World Bank released a new report on how urban residents are responsible for 80 percent of global greenhouse gas emissions while facing impacts from climate changes on Dec. 3 in Cancun.

The report, Cities and Climate Change: An urgent Agenda, showed that up to 80 percent of the expected US$80 billion to US$100 billion per year in climate change adaptation costs is from urban areas.

Andrew Steer, World Bank Special Envoy for Climate Change, said climate change let cities alter course, implement smart policies and develop sustainable communities.

He said: "Many world cities, such as New York, Mexico City, Amman or Sao Paulo are not waiting for a comprehensive and global climate deal to emerge, they are already acting on climate change."

He praised these cities have showed how to address mitigation, adaption, the delivery of basic urban services and poverty reduction through smart ideas, local initiatives and support from the international community.

The report conveys a need to act – massive investments in buildings and infrastructure that cities in developing countries are undertaking today will lock in urban form and lifestyles for many decades to come, foretelling emission and vulnerability to climate events like wind storms, flooding, heat waves and sea level rise.

The report indicated that aggregate size of cities is driving their contributions to GHG emissions and how they will be affected by climate change. More than half of the people in the world now live in urban areas, a proportion that is growing fast.

The world’s 50 largest cities alone have a combined population (500 million people) larger than the US. They are also estimated to emit about 2,606 million tons of GHGs (third leading source). And, they have a combined GDP of US$9.55 billion (larger than the US).

The report outlined a climate-smart way forward for cities, as long as they work together. For instance, cooperative efforts like the recent Mexico City Pact and the C40 large cities association, highlight how, by working together, cities are able to move more quickly and more comprehensively as they address climate change.

Organizations like the World Bank are responding, providing targeted assistance in urban areas such as Mexico City, Cairo, and Bangkok and detailed vulnerability assessments for several coastal cities.