City councils have been urged to work together by London's mayor to cut waste. How local authorities could make better use of waste was explored this week at London's City Hall, on behalf of the C40 Cities Climate Leadership Group and Clinton Climate. Leading cities, including San Francisco, Madrid and New York showcased systems implemented to achieve record recycling rates and other leading sustainability results. Opening the summit, London mayor, Boris Johnson, said: ‘When governments fail to act it is more necessary that cities act together.' He added that it was healthy local authorities could learn from each other while enjoying a discrete friendly rivalry as they vied to be the world's greenest city.