ROME, Italy — Never trust a man in Birkenstocks.

That’s one lesson you could take from a recent study that found that people are more likely to cheat and steal after purchasing green goods as opposed to conventional goods.

“Most likely, the people who purchased the green product felt a ‘moral glow,’” said Nina Mazar, a professor of marketing at the University of Toronto and one of the authors of the study. “And subsequently they felt they had this moral credit to engage in selfish behavior.”

But the findings have implications that go far beyond whether it’s safe to leave a hippie alone with your wallet.

With health care out of the way, the U.S. Senate is turning its attention to climate change. We’ve long known that convincing people to emit fewer greenhouse gases was going to be difficult. There are too many opportunities for people to unfairly benefit from the sacrifices of others. What Mazar’s research shows is that it could be even harder than we thought.

At work is a phenomenon that scientists call “moral licensing,” our propensity to balance out our behavior.

“It’s almost like we keep a moral tab inside of us,” said Mazar. “A moral act can actually have a spill over effect in unrelated domains.” In realms ranging from racial tolerance to charitable giving, scientists have shown that once we feel like we’ve done our part, we’re unlikely to go any further.

In fact, we’re likely to cash in our credit elsewhere. Psychologists at Stanford have shown that test subjects who were allowed to express support for then-presidential candidate Barack Obama were more likely to discriminate against blacks when choosing between white and black job candidates. The Obama supporters figured they had, assumedly, already done their part for racial equality.

In another experiment at Northwestern University, students who were primed to think of themselves as moral were less likely to donate to charity.

When it comes to caring for the environment, we don’t behave any differently. Worse yet, we often face financial incentives that encourage us to backtrack. “If my car doubles in fuel efficiency, it’s now half as costly for me to drive-per mile,” said Matthew Kotchen, an environmental economist at Yale. “So, I’m likely to drive more.”

Increasing energy efficiency, it turns out, doesn’t necessarily reduce consumption. “Chances are you’ll have a smaller effect than you hoped,” said Kotchen. Homeowners with energy efficient lights often leave them on longer. Those with environmentally friendly washing machines tend to do more loads. People who have insulated their homes tend to turn the thermostat higher and leave the heat on longer.

Nor are individuals the only ones to engage in a moral balancing act. When Kotchen studied why corporations engaged in acts of corporate social responsibility — nominally altruistic behavior that doesn’t directly impact the bottom line — he found that a bad track record in one realm was a strong predictor of good behavior in another.

“It’s consistent with the idea that you’re compensating one thing for another,” said Kotchen. The correlation was particularly strong when it came to the environment — something that will come as no surprise to those who’ve followed the oil industry’s efforts to present itself as green.

The real lesson to take from Mazar’s study is that fighting climate change will require a hard price on carbon. Moral licensing only kicks in when we think we’re being altruistic. Once good behavior becomes standard, we rebalance our moral credit cards so that we’re less likely to backtrack.

Afterall, once everybody on your block has started to recycle you're unlikely to feel much of a moral glow about separating your garbage — in fact, you'll probably feel pressure to keep on doing it. So, while we may not be able to trust ourselves to do the right thing, an economic motivation (remember last year's gas prices?) might be just what's need to reset the norms.

Stephan Faris covers climate change for GlobalPost and is the author of "Forecast: The Consequences of Climate Change, from the Amazon to the Arctic, from Darfur to Napa Valley."

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