Impact of Compact City on Carbon Emission Reduction Based on Urban Size: A Spatial Analysis Using Satellite Imagery

Cities contribute significantly to global carbon emissions, making sustainable development through efficient spatial planning essential for achieving carbon neutrality. Compact cities are crucial for urban planning because of concerns regarding the impact of dispersed development on society and the environment. However, researchers hold differing opinions, and debates continue. As cities expand, they develop different influences, underscoring the need to consider regional characteristics rather than rely on a single assessment framework. Understanding the interaction between urban size and spatial structure is vital because the relationship between compact city elements and carbon emissions is complex. This study aimed to clarify the carbon emission reduction effects of compact cities by considering their urban size and analyzing cities in the United States and South Korea. For example, although the compactness in larger cities may reduce emissions, the opposite effect may occur in smaller cities. Using satellite imagery, this study not only measured carbon emissions and three compact city characteristics but also conducted a panel threshold regression analysis to assess how these elements influenced emissions across various urban sizes. The results indicated that the impact of compact city characteristics on emissions varied with urban size, highlighting the significant interaction between urban size and spatial structure. For example, the analysis confirmed that reducing per capita VKT is essential despite environmental regulations and technological advancements. In small cities, greater compactness tends to increase carbon emissions, but beyond a certain size it contributes to their reduction. Likewise, while polycentricity increase emissions in smaller cities, it helps lower them as the city grows. This underscores the importance of understanding emission trends in relation to urban size and structure, while advocating for tailored spatial planning and strategic approaches rather than uniform policies.