Why Are Cities Important?

Cities and their power plants are the largest sources of greenhouse gas emissions from human activity. As of 2010, urbanization has concentrated more than half of the world's population, at least 70% of fossil fuel carbon dioxide emissions, and a significant amount of anthropogenic methane into a small fraction of the Earth’s land surface. Currently, the 40 or 50 largest cities together represent the third largest emitter of fossil fuel CO2 after China and the US.

Source: Cities and Climate Change: an urgent agenda, World Bank, 2010