生命周期视角下城市碳足迹核算及实现碳中和的路径建议

基于生命周期视角构建了城市碳足迹核算框架及方法学模型，系统地核算及追溯了碳排放在开放的城市“自然-经济-社会复合生态系统”中的足迹，主要涵盖城市地域边界内的直接生产碳排放以及跨境间接碳排放（主要包括城市所需的关键支撑物质、排放的主要废弃物，以及跨境交通分别在上游、下游产生的间接碳排放），并选取深圳市作为案例进行分析．结果表明，2015年深圳市碳足迹总量为6566.19万t CO_2e，具体为:1）城市内主要产业部门及居民消费的能源活动及非能源活动引起的直接碳排放量（Scope 1）为3282.38万t CO_2e，占深圳市碳足迹总量的49.99%，其中工业能源部门占比最大，为36.95%；2）城市外调电力消费引起的间接碳排放（Scope 2）占城市碳足迹总量的18.89%；3）跨境运输、关键支撑物质的上游产业链以及废弃物在下游处理过程中隐含的间接碳排放（Scope 3）占城市碳足迹总量的31.12%，其中5.37%来自跨境交通，22.26%来自主要物质上游供应链，3.49%来自下游废弃物处理．由此可知，2015年深圳市在城市上下游跨边界的间接碳排放量与城市内部的直接排放量相当，不容忽视．研究结果可为厘清城市自身碳排放现状及应对碳中和战略提供政策建议及管理启示． 

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．