Integrated Life Cycle Assessment of Resource Efficient Urban Systems

The growth of cities is a key driver of global environmental impacts and resource consumption. As urban areas continue to grow over the coming decades, they will face the challenge of lifting their populations out of poverty... [ view full abstract ]

The growth of cities is a key driver of global environmental impacts and resource consumption. As urban areas continue to grow over the coming decades, they will face the challenge of lifting their populations out of poverty through economic development while simultaneously contributing to global efforts to mitigate climate change. Addressing this challenge will involve an unprecedented transformation of cities’ infrastructure and the socio-technical systems that fulfill key urban services, including passenger transportation, thermal comfort and commercial buildings. Further complicating matters, the environmental sustainability of these urban socio-technical systems can be influenced by the regional electricity mix as well as local and global demographic trends. Therefore, it is necessary to understand how these factors come together to influence the life-cycle environmental impacts and resource consumption of cities over the coming decades.

In this paper, we use an integrated hybrid life cycle assessment (LCA) approach to understand the potential for resource-efficient socio-technical systems to reduce greenhouse gas emissions, water use, land occupation and metal consumption in cities by 2050. We assess the life-cycle impacts of Bus Rapid Transit (BRT) systems with electric buses, energy and water efficient commercial buildings and district energy systems relative to conventional alternatives under business-as-usual and electricity decarbonization scenarios consistent with the International Energy Agency’s 6°C and 2°C scenarios, respectively. We then use cross-sectional data on 84 cities around the globe to relate the demand for key urban services and the natural market shares of efficient technologies to the socio-economic and climate variables of GDP, population, population density, heating degree-days and cooling degree-days. Understanding these relationships allows us to scale-up LCA results with population and GDP projections to estimate the aggregate resource and environmental impacts of providing key urban services in a wide variety cities around the globe. We then analyze how environmental impacts and resource consumption can be reduced through aggressive deployment of resource-efficient technologies, electricity decarbonization and strategic urban densification.

Individually, most resource-efficient technologies considered show absolute reductions compared to present day impacts, or relative reductions compared to those of the business-as-usual scenario. However, district energy systems likely require greater amounts of metal and water resources for their infrastructure in comparison with traditional natural gas and electric heating and cooling systems. When the effects of all these socio-technical systems are combined, resource-efficient systems show considerable potential to reduce environmental impacts and resource consumption for all impact categories analyzed. High-penetration of resource-efficient technologies can generate 24-27% reductions in resource and environmental impacts by 2050 compared to business-as-usual, with an additional 2-12% possible through strategic densification. While not strictly comparable to Direct Material Consumption (DMC), these results suggest that resource consumption targets set by the United Nations International Resource Panel (IRP) of 6-8 metric tons per capita per year may be feasible.