在当今的发展趋势下，城市日益成为人口、交通和商业活动的中心，需要消耗大量能源来维持经济社会发展和日常运转，世界上大约三分之二的能源在城市消耗，所释放的二氧化碳占全球碳排放的70%以上。同时，随着城镇化进程的不断推进，城市逐渐向群体化发展，城市群成为经济社会发展和生态文明建设的重要空间载体，因此，城市群是制定与实施政策减少碳排放的重要主体。长三角城市群是我国经济总量最大、经济活力最强的城市群，对我国国内生产总值的贡献超过总量的五分之一，同时也是我国碳排放量最大的城市群。党的二十大报告指出，推进“碳达峰、碳中和”是实现可持续发展、推动经济结构转型升级、促进人与自然和谐共生、推动构建人类命运共同体的迫切需要。如何平衡好经济发展和绿色减排的关系，在不减少城市群生产能力的前提下减少碳排放，是长三角城市群发展面临的重要课题。
测度二氧化碳排放情况是各级行政区域确立政策减少碳排放的基础。本文对2017年长三角城市群26个城市化石燃料燃烧和工业过程中的直接二氧化碳排放量进行了核算，并使用Ghosh投入产出模型核算各城市基于收入的二氧化碳排放量。在此基础上，对长三角城市群生产角度、消费角度以及收入角度的碳排放进行了对比，分析不同核算角度下各城市及部门的排放情况。
对核算结果进行分析，从碳排放总量来看，不同角度下各城市碳排放情况有很大差别，各城市在基于生产与基于收入的碳排放量平均相差26.6%，而基于消费与基于收入的碳排放量平均相差35.5%。从碳乘数来看，大部分城市的前向碳乘数都小于后向碳乘数，表明长三角城市群的产业整体处于相对下游的位置，在供应链当中对上游产业碳排放的拉动作用大于对下游产业碳排放的推动作用。关于碳排放的关键城市，马鞍山和铜陵不仅对下游产业的碳排放有很大的推动作用，也极大拉动了上游产业的碳排放；而上海市虽然碳排放量很高，但其每单位最终需求和增加值引致的碳排放量较小，高碳排放量来自其较大的经济体量。关于碳排放的重点部门，除了通常被认为是高碳排放产业的制造业和电力、热力、燃气、水的生产和供应部门外，第三产业虽然直接碳排放量较少，但在收入角度下，其对其它部门的资金等生产要素的投入也导致了大量的碳排放；与之相似的还有建筑业，虽然在生产角度下碳排放量较低，但在消费角度下，建筑行业中的产品需求对上游的碳排放有极大的拉动作用。
在本文的研究当中，三种核算角度下各城市有不尽相同的碳排放情况，并且能够分别识别出不同的重点排放部门，因此仅从一个角度出发得到的信息是片面的，需要从不同角度进行分析才能对整体有较为全面的了解。基于本文得到的结论，给出全面了解区域碳排放情况，加强宏观统筹；关注碳排放重点城市，加快产业体系转型；多角度识别碳排放重点部门，确立完整减排路径的减排建议。

Under today's development trend, cities are increasingly becoming centers of population, transportation and commercial activities, and need to consume a large amount of energy to maintain economic development and daily operation. About two-thirds of the world's energy is consumed in cities, which release more than 70% of global carbon emissions. At the same time, with the continuous promotion of urbanization, cities gradually develop into groups in economic and social activities, and urban agglomerations become important spatial carriers for economic development and ecological civilization construction, therefore, urban agglomerations are important subjects for formulating and implementing policies to reduce carbon emissions. The Yangtze River Delta urban agglomeration is the city cluster with the largest economic volume and the strongest economic vitality in China, contributing more than one-fifth of the total GDP of China, and also the urban agglomeration with the largest carbon emission in China. The report of the 20th Party Congress pointed out that promoting "double carbon" is an urgent need to achieve sustainable development, promote the transformation and upgrading of economic structure, promote the harmonious coexistence of human beings and nature, and promote the building of a community of human destiny. how to balance the relationship between economic development and emission reduction, and reduce carbon emission without reducing the production capacity of the urban agglomeration is an important issue facing the development of the Yangtze River Delta urban agglomeration.
Measurement of carbon dioxide emissions is the basis for establishing policies to reduce carbon emissions in administrative regions at all levels. This paper accounts for direct CO2 emissions from fossil fuel combustion and industrial processes in 26 cities in the Yangtze River Delta urban agglomeration in 2017, and uses the Ghosh Input-Output model to account for the income-based CO2 emissions of each city. On top of that, carbon emissions from the production perspective, consumption perspective and income perspective of the Yangtze River Delta urban agglomeration were compared to analyze the emissions of each city and sector under different perspectives.
The accounting results were analyzed, and from the perspective of total carbon emissions, the carbon emissions of each city under different perspectives differed greatly, with an average difference of 26.6% between production-based and income-based carbon emissions of each city, and an average difference of 35.5% between consumption-based and income-based carbon emissions. In terms of carbon multipliers, the forward carbon multipliers of most cities are smaller than the backward carbon multipliers, indicating that the industries in the Yangtze River Delta urban agglomeration is in a relatively downstream position, and the pulling effect on carbon emissions of upstream industries in the supply chain is greater than the driving effect on carbon emissions of downstream industries. As for the key cities of carbon emissions, Maanshan and Tongling not only have a strong contribution to the carbon emissions of downstream industries, but also greatly contribute to the carbon emissions of upstream industries; while Shanghai has high carbon emissions, its carbon emissions per unit of final demand and value added are smaller, and the high carbon emissions come from its large economic volume. Regarding the key sectors of carbon emissions, in addition to the manufacturing industry and the production and supply of electricity, heat, gas, and water, which are usually considered as high carbon emission industries, the tertiary industry, although it has less direct carbon emissions, its input of production factors such as capital to other sectors also leads to a large amount of carbon emissions under the income perspective, and similarly, the construction industry, although it has low carbon emissions under the production perspective, has high carbon emissions under the production perspective. The demand for products in the construction industry has a great pulling effect on the upstream carbon emission from the consumption perspective.
In this paper, each city has different carbon emissions under the three accounting perspectives, and different key emission sectors can be identified separately, so the information obtained from only one perspective is one-sided and needs to be analyzed from different perspectives to have a more comprehensive understanding of the whole. Based on the conclusions obtained in this paper, we give suggestions to comprehensively understand the regional carbon emission situation and strengthen macro coordination; focus on key cities with carbon emission and accelerate the transformation of industrial system; identify key sectors with carbon emission from multiple perspectives and establish a complete emission reduction path.