This study is led by Assoc. Prof. Yuli Shan (University of Birmingham / University of Groningen), Yuru Guan (PhD researcher, University of Groningen), Prof. Dabo Guan (Tsinghua University), Prof Klaus Hubacek (University of Groningen) and 5 other researchers. The study presents the most comprehensive and long-reaching time series (2001 to 2019) of CO2 emission inventories of 287 Chinese cities, covering 98%+ of China’s population, 99%+ of GDP, and 97%+ of CO2 emissions (compared to the national emissions from EDGAR) in 2014.
The emission inventories were compiled for 47 economic sectors and included energy-related emissions for 17 types of fossil fuels and process-related emissions from cement production. The inventories capture all direct emissions from human economic activities within the city boundary based on the administrative-territorial accounting approach recommended by the Intergovernmental Panel on Climate Change (IPCC). Dr Shan tells us “This accounting approach has been widely used for designing low-carbon policies and allocating responsibility for global climate change targets”. “It’s also worth mentioning that the emission factors of fossil fuels we used were collected from our previous studies, which are based on a wide survey of over 4,243 state-owned Chinese coal mines in China”, Dr Shan emphasizes.
Prof. Guan mentions that “this city-level emission estimates are consistent with our CEADs team’s previous accounting of national and provincial emissions in terms of methods, scope, and data sources. So, we are now able to compare emissions across scales”. Prof. Guan and Dr. Shan have established an open-access dataset called CEADs (Carbon Emission Accounts and Datasets for Emerging Economies) since 2016. CEADs team works on the emission accounting methods and applications for China and other emerging economies. Dr Shan is the subject leader in environmental accounting and Prof. Guan is the founder of CEADs.
Based on the long time-series city-level emission data, Dr Shan and his colleagues tested the status of the emissions peak in 287 Chinese cities based on several conditional functions, the Mann-Kendall (MK) trend test, and cities’ decoupling of emissions and social development indexes (e.g., level of economic development and size of the population). The MK trend test is a nonparametric statistical method recommended by the World Meteorological Organization (WMO) and has been widely used to detect time-series trends of climate sequences.
They found that 38 Chinese cities have proactively peaked their emissions (i.e., cities reduced emissions significantly for at least five years while economy and population kept increasing), 21 cities have passively declined their emissions (i.e., cities have achieved emission decline for more than five years but their economy or population also decreased during the same period), 20 cities are at a plateau phase (i.e., emissions declined for more than five years but might rebound to a higher level afterward), and the remaining 139 cities are still increasing their emissions or reduced emissions temporarily for less than five years. Looking into the emission drivers in each city, Dr Shan found that proactively peaked cities have achieved emission decline mainly due to efficiency improvements and structural changes in energy use, while passively emission declined cities have an economic recession or population loss as one possible reason for emission decline.
This study provides policy recommendations for achieving emission peaks and carbon neutrality in different types of cities. “It is not easy to reduce every ton of emissions”, Dr Shan says, “the reduction strategy cannot be designed with one-size-fits-all mitigation policies for all cities, but has to be individualized, considering cities’ resource endowment, industrialization level, socio-economic characteristics, and development goals.” Prof. Hubacek says that “emission peaked cities should provide successful models for other non-peaked cities. Super emitters with laggard technologies and production efficiency should have more stringent policies and targets for emission reduction, while less developed regions could have more emission space for economic development.”
This study also suggests that passively emission declined cities need to face up to the reasons that caused the emission to decline, and fully exploit the opportunities provided by industrial innovation and green investment brought by the low-carbon targets to achieve economic recovery and carbon mitigation goals. The proactively peaked cities need to seek strategies to maintain the downward trend in emissions and avoid an emission rebound.