Impactful environmental psychology needs formal theories

Changing individual and collective behavior is critical to addressing the climate and ecological crisis. Behavioral science, and environmental psychology in particular, is thus well positioned to contribute knowledge to guide impactful climate action. However, we argue that it is not living up to its full potential, partly because its theories often remain verbal. Formalizing theories (i.e. expressing them in the precise language of mathematics or computer code) offers many benefits to the field: it increases conceptual clarity; advances cumulative science; allows integration with other disciplines; and guides future research. Theory formalization is especially important to give substance to thinking about complex systems, where it can help evaluate the effects of candidate interventions. We illustrate how environmental psychologists can start incorporating theory formalization in their work.