Cities are both a predominant source of greenhouse gas (GHG) emissions and one of the most vulnerable places to the consequences of climate change. More than half the global population lives in these large, concentrated settlements. 1 A variety of activities in cities-including mass-transportation, production, and consumption-produce a large amount of GHGs. Built environments, such as residential and commercial buildings and roads, are the major sources of GHG emissions. Urban areas, which account for just 2 percent of the Earth’s surface, are estimated to emit 71 percent of global energy-related GHG emissions. 2
At the same time, cities are vulnerable to the impact of climate change, including damage to their infrastructure from heat waves, energy usage, water shortages, and health threats. 3 For example, the Organisation for Economic Co-operation and Development (OECD) reports that cities in coastal or riparian locations are those most likely to be vulnerable to extreme weather events. About 40 million people who live in 136 port cities around the world are at risk from a 1-in-100-year coastal fl ood event. The total value of assets exposed in an extreme climatic event is estimated to be US$3 trillion. 4
In response to climate change, city governments are able to infl uence, and even directly control, activities that produce GHGs. Urban planning, energy effi ciency measures by public utilities, and building codes are the primary measures that municipal governments can use to cope with climate change. For many cities, climate change is becoming a signifi cant local policy issue. However, only a small fraction of cities seek to cooperate globally on climate change mitigation and adaptation measures. Thus, the depth and breadth of internationally cooperative climate change policy vary greatly between individual cities.