Research

Published works

Picard, J. & Banerjee, S. (2026). Unpacking the Side Effects of Social Norm Nudges (Ecological Economics, full text here)

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 by-product 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.

Picard, J., Kobrich, A., Schobin, J. (2024). Experimental evidence on the role of framing, difficulty and domain similarity in shaping behavioral spillovers (Scientific Reports, full text here)

We develop a between-subject online experiment to study when encouraging a climate-friendly behavior spur or hamper further engagement for the environmental cause. First, respondents read a newspaper article dealing with a first pro-environmental behavior (helping scientists as a new form of climate activism). Second, participants choose whether to undertake the behavior emphasized. Third, respondents are offered to do a second, subsequent, pro-environmental behavior (signing a petition to call for political action against climate change). In study 1, we manipulate the narrative of the newspaper articles. It either condemns individual inaction, or encourage being pro-environmental. We compare these narratives against a neutral narrative (control) and an article dealing with an unrelated subject (placebo). In study 2, we investigate how the difficulty of the first pro-environmental behavior moderates behavioral spillovers. In study 3, we test the moderating effects of behavioral distance, i.e. the domain-similarity of the two subsequent behaviors.

Banerjee, S. & Picard, J. (2023). Thinking Through Norms Can Make Them More Effective. Experimental Evidence on Reflective Climate Policies in the UK (Journal of Behavioral and Experimental Economics, full text here)

Adopting low-carbon diets is important to meet our climate goals. Prior experimental evidence suggests green nudges help people adopt such diets, more so when they are encouraged to think through them. In this paper, we re-evaluate this role of reflection in a “social norm” nudge to promote intentions for climate-friendly diets in the United Kingdom. Using 5,555 British respondents, we find the social norm nudge increases meal order intentions for low-carbon diets versus the control condition. Asking people to reveal their personal dietary norms, after exposing them to these social norms (“lower-order nudge+”), does not produce any measurable change compared to the nudge. However, when people are subsequently encouraged to think and pledge to climate-friendly diets (“higher-order nudge+”), the effectiveness of the social norm nudge increases by 90% or more.

Working Papers

Sanford, M., Picard, J., Tallent, T. Experimental evidence of the role of second-order beliefs and conditional cooperation in shaping individual pro-environmental efforts (full text here)

Does carbon inequality affect support for climate policies? Previous research suggests that awareness of carbon inequality across income groups increases policy support, but relies on stylised treatments far from real-world conditions. We conducted a pre-registered experiment in France to assess the effect of real newspaper headlines about emissions from private jets on support for climate policies and willingness to donate to a climate organisation. We find that the treatment polarises respondents, with diverging responses between anti-elite and mainstream voters. Information about carbon inequality increases support for elite-targeting policies among mainstream voters, such as private-jet bans, while reducing support among anti-elite voters. It also increases mainstream voters’ support for a progressive policy that would constrain short-haul flights for everyone. Our results offer evidence of a polarising effect of carbon inequality information among politically divided publics.

Picard, J., Bonan, J., Barreiro-Hurle, J., Cerroni, S., Ouvrard, B. Green nudges and information avoidance, an experimental investigation among farmers from five European countries

We investigate why farmers actively avoid climate change information and how it affects the effectiveness of information campaigns. We administered a preregistered experiment on a sample of European farmers and foresters from Italy, Belgium, Lithuania, and Finland. We collected two samples: one where respondents could skip climate change information and another composed of a control group and a treatment group where respondents are shown climate change information. Around 34% of farmers and forest owners actively avoid the information in the first sample. Distrust in scientists and low pro-environmental attitudes correlate positively with information avoidance. The information nudge increases respondents' willingness to implement environmentally sustainable practices in the second sample. Using machine learning, we find that those with a similar profile to the information seekers of the first sample drive the effect of the nudge. Our results suggest that the null effects of information nudges found in the literature might be explained by information avoidance, creating hidden heterogeneity.

Picard, J. A Model of Pro-Social Policies (full text here)

We act pro-socially whenever we forgo immediate hedonic pleasure to do what is right (e.g., being pro-environmental, helping others). I model pro-social decisions as either intrinsically motivated (done as an end to themselves) or extrinsically motivated (done as a means to an end). Individuals' pro-social nature evolves with the context and their past choices. This model reconciles several contradicting findings in the social psychology literature. It also provides micro-foundations to behavioural spillover effects, backfiring effects, and the heterogeneity of pro-social policies.

Ongoing Projects

Picard, J., Bonan, J., Cerroni, S. Unpacking the causes of information avoidance, an experiment on climate change and meat consumption

Why do people avoid climate change information, and how does it affect the effectiveness of information campaigns? We use economic theory to explain why some people voluntarily ignore such information. Then, focusing on the impact of meat-based diets on the environment, we design an experiment to identify the different "types" predicted by the model. Finally, we use predictive machine learning algorithms to identify these types in another experimental sample to understand how these different profiles react to an information nudge.

Barba, F., Picard, J., Barreiro-Hurle, J., Bonan, J., Cerroni, S. Experimental evidence on the acceptability and perceived effectiveness of green nudges among farmers from seven European countries.

Picard, J. Barreiro-Hurle, J., Bonan, J., Cerroni., S., Best practices for nudging sustainable farming practices

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