25 Cities Produce More Than Half of World's Urban Greenhouse Gas Emissions

The world’s cities are responsible for more than 70% of the world’s greenhouse gas emissions and therefore have a major role to play in fighting the climate crisis, but how much progress are they actually making? 

To answer that question, a team of Chinese researchers conducted the first sector-level analysis of greenhouse gas emissions for 167 major cities around the world and then tracked their progress at reducing those emissions so far, as well as their future targets. The results, published in Frontiers in Sustainable Cities this summer, show the world’s urban areas still have a lot to do to meet the goals of the Paris agreement. 

“Many cities do not have clear and consistent emission reduction targets to address climate change, and some of them are still increasing their emission during economic development,” study co-author and associate professor at Sun Yat-sen University Dr. Shaoqing Chen tells Treehugger in an email. 

167 Megacities

The researchers looked at 167 cities from 53 different countries around the world, selected based on global coverage and representativeness, as well as data availability. They used emissions data from C40 Cities and the CDP (Carbon Disclosure Project) in order to complete their analysis. 

What they found was that the top 25 emitting cities were responsible for 52% of total emissions. These were largely megacities in Asia like Shanghai, Beijing, and Tokyo. However, Moscow and New York City also made the list. 

The researchers also looked at per capita emissions and found that cities in Europe, the U.S., and Australia generally had higher emissions in this category than cities in the developing world. One notable exception to this was China, where three of the top five cities for per capita emissions are located. The study authors attribute this to the Chinese cities’ rapid development, their reliance on coal, and the structure of the global economy. 

“‘[M]any high-carbon production chains were outsourced from developed nations to Chinese cities, thus increasing the export-related emission of the latter,” the study authors write.

Overall, the leading source of emissions for the cities in the study was something the study authors called “stationary energy,” meaning emissions from fuel combustion and electricity use in residential, commercial, and industrial buildings. This represented more than 50% of emissions for more than 80% of 109 cities. Another important factor was transportation, which represented more than 30% of emissions for about a third of the cities analyzed. 

However, Chen tells Treehugger that there were important variations by country. In the U.S., for example, building emissions and transportation were both important factors, while manufacturing played an important role in many Chinese cities. 

Progress Made? 

The study also tracked the progress that cities had made in reducing emissions and the ambition of their future goals. Ultimately, the cities’ ambitions were stacked against the Paris agreement goal of limiting global warming to well below two degrees Celsius above pre-industrial levels and ideally 2.7 degrees Fahrenheit (1.5 degrees Celsius).

“Although current global cities have made great progress in reducing their GHG emissions, current mitigation measures are generally insufficient to [] realize the reductions in emissions that [are] consistent with the Paris Agreement,” Chen says. 

He adds that only 60% of the cities in the study had emission reduction targets with clear benchmarks, which he argues is “insufficient.” Of the 167 cities in the study, only 42 had enough data for the researchers to assess how their emissions had changed over two years.

Of those cities, a total of 30 did manage to reduce their emissions between 2012 and 2016, according to a Frontiers press release, with Oslo, Houston, Seattle, and Bogotá seeing the greatest reduction in per capita emissions. Chen noted these cities had greatly improved their energy systems and carbon trading mechanisms. However, he noted that many of the cities that managed to reduce their emissions were located in developed countries. 

“[I]t should be cautioned that many high-carbon production chains were outsourced from developed nations to cities in developing nations (such as China and India), thus increasing the export-related emission of the latter,” he notes.

On the other side, several cities saw an increase in emissions, with Rio de Janeiro, Curitiba, Johannesburg, and Venice taking the lead. These were cities that relied on emission-intensive industries like chemical manufacturing, steel, or mining and had high-emission ground transportation, Chen says. 

Urban Futures

Chen offered three recommendations for what cities could do to reduce their emissions in line with Paris agreement:

1. Identify and target the highest emitting sectors.
2. Create a consistent methodology for tracking emissions in a timely manner, which can be used to assess progress worldwide.
3. Set more ambitious and trackable emissions reduction goals.

Several of the cities highlighted in the report have already been working to reduce their emissions under the banner of C40 Cities, whose publicly available data the study used. 

“C40 was founded to connect cities around the world to facilitate knowledge and data sharing that helps accelerate climate action in line with the goals of the Paris Agreement and ultimately create a healthier, more resilient future,” spokesperson Josh Harris tells Treehugger. 

That coalition currently includes nearly 100 of the world’s largest cities, representing more than 700 million people. Member cities have pledged to take actions such as increasing urban green space, using zero-emission buses beginning in 2025, making sure all new buildings emit net-zero carbon by 2025 and all buildings period do the same by 2030, and divesting city assets from fossil fuel companies. 

However, of the 25 highest-emitting cities cited in the study, 16 of them are members of C40. 

Harris noted many C40 member cities are highly populated commercial hubs that are naturally resource-intensive. Further, current emissions are not necessarily a prediction of the future. A 2020 analysis found that 54 world cities are on track to do their fair share of limiting temperature rise to 1.5 degrees. However, that doesn’t mean the cities couldn’t do more, but they aren’t the only polities that need to step up to the plate.

“We recognize that all cities and communities—both those in the C40 network and beyond—must do more to address the climate crisis, but they cannot do it alone,” Harris tells Treehugger. “Cities need more support from their national governments, who can provide the necessary funding, technical assistance, policies, and data collection needed to mitigate pollution and build resilience to withstand climate change impacts.”