Despite ambitious climate policies globally, the gap between policy targets and actual behavioural change continues to widen, with energy demand, transport emissions, and food-related impacts all rising rather than falling. Using novel Multilevel Latent Class Analysis (MLCA) on 17,000+ respondents across 61 regions in nine OECD countries, we reveal that the majority of populations fall into the least sustainable behavioural segments across energy, transport, and food sectors, with stark regional variations highlighting the importance of understanding contextual influences. Our analysis shows within-country variations can be dramatic, with some regions showing much higher proportions of engaged energy users than neighbouring regions under the same national policies, while demographic targeting proves unreliable as age, income, and education fail to consistently predict sustainable behaviours. Most critically, we find that individuals engaging in sustainable behaviours in one sector are more likely to do so in others, while unsustainable patterns are similarly associated with each other, suggesting coordinated cross-sector interventions could amplify impact. Moving beyond traditional ad-hoc policy transfer approaches, we present a systematic framework for identifying evidence-based transfer opportunities, to show policymakers not just who needs interventions, but where successful patterns emerge and which contexts appear to enable sustainable behaviours. These findings challenge current siloed, demographically-targeted approaches and provide actionable insights for the international policy community seeking to accelerate behavioural change at the scale and speed required for climate mitigation.
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