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Welcome to another edition of Psy-Q, the column that delves into the JSTOR archives to give you the psychological intelligence behind the stories currently making the headlines.

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Potentially the most important story of the past week was the China-US agreement on greenhouse gas emissions, which was hailed as a “milestone” by US President Barack Obama. I say “potentially” because, sadly, psychology tells us not only that this agreement is doomed to fail, but that, in all likelihood, no solution to the problem of global warming will ever be reached.

The story starts with a famous thought experiment from the 1950s, originally proposed by Merrill Flood and Melvin Dresher at RAND corporation, and popularized by Albert Tucker. Two prisoners are held in separate cells and cannot communicate with one another. The police offer a deal: If both confess, they get 1 year in prison each. If each testifies against the other, they get 2 years each. But if one testifies against the other while the other confesses, the confessor gets 3 years and the testifier walks free. What should you do?

The point of the dilemma is that it is impossible to say. From a bird’s eye view, the best thing is for both prisoners to confess, and so get only 1 year each. But from the point of view of each individual prisoner, the best strategy is to testify against the other in order to be guaranteed a maximum of 2 years instead of 3, as well as an outside chance of walking free. What is rational for each individual player is irrational in the context of the game as a whole, and vice versa.

Under the traditional formulation of the dilemma, the prisoners are held in separate cells and cannot communicate. What happens if we relax this condition, and allow them to make deals? The perhaps-surprising answer is that nothing changes. Even if each prisoner swears on his life that he will confess, there is no reason for the other to believe him. Even a well-intentioned prisoner who genuinely wanted to keep his promise to confess would find it almost impossible to do so, when this means opening himself up to the maximum possible sentence if the other guy squeals.

And so it is with global warming. Even if we set aside the charge that the targets agreed by China and the US do not go far enough, the prisoner’s dilemma tells us that there is little chance of either side sticking to even these modest pledges. Indeed, in the cold hard logical sense of the word, it would be irrational for either side to do so. Just as in the prisoner’s dilemma, the interests of each individual player are misaligned with the interests of the two players taken together. If one country cuts its emissions, and damages its economy in the process, it has no reason to believe that the other will follow suit. “Pledges”, “targets”, “goals” and “commitments” are worth no more than the “swear on my life” pleadings of Flood and Dresher’s prisoner: only a mug would just take the other guy at his word. If you think I’m being too pessimistic, just look what has happened since the Kyoto Protocol: a commitment to a 5% reduction in emissions compared with 1990 levels was followed a by a global increase.

So is a solution possible? Many experimental and computer studies (reviewed here) have shown that, if the prisoner’s dilemma game is played repeatedly by the same players, the best strategy is “tit-for-tat”: confess on the first move, then – whenever the other guy testifies against you – punish him by testifying right back on the next go. Applied to global warming, this strategy would mean that as soon as one country failed to meet its emission targets, the others would respond by giving up any attempt to meet their own.

Another potential solution suggested by the prisoner’s dilemma looks similarly unpromising. If both prisoners are able to enter into a legally-binding contract, then the dilemma turns into a no-brainer, with both happily agreeing to confess. In the same way, if every country in the world were to sign up to a legally-binding contract to cut emissions, then the planet would be saved at the stroke of a pen. The problem is that the only way to create an enforceable contract would be to give the UN the power to impose economic or military sanctions against non-compliers; something that neither the US nor China – or, for that matter, any of the world’s economic powerhouses – look ready to agree to.

A glimmer of hope comes from the successful 1987 agreement to ban CFCs, as a result of which the ozone layer has started to recover. Presumably the reason that we managed to sidestep a prisoner’s dilemma in this case is that it turned out to be relatively cheap and easy to find alternatives to CFCs. The lesson for climate change is that any attempt to get countries to reduce their emissions is – for the reasons elucidated by the prisoner’s dilemma – doomed to failure, unless there is some way to develop alternative technologies that allow them to do so at negligible cost. Without such technologies, the US-China agreement isn’t worth the paper its written on.


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Management Science, Vol. 5, No. 1 (Oct., 1958), pp. 5-26
The Journal of Conflict Resolution, Vol. 24, No. 3 (Sep., 1980), pp. 379-403
Sage Publications, Inc.
Journal of Peace Research, Vol. 31, No. 3 (Aug., 1994), pp. 317-332
Sage Publications, Ltd.