On the road to reducing greenhouse gas emissions? Spatio-temporal analysis of built environment stocks and passenger cars

Abstract

The built environment, composed of buildings and infrastructure, forms a large stock of materials. Used in combination with equipment, vehicles and other resources, it delivers essential services such as shelter and mobility. The building, transport, and material production sectors are significant sources of greenhouse gas (GHG) emissions and about two-thirds of global GHG emissions are from urban areas, illustrating the need for mitigation strategies targeting these sectors and adapted to urban environments. Moreover, global resource extraction, which increased from 31 gigatonnes in 1970 to 107 gigatonnes in 2024, is expected to continue to grow: many still do not have access to essential services, several world regions are going to be more and more urbanized, and large flows of resources in high income countries are persisting.

This thesis is a contribution to the growing research that analyzes stocks and flows of materials and the associated GHG emissions in the built environment and mobility sectors. Different geographic (from global to district level) and temporal (past, relatively close present, future) scopes are considered.

Starting with a study of global paved roads, we found large differences in material stock per capita at national and urban levels. Among European capitals, Oslo has the highest road material stock per capita. A closer investigation of roads and paths, residential buildings and passenger cars in the city and its surrounding areas, highlighted further spatial differences in the built environment composition, car ownership, and car use. By modeling a sufficiency scenario where we gradually ban new single-family houses and reduce floor area per capita towards 2050, we observe a decrease in material demand and material production-related GHG emissions. Assuming the current relationship between settlement characteristics and transport demand, car ownership rates and traveled distance per capita decrease by 11% compared to 2022, but total driving distance does not decline due to population growth. Even if we were not investigating future direct GHG emissions, one could think that fortunately, Norway is a leader in the adoption of electric vehicles. However, our study of historical trends in Norwegian passenger car fleet and life cycle GHG emissions shows that despite a significant decrease of use phase emissions, production-related emissions have increased due to the electrification and a trend towards bigger vehicles.

Overall, the three papers highlight how the built environment and its different components play an intricate role in shaping resource use and GHG emissions. Addressing and reducing this consumption and associated impacts require efforts at all levels, from the material production side to choosing the size of our cars.