Cheap-talk and left-wing political orientation boost cooperative sustainability when politically outnumbered

Abstract Intensifying partisan animosity poses a significant challenge to sustainability. This research examined whether partisan differences in cooperative sustainability emerged in politically homogeneous and heterogeneous groups and whether non-binding communication through numerical pledges of intended behaviour (cheap-talk) could foster cooperative sustainability in an online experimental common-pool resource dilemma. American Democrats and Republicans ( N = 324) were randomly allocated to politically homogeneous groups of four. Each group was assigned a communication condition (cheap-talk versus no cheap-talk) and received information manipulating perceived group political alignment: aligned (intra-group condition: shared political orientation), mixed/balanced (inter-group condition: 50:50 political split), or mis-aligned (inter-group minority condition: all others belong to the other political group). Partisan differences in cooperative sustainability emerged when groups were perceived as politically mixed or mis-aligned, with Democrats cooperating more than Republicans; no differences emerged in politically aligned groups. In mixed groups, cheap-talk had a negligible effect on cooperative sustainability. However, in both aligned and mis-aligned groups, cheap-talk allowed Democrats and Republicans to more effectively sustain their common-pool resource. Overall, partisan differences in cooperative sustainability depend on perceived group political composition, but enabling people to express their intentions through simple communication may help bridge political divides, facilitating cooperation toward achieving environmental goals.