Unpacking the side effects of social norm nudges

Growing evidence shows that green nudges can affect secondary (non-targeted) behaviours. However, it is unclear whether such spillovers arise as a result of engaging in the targeted behaviour or if they are a byproduct of policies. In a survey experiment with 2775 English respondents, we test whether a social norm nudge promoting vegetarianism alters a non-targeted action: environmental donations. Social norm messaging increases intended vegetarian choices, but not uniformly. A subgroup identified with machine learning drives this effect. However, we find the social norm nudge crowds out donations from respondents in this subgroup. Our experimental design allows us to rule out the possibility that this crowding-out effect is driven by respondents substituting climate-friendly food choices with environmental donations. This suggests that social norm nudges may work, but at the risk of discouraging other environmentally friendly actions.