Approaches and system boundaries for urban carbon accounts

More than half of the global population now lives in cities, and the share of the urban population is projected to further increase to about two-thirds by 2050. The majority of human economic activities, 80% of global GDP, 60% to 80% of final energy consumption, and 75% of final-energy-use carbon emissions are related to urban activities. Therefore, cities are central to climate change mitigation. Given the fact that global supply chains play a significant role in urban activities, cities predominantly rely on their hinterlands to supply the resources they need. When accounting for emissions associated with the entire supply chain of products that enter the city for further processing or consumption, so-called consumption-based emissions (CBE), typically, more than half of emissions of cities are imported from outside their borders. Thus, it is important to distinguish between different scopes of urban emissions. Different accounting scopes, such as production-based emissions (PBE) and CBE, may lead to significant differences in emission patterns of cities and may greatly change the interpretation of the success of cities’ carbon mitigation efforts. This chapter provides a brief summary of the relevant literature on urban carbon footprints with a specific focus on different system boundaries and embodied carbon emissions. We show how the choice of a footprint metric will influence the outcome of carbon accounting, mitigation policies, and policy evaluation.