Nature: The collapse of legislation to reduce US greenhouse-gas emissions was one of the most significant failures of President Barack Obamas first term in office. Halfway through his second, in the face of an entrenched Republican majority on Capitol Hill, Obama is now trying to build an environmental legacy through actions that he can take without congressional approval.
Over the past six years, weve done more than ever to combat climate change, from the way we produce energy to the way we use it,...