As our climate changes, one American city is leading the fight-back. Across Chicago, innovative green roofs are having a dramatic impact on emissions and the benefits are being felt in some surprising places. They conserve water, reduce noise, stem storm-water runoff, minimise urban heat island effect and provide necessary habitat for native birds and insects. Green roofs are growing in popularity and also helping to cool cities. In this films we travel to Chicago to look at the benefits of the green-roofs and speak with the designer of the most famous garden roof in the city and the long time mayor of Chicago.