According to research from China, 25 mega-cities are responsible for more than half of the world's urban greenhouse gas emissions. Cities in China, as well as in Japan and Russia, are notably singled out in the study.
Global greenhouse gas emissions are largely being driven by a small fraction of cities, according to a new study by researchers from China's Sun Yat-sen University and the Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology in Guangzhou. The research reveals that, among 167 cities studied, more than 50% of urban greenhouse gas emissions are emitted by 25 very large cities. Among these are 23 Chinese cities -- including Shanghai, Beijing and Handan -- as well as Tokyo and Moscow.
The researchers set out to investigate the effectiveness of the greenhouse gas emission reduction policies in place in cities around the world. To do this, they looked at 167 cities or metropolitan areas in 53 countries, at different developmental stages, and with various policies and targets.
"We found that, although Asian cities are the biggest carbon emitters in totals, the per capita GHG emissions of cities in developed countries are still generally higher than that in developing countries," write the researchers.
Out of the 167 cities studied, 30 managed to reduce greenhouse gas emissions between 2012 and 2016, led by Oslo, Houston, Seattle and Bogotá. Conversely, the Brazilian cities of Rio and Curitiba, as well as Johannesburg and Venice, saw sharp increases in emissions.
Towards "more ambitious" targets?
Buildings and transportation were identified as the two main sources of emissions. And, in one third of the cities, more than 30% of emissions come from road transport. In fact, on-road transportation was found to account for 44% to 42% of total greenhouse gas emissions in Bangkok and Seoul, respectively, the study cites as an example.
To reduce these sources of pollution, the researchers suggest encouraging the purchase or use of green vehicles through subsidies or incentives for users: "People [who] travel [by] bicycle and public transportation should be encouraged through incentive economic measures (e.g., a carbon currency system that rewards low-carbon transport choices)."
The researchers also suggest greater transparency in the publication of data and "more ambitious" targets from cities to achieve common goals for reducing global greenhouse gas emissions.