Trade-offs and synergies in urban climate policies

Cities are at the forefront of climate policies(1-6). However, urban climate policies are not implemented in a vacuum; they interact with other policy goals, such as economic competitiveness or social issues. These interactions can lead to trade-offs and implementation obstacles, or to synergies(7,8). Little analysis investigating these interactions exists, in part because it requires a broad interdisciplinary approach. Using a new integrated city model, we provide a first quantification of these trade-offs and synergies, going beyond the qualitative statements that have been published so far. We undertake a multicriteria analysis of three urban policies: a greenbelt policy, a zoning policy to reduce flood risk and a transportation subsidy. Separately, each of these policies seems to be undesirable because each one negatively affects at least one of the different policy goals; however, in a policy mix, the consequences of each policy are not simply additive. This nonlinearity permits building policy combinations that are win-win strategies. In particular, flood zoning and greenbelt policies can only be accepted if combined with transportation policies. Our results show that stand-alone adaptation and mitigation policies are unlikely to be politically acceptable and emphasize the need to mainstream climate policy within urban planning.