I had a good discussion with a couple of fellows from the Science College that produced perhaps the most visual example of why it is so difficult to find solutions to problems that affect several parties. Put simply, multilateral agreements are closely related to the prisoner's dilemma.
The prisoner's dilemma illustrates how two people could refuse to cooperate despite the fact doing so would be beneficial to both. Here's one of several versions of the game:
Two criminals are arrested, isolated and prosecuted separately. The judge tells them they can either confess or remain silent. If A confesses and B remains silent, A will be released and B will serve a life sentence. Likewise, if A remains silent and B confesses, A will be the one to serve the life sentence. Should both confess, they will each get early parole. If they both remain silent, they will be released for lack of evidence.
The idea behind the prisoner's dilemma is that cooperation benefits the other while defection benefits the player. Furthermore, the optimal results are obtained if and only if everyone cooperates. However, the more players there are, the harder it is to justify cooperation as one defector is enough to hurt everyone.
With that said, one can see why the Coopenhagen conference produced poor results. Limiting CO2 emissions would potentially slowdown the economy of larger countries giving an advantage to those who ignore the agreement. But in reality, with the way climate changes affect our lands, everybody lose.
