Benefits of Cooperation vis-à-vis Mitigating Climate Change Global Video-Conference on Copenhagen Treaty Common Future 27–28 November 2009 Martin Sewell University of Cambridge The Cambridge Centre for Climate Change Mitigation Research (4CMR)

Tragedy of the commons Human-induced climate change is a classic case of Garrett Hardin’s tragedy of the commons—the benefits of burning fossil fuels accrue to individuals, companies and nations, whilst the costs accrue to the planet as a whole.

Prisoner’s dilemma The tragedy of the commons is essentially a multi-player generalization of the prisoner’s dilemma. Cooperation involves limiting greenhouse gases, whilst defection involves emitting greenhouse gases. If the game is played a fixed number of times, it is optimal to defect. If the game is played an indefinite number of times, the incentive to defect can be overcome by the threat of punishment. CooperateDefect Cooperate win win much lose much Defect lose much win much lose

Advantages of cooperation vis-à-vis climate change mitigation The law of comparative advantage would work against mitigation with a unilateral agreement (due to carbon leakage), but for mitigation with a multilateral agreement (e.g. trading solar power for wind power). Less fossil fuels burned by ‘clean’ countries means more fossil fuels left to be burned inefficiently by other countries. Individual countries may wish to be seen to go green, but are afraid of going it alone as they may lose out to the competition. In this sense, they want to be forced to go green, along with everyone else. Unilateral action would be ineffective anyway, it wouldn’t prevent climate change.

COP15 United Nations Climate Change Conference Copenhagen 7–18 December 2009 Delegations from 192 countries More than 15,000 environment ministers, officials, diplomats, campaigners, journalists and even heads of state Aim: establish a new global treaty for climate change mitigation beyond 2012 The key date for these commitments is 2020, although some countries are looking beyond that, to 2050.

Trust The prisoner’s dilemma ceases to be a dilemma if both players trust each other—mutual trust leads to the win-win situation. Ultimately, the solution to the tragedy of the global commons relies on trust. An international treaty relies on trust, but sets countries up so that they can cooperate by honouring the treaty, or defect by failing to honour the treaty. The latter would be considered a form of cheating. Although we are bad at looking for altruism, we are good at detecting cheating.

Martin Sewell