Representing the drivers of lifestyle change in Integrated Assessment Models using theories from environmental psychology: introducing the Motivation, Agency, and Past Behaviour (MAP) framework

Sustainable lifestyle changes are an important demand-side solution to reducing CO₂ emissions. While sustainable lifestyles are increasingly included in integrated assessment models, modellers have so far not managed to realistically model what drives changes in lifestyles. Important questions about the feasibility and likelihood of lifestyle change, and how lifestyle changes can be accelerated or promoted thus go unanswered. Environmental psychology is a discipline dedicated to understanding environmental behaviour, and its theories and findings could therefore be instrumental to informing the modelling of lifestyle change in integrated assessment models. Yet, we identify two barriers currently hindering the systematic integration of this knowledge into integrated assessment modelling. The first barrier is plurality: there are many theories and findings that are potentially relevant to modelling lifestyle change, but guidance is lacking on which to apply when. The second barrier is ambiguity: many theories in psychology are not precise enough to unambiguously translate them into a mathematical model. To overcome the barrier of plurality, we introduce the Motivation, Agency, and Past behaviour (MAP) framework, which summarises and integrates the insights of 8 prominent behavioural theories used in environmental psychology and that can be used to determine which theories and determinants are most relevant for specific modelling applications. To overcome the barrier of ambiguity, we identify three areas where the precision of theorizing in environmental psychology can be improved, namely definitions and consistent use of constructs, the specification of relationships between constructs, and describing the strength and boundary conditions of these relationships. We urge for closer collaborations between modellers and environmental psychologists to successfully model the drivers and impacts of sustainable lifestyle change.