Mark Watts is Executive Director  of the C40 Cities Climate Leadership Group, a network of cities – there are currently 69, including London, Toronto, Singapore, Sydney, Jakarta, Beijing, Johannesburg and San Francisco – that work together to mitigate both greenhouse gas emissions and climate risks. Before joining C40, Watts worked for engineering firm Arup, focusing on cities and sustainability and, as climate change and sustainable transport adviser to the Mayor of London. It works through a set of networks tackling topics such as green growth, transport, reporting city emissions, and private sector building efficiency, all reflecting the key role cities not only increasingly play in life in the 21st century, but their role in causing and responding to climate change. For overlapping reasons, mayors increasingly hold powerful political roles, so names that pass through this network also often flow through others.