Game theory: building up cooperation

Can we achieve the ambitious mitigation targets needed to avert dangerous global warming? Research now shows that local sanctioning institutions may succeed where global agreements fall short. In spite of some 18 Conferences of the Parties, global efforts to curb emissions have failed to achieve tangible results (Fig. 1). Although participation is broad — there are 192 parties to the Kyoto Protocol under the United Nations Framework Convention on Climate Change (UNFCCC) — only a handful of nations are actually bound to reduce emissions. Furthermore, the lack of a supranational sanctioning institution means that countries are effectively free to disregard their commitments or to withdraw from the agreement (as Canada did). Due to the inherent trade-off between the breadth of the treaty, in terms of number of acceding countries, and the depth of the emission-reduction commitments, game theorists have come up with the dismal prediction that little will be achieved by a self-enforcing agreement. Either the number of signatories will be small, or many countries will partake in a shallow agreement and achieve only modest reductions. In Nature Climate Change, Vasconcelos and colleagues provide reasons for optimism: local climate governance may be less riddled with barriers to cooperation than international agreements.