<p>Urban agglomeration is critical for regional carbon peaking. In China, regionally coordinated development based on urban agglomerations has been proposed as a pivotal national strategy. This study focuses on the carbon peaking of Chengdu-Chongqing Economic Circle (CCEC), the “fourth pole” of China’s economic development. Considering the coexistence of administrative division and regional integration of government-planned urban agglomerations in China, this paper simulates the carbon emissions of CCEC with both top-down and bottom-up approaches to predict the possibility to peak emissions by 2030. The former approach evaluates CCEC’s socioeconomic development at the aggregate level, whereas the latter accounts for inter-city heterogeneity in developmental patterns. The results reveal a notable divergence between the two approaches: the top-down method suggests a 13.35%-46.67% probability for CCEC to peak emissions by 2030, whereas the bottom-up approach yields a significantly higher probability of 84.59%-99.56%. The significant divergence underscores how the level of spatial aggregation affects uncertainty propagation and reveals the inherent spatial heterogeneity of this non-linear system. Policymakers should thus prioritize adaptive governance and robust uncertainty management to establish a dynamic and synergistic emissions reduction mechanism that integrates top-down policy and bottom-up strategies.</p>