Uncertainty in Integrated Assessment Modelling. A Cultural Perspective Based Approach

This report introduces an approach in which uncertainty due to disagreement among experts and subjective judgement is identified, illuminated and clarified, and in which it is possible to cluster uncertainties in a methodological, systematic, coherent and consistent way. Because subjective judgement and disagreement arise due to the fact that people have adopted various perspectives, we propose perspective-based alternative model routes as methodology to articulate those uncertainties.

Alternative model routes are model interpretations in which the uncertainties are colored with the bias and preference of a certain perspective. In other words, interpretations of uncertainties are clustered along various perspectives. The alternative model routes are used to translate the concept of uncertainty into risks of policy strategies. Taking into account that decision makers are used to the concept risk to evaluate strategies, we think that this approach can be a useful contribution to integrated assessment modelling aiming at policy support.

We applied the methodology to the fertility submodel and the climate part of the global cycles model of TARGETS, to assess the usefulness and limitations of this kind of uncertainty analysis for both the human and the environmental system. Preliminary experiments with the alternative model routes in the fertility submodel show that differences in future projections can be motivated and explained by differences in the interpretations of the uncertainties, instead of just showing minimum, maximum and best guess values.

The evaluation of uncertainties by risks of response strategies enables us to assess which uncertainties due to subjective judgement and disagreement among experts are most relevant for the policy debate. Such insights can be used to (re)establish the research agenda. Experiments with models equipped with alternative model routes provide the possibility of scenario-development in a coherent and consistent way. Due to delays in the model development it was not possible to implement alternative model routes in the global cycles model in time.

The case-study on the climate issue should therefore be considered as a feasibility study, leading to qualitative descriptions of perspective-based alternative model routes for the climate part of the global cycles model of TARGETS. The model routes will be implemented in the coming months to be able to analyse and to explain the consequences of perspective-related uncertainties concerning climate change in a systematic, coherent and consistent way.