Low-Carbon Cities: Accounting, Infrastructure Analysis, and Transitions

Abstract

Cities and urban areas are likely to be the important foci for greenhouse gas (GHG) mitigation efforts at the global scale. The Intergovernmental Panel on Climate Change report pointed out that approximately 71% of global energy-related GHG are associated with urban areas, which house about 54% of world population. The proportion of anthropogenic GHG associated with urban areas and cities is expected to increase in the future, when urban areas are expected to accommodate approximately 66% of world population by 2050 as predicted by the United Nations. Infrastructure which includes the provisioning of energy, transportation, water, municipal waste management, and building material plays a big role in urban energy use and GHG emissions. Studies in my dissertation investigated low-carbon cities through an interdisciplinary focus on infrastructure systems. Four chapters in my dissertations have made contributions 1) to evaluate carbon impacts of urban infrastructure at the city level to provide customized mitigation actions and scaling-up cities’ carbon impact aggregately to national level; 2) to identify a new and unique cross-sectoral infrastructure action and quantify its carbon mitigation potential; and 3) to investigate infrastructure operators’ motivation for low-carbon transitions and the enabling factors for the transitions from co-evolutionary perspectives. Details of each study are presented below. Quantify carbon impacts of urban infrastructure at the city level to provide customized mitigation actions (Chapter 2): With massive urbanization and infrastructure investments occurring in China, understanding GHG emissions from infrastructure use in small and large Chinese cities with different administrative levels is important for building future low-carbon cities. This paper identifies diverse data sources to assess greenhouse gas (GHG) emissions based on the community-wide infrastructure footprints (CIF) method in four Chinese cities of varying population (1 to 20 million people) and administrative levels: Yixing, Qinhuangdao, Xiamen and Beijing. CIF quantifies GHGs associated with seven infrastructure sectors providing energy (fuels/coal), electricity, water supply and wastewater treatment, transportation, municipal waste management, construction materials, and food to support urban activities. Industrial energy use dominates the infrastructure CIFGHG in all four cities, ranging from 76% of total CIF in Yixing to 30% in Beijing, followed by residential energy use (6-13%), transportation (4-12%), commercial energy use (2-25%), food (6-11%), cement use (3-8%) and water (about 1%), thereby identifying priorities for low-carbon infrastructure development. Transboundary footprint contributions ranged from 31% (Beijing) to 8% (Qinhuangdao), indicating that infrastructure supply chains of cities are important. GHGs from energy use are dominated by electricity (35-45%) and non-electricity coal use (30-50%). The authors demonstrated that disaggregated infrastructure use-efficiency metrics in each infrastructure sector provide useful baseline performance data for comparing different cities. Database development for scaling-up all cities’ carbon impact aggregately to the national level in China (Chapter 3): Many studies have quantified carbon emissions from a few cities in a nation, while few studies have estimated emissions from all cities in a nation to assess their collective contributions towards national total. This paper, focusing on Chinese cities, assesses the collective contribution of all cities to national carbon emissions, the share of carbon emissions by city types, and carbon emission per capita and per GDP. This paper describes the Chinese City Industrial-Infrastructure database including fuel/electricity use and heat supply in 644 cities, in which energy use is aligned with national data with ~1% difference. It is found that direct carbon emissions from 644 Chinese cities collectively contribute to 62.4% of the national CO2 emissions. Further categorizing these cities based on population size, economic structure, and administrative level, it is found that Midsize cities (0.5-3 million) accounted for 38.1% of national CO2 emissions; Mixed-Economy cities contributed to about 40% of the national CO2 emissions; and city propers (all urban administrative districts in a city) collectively contribute to 42.9% of the national CO2 emissions. Direct emissions per capita ranged from 0.94 to 83.3 tonnes CO2 per person (8.85 tonnes/person on average). Direct emissions per GDP ranged from 0.01 to 2.60 kg CO2 per yuan-GDP (0.26 kg CO2/yuan-GDP on average). Direct plus embedded emissions in electricity were also evaluated and found to have similar patterns as direct carbon emissions. These results enhance our understanding of the share of carbon emissions from Chinese cities and suggest the importance of focusing on certain city types for mitigation efforts. Identify a new and unique cross-sectoral infrastructure action and quantify its carbon mitigation potential in Chinese cities (Chapter 4): Utilizing low-grade waste heat from industries to heat and cool homes and businesses through the 4th generation district energy systems (DES) is a novel strategy to reduce energy use. This paper develops a generalizable methodology to estimate the energy saving potential for heating/cooling in 20 cities in two Chinese provinces, representing cold winter and hot summer regions respectively. We also conduct a life-cycle analysis of the new infrastructure required for energy exchange in DES. Results show that heating and cooling energy use reduction from this waste heat exchange strategy varies widely based on the mix of industrial, residential and commercial activities, and climate conditions in cities. Low-grade heat is found to be the dominant component of waste heat released by industries, which can be reused for both district heating and cooling in the 4th generation DES, yielding energy use reductions from 12% to 91% (average of 58%) for heating and 12% to 100% (average of 73%) for cooling energy use in different cities based on annual exchange potential. Incorporating seasonality and multiple energy exchange pathways resulted in energy savings reductions from 0 to 87%. The life-cycle impact of added infrastructure was small (<3% for heating) and 1.9% ~ 6.5% (cooling) of the carbon emissions from fuel use in current heating or cooling systems, indicating net carbon savings. This generalizable approach to delineate waste heat potential can help determine suitable cities for the widespread application of industrial waste heat re-utilization. Investigate DES operators’ motivation for low-carbon transitions and the enabling factors for the transitions in the U.S. (Chapter 5): Advanced district energy systems (DES) using low-temperature heat, as one of the community-wide energy infrastructures, can contribute to cities’ sustainability through reducing carbon emissions from heating and cooling services. However, the majority of current community-wide DES in the U.S. is not the advanced systems and need to be upgraded. This research, focusing on DES operators as the front-runners in infrastructure transitions, investigated their understanding of sustainable transitions of DES in the near future, as well as motivations and enablers for these transitions. Interviews were conducted to investigate how the business strategies of DES operators interact with factors related to ecosystem, technology, institutions, and users to influence the transitions. We conducted semi-structured interviews with fourteen DES professionals working in private companies, universities, cities, and the DES industrial associations. Interview data were analyzed in NVivo software applying the grounded-theoretical approach. Results indicate that community-wide DES in the U.S. is slowly moving from current steam-based second generation toward the fourth generation DES. Some universities, hospitals, and cities are leading this transition as units that demand sustainable and reliable energy systems. This transition in the U.S. is market driven, meaning that DES operators are motivated by the customers’ demand to take transitioning actions. However, the wide-spread transition is slow in the U.S., according to interviewees, because a) fossil fuel is cheap; b) electric utilities are competitors although they could also offer DES services in their business model; and c) energy policies and incentives do not systematically consider heating service. Most DES customer’s and policymakers’ lack of understanding about energy choices is indicated by interviewees to be a major barrier for changing status quo. Effective Strategies identified by DES operators to overcome these challenges include work closely with users and policymakers, such as by identifying a local champion, continuously engaging with customers to explain emerging opportunities in the field, tapping technical expertise to understand the emerging technological opportunities. Future work comparing successful and shrinking DES can further shed light on the enabling factors/barriers. In sum, I implemented multiple research methods in my dissertation to explore carbon emissions associated with cities at multi-scales, identify and quantify new cross-sectoral carbon mitigation strategies, and infrastructure operators in low-carbon urban infrastructure transitions. Studies in my dissertation chapters focused on both physical and social subsystems in cities to explore how cities with diverse activities can provide new opportunities for carbon mitigation beyond national policies through the advanced low-carbon urban infrastructure. Due to the complexity of urban infrastructure, the investigation of community-wide DES in the U.S. revealed that the challenges of changing existing infrastructure to the advanced ones are more related to users and institutional factors. Studies in my dissertation demonstrated that working under an integrated interdisciplinary framework can address key questions at both physical and social sides to investigate low-carbon urban transitions.