Carbon sequestration and avoided emissions reveal the net carbon benefit of urban green space in Beijing (2000–2024)

Urban green spaces (UGS) are widely promoted as nature-based solutions for climate mitigation, yet their carbon benefits are difficult to compare because ecosystem sequestration and demand-side emission reductions are often estimated separately under inconsistent accounting boundaries. We developed a spatially explicit carbon-budget framework to assess the metropolitan green-space system of Beijing from 2000 to 2024, integrating net ecosystem productivity (NEP), life-cycle carbon emissions, and cooling-induced avoided emissions. Under the baseline parameterization, linear interpolation between the 2010 and 2015 estimates suggested that NCB crossed zero around 2012, slightly earlier than net carbon sequestration (NCS) around 2013. This difference reflects the additional contribution of cooling-induced avoided emissions, which allowed the overall carbon budget to become positive before net sequestration alone did. The long-term transition was dominated by increasing ecosystem carbon uptake, with NEP increasing approximately sevenfold, whereas cooling-induced avoided emissions provided a smaller, spatially concentrated contribution, equivalent to about 5–6% of citywide NEP in recent years. The two components showed contrasting spatial patterns: ecological conservation areas contributed most of the NCS through extensive and productive vegetation, whereas central urban green spaces generated higher area-normalized avoided emissions because they overlapped more closely with areas of high population exposure and cooling demand. NCS was mainly associated with environmental and vegetation conditions, whereas avoided emissions were more strongly associated with population exposure and landscape configuration. These results support functionally differentiated green-space planning across the urban–rural gradient: maintaining extensive ecological capacity in peripheral areas while strategically locating urban green space where cooling demand and population exposure are concentrated.