ARE BIG INTERNATIONAL climate conferences useless?

Cheerleaders say the agreement last weekend from the climate talks in Durban, South Africa, is a great achievement: It foresees a system that binds all big polluters — not just developed countries — to reduce their emissions.

Some environmentalists counter that the system is still unforgivably weak — emissions cuts could easily be too small and won’t kick in for another decade, and that’s if the agreement holds. “Developing countries have been bullied and forced into accepting an agreement that could be a suicide pill for the world,” maintained Nnimmo Bassey of Friends of the Earth International.

Another group of skeptics insists that the whole effort is pointless. To achieve even small temperature reductions over the next half-century would require massive emissions cuts. Addressing other environmental priorities, such as reducing deadly particulates that power plants emit or making coastal communities more resilient to storms, pays off more in the short term. Why not focus on those, in the process making it easier to adapt to slow temperature rise as it happens?

The answer is that leaders cannot afford to ignore the long-term threat. Carbon dioxide lives in the atmosphere for decades, which means that global warming is a problem that could slowly escalate over the next century, ultimately producing temperatures that could be extremely costly to human society.

How, then, should policymakers respond? National governments will set most anti-carbon policies. But, because the problem is global, it’s hard to do even that without some international agreement. The United Nations was supposed to be the forum to sort that out. It has not been easy. U.N. negotiators have struggled for decades to produce a comprehensive accord, often distracted by a near-200-nation convention that privileges scores of small, poor nations, which produce little pollution and don’t really need to be in the room.

The biggest obstacle, though, is not the U.N. structure but politics among the big polluters. In Durban, U.S. negotiator Todd Stern was right to refuse an accord that left out some of the world’s largest emitters — countries such as China and India, which have clung to the notion of “differentiated” responsibilities between developed and developing nations. The outcome was a commitment by all the major polluters to agree in 2015 on a program of emissions reductions beginning in 2020. China’s shift of position was a step forward — but the long time frame dilutes the deal’s significance. So does the United States’ toxic domestic debate on climate change, which could limit future action at home and abroad.

For now, the U.N. process at least provides attention to the climate issue and regular deadlines. But leaders should still give themselves every opportunity to do better, instead of laboring exclusively for the dream of a single, grand climate bargain. It’s good that, increasingly, climate change is on the agenda of other international forums and country-to-country meetings. The Council on Foreign Relations’s Michael Levi argues this at least puts more pressure on leaders to make and keep international commitments. If international pressure or domestic sentiment continued to move China toward a more responsible position, and if U.S. leaders, too, became more responsible on climate change, this trend could also provide the big players flexibility to sort out specific deals among a few relevant countries.