America and the world must reduce emissions of greenhouse gases immediately and dramatically if we are to prevent the worst impacts of global warming. If the world is to meet the promises of the Paris Climate Agreement, and limit global warming no more than 2 degrees Celsius, the United States will have to virtually eliminate carbon pollution by mid-century. Our transportation system has emerged as Climate Enemy #1, with cars, trucks and other vehicles now representing the nation’s largest source of carbon pollution. We must reimagine our transportation policies and empower cities and state to implement effective solutions.