The C40 Cities Climate Leadership Group is a worldwide network of megacities that has been founded with the aim of reducing climate change. Among the group's main action areas are water and waste management. The initiative has led to the development of biogas in developing areas such as Durban (South Africa), Jaipur (India), Johannesburg, Rio de Janeiro and Bogotà, but also, for example, to an increase in separate waste collection in the city of Milan.