Understanding interactions between complex human and natural systems involved in urban carbon cycling is important when balancing the dual goals of urban development to accommodate a growing population, while also achieving urban carbon neutrality. This study develops a systems breakdown accounting method to assess the urban carbon cycle. The method facilitates greater understanding of the complex interactions within and between systems involved in this cycle, in order to identify ways in which humans can adapt their interactions to reduce net greenhouse gas emissions from urban regions. Testing the systems breakdown accounting method in Stockholm County, Sweden, we find that it provides new insights into the carbon interactions with urban green-blue areas in the region. Results show how Stockholm County can reduce its emissions and achieve its goal of local carbon net-neutrality, if the green areas protect its carbon sequestration potential and maintain it to offset projected remaining active emissions. Results also show that the inland surface waters and inner archipelago waters within Stockholm County are a considerable source of greenhouse gases to the atmosphere. A better understanding of these water emissions is necessary to formulate effective planning and policy measures that can reduce urban emissions. The insights gained from this study can also be applied in other regions. In particular, water bodies could play a significant role in the urban carbon cycle and using this knowledge for more complete carbon accounting, and a better understanding of green-blue interactions could help to reduce net urban emissions in many places.

Addressing urban challenges with nature-based approaches can improve and protect ecosystem services. Yet, urban planning has not efficiently integrated such approaches to manage land use. This paper examines interactions between human and natural systems that result in ecosystem services and changes in land use and land cover in urban areas. It develops a social-ecological model for land use and land cover change, and for ecosystems services that integrates nature-based solutions in urban planning. The model treats spatial variations in ecosystems services as both drivers and consequences of human decision-making in choosing commercial and residential locations that drive land use and land cover change. We tested the social-ecological model in Stockholm County, Sweden, on a 30 x 30 m grid. Results show that accessibility in ecosystem services drives urban residential and commercial development, characterized by non-linearity. Areas around existing urban centers show high accessibility in ecosystem services and high development probabilities, whereas smaller population centers in large areas enjoy high accessibility to ecosystem services and low urban development probabilities. Model results suggest place-specific nature-based strategies for addressing the heterogeneous spatial relationships between ecosystem services and urban development.

Human-induced urban growth and sprawl have implications for greenhouse gas (GHG) emissions that may not be included in conventional GHG accounting methods. Improved understanding of this issue requires use of interactive, spatial-explicit social-ecological systems modeling. This paper develops a comprehensive approach to modeling GHG emissions from urban developments, considering Stockholm County, Sweden as a case study. GHG projections to 2040 with a social-ecological system model yield overall greater emissions than simple extrapolations in official climate action planning. The most pronounced difference in emissions (39% higher) from energy use single-residence buildings resulting from urban sprawl. And this difference is not accounted for in the simple extrapolations. Scenario results indicate that a zoning policy, restricting urban development in certain areas, can mitigate 72% of the total emission effects of the model-projected urban sprawl. The study outcomes include a decision support interface for communicating results and policy implications with policymakers.