Physical and virtual carbon metabolism of global cities

• Published in: Nature communications Vol. 11; no. 1; pp. 182 - 11
• Main Authors: Chen, Shaoqing, Chen, Bin, Feng, Kuishuang, Liu, Zhu, Fromer, Neil, Tan, Xianchun, Alsaedi, Ahmed, Hayat, Tasawar, Weisz, Helga, Schellnhuber, Hans Joachim, Hubacek, Klaus
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 10-01-2020; Nature Publishing Group; Nature Portfolio
• Subjects: 704/844/2175; 704/844/4066; Carbon; Carbon dioxide; Cities; Emissions; Environmental impact; Fluxes; Fossil fuels; Household goods; Humanities and Social Sciences; Inflow; Metabolism; multidisciplinary; Outflow; Outsourcing; Science; Science (multidisciplinary); Supply chains; Urban areas; Urban metabolism
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-13757-3

Urban activities have profound and lasting effects on the global carbon balance. Here we develop a consistent metabolic approach that combines two complementary carbon accounts, the physical carbon balance and the fossil fuel-derived gaseous carbon footprint, to track carbon coming into, being added to urban stocks, and eventually leaving the city. We find that over 88% of the physical carbon in 16 global cities is imported from outside their urban boundaries, and this outsourcing of carbon is notably amplified by virtual emissions from upstream activities that contribute 33–68% to their total carbon inflows. While 13–33% of the carbon appropriated by cities is immediately combusted and released as CO
2
, between 8 and 24% is stored in durable household goods or becomes part of other urban stocks. Inventorying carbon consumed and stored for urban metabolism should be given more credit for the role it can play in stabilizing future global climate.
Activities in cities are important drivers of global carbon fluxes. Here the authors trace the carbon metabolism in 16 global cities in terms of both physical and virtual carbon inflows, stock changes and outflows in relation to the supply chains of urban production and consumption and show that the total carbon impacts of global cities are found to be highly varied in either per capita, intensity or density measures.