In Europe, around 75 % of the population lives in urban areas and this is projected to increase to about 80 % by 2020.
Cities emit 69 % of Europe's CO2.
Urban transport accounts for 70 % of the pollutants and 40 % of the greenhouse gas emissions from European road transport.
A city affects a large area outside its own boundaries. For example, London alone is thought to need an area of almost 300 times its geographical size to satisfy its demands and for disposal of its waste and emissions.
Air pollutants, including fine particles and ozone precursors, can travel thousands of kilometres across the continent by air. In many cities, only a part of local air pollution is generated by the city itself.