Nudging when the descriptive norm is low: Evidence from a carbon offsetting field experiment

Produced as part of the Incentives for behaviour change CCCEP research programme theme

‘Nudges’ and behavioural interventions have become popular tools for stimulating behaviours that benefit other people or society as a whole. Little is known, however, about how to design effective social interventions in contexts in which a desirable behaviour is uncommon and only practised by a minority – i.e. where there is a low incidence of the ‘descriptive norm’. Examples are climate-friendly behaviours like carbon offsetting or the use of renewable energy tariffs. These behaviours are still very far from being mainstream; to tackle the crisis posed by climate change, they need to become common.

The authors of this paper take up this challenge, devising a new strategy for social interventions designed to increase climate-friendly behaviour. They tested the proclivity of an especially sophisticated target group, attendees at a major European environmental economics conference, to offset their carbon emissions from travelling to those conferences. They found that the conference attendees were more likely to offset their emissions when exposed to a social norm intervention that told them past attendees had done so, and even more likely the more they related to the group of attendees and when exposed to this information two years in a row.

In other words, the authors find that interventions leveraging social norms can be effective in changing behaviour when incidence of the desirable behaviour is low and when the target group is composed of experts, if the targeted individuals relate well to the peer group referenced by the intervention. The effectiveness of such interventions increases as individuals are exposed to multiple ‘doses’ of treatment.

As such, the paper provides novel insights to policymakers and practitioners on the use of social interventions when incidence of the descriptive norm is low as well as on the ability of nudges to affect experts.

Key points for decision-makers

  • The authors chose to implement the social intervention with experts, as sophisticated agents are notoriously known to be less influenced by nudges. Thus, they chose to conduct their field experiment at two consecutive annual conferences of the European Association of Environmental and Resource Economics (EAERE), in Zurich in 2016 and in Athens in 2017.
  • They examined the conference participants’ proclivity to offset their carbon emissions as part of the standard conference registration process, with the support of the conference organisers. EAERE has been providing the option to participants to voluntarily offset their emissions from travelling to the conference for years, but uptake has remained relatively low.
  • Previous research has shown that interventions leveraging social norms can stimulate a wide range of pro-social and pro-environmental behaviours, including the uptake of voluntary carbon offsets, and that priming social identities, which can be defined as identities emanating from group membership, can also lead to behavioural changes. However, these interventions have so far largely addressed behaviours that are already normative (common).
  • The authors therefore introduced two randomised treatment conditions to the registration process, one relying on social norms and one on social identity, to be compared with a neutral control group.
  • The social norm treatment leveraged past contributions to voluntary carbon offsetting by delegates at EAERE conferences: at the time of registering online, this target group were faced with the text, “For many years EAERE has given to participants the possibility to offset the carbon emissions related with their traveling to the conference venue and thereby successfully contributed to decrease the conference’s carbon footprint.”
  • The social identity treatment primed participants’ social identity as environmental economists and members of a ‘green’ group, through questions about what they might enjoy through their membership of EAERE, to motivate them to offset their emissions.
  • The authors find that the social norm treatment in particular can effectively increase carbon offsetting rates among experienced subjects, especially if they relate to the peer group that is referenced in the treatment, i.e. past conference attendees contributing to the same global public good. The effect was amplified when a second dose of treatment was administered in a consecutive year, although with decreasing marginal returns. The authors found up to a 200% increase in offsetting.
  • The costs of implementing the treatment were minimal, given that it was administered through a pre-existing online platform.