Self-enforcing international environmental agreements revisited

In Barrett obtains this result using numerical simulations and also ignoring the fact that emissions must be non-negative. Recent attempts to use analytical approaches and to explicitly recognize the non-negativity constraints have suggested that the number of signatories of a stable IEA may be very small. The way such papers have dealt with non-negativity constraints is to restrict parameter values to ensure interior solutions for emissions. We argue that a more appropriate approach is to use Kuhn-Tucker conditions to derive the equilibrium of the emissions game. When this is done we show, analytically, that the key results from Barrett's paper go through. Finally, we explain why his main conclusion is correct although his analysis can implicitly imply negative emissions.