Academician Li Qingquan and Assistant Professor Yang Chao from Shenzhen University (SZU) have recently published a research paper titledRoof greening in major Chinese cities possibly afford a large potential carbon sinkinScience Bulletin. Co-hosted by the Chinese Academy of Sciences and the National Natural Science Foundation of China, and published byScience China Press,Science Bulletinis a comprehensive academic publication in the natural sciences. With the latest impact factor of 18.8, it is classified as a Tier-1 journal by the Chinese Academy of Sciences' journal ranking system.
China is currently the world's largest carbon dioxide emitter. Approximately 85% of its emissions come from urban areas, especially large cities. Reducing carbon emissions without compromising economic growth presents a significant challenge. Studies have shown that large-scale greening initiatives, such as afforestation and urban landscaping, can act as carbon sinks to offset some of these emissions. However, much of China's fertile land, particularly in suburban areas, is already dedicated to agriculture and natural vegetation, making it rather difficult to establish new carbon sinks. Additionally, greening deserts presents both technical challenges and high costs, and it could put pressure on groundwater resources. With limited vacant space in cities, large-scale urban greening is not feasible. Fortunately, China's rapid urbanization has created abundant rooftop space, which could be a valuable resource for addressing our carbon sink needs. Rooftop greening offers a practical solution that reduces the need for investment in scarce urban areas, conserves land, and increases green space, all of which contribute to combating climate change.
The research team utilized extensive Earth observation data from 2020 and analyzed scenarios involving grass and shrubs to explore the potential of rooftop greening under optimal conditions. They assumed that, with the best technology, management practices, and investment, rooftop greening could achieve carbon sequestration levels comparable to those of natural grasslands and shrubs. The study examined all large cities in China, including 102 cities with urban populations exceeding one million people, to evaluate the potential carbon sink that rooftop greening could provide and its contribution to carbon neutrality, specifically the proportion of urban carbon emissions that could be offset.
The research shows that rooftop greening in China's major cities could offer significant carbon sink potential. Planting grass on rooftops could capture approximately 52.2 Tg of carbon per year while planting shrubs could sequester around 41.0 Tg of carbon annually. Together, these measures could offset roughly 2.4% to 3.0% of the carbon emissions from these cities, which is comparable to the emissions produced by households. Additionally, rooftop greening could yield substantial carbon tax benefits, estimated at USD 19.6 billion to USD 24.9 billion per year. It also has the potential to improve urban heat management and reduce energy consumption by decreasing the need for air conditioning and heating. Focusing on greening the rooftops of low-rise and mid-rise buildings could achieve over 90% of the total carbon sink potential. These insights are valuable for advancing China's goals of carbon neutrality.
Figure 1: Diagram of carbon sink estimation for rooftop greening and its potential carbon sink capacity in 102 major Chinese cities
Assistant Professor Yang Chao from the School of Architecture & Urban Planning at SZU is the first author of the research, with Academician Li Qingquan serving as the corresponding author. Other key contributors include Professor Chen Min from Nanjing Normal University, Professor Tang Bohui from Kunming University of Science and Technology, Dr. Zhang Zhixin from Nanjing University, and Professors Tu Wei, Zhang Dejin, and Huang Zhengdong from Shenzhen University.
You can read the full paper by clicking the link below:https://www.sciencedirect.com/science/article/pii/S2095927324006017
