## 4 Discussion
### Comparative Analysis of Results
The land use of green space is mainly dominated by forests and grasslands, which have long growth cycles, and therefore management is a long-term process [41]. If not taken seriously, huge areas of ecological space can, in turn, become a source of carbon emissions and a barrier to climate mitigation [42]. Compared to the existing literature, this paper not only examined the relationship between climate factor and NPP using traditional modeling methods (e.g., OLS) but also examined its spatial spillover effects using spatial measurement methods and the results of a spatial panel Durbin model of carbon sink with a spatiotemporal effect. Results showed that precipitation had little effect on carbon sinks in ecological spaces in urban clusters; however, many large-scale studies only consider precipitation factors [43; 44], which provides limited information on carbon balance and sinks in small regions [45]. The spatial spillover effects of annual average temperature, evaporation, and relative humidity were significant, positively impacting carbon sequestration in local areas but limiting others. One possible reason for these results could be higher temperatures that  
Figure 5: Beijing–Tianjin Wind and Sand Source Control Project. cause water to evaporate faster [46], thus increasing relative humidity. In general, climate factors have a consistent impact on carbon sequestration in ecological spaces at different spatial scales [47]. More than rainfall, evapotranspiration and relative humidity at the scale of urban agglomerations can reflect the combined effects of both temperature and the water environment [48]. Sunshine duration also played an important role in carbon sequestration in the B-T-H ecosystem, but the direction of effects varied with the scale. For instance, the annual average sunshine duration and ground temperature showed a negative impact on local-scale carbon sequestration; the same variables increased carbon sequestration in neighboring areas. The scale-dependent effect of sunshine on carbon sequestration is likely due to changes in cloud cover resulting from the interaction between sunshine duration and atmospheric conditions [49], such as an increase in relative humidity that leads to more cloud cover, reducing sunshine duration. Therefore, sunshine duration and relative humidity have contrasting effects on the NPP across ecological spaces. Ground temperature generally affects the carbon sequestration capacity of ecological spaces by influencing vegetation growth. High temperatures inhibit vegetation growth, but the direction of their effect is the opposite [50]. The mechanism of the transition between atmospheric and ground temperatures and its effect on NPP needs further study. Annual average wind speed had a negative impact on NPP on both the local and regional scales. These findings may be related to the changes in carbon dioxide concentration in the atmosphere caused by higher wind speed as shown in previous studies [51]. As the influence mechanism of carbon sinks is an integrated and complex system, with climate, CO\({}_{2}\) concentration, and nitrogen deposition interacting with each other, the role of other driving factors cannot be completely excluded. Therefore, the limitations in factor selection and data acquisition made the explanatory power of climate factors in this study somewhat subjective.