Hopes have faded that a legally binding climate treaty will emerge from next month's UN conference in Copenhagen, with even some of its most ardent backers looking to reset the deadline for agreeing a deal to early 2010. If December's summit fails in this regard, there will be some obvious culprits: the global recession, which has made nations reluctant to commit cash to the problem, and the US Senate, where horn-locking among lawmakers has delayed the passage of domestic legislation.

But even without these bumps in the road — which were perhaps unforeseen when the Bali Roadmap was laid out in 2007 — the challenge set out for negotiators in Copenhagen may have been too great from the outset. In this issue, Nature Reports Climate Change looks at the UN summit from the perspective of researchers who study cooperation (see page 130), some of whom argue that trying to get an effective multi-faceted treaty agreed between 192 nations is a waste of time. Many behavioural economists say — and common sense dictates — that a strong agreement would be more easily negotiated between fewer parties.

The legitimacy of this claim is evidenced by the recent bilateral talks between two of the world's major greenhouse gas emitters, China and India, who in late October signed a five-year pact to present a united front at international climate negotiations. The US is now seeking to broker similar agreements with both nations in the coming month, and strongly believes that such bilateral deals — with Russia and Brazil also — will form the basis of an international agreement in December. From the perspective of political haggling, this makes sense. Cooperation in Copenhagen will only be achieved if those responsible for the majority of emissions can agree on how to apportion responsibility for climate change fairly, as well as on the carrots and sticks that will ensure compliance, rather than encourage free-riding.

While bilateral — or small multilateral — agreements may be more effective in this regard, that in no way means that the Copenhagen conference is, in itself, a waste of time. An international agreement on how to resolve climate change equitably would, after all, carry more clout than deals brokered behind closed doors. But this is no mean feat, requiring resolution of several key issues: ambitious emissions targets for the world's rich, the ability of emerging economies to slow their emissions growth and the transfer of capital from rich to poor nations for adaptation and green technology development.

Smaller deals can bring us a long way to achieving agreement on those issues of equity, but they alone cannot solve the problem of climate change. Without an international deal in place, lawmakers risk setting aside the notion of controlling global greenhouse gas emissions in order to limit warming to within a specific temperature threshold. That is - after all - the intended objective of a climate deal.