| 英文摘要: | Motivating individuals to choose energy from sustainable sources over conventionally produced power constitutes one of the biggest policy challenges for societies1, 2. Here we present the results of a randomized controlled trial in Germany that tested the impact of default rules (that is, a type of ‘nudging’) on voluntary purchases of ‘green’ energy contracts that entirely stem from renewable resources. Setting the default choice to more expensive ‘green’ energy (that is, where consumers have to actively opt out if they do not want it) increased purchases of such nearly tenfold. Furthermore, county-level political preference for the green party uniquely predicted behaviour in the absence of the nudge, suggesting that default setting potentially overrules motivational aspects of green energy purchases. In follow-up experiments, we provide further evidence that the effect does not seem to be driven by unawareness. Summarizing, the present research provides an example of using behavioural science3, 4, 5, 6, 7, 8, 9 for climate change mitigation and shows alternatives to the use of subsidies or other economic incentives. As there is a broad consensus that consumer behaviour presents a viable opportunity for mitigating climate change, a core question for scientists and policymakers alike is how to effectively promote environmentally friendly behaviour on the large scale. Especially regarding climate change mitigation, scientists have tried to augment ‘green’ (that is, pro-environmental) behaviours of the general public by scaling up ‘behavioural principles’ derived from laboratory experiments1, 2, 3, 4, 5, 6, 7, 8, 9. Being coined ‘nudging’7, 10, this method has become popular among policymakers who are now capable of subtly steering individual decisions towards goals set by them without using coercion. However, even though research on ‘nudges’ and, in particular, non-binding defaults11, 12, 13 has delivered promising results in various domains of social and economic policy, no research has thus far tested its efficacy in the case of energy-related behaviours. ‘Default nudges’ typically manipulate initial choice-sets without infringing liberty or autonomy but still affect a person’s decision. They have been characterized as the ‘choice alternative a consumer receives if he/she does not explicitly specify otherwise’ (p. 592; ref. 14), a notion that is widely agreed on in the literature15, 16, 17. Defaults allow a pronounced change in outcomes and help to promote policy goals such as sufficient organ availability, lack of old-age poverty, or—in our case—reduction of greenhouse gases. Probably the most widely known example of nudging by default-setting stems from organ donation11. A simple difference can be sufficient to provide different participation rates as shown by country-level correlations between locally set default rules and outcomes. Opt-out rules lead to high participation, whereas actively opting in keeps participation at low levels in the respective countries11. Here, we test whether this principle can also be applied to the domain of energy choices in a large sample of German households, trying to nudge households towards purchases of ‘green’ energy in a randomized controlled trial (RCT). With purchasing a ‘green’ energy contract, the company guarantees the consumer to add their individual consumption to the energy mix in the form of energy from renewable resources. Although the impact of a single consumer’s energy use on a country’s total energy consumption is negligible, purchasing ‘green’ energy can be viewed as the consumer’s decision to voice their preference regarding a country’s energy mix. Therefore, we augment previous behavioural scientific research interested in sustainable behaviour. This research has addressed, for example, social effects such as comparisons and norms3, 9, technical advice8, and public commitment2 as tools to pursue energy-policy-related goals involving energy and water conservation. Besides social effects, behavioural science that aimed to increase pro-environmental behaviour has also focused on people’s psychological self-concepts1. Results suggest that biospheric framing can be sometimes more effective than economic framing as many consumers like to perceive themselves as pro-environmental. Therefore, we attempt to use a ‘nudge-based’ approach to steer consumers towards the purchase of ‘green’ energy despite additional costs. But why are choices of ‘green’ energy particularly suitable for behavioural interventions using defaults? It is plausible that decisions that are highly relevant for one’s moral identity18 are particularly influenced by default setting. As previous research has shown1, individual morality is an important driver of pro-environmental behaviour. Actively negating one’s moral convictions regarding the environment by opting out of a pre-selected pro-environmental option might be much more aversive compared with not opting in. Therefore, defaults could be particularly effective in the domain of environmental decision making, including energy choices. A total of 41,952 households participated in the 4.5-week-long RCT and were randomly assigned into one of two treatments. The RCT was embedded into the webpage of a nationwide energy supplier and it uniquely targeted prospective customers of the firm. Households chose between energy contracts with a high or low service quality, and both types offer the option to uniquely use energy from renewable sources. This option was varied by letting people either actively opt into ‘green’ energy or passively purchase it if not opting out (see Fig. 1 and Methods for details). The corresponding box was either pre-selected (opt out) or not (opt in). Our main dependent variable is the purchase of an indefinite energy contract that equips the household with energy until revoked by either party.
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