Cities are both the culprits and victims of climate change, according to a new report from the World Bank released on Friday, but cities can play a major role in slowing down global warming. Urban residents, who now make up more than half of the world's population, are responsible for as much as 80 percent of global greenhouse gas (GHG) emissions, says the report, titled "Cities and Climate Change - an Urgent Agenda."

The world's 50 largest cities alone have a combined population (500 million people) larger than that of the United States, and a combined GDP of $9.55 billion. These cities are also estimated to emit about 2.6 billion tonnes of GHGs.

Climate change also poses a great threat for cities. The Intergovernmental Panel on Climate Change predicts a rise in average sea level over the next 100 years ranging between 13 to 28 centimeters in a low scenario and 26 to 59 centimeters for a high scenario.

Whether they are cities of rich or developing countries, most major cities, located near rivers and oceans, are vulnerable to rising sea levels, in addition to the impacts of wind storms that will likely increase in severity and frequency in the coming decades.

"Urbanization creates problems as well as solutions. We have to turn cities from a problem into a solution," said Dr. Andrew Steer, climate change special envoy of the World Bank Group, in an interview with China Daily.

Many cities in the world are taking actions to move toward low-carbon, and to build up resilience in vulnerable communities, he said.

"Many cities in China are doing really interesting experiments," said Steer, who has visited China many times.

Some actions in Chinese cities are already "at scale," he said, such as Tianjin and Shanghai. "So we [the rest of the world] are learning from China."