Economic agglomeration and emissions reduction: Does high agglomeration in China's urban clusters lead to higher carbon intensity?

Urban clusters are areas that feature both high degrees of economic agglomeration and relatively serious pollution challenges; however, there is no unified conclusion regarding whether economic agglomeration is correlated with the increase of carbon emissions. In this study, we investigate the nonlinear impact of economic agglomeration on carbon intensity in urban clusters at different development stages using spatial econometric modeling. The urban clusters of Beijing–Tianjin–Hebei, the Yangtze River Delta, the Pearl River Delta, Chengdu–Chongqing, the Middle Reaches of the Yangtze River, and the Central Plains are selected as the research objects for this investigation. The development of urban clusters is categorized into primary, middle, late, and developed stages according to per capita GDP level and the proportion of the three major industries. The results indicate that economic agglomeration and carbon intensity in the six urban clusters are highly consistent from 2005 to 2019. In the primary development stage, economic agglomeration follows an inverted U-shaped pattern in relation to carbon intensity in Beijing–Tianjin–Hebei, Middle Reaches of the Yangtze Riverand Chengdu–Chongqing, indicating that advancement of economic agglomeration reduces carbon intensity. In the late development stage, the effect of economic agglomeration on carbon intensity has a U-shaped pattern in Yangtze River and Pearl River Delta. The problems of diseconomies of scale caused by excessive economic agglomeration lead to an increase in regional carbon intensity. Findings can provide a reference for urban clusters in other developing countries to formulate reasonable and effective policies in the process of agglomeration.