This paper focuses on the link between the group co-operation and the unilateral commitment behaviour of some countries in the presence of global environmental problems. As we consider that this last behaviour occurs when bargaining failed, we call it a precautious commitment. We also show that the emergence of a non-coordinate global co-operation can result from a strategic action from the members of the coalition. The insiders of the coalition create an incentive for the non-members to reduce without co-ordination their emissions. Finally, when we introduce an environmental tax prescribed by the co-operating countries to the non-co-operating ones, co-operation becomes global and co-ordinate.
Global environmental problems coalition unilateral commitment Nash equilibrium environmental tax