‘Sustainable Choices’ - An Intervention to Promote Climate Change Mitigation Behaviours: A Randomized Controlled Trial

Background: Individual climate change mitigation behaviours (CCMBs) can meaningfully reduce greenhouse gas emissions, yet many people report uncertainty about what actions to take and difficulty changing established habits. Scalable, digital behavioural interventions remain largely untested. This randomized controlled trial evaluated the effectiveness and acceptability of Sustainable Choices, a five-week, internet-delivered intervention designed to promote CCMBs and psychological well-being.Methods: Adults in Sweden (N = 694) were randomized 1:1 to Sustainable Choices or a waitlist control. The primary outcome was CCMBs at post-intervention, assessed with the Climate Mitigation Behaviour Scale (CLIMBS) and analysed using item-response-theory–derived latent scores in mixed-effects models under an intention-to-treat framework. Secondary outcomes included well-being (SWEMWBS), climate-related worry (GAD-2), low mood (PHQ-2), and meaning and purpose (PROMIS-6a). Follow-ups were conducted at 1, 3, and 6 months. Complier Average Causal Effect analyses examined dose–response relations, and acceptability was assessed through adherence and satisfaction.Results: Compared with controls, the intervention produced significantly greater increases in CCMBs on the CLIMBS general factor (d = 0.34, p < .001), with improvements in food, consumption, and engagement domains but not mobility. Meaning and purpose increased relative to controls (d = 0.23, p = .004), whereas changes in well-being, worry, and low mood were not significant. Engagement showed robust dose-dependent effects: each completed module increased CCMBs by 0.09 points, and full adherence yielded a 0.45-point gain. Satisfaction was high, with 84% recommending the course.Conclusions: Sustainable Choices achieved small-to-moderate improvements in climate mitigation behaviours and enhanced perceived meaning and purpose. Fully digital behavioural interventions may provide a scalable complement to broader climate strategies, meriting further evaluation in diverse populations and with objective behavioural measures.