Departamento de Física, Universidade Federal do Ceará, 60451-970 Fortaleza, Ceará, Brazil.
1] Departamento de Física, Universidade Federal do Ceará, 60451-970 Fortaleza, Ceará, Brazil [2] Levich Institute and Physics Department, City College of New York, New York, New York 10031, USA.
Sci Rep. 2014 Feb 28;4:4235. doi: 10.1038/srep04235.
We study how urban quality evolves as a result of carbon dioxide emissions as urban agglomerations grow. We employ a bottom-up approach combining two unprecedented microscopic data on population and carbon dioxide emissions in the continental US. We first aggregate settlements that are close to each other into cities using the City Clustering Algorithm (CCA) defining cities beyond the administrative boundaries. Then, we use data on CO2 emissions at a fine geographic scale to determine the total emissions of each city. We find a superlinear scaling behavior, expressed by a power-law, between CO2 emissions and city population with average allometric exponent β = 1.46 across all cities in the US. This result suggests that the high productivity of large cities is done at the expense of a proportionally larger amount of emissions compared to small cities. Furthermore, our results are substantially different from those obtained by the standard administrative definition of cities, i.e. Metropolitan Statistical Area (MSA). Specifically, MSAs display isometric scaling emissions and we argue that this discrepancy is due to the overestimation of MSA areas. The results suggest that allometric studies based on administrative boundaries to define cities may suffer from endogeneity bias.
我们研究了随着城市群的发展，二氧化碳排放如何导致城市质量的演变。我们采用了一种自下而上的方法，结合了美国大陆上关于人口和二氧化碳排放的两项前所未有的微观数据。我们首先使用城市聚类算法（CCA）将彼此靠近的定居点聚集在一起，定义了超越行政边界的城市。然后，我们使用精细地理尺度上的 CO2 排放数据来确定每个城市的总排放量。我们发现 CO2 排放与城市人口之间存在超线性缩放关系，用幂律表示，美国所有城市的平均比例指数β=1.46。这一结果表明，与小城市相比，大城市的高生产力是以排放比例更大为代价的。此外，我们的结果与城市的标准行政定义（即大都市统计区（MSA））得出的结果有很大的不同。具体来说，MSA 显示等距缩放排放，我们认为这种差异是由于对 MSA 区域的高估。研究结果表明，基于行政边界定义城市的比例研究可能存在内生性偏差。
