Global urban low-carbon transitions: Multiscale relationship between urban land and carbon emissions

Recent decades have witnessed rapid global urban land (UL) expansion, which has caused severe ecological and environmental issues. As major contributors to carbon emissions (CEs), urban areas play a key role in global warming, and therefore, the conflict between UL expansion and CE reduction must be resolved. Identifying the coupling and decoupling relationships between UL and CEs is important for the coordinated development of global UL and CE reduction and urban low-carbon transitions. However, few studies have explored this aspect, resulting in a lack of identification of the coupling mechanism between global UL and CEs. To compensate for this, we conducted spatiotemporal coupling coordination and decoupling analysis of global multiscale UL and CEs with global annual UL and CE data from 2000 to 2019. The results showed global CEs increased markedly from 6.275 billion tonnes in 2000 to 9.293 billion tonnes in 2019. The growth rate of China's CEs slowed considerably, indicating that China has contributed greatly to the global reduction of CEs in recent decades. Global UL expansion was considerable and increased from 5.173 x 105 km2 in 2000 to 9.635 x 105 km2 in 2019, representing an increase of 86.256%. A significant spatial dependence was observed between global UL and CEs, and the low-low type was the dominant relationship. During the study period, the gravity centers of the global UL and CEs moved east, and the overall distance between them increased. Areas with substantial coupling coordination were distributed mainly in high-value areas of CEs and UL. Global UL and CEs exhibited a trend of decoupling and varied considerably at different scales. The results indicate a decarbonization trend in the expansion of global UL, especially in developing regions. These findings can provide a scientific reference for rational UL planning and urban low-carbon transitions.