High carbon density persists in shrinking industrial cities without integrated population–socioeconomy–land governance: evidence from Siping City, Northeast China

As key pillars of China’s national economy, old industrial cities exhibit significantly higher carbon emission intensity than the national urban average. A progressive research framework was established, with Siping City, a typical old industrial city in Northeast China, as the case study to analyze the coupling coordination between three urban development subsystems (population, socioeconomy, and land use) and carbon emissions. The findings revealed: (1) The coupling coordination between population, socioeconomy, and land use subsystems and carbon emissions remained relatively weak, with each subsystem retaining the potential for further emission reduction. (2) Carbon emissions were primarily driven by carbon efficiency, land economic efficiency, and intensive land use. Although the population declined since 2011 and exerted a certain inhibitory effect on emissions, its strength remained insufficient to offset the influence of these dominant drivers. (3) Given the relatively weak direct impact of the population subsystem on carbon emissions, its influence could be transmitted through the land use subsystem to the socioeconomic subsystem, thereby indirectly affecting emissions. (4) Economic indicators such as the number of employees (NEP), along with the land use metric, perimeter-area fractal dimension (PAFRAC), exhibited significant lagged effects on carbon emissions, indicating a close link between current environmental pressure and historical economic development patterns. Accordingly, when formulating emission reduction policies, a forward-looking, multi-system collaborative governance framework integrating population, socioeconomy, and land use dimensions should be established. Strengthening coupling coordination among these systems will support the dual goals of green and low-carbon transformation and sustainable development in old industrial cities.