Linking scenarios across geographical scales in international environmental assessments

The development and analysis of scenarios or plausible futures has evolved to be a useful approach for dealing with uncertainty about future developments in a structured and integrated manner. Commonly, scenario exercises have focussed on processes at one specific geographic scale. Recently scenario-based approaches have also been used to address multi-scale processes or to link scenarios developed at various geographical scales with each other in order to better understand the interaction of processes across scales. The level of interconnectedness across scales will vary, and depends largely on the approaches used to develop multi-scale scenarios. We distinguish five levels of interconnectedness scenarios may display across scales: (a) Equivalent, (b) Consistent, (c) Coherent, (d) Comparable, and (e) Complementary. Furthermore, we describe five different types of coupled scenario development processes: (a) Joint, (b) Parallel, (c) Iterative, (d) Consecutive, and (e) Independent. Based on this nomenclature, the relationship between the level of interconnectedness of scenarios and the degree of coupling of scenario development processes across geographical scales is discussed. Which process is best suited and how much interconnectedness is needed, will depend both on the focal issue and the primary purpose of the scenario exercise, i.e. whether the aim is education, scientific exploration, or decision-support.