Cities emit around three-quarters of the world’s greenhouse gas emissions, according to the United Nations, and over half of the world’s population now live in one. Many have set ambitious targets to slash and offset their emissions, in the hope of neutralising their impact on the environment and slowing climate change. Some are aiming to do this very soon. Copenhagen’s goal is 2025. More than 700 others have committed to targets over the following decades. But how does a city, choked with traffic and packed full of buildings that require huge amounts of energy, actually go about achieving carbon neutral goals? Joining presenters Graihagh Jackson and Neal Razzell: Nick Garnett, BBC reporter Dr Seppo Junnila, professor of real estate business at Aalto University, Finland Yvonne Aki-Sawyerr, mayor of Freetown, Sierra Leone Mark Watts, executive director, C40 Cities Producer: Darin Graham Series producer: Rosamund Jones Editor: Emma Rippon Sound engineer: Tom Brignell