Are these results applicable in the United States?

Because fair trade, organic and ISO 14001 are international certifications that are commonly used in the United States, the findings are applicable in the U.S. and around the world, the authors said.

All three eco-labels are third-party certified: Fair trade certification requires fair wages and treatment for employees; organic certification recognizes commitments such as working without pesticides and other chemicals; and ISO 14001 certification requires firms to set up an organizational structure to investigate the company's environmental impact and how to reduce it.

The higher-productivity effect stems from employees' appreciation for their workplace, Delmas said. The certifications, especially ISO 14001, include educating employees about a firm's environmental commitment and require employees to work together across departments to reduce the organization's environmental impact. This education and training helps increase employees' identification with their office, while interdepartmental cooperation increases employees' engagement.

"It's a virtuous circle," Delmas said — the opposite of a vicious cycle. "You attract the best people, and because you're open-minded, then you adopt green standards, and then you attract even better people, and this continues to feed itself. Companies that adopt these policies tend to be better. It could be they were better to start with, but there are mechanisms built into these policies that mean they continue to get better."

Real-life examples

Although the companies from the survey retain confidentiality, it's an effect Delmas said she has seen elsewhere many times. At Patagonia, a sports-clothing company well known for its sustainable practices, every job opening receives an average of 900 applicants eager to work for a green company, she said. At the Ambrose Hotel, a boutique hotel in Santa Monica, Calif., adopting wide-ranging sustainability measures made employees happier and healthier, Delmas found in a case study. Housekeeping workers reported fewer headaches, allergies and sick days after switching from chemical cleaners to non-toxic, green cleaning products.

In her research, Delmas has found that wineries also adopt the organic label to improve employees' health.

"I hope managers look at this and see the potential for their firms and employees," she said. "Socially responsible investors say green practices are a proxy for good management. It's also important for regulators to see that some voluntary practices can have beneficial effects."