The study was conducted by China’s Sun Yat-sen University and the Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology in Guangzhou.

It said among 167 cities studied, more than 50% of urban GHG emissions are attributable to 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 GHG-reduction policies in cities around the world. 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 total, the per-capita GHG emissions of cities in developed countries is still generally higher than that in developing countries,” the researchers wrote.

Out of the cities studied, 30 managed to reduce GHG emissions between 2012 and 2016, led by Oslo, Houston, Seattle and Bogota.

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.

On-road transportation was found to account for 42% to 44% of total GHG emissions in Seoul and Bangkok, respectively, the study cited as an example.

To reduce these sources of pollution, the researchers suggested encouraging the purchase or use of green vehicles through subsidies or incentives for users.

They also called for greater transparency in the publication of data, and “more ambitious” targets from cities to achieve common goals for reducing global GHG emissions.