A quantitative synthesis of heterogeneous impacts of urban spatial structure on carbon emissions

Reducing carbon emissions has emerged as a prominent concern in sustainable urban development, driven by growing interest in the impact of urban spatial structure on carbon emissions. Existing empirical evidence showed substantial heterogeneity in various studies, posing challenges toward systematically understanding the mechanisms. This study aims to analyze the complex interactions between urban spatial structure and carbon emission and unveil heterogeneity of conflicting effects across demographic and spatial contexts. This study employs meta-analysis to synthesize and quantitatively examine the effects of various urban spatial structure factors – including land use, density, and landscape pattern – on carbon emissions, based on 35 relevant published studies. The impact of land use diversity on carbon emission was the largest, followed by area, building and road density, industrial and commercial areas, and green areas – land use mitigation strategies are more successful than carbon absorption. Additionally, we reveal the heterogeneous effects of urban spatial structure depending on the population size, land area, and spatial scale through subgroup analysis and meta-regression. The increase in built-up areas and single-use areas was related to the overall increase in carbon emissions only at the municipal level, whereas large green spaces and aggregation were negatively related to carbon emissions at the regional level. As population and land size increase, land use diversity has a larger mitigating effect, but fragmented and irregular landscapes tend to elevate carbon emissions. This study offers insights and implications for developing more sustainable low-carbon strategies and urban planning.