Studies show that 25 of the world’s largest cities account for about half of the world’s total greenhouse gas emissions, 23 of which are in China

A new study of greenhouse gas emission trends shows that 25 of the world’s largest cities emit more than half of the greenhouse gases emitted by a sample of 167 cities worldwide. The vast majority of these 25 large cities are in China.

The study, published Monday (July 12) in the journal Frontiers in Sustainable Cities, compared the greenhouse gas emissions of 167 cities in 53 countries worldwide and found that 23 Chinese cities, including Shanghai, Beijing and Handan, plus Moscow and Tokyo, are among the top 25. The study found that 23 Chinese cities, including Shanghai, Beijing and Handan, together with Moscow and Tokyo, emit 52 percent of the total greenhouse gas emissions of the 167 cities.

Other cities included in the study were from China, India, the United States and the European Union, which were selected because of their relatively large greenhouse gas emissions and are often the subject of climate change debates.

Still, when calculated on a per capita basis, emissions from cities in the world’s richest countries are generally higher than those from cities in developing countries.

Chen Shaoqing, co-author of the study and an environmental scientist at Sun Yat-sen University in Guangzhou, China, said in an interview with Reuters that the study demonstrates the important role of cities in reducing emissions. “It’s simple and logical,” he noted. “If you don’t act, eventually you will suffer.”

Average global temperatures have already risen more than 1 degree Celsius compared to pre-industrial times and are set to rise beyond the 1.5-2 degree Celsius limit set by the Paris climate agreement.

Shaoqing Chen and other scientists point out that some of the data provided to them for their study was actually incomplete, with some cities providing data that was still collected in 2005. They argue that the lack of consistency in how cities report emissions also makes comparisons difficult.

“A 2018 report published in the journal Environmental Research Letters looked at a global sample of 1,300 cities, large and small, and found that 100 cities representing just 11 percent of the world’s population were responsible for 18 percent of global carbon emissions.

Karen Seto, co-author of the 2018 study and professor of geography and urban science at Yale University, told Reuters that the latest study “is relevant to the growing discussion and call for urban emissions and what we know about them.

Dan Hoornweg, a professor at Ontario University of Science and Technology, said in an interview with Reuters that “it’s hard to compare apples to apples on urban greenhouse gas emissions, but you have to try to do it, and this study does a very good job of that.

Shaoqing Chen of Sun Yat-sen University said this latest study is the first to look at emission reduction targets for mega-cities and the tension to reduce them.

Sixty-eight percent of cities – the vast majority in developed countries – have hard emissions reduction targets. But of the 42 cities tracked in the study, only 30 actually reduced their emissions. And most of those cities with actual emissions reductions were in the United States and Europe.

The study also confirms the scientists’ previous expectation that in China, cities with high per capita emissions are largely important manufacturing centers, while in developed countries, cities with high per capita emissions are largely cities with high levels of consumption.

Economies in places like more developed Europe can now grow their economies without increasing emissions, said Hornwag, a professor at Ontario University of Science and Technology. Yet the pace of global progress toward that goal is not uniform.

“These countries have emitted a lot of greenhouse gases before they got to where they are today; China is getting to that point (of significant emissions). We know India will get there sooner or later, and it will be Africa that will get there eventually and inevitably,” he said.