Michail Fragkias, Boise State University, Boise, ID, USA

Presentation Title: A new science for cities and Global Environmental Change: An overview




This research examines CO2 emissions and energy use from a system of cities perspective, and the relationship between city size, CO2 emissions and energy use for U.S. metropolitan areas using a production accounting allocation of emissions.  Larger cities in the U.S. are not more energy and emissions efficient than smaller ones and do not exhibit gains from economies of scale with regard to emissions.   For the time period of 1999–2008, CO2 emissions and energy use scale proportionally with urban population size. Contrary to theoretical expectations, larger cities are not more emissions efficient than smaller ones.

Key Lessons Learned

  • Scaling analysis is important when examining issues at the intersection of urbanization and global environmental change. Scaling is simply an emergent relationship between systemic size and emissions. Emissions in urban areas belong to a broader paradigm since every system needs to consume energy to maintain structure and order. The existence of approximate scaling phenomena for urban areas ― documented using a variety of socio-economic metrics ― is an indication that there are generic social mechanisms and properties of social systems at play across the entire urban system. Mechanisms such as networks and flows, non-linearities and feedback loops integrate complex interactions among the individuals, households, firms and institutions living, residing and operating in these spaces, leading to emergent phenomena such as scaling laws.
  • The analogy between urban metabolism and biological metabolism may have empirical limits. Cities exhibit characteristics that make the natural organism analogy difficult, such as the urban phenomena that produce super-linear scaling.

Policy/Practice Implications of Research

  • These results have important energy policy implications for a rapidly urbanizing planet since they reveal the importance of urban scale/size relative to factors such as population density and wealth.
  • Policymakers must renew their attention on issues of distributions of city sizes within national urban systems; size trumps the effects of all other variables (such as population density and wealth) in explaining variation in CO2 emissions and energy use.
  • A focus on urban densities and wealth is still required, as these factors are critical for addressing various facets of global environmental change related to urban development. But as (new) world cities continue to grow, policymakers need to consider the CO2 emissions and energy use effects of urban size and contrast it to the effects of urban form, building materials and transportation network structure.
  • The intuitive interpretation of the linear to superlinear scaling finding can be explored first through the analogy urban metabolism. This finding creates a paradox when one considers that in nature, as organisms grow in size they become more efficient. A linear to superlinear scaling in CO2 emissions and energy use suggests no gains and losses in efficiency from larger cities. This casts doubt on the hypothesis that urban systems function similarly to biological ones.
  • A 'closed system' approach to urban research brings into question the efficacy of using urban size as a climate change mitigation strategy. The results show that, at least in the case of U.S. cities, there are no significant economies of scale with city size and CO2 emissions and energy use. More recent research points to actual significant diseconomies of scale. Therefore, cities and policies must consider other mitigation strategies that have been shown to have greater impacts on emissions than population size.
  • Dis-economies of scale with respect to CO2 and energy use should be viewed in conjunction to the build-up of additional evidence on urban scaling. Any strategic decision on city growth considering sustainability must carefully weigh the implications of urban scale on a variety of urban metrics (including innovation, crime, environmental indicators, etc.). The results contribute to the larger picture of scaling relationships present in urban systems: given that larger cities 'speed up' the process of wealth creation and innovation and do not offer economies of scale in CO2 emissions, a policy favoring larger city sizes may bring about carbon reductions primarily through technological advancements and eco-innovations.

Knowledge Gaps and Needs

Scaling these findings requires an interpretation from economics, combined with an understanding of the nature of greenhouse gas emissions in the US. CO2 emissions depend significantly on the carbon intensity of the energy source and the drivers of demand for fossil fuels. Several hypotheses can be made on the basis of a decomposition of factors that drive demand for fossil fuels in localized markets. Expecting a pattern of increased savings in CO2 in larger urban agglomerations, a linear scaling of CO2 emissions may signify that larger urban areas are lagging in their capacity to curb demand for fossil fuels proportionally to smaller urban areas. It may be the case that residents in larger urban areas are not incentivized structurally (through urban form) or economically (through energy prices) to demand lower proportions of fossil fuels in their energy mix. Although large urban areas are more innovative than smaller ones, they may lack capacity in steering eco-innovations towards their local markets for fossil fuels. These important hypotheses remain untested and need to be addressed in future research.

The issues associated with emissions and energy accounting methods highlight the limitations of assuming cities as 'closed systems'. This perspective is in large part driven by the dominant conceptualization of a city through its narrow administrative boundaries – a definition of urban areas that drives data collection globally and dominates research practice surrounding urban phenomena. As we build our capacity to associate the increase of a city’s size to effects that occur far away from a city’s boundaries, we can overcome the data-specific challenge and adopt an “open system” perspective that could drastically alter our perspective on urban scaling. Through this new perspective, wealth, for example, may be found to be a more significant driver of total urban emissions; this is especially the case when considering emissions that occur in distal locations (or carbon sequestration capacity that is lost in distal places) but can be attributed to demand of goods and services that arises in specific urban areas.

While scaling laws characterize the structure and order of urban systems globally, whether these specific U.S. results hold for all typologies of cities is subject to further research.