Meta-analysis of pro-environmental behaviour spillover

When people engage in a first pro-environmental behaviour (PEB1; for example, conserving energy at home), are they more or less likely (positive and negative spillover, respectively) to engage in other pro-environmental behaviours (‘PEB2’; for example, conserving water at home)? We examined evidence for spillover using a meta-analysis of interventions. We coded 22 studies and unpublished data that fulfilled the following criteria: used experimental or quasi-experimental design, showed change in a PEB1 and measured at least one PEB2. Analysis of the 77 effect sizes found in these studies showed that the overall spillover from a PEB1 was positive, though small, on the intention to perform a PEB2 (pooled mean effect size estimate d+ = 0.17). However, the spillover effect was negative and small for actual behaviour (d+ = −0.03) and policy support (d+ = −0.01) for PEB2. Positive spillover was most likely when interventions targeted intrinsic motivation and when PEB1 and PEB2 were similar. Future research in the area should target and measure spillover processes, collect larger samples and statistically test for spillover in more consistent ways.