To accommodate a growing global population while mitigating climate change, urban areas must grow while minimising environmental impacts. To achieve this, a city must be treated as a complex socio-ecological system in which many actors and subsystems act in unclear and unpredictable ways. This thesis explores the workings and interactions of this complex socio-ecological system by assessing how urban and regional planning and policy decisions affect the contributions of cities to climate change, and whether appropriate planning and policy tools can minimise these contributions. Computer models were developed to investigate and couple planning and policy decisions and their potential impacts on the environment, particularly in terms of greenhouse gas (GHG) emissions to the atmosphere. The models were then employed for generation of scientific knowledge and for converting this knowledge into practical planning tools and recommendations.

Methods used in developing models that reflect complex urban systems included cooperation with experienced county planners to improve model accuracy; coupling of sub-system models in a socio-ecological framework for scenario analysis of the outcomes of planning and policy decisions in terms of GHG emissions; systems breakdown analysis of green-blue contributions to the urban carbon cycle; and modelling to identify how these contributions could be harnessed to reduce net urban emissions. The main study area was Stockholm County, Sweden, with later extension of the modelling approach to 54 major European cities. 

Cooperation with Stockholm County planners during model development resulted in an improved tool for scientific research that was also suited to practical planning, increasing the potential for knowledge developed through scientific research to be applied in reality. Scenario analysis of policies for Stockholm County revealed that zoning reduced the extra GHG emissions associated with necessary urban growth by 72% compared with a baseline scenario. Analysis of the urban carbon cycle in Stockholm County showed that vegetative carbon sequestration helped offset GHG emissions locally, but that re-emissions via surface waters compromised the potential to reach ‘net-zero’ emissions from Stockholm County. However, climate action goals for Stockholm could still be achieved if its ambitious emissions reduction plans are realised and if the current sequestration capacity of Stockholm County’s many green areas can be maintained in coming decades.

 Extensive modelling of urban emissions in multiple European cities showed potential for green-space sequestration and revealed that nature-based solutions (NbS) applied at city scale could help reduce urban emissions. Incorporation of NbS into climate action plans for these cities would maximise the associated GHG emissions reduction and increase the likelihood of the cities achieving their climate action goals. 

In conclusion, the climate change impacts of future urban expansion could be mitigated by incorporating planning and policy tools such as zoning, protection of green-blue spaces and NbS into whole-system urban and regional development plans. This could bring cities closer to achieving truly sustainable urban development.