This document discusses the role that cities must play in addressing climate change by reducing CO2 emissions and moving toward a more sustainable urban lifestyle. It notes that over half of the world's population now lives in cities, and cities in Europe and North America are especially urbanized. The challenges facing humanity include surviving the impacts of climate change by the end of the century. Cities will need to strategically reduce CO2 emissions over the next decade to limit global warming to 1.5 degrees Celsius.