A visitor inspects photovoltaic panels operating in the Sishen solar park, operated by Acciona SA, in Kathu, Northern Cape, South Africa, on June 2. (Waldo Swiegers/Bloomberg)

In recent years, psychologists and behavioral scientists have begun to decipher why we make the choices that we do when it comes to using energy. And the bottom line is that it’s hard to characterize those choices as fully “rational.”

Rather than acting like perfect homo economicuses, they’ve found, we’re highly swayed by the energy use of our neighbors and friends — peer pressure, basically. At the same time, we’re also heavily biased by the status quo — we delay in switching to new energy choices, even when they make a great deal of economic sense.

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All of which has led to the popular idea of “nudging,” or the idea that you can subtly sway people to change their behavior by changing, say, the environment in which they make choices, or the kinds of information they receive. Not in a coercive way, but rather, through gentle tweaks and prompts. And now, a major study in Nature Climate Change demonstrates that one very popular form of energy-use nudging that might be called “default switching,” or the “default effect,” does indeed work — and indeed, could possibly work at a very large scale.

“This is the first demonstration of a large-scale nudging effect using defaults in the domain of energy choices,” says Sebastian Lotz of Stanford University and the University of Lausanne in Switzerland, who conducted the research with Felix Ebeling of the University of Cologne in Germany.

The study was gigantic – the research started out with 41,952 German households. That’s because the researchers had the cooperation of a large energy company.

The researchers conducted a randomized, controlled trial of individuals who were buying a home electricity contract online. Individuals had the option of choosing a contract with a high or low level of service andwhether or not they wanted 100 percent of their power to come from renewable sources.

But here’s where the experiment kicked in: Individuals were randomly assigned to one of two cases. In one case, the box presenting “100 % green” as an “optional choice” was already checked — meaning, if you did not want green energy you had to actively uncheck it and opt out. In the other case, by contrast, the box was unchecked — so if you wanted 100 percent green energy you had to actively check it and opt in.

In other words, in some scenarios 100 percent clean energy was the default — the status quo — and in other cases, it was not.

The difference in responses in the two scenarios was dramatic, especially among the customers who went all the way through the process and purchased an energy contract. “Conditional on the purchase of a contract, merely 7.2% of purchased contracts in the opt-in treatment were ‘green’, whereas in the opt-out treatment, a majority of 69.1% of purchased contracts were ‘green,'” wrote Ebeling and Lotz.

And crucially, this occurred even though the clean energy option was slightly more expensive than the dirty energy one.

In subsequent analysis, Ebeling and Lotz correlated the postal codes of study participants with how their region voted in the last German election. And they found something very surprising: In places where the left-wing Green party was very popular, people were more inclined to actively opt in to buying green energy even when it was not the default. But for other, less environmentally attuned Germans, such behavior was rare.

“We find that ‘green party’ approval is associated with ‘green’ energy choices in the absence of the default nudge, but not when the ‘green’ default is in place,” the authors wrote. Thus, it may be that shifting the default in favor of clean energy is an ideal way to reach people who are not already highly engaged and used to thinking about their energy choices.

Other analyses conducted by the authors suggested that the large default shifting effect was not achieved because people were confused or unaware — the vast majority of respondents appeared consciously aware that they had chosen to power their homes with 100 percent clean energy. “They must know, because they can recall what they do,” says Lotz. Nonetheless, the study overwhelmingly suggests that most of them would not have done so if it had not been set as the default option.

The implications are far-reaching. As the authors note, we could try to tax dirty energy or ban or restrict its use through carbon taxes or caps on emissions, but we could also try to spark changes without any coercion at all. It may be possible to simply set up the situation differently, and let people choose a cleaner world of their own volition.

“We have provided a simple example of how behavioural science can be used to incur large-scale behavioural changes among consumers that may help us mitigate adverse effects of climate change,” wrote Ebeling and Lotz.