Large-scale scenarios as ‘boundary conditions’: A cross-impact balance simulated annealing (CIBSA) approach

There is increasing interest in cross-scale scenario development, driven in part by developments in climate scenarios. Climate mitigation and adaptation studies have long emphasized the link between global change and local action, and recent climate community scenarios have been developed with cross-scale application in mind. Conceptually, global scenarios have been proposed as ‘boundary conditions’ on regional and local scenarios. However, while the concept is compelling, to date we have found only one formal proposal (by Schweizer and Kurniawan) of what it might mean from a scenario development perspective. That proposal used cross-impact balances (CIB), which offer a promising route to formalization of cross-scale scenario analysis. In this paper we also apply CIB, but allow for weak, rather than zero, cross-scale interactions. We formalize the concept of weak interactions by extending CIB analysis to allow for metastable states, which are stable under small disturbances. We propose an algorithm for identifying metastable states and for combining states that become connected when small disturbances are present. Arguing that large-scale scenarios can be applied as boundary conditions when they are metastable under the influence of processes at smaller scales, we demonstrate how a simplified CIB can replace a full multi-scale CIB when a metastable scenario kernel is adopted at large scale.