The United Nations climate meetings began this week in Peru, a dress rehearsal of sorts for treaty talks in Paris next year. But whether world leaders forge a deal or not, Scientific American‘s David Biello and environmental economist Robert Stavins say the fight against climate change has already begun—at the state and local level, and in the private sector. Last year, for example, new solar plants outpaced coal installations in the U.S., and carbon-trading schemes across state and national borders have already begun.