finding 4.1 : key-message-4-1

Urban areas in North America are the primary source of anthropogenic carbon emissions, with cities responsible for a large proportion of direct emissions. These areas are also indirect sources of carbon through the emissions embedded in goods and services produced outside city boundaries for consumption by urban dwellers (medium confidence, likely).

This finding is from chapter 4 of Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report.

Description of evidence base: Key Finding 1 is supported by empirical evidence and modeling studies aimed at quantifying and understanding urban extent, energy, carbon, and material flows (Jones and Kammen 2014; Hoornweg et al. 2011; Seto et al., 2014). Research has highlighted the importance of direct versus indirect carbon fluxes in addition to the relative importance of urban carbon flows within the national landscape (Lin et al., 2015).

New information and remaining uncertainties: Very few studies have attempted a comprehensive assessment of the urban portion of North American carbon emissions. Only two have attempted estimates for the North American domain (Marcotullio et al., 2013; Grubler et al., 2012). Both contain unquantified uncertainties acknowledged to include not only the underlying data, but also the definition of “urban” and objective methods to spatially enclose urban areas (Parshall et al., 2010). Uncertainty also exists in the exact quantification of urban versus nonurban carbon emissions because of limited data and methodological inconsistencies in defining direct and indirect carbon fluxes.

Assessment of confidence based on evidence: Key Finding 1 is supported by a growing number of urban carbon footprint studies in North America. Much of this work is in the United States, with some work in Canada and very few studies in Mexico. There is general agreement that urban areas constitute the majority of anthropogenic carbon emissions in North America. However, a more precise assessment remains uncertain because of a lack of comprehensive data. Recent formalization of methods now defines direct versus indirect anthropogenic carbon emissions, but these methods are applied inconsistently in studies of urban carbon emissions, challenging attempts to compare emissions among cities.

This finding was derived from figure P.2: P.2. Likelihood and Confidence Evaluation

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