We live in an urbanised world. Cities have the power to change that world.

Cities consume over two thirds of the world's energy and generate over 70% of global CO2 emissions. Cities are centres of commerce and culture but over 90% of all urban areas are coastal, exposing them to sea level rise and storm surges. Climate impacts such as storms, flooding and drought have financial impacts, with major disruption to business operations and city finances.

Cities are rising to this challenge. Urban density provides an opportunity for a better quality of life and a lower carbon footprint through more efficient infrastructure and planning. Low carbon mass public transport, cycle hire and walking, with higher density urban living, smart grids, green roofs, rainwater harvesting and garden cities can all add up.

City Mayors can be more nimble than state or national level politicians and need to act fast to stay in office, so they get results. There are a number of global collaborations at city level including the new Rockefeller 100 Resilient Cities and the decade long C40 initiative. The 70 mega cities of the C40 initiative represent half a billion citizens, one quarter of global GDP and have taken over 8000 climate actions, with a commitment to reduce one gigaton of CO2e by 2020.

Cities are three times more likely to take action if a goal or target is set.

This year's CSCLeaders challenge is 'What makes a city smart?'

By 2050, nearly 75% of the world's population will live in cities. This growth creates new opportunities but also presents cities with huge economic, environmental and social challenges. Can 'Smart' solutions be found? And not just in the form of technology, but also crucially through leadership, innovation and collaboration?