Consensus group decision making under model uncertainty with a view towards environmental policy making

In this paper we propose a consensus group decision making scheme under model uncertainty consisting of a two-stage procedure and based on the concept of Fr´echet barycenter. The first stage is a clustering procedure in the metric space of opinions leading to homogeneous groups, whereas the second stage consists of a proposal most likely to be accepted by all groups. An evolutionary learning scheme of proposal updates leading to consensus is also proposed. The schemes are illustrated in examples motivated from environmental economics.