Just 25 cities globally are responsible for 52 percent of urban greenhouse gas emissions, according to a new study that highlights the role that cities must play in reaching the goals of the 2015 Paris Climate Agreement.
For the study, researchers gathered data on greenhouse gas emissions in 167 cities in 53 countries. They found that megacities in Asia, such as Shanghai and Tokyo, ranked among the biggest total emitters, while major cities in Europe, the United States and Australia tended to have larger per capita emissions. In several major Chinese cities, however, per capita emissions matched levels seen in developed countries. The findings were published in the journal Frontiers in Sustainable Cities.
Power generation, industry and transportation were the biggest sources of emissions. In one third of the cities, road transportation accounted for more than 30 percent of emissions. Railways, waterways and aviation, by contrast, accounted for less than 15 percent of total emissions.
Researchers were able to track changes in emissions over time in 42 cities. Of these, 30 saw pollution levels decline between 2005 and 2016, with Oslo, Houston, Seattle and Bogotá experiencing the biggest drops. Emissions grew in the remaining 12 cities, with Rio de Janeiro, Johannesburg and Venice having the biggest increases.
Of the 167 cities included in the study, 113 have set emission-reduction targets, but the findings support the conclusion of many other studies, which show that cities have to do considerably more work to meet the aims of the Paris Agreement.
“More than 50 percent of the global population resides in cities. Cities are … responsible for more than 70 percent of [greenhouse gas] emissions, and they share a big responsibility for the decarbonization of the global economy,” said Shaoqing Chen, associate professor of urban environmental management at Sun Yat-sen University in China and co-author of the study. “Cities should set more ambitious and easily traceable mitigation goals.”