How our cities are run and designed can have a huge impact on the carbon footprint we have as individuals. Is there convenient and affordable transit available for example? Or are the buildings heated and cooled efficiently? But fortunately cities around the world are increasingly making their planning decisions with climate emissions in mind. In fact, actions by cities have been a rare bright spot in an otherwise mostly stagnant decade when it comes to climate action. We speak to Mark Watts - who leads a group called the C40 made up of some of the world's biggest cities - about some of the ways that cities are leading the way on climate.