Kristian S. Nielsen is a research associate in the Department of Zoology at University of Cambridge. He received a PhD from Copenhagen Business School in 2019 with a dissertation focused on the role of self-regulation in environmental behavior change. His current research focuses on bridging research in behavioral science and biodiversity conservation as part of an interdisciplinary project called Nudging for Nature. His other research interests revolve around behavior change as a climate change mitigation strategy, the dynamics of the behavior change process, self-regulation and self-control, and sustainable clothing consumption.Sander van der Linden is Reader in Social Psychology in Society and director of the Cambridge Social Decision-Making Lab in the Department of Psychology at the University of Cambridge. He is also a fellow in Psychological and Behavioral Sciences at Churchill College, Cambridge and the editor-in-chief of the Journal of Environmental Psychology. His research on the psychology of human judgment and decision-making, especially in the context of climate change, has received numerous awards including the Rising Star award from the Association for Psychological Science and the Sage Early Career Award from the Society for Personality and Social Psychology .Paul C. Stern is president of the Social and Environmental Research institute and was previously a principal staff officer at the US National Academy of Science, Engineering, and Medicine where he directed its Board on Environmental Change and Society. He is a fellow of the American Association for the Advancement of Science and the American Psychological Association. His research interests include the integration of social science into research and practice for governing environmental change and into risk assessment and management. Among his publications are Environmental Problems and Human Behavior (coauthor) and Understanding Risk: Informing Decisions in a Democratic Society (coeditor). Kristian S. Nielsen is a research associate in the Department of Zoology at University of Cambridge. He received a PhD from Copenhagen Business School in 2019 with a dissertation focused on the role of self-regulation in environmental behavior change. His current research focuses on bridging research in behavioral science and biodiversity conservation as part of an interdisciplinary project called Nudging for Nature. His other research interests revolve around behavior change as a climate change mitigation strategy, the dynamics of the behavior change process, self-regulation and self-control, and sustainable clothing consumption. Sander van der Linden is Reader in Social Psychology in Society and director of the Cambridge Social Decision-Making Lab in the Department of Psychology at the University of Cambridge. He is also a fellow in Psychological and Behavioral Sciences at Churchill College, Cambridge and the editor-in-chief of the Journal of Environmental Psychology. His research on the psychology of human judgment and decision-making, especially in the context of climate change, has received numerous awards including the Rising Star award from the Association for Psychological Science and the Sage Early Career Award from the Society for Personality and Social Psychology . Paul C. Stern is president of the Social and Environmental Research institute and was previously a principal staff officer at the US National Academy of Science, Engineering, and Medicine where he directed its Board on Environmental Change and Society. He is a fellow of the American Association for the Advancement of Science and the American Psychological Association. His research interests include the integration of social science into research and practice for governing environmental change and into risk assessment and management. Among his publications are Environmental Problems and Human Behavior (coauthor) and Understanding Risk: Informing Decisions in a Democratic Society (coeditor). A recent Intergovernmental Panel on Climate Change assessment emphasizes the urgency of reducing consumption of fossil fuels to cut the greenhouse gas (GHG) emissions that drive anthropogenic climate change. It also points out that mitigation efforts have not taken advantage of all the available tools for intervention. As noted in one of these assessments,1IPCCSummary for Policymakers.in: Masson-Delmotte V. Zhai P. Pörtner H.-O. Roberts D. Skea J. Shukla P.R. Pirani A. Moufouma-Okia W. Péan C. Pidcock R. Connors S. et al Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. World Meteorological Organization, 2018: 32Google Scholar policies to accomplish this emphasize “infrastructural and technology development, regulation, financial incentives, and information provision” but pay insufficient attention to social and psychological factors that can be incorporated into interventions to enhance their impact. The term “behavioral interventions” is sometimes used to refer to a class of initiatives that may, either by themselves or in conjunction with the more typical policy tools (e.g., infrastructure, incentives), achieve greater GHG reductions than have been achieved by the typical tools alone. Such initiatives apply understandings of the social, motivational, cognitive, cultural, and contextual processes underlying behavior. They consider the effects on choice of cognitive heuristics and biases, values and norms, individual habits, political processes, challenges of policy implementation, and other individual, organizational, and social processes that are not typically considered in the design of policy interventions.2Stern P.C. Janda K.B. Brown M.A. Steg L. Vine E.L. Lutzenhiser L. Opportunities and insights for reducing fossil fuel consumption by households and organizations.Nat. Energy. 2016; 1: 16043Crossref Scopus (92) Google Scholar,3Nielsen K.S. Clayton S. Stern P.C. Dietz T. Capstick S. Whitmarsh L. How psychology can help limit climate change.Am. Psychol. 2020; https://doi.org/10.1037/amp0000624Crossref PubMed Scopus (37) Google Scholar They also engage a developing understanding of non-governmental analogs of governmental policies such as supply chain contracting and standards setting in communities of lenders and investors.4Vandenbergh M.P. Gilligan J.M. Beyond Politics. Cambridge University Press, 2017Crossref Scopus (38) Google Scholar Behavioral interventions have included altering decision environments (often referred to as choice architecture), appealing to norms, providing easily interpretable and credible information at the point of decision-making, and improving skills required to perform or forego behaviors.5Michie S. van Stralen M.M. West R. The behaviour change wheel: a new method for characterising and designing behaviour change interventions.Implement. Sci. 2011; 6: 42Crossref PubMed Scopus (3252) Google Scholar Some of these techniques have been applied by marketing practitioners with or without explicit use of behavioral science methods.6McKenzie-Mohr D. Fostering sustainable behavior: An introduction to community-based social marketing. New Society Publishers, 2011Google Scholar Effective behavioral interventions are tailored to the characteristics of the target behavior and its underlying choice processes, the environment within which it is performed, the other decision factors present (e.g., prices, incentives), and the actors whose behavior is to be changed. Research on the efficacy of behavioral interventions is both long-standing and underdeveloped in terms of funding and the creation of strong research communities, although that is changing, as indicated by the recent development of journals in the field, such as Energy Research & Social Science. It draws on theoretical insights from a range of disciplines in social and behavioral science, including psychology, economics, sociology, and anthropology. Although disciplinary approaches vary in their focus and use different theories and methods, several major cross-disciplinary lessons can be extracted that apply to the design of initiatives to increase their efficacy by integrating social and behavioral insights. In this brief examination of the field, we summarize these major lessons and discuss how to apply them in research and practice. First, we address the question of whether behavioral interventions can make a meaningful difference in reducing GHG emissions from energy use. A recent meta-analysis of randomized controlled trials of behavioral interventions for reducing household GHG emissions reported low average levels of behavioral change,7Nisa C.F. Bélanger J.J. Schumpe B.M. Faller D.G. Meta-analysis of randomised controlled trials testing behavioural interventions to promote household action on climate change.Nat. Commun. 2019; 10: 4545Crossref PubMed Scopus (42) Google Scholar suggesting that the potential is small. However, this analysis examined single behavioral interventions outside of their contexts and did not take into account the likelihood that their most effective use is in combination with other tools.8Stern P.C. A reexamination on how behavioral interventions can promote household action to limit climate change.Nat. Commun. 2020; 11: 918Crossref PubMed Scopus (17) Google Scholar Much different conclusions are reached by considering the effects of state-of-the-art behavioral interventions applied at population level in combination with policies and incentives already in place. For example, Dietz et al.9Dietz T. Gardner G.T. Gilligan J. Stern P.C. Vandenbergh M.P. Household actions can provide a behavioral wedge to rapidly reduce US carbon emissions.Proc. Natl. Acad. Sci. USA. 2009; 106: 18452-18456Crossref PubMed Scopus (813) Google Scholar estimated the reasonably achievable household emissions reduction (RAER) from behavioral interventions when applied in this way. They calculated the emissions reduction that would be achieved if all households adopted a technology or behavior (called technical potential, or TP) and the percentage of those households not currently engaging in the behavior who have been shown to respond to the most effective documented packages of interventions (called behavioral plasticity, or BP). Those most effective packages indicate the state of the art. RAER was estimated as the product of TP × BP. This analysis of US households found that national implementation of state-of-the-art behavioral interventions could reduce GHG emissions from direct household energy consumption by 20%, or close to 7.5% of total U.S. territorial emissions, in a decade. However, this level of emissions reduction is rarely achieved in practice for several reasons, including (1) policies emphasizing behavioral interventions may not be politically acceptable, (2) the targets of interventions may not maintain behavioral change over time, and especially (3) typical initiatives, such as providing financial incentives or information, may fail to employ state-of-the-art behavioral methods.3Nielsen K.S. Clayton S. Stern P.C. Dietz T. Capstick S. Whitmarsh L. How psychology can help limit climate change.Am. Psychol. 2020; https://doi.org/10.1037/amp0000624Crossref PubMed Scopus (37) Google Scholar,4Vandenbergh M.P. Gilligan J.M. Beyond Politics. Cambridge University Press, 2017Crossref Scopus (38) Google Scholar,10Wolske K.S. Stern P.C. Contributions of psychology to limiting climate change: opportunities through consumer behavior.in: Clayton S. Manning C. Psychology and Climate Change. Elsevier, 2018: 127-160Crossref Scopus (20) Google Scholar Behavioral interventions can overcome several of these practical limitations to significantly reduce GHG emissions at population level. To help achieve the full potential of policy initiatives, they need to consider four major lessons from behavioral science. Although it is daunting to encapsulate decades of behavioral science research in a few paragraphs, we try to do this here. A fundamental insight is that BP is a function of the target behavior, the external context that promotes or constrains behavioral change, the characteristics of the individuals or organizations that are targeted, and the degree to which change initiatives are designed and implemented to address these factors.3Nielsen K.S. Clayton S. Stern P.C. Dietz T. Capstick S. Whitmarsh L. How psychology can help limit climate change.Am. Psychol. 2020; https://doi.org/10.1037/amp0000624Crossref PubMed Scopus (37) Google Scholar,9Dietz T. Gardner G.T. Gilligan J. Stern P.C. Vandenbergh M.P. Household actions can provide a behavioral wedge to rapidly reduce US carbon emissions.Proc. Natl. Acad. Sci. USA. 2009; 106: 18452-18456Crossref PubMed Scopus (813) Google Scholar Analyzing the characteristics of the target behavior provides insights into its key determinants and possible intervention points, which in turn informs the selection of effective behavioral intervention techniques. Among household actions that reduce GHG emissions, some can be performed quickly and at low cost but reduce perceived benefits and need to be repeated over time to accumulate impact (e.g., lowering thermostat settings in winter, carpooling). These tend to be driven by habits and other automatic and less conscious processes (e.g., switching off lights). Others involve single actions that require financial investment and have impacts that are usually larger and last years or longer (e.g., insulating homes, acquiring fuel-efficient vehicles). These may have many attributes other than energy use that can affect choices (e.g., convenience of mobility), which need to be considered in designing initiatives. The determinants of these different kinds of behaviors often differ11van der Linden S. Warm glow is associated with low- but not high-cost sustainable behaviour.Nat. Sustain. 2018; 1: 28-30Crossref Scopus (32) Google Scholar and some are easier to change with state-of-the-art behavioral interventions than others.9Dietz T. Gardner G.T. Gilligan J. Stern P.C. Vandenbergh M.P. Household actions can provide a behavioral wedge to rapidly reduce US carbon emissions.Proc. Natl. Acad. Sci. USA. 2009; 106: 18452-18456Crossref PubMed Scopus (813) Google Scholar Individuals, households, and organizations differ in their opportunities and abilities to change their behavior. Some differences are attributable to infrastructure and not amenable to behavioral interventions in the near term. For example, use of public transit is constrained in rural areas compared with dense, urban ones. Some result from preexisting policies: what is attractive in one country or region might not be in another because laws, incentives, norms, and rules governing behavior vary. For private companies, investor pressures for short-term profit maximization can impede investments that are more easily made in cultural environments that prioritize social benefits. Individual choices are affected by their settings (e.g., at home versus the workplace) and the costs of choice options. Much of what we know about behavior change and energy comes from interventions in WEIRD (Western, educated, industrialized, and rich democracies) countries and may not apply to behavioral interventions in non-Western cultural contexts. Interventions are more likely to be effective when they are designed with important and relevant contextual factors in mind. Individuals, households, communities, and organizations have multiple, and sometimes even conflicting, motives and goals; have dispositions and entrenched habits that can limit behavioral plasticity; have different financial and cognitive resources; have different value priorities, behavior-specific beliefs, attitudes, and norms; and differ in their social circumstances, social support, and social networks.3Nielsen K.S. Clayton S. Stern P.C. Dietz T. Capstick S. Whitmarsh L. How psychology can help limit climate change.Am. Psychol. 2020; https://doi.org/10.1037/amp0000624Crossref PubMed Scopus (37) Google Scholar Complex actors, such as organizations, additionally have subunits within them that differ on many of the above characteristics and different roles that may enable or impede responses.2Stern P.C. Janda K.B. Brown M.A. Steg L. Vine E.L. Lutzenhiser L. Opportunities and insights for reducing fossil fuel consumption by households and organizations.Nat. Energy. 2016; 1: 16043Crossref Scopus (92) Google Scholar All these factors may influence how they respond to interventions and their capability, motivation, and opportunity to maintain new behaviors over time. Research using big data shows how targeting persuasive appeals to the characteristics of an audience enhances their effectiveness.12Matz S.C. Kosinski M. Nave G. Stillwell D.J. Psychological targeting as an effective approach to digital mass persuasion.Proc. Natl. Acad. Sci. USA. 2017; 114: 12714-12719Crossref PubMed Scopus (198) Google Scholar Another important example is differences in economic and informational resources. The ability of households to adopt costly, lower-emitting technologies is affected by levels of income, wealth, and power; the ability to access and process decision-relevant information; and the influences of social networks. Economically disadvantaged populations are often under financial stress and have limited cognitive resources to plan ahead and deal with future risks compared to higher-income ones.13Shah A.K. Mullainathan S. Shafir E. Some consequences of having too little.Science. 2012; 338: 682-685Crossref PubMed Scopus (477) Google Scholar The same differences often apply to small businesses compared with large ones. Financial incentives can overcome such barriers, especially if they apply design principles discussed below.10Wolske K.S. Stern P.C. Contributions of psychology to limiting climate change: opportunities through consumer behavior.in: Clayton S. Manning C. Psychology and Climate Change. Elsevier, 2018: 127-160Crossref Scopus (20) Google Scholar Behavioral interventions are sometimes studied on their own.7Nisa C.F. Bélanger J.J. Schumpe B.M. Faller D.G. Meta-analysis of randomised controlled trials testing behavioural interventions to promote household action on climate change.Nat. Commun. 2019; 10: 4545Crossref PubMed Scopus (42) Google Scholar However, their effects are typically greatest when coupled with more traditional policy tools and initiatives that reduce institutional, infrastructural, or procedural barriers to change; restructure physical environments; or provide economic incentives (e.g., taxes, subsidies) in ways that make them more user friendly.10Wolske K.S. Stern P.C. Contributions of psychology to limiting climate change: opportunities through consumer behavior.in: Clayton S. Manning C. Psychology and Climate Change. Elsevier, 2018: 127-160Crossref Scopus (20) Google Scholar Behavioral interventions can also be strategically employed to increase the public acceptance of ambitious system-level policies, such as by showing their connections to citizens’ value priorities. For example, proposals for a “Green New Deal” link desires for environmental and economic improvements. Many policies and initiatives intended to reduce GHG emissions have relied on overly simplistic assumptions about behavior, such as that the targets of interventions automatically follow regulations, use available information fully, and have economically rational responses to financial incentives. State-of-the-art behavioral interventions incorporate more nuanced understandings of the behavior of individual and organizational energy consumers. Behavioral scientists have shown the importance of how initiatives are “framed” (e.g., in terms of gains or losses), how choice options are presented, and what messenger(s) are chosen to introduce an initiative. Also, adding well-designed labels, such as the EU energy label, on products and homes may considerably enhance their effect on both consumer and producer behavior. Although it is important that scholars and practitioners continue to rigorously evaluate behavioral interventions, multi-method research has yielded several behaviorally informed principles for designing government policies and private-sector initiatives that increase effectiveness in many contexts beyond business as usual. Some are described here.10Wolske K.S. Stern P.C. Contributions of psychology to limiting climate change: opportunities through consumer behavior.in: Clayton S. Manning C. Psychology and Climate Change. Elsevier, 2018: 127-160Crossref Scopus (20) Google Scholar Financial incentives can get consumers’ attention, but effective incentives must also be designed and marketed to address personal and social influences on choice.11van der Linden S. Warm glow is associated with low- but not high-cost sustainable behaviour.Nat. Sustain. 2018; 1: 28-30Crossref Scopus (32) Google Scholar In general, it is important to keep in mind that external financial incentives need to be designed in a way that does not undermine or compete with people’s intrinsic motivation to reduce their energy consumption.9Dietz T. Gardner G.T. Gilligan J. Stern P.C. Vandenbergh M.P. Household actions can provide a behavioral wedge to rapidly reduce US carbon emissions.Proc. Natl. Acad. Sci. USA. 2009; 106: 18452-18456Crossref PubMed Scopus (813) Google Scholar, 11van der Linden S. Warm glow is associated with low- but not high-cost sustainable behaviour.Nat. Sustain. 2018; 1: 28-30Crossref Scopus (32) Google Scholar Mass media marketing can help but is often less effective than marketing through informal social networks. For newer technologies, a useful strategy is to target likely early adopters, who can diffuse the innovations by example. It can also be useful to employ incentives to leverage the marketing expertise of industries. This includes making valid information from credible sources available at the times and places where choices are being made (for example, as part of sales processes) and may involve working with intermediaries, such as retailers and consumer groups, to ensure that they deliver valid and credible information, to train them in information provision, or to change standard retailing practices.10Wolske K.S. Stern P.C. Contributions of psychology to limiting climate change: opportunities through consumer behavior.in: Clayton S. Manning C. Psychology and Climate Change. Elsevier, 2018: 127-160Crossref Scopus (20) Google Scholar Consumers do not evaluate available information in detail, which makes the perceived credibility of the source important. Information should be designed to overcome common misunderstandings and address the many non-financial attributes of choices. Incentive policies should minimize paperwork and delay in delivering benefits. Structuring choices to make low-emissions options more convenient can also be important, especially as people often economize their cognitive resources.13Shah A.K. Mullainathan S. Shafir E. Some consequences of having too little.Science. 2012; 338: 682-685Crossref PubMed Scopus (477) Google Scholar For example, setting the default choice in energy contracts to renewable energy instead of fossil-based energy has increased choices of renewable energy, even in spite of price premiums.14Ebeling F. Lotz S. Domestic uptake of green energy promoted by opt-out tariffs.Nat. Clim. Chang. 2015; 5: 868-871Crossref Scopus (68) Google Scholar Consumers need to be confident that they will actually get the promised benefits. This may mean certifying products or their providers, independently inspecting retrofits, and strengthening institutions for consumer protection. In sum, behavioral interventions can greatly strengthen the effectiveness of policy initiatives if applied to address the barriers to desired choices that typical policies often miss.