Urban carbon footprint accounting and implications for carbon neutrality from a life cycle perspective: a case study of Shenzhen

Cities take up only 3% of the Earth’s land surface but consume 67%-76% of global energy, emit 75% of total carbon．As a vital battleground to control carbon emission, cities have undertaken a leading role in carbon neutrality strategy．Cities consume lots of final products and services derived from outside the city during urban expansion and development．In the open urban economic system, spatial mismatch between production and consumption of final products and services results in carbon emissions embodied in the trade flowing into producing regions．However, current urban carbon governance policies are primarily formulated from a traditional production-based perspective, ignoring transboundary carbon emissions driven by final demand in the cities．The resulting carbon leakages can easily cause unequal distribution of urban and regional carbon emission reduction responsibilities．Building a systematic urban carbon accounting method is urgently needed for national carbon neutral strategy．Therefore, we constructed urban carbon footprint accounting framework and methodology from a life cycle perspective．This system was used to account for and track carbon footprint in open urban “natural-economic-social complex ecosystem”, taking into account of both direct geographical carbon emissions and indirect transboundary carbon emissions．We selected Shenzhen in a case study．Data show total carbon footprints of 6545.01×10⁴ tons of CO_2e in Shenzhen in 2015．The direct carbon emissions (Scope 1) caused by energy and non-energy activities by main industrial sectors and residential consumption were 3282.38×10⁴ tons of CO_2e, accounting for 50% of total carbon footprint, of which industrial energy sector accounted for 29.2% of the total．Indirect carbon emissions (Scope 2) caused by purchased electricity consumption accounted for 19% of the total footprint．Indirect carbon emissions (Scope 3) embodied in transboundary transportation (5.27%), upstream supply chain of critical materials (22.01%) and downstream chain of waste disposal (3.72%) accounted for 31%．These data indicate that Shenzhen's indirect carbon emissions in 2015 were comparable to direct emissions．These results will provide policy suggestions and management implications for cities to clarify their carbon emission status and respond to carbon neutralization strategy．