Should a subset of member states of a federation be allowed to form a sub-union on some policy issue? When centralization is not politically feasible, allowing an enhanced cooperation agreement among a subset of countries permits the latter to gain benefits which would otherwise be lost....

The stabilisation of GHG atmospheric concentrations at levels expected to prevent dangerous climate change has become an important, global, long-term objective. It is therefore crucial to identify a cost-effective way to achieve this objective. In this paper we use WITCH, a hybrid...