Consider an extremely simple climate game with only two countries. Both can either abate or defect from the agreement and conduct business as usual. If one country abates, both get a climate benefit of 3 and if both abate, they each get a climate benefit of 5. But abating has a cost of 4.

This leads to the following payoffs:

- If both abate, both get 5−4 = 1
- If both defect, both get 0−0 = 0
- If only one abates, the abater gets 3−4 = −1, and the defector gets 3−0 = 3.

Imagine you know the other country will abate. If you are good you get 1; if you are bad you get 3.

Imagine you know the other country will defect. If you are good you get −1; if you are bad you get 0.

So either way you win more if you are bad. And the same goes for the other country. The only logical choice is to defect, not abate. This is the notorious prisoners’ dilemma game.

Fortunately, with two players that play repeatedly, there is good experimental evidence that they will cooperate much of the time. Unfortunately, when there are more than two prisoners, experiments show that over time cooperation deteriorates almost completely.