Professor Michael Wara spoke with Elisabeth Rosenthal and Andrew W. Lehren from the New York Times about how some manufacturers of gases have turned carbon credits into a lucrative money-making opportunity.

When the United Nations wanted to help slow climate change, it established what seemed a sensible system. Greenhouse gases were rated based on their power to warm the atmosphere. The more dangerous the gas, the more that manufacturers in developing nations would be compensated as they reduced their emissions.

But where the United Nations envisioned environmental reform, some manufacturers of gases used in air-conditioning and refrigeration saw a lucrative business opportunity.

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Michael Wara, a law professor at Stanford University, has calculated that in years when carbon credits were trading at high prices and coolant was dirt-cheap because of the oversupply, companies were earning nearly twice as much from the credits as from producing the coolant itself.