and Policy (CCCEP), London School of Economics and Political Science. This article is based on his policy paper, “This time is different”: The prospects for an effective climate agreement in Paris 2015.