One of the key arguments behind a federalist approach to the fight against climate change, as opposed to an intergovernmental fight, is that different countries will be affected in different ways. To rely on each country contributing to the effort purely as it sees fit is to invite disappointment. The incentives will lie in free-riding rather than in serious attempts to reduce carbon dioxide emissions.
I saw a very clear illustration of this at a conference two weeks ago. A slide was displayed showing the predicted effect of global warming on agricultural productivity in different parts of the world.
Broadly speaking, the hot parts of the world get worse whereas the cooler parts get better. (I am not sure why Egypt, Kenya and Israel are exceptions to this rule.)
The significant point is that different countries will feel different degrees of urgency in acting, which threatens to undermine the benefit to humanity as a whole of resisting global warming. If there is to be collective action, there has to be a collective decision to act, but the institutions for that collective decision are still lacking.