Earnest, well-meaning environmental messages are supposed to be ineffective relics of a bygone age, when bumper stickers still worked and treehuggers hadn't realized that self-interest speaks louder than Mother Earth ever could.

But don't put that Save the Whales t-shirt on eBay just yet. In experiments published August 12 in Nature Climate Change, psychologists found that telling people about carpooling's money-saving benefits seemingly makes them less likely to recycle.

In short, appeals to self-interest backfired, accidentally encouraging people to behave selfishly in other areas.

"These results reveal the potential for self-interested concerns to inhibit pro-environmental behavior," wrote the researchers, who were led by Laurel Evans and Greg Maio of the United Kingdom's Cardiff University.

In the study, 80 Cardiff University undergraduate students were each asked to read statements on a computer about carpooling. Some learned that it saved money, others that it's good for the environment. A control group learned neither.

The students also filled out paper questionnaires about unrelated topics, which they were told to dispose at the session's end. Unbeknownst to them, this was the experiment's purpose, and a microcosm of environmental tensions: Would they use a recycling basket inconveniently located under another table, or a general waste bin at arm's length?

Among those students "primed," as psychologists say, with a message of carpooling's self-transcending benefits, 89 percent recycled. Of the group that learned about the cost saving, just 50 percent recycled, as did 49 percent of the control group.

In a second version of the experiment, some students were told that carpooling is environmentally friendly and that it saves money. Their recycling rates were still just 50 percent, while 83 percent of those told only about environmental benefits recycled. Forty percent of a control group and just 15 percent of the cost-savings group recycled.

Percentage of students who practiced recycling after being psychologically primed with environmental messages emphasizing self-interest (far left) or the self-transcending value of nature (far right). Image: Evans et al./Nature Climate Change

While the findings are preliminary, involving an artificial situation and demographically unrepresentative participants, they're also intriguing. Some researchers have argued that precisely this pattern of behavior would appear in response to bottom-line-based environmental marketing campaigns, which try to accommodate both narrow self-concern and broader community well-being.

This tension isn't unique to environmentalism, write Evans and Hahn, but may reflect human nature: Studies show that when people are encouraged to be self-interested, they become less helpful, even if there's no reason why they can't be both.

With mainstream environmental groups like the Nature Conservancy pushing utility, rather than nature's intrinsic value, as a rationale for conservation, there's another danger: Over a long period of time, appeals to self-interest can change how people see themselves.

"The erosion of a green self-identity over time is a threat," write Evans and Maio. Constantly encouraged to care about nature because it'll save them money and time, people could forget it's possible to just care.

Citation: "Self-interest and pro-environmental behaviour." By Laurel Evans, Gregory R. Maio, Adam Corner, Carl J. Hodgetts, Sameera Ahmed and Ulrike Hahn. Nature Climate Change, August 12, 2012.