<b>Hayes</b>, D. J., R. <b>Vargas</b>, S. R. Alin, R. T. Conant, L. R. Hutyra, A. R. Jacobson, W. A. Kurz, S. Liu, A. D. McGuire, B. Poulter, and C. W. Woodall, 2018: Chapter 2: The North American carbon budget. In Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 71-108, https://doi.org/10.7930/SOCCR2.2018.Ch2.
The North American Carbon Budget
Changes from local to global carbon dynamics in natural and anthropogenic systems have imminent consequences for humans because carbon is embedded in almost all social activities (see Ch. 6: Social Science Perspectives on Carbon). The resultant social reliance on carbon by North American societies causes dependence on ecological, economical, and technological networks and systems that have carbon embedded in them (e.g., forestry, energy generation, transportation, fisheries, and agriculture). Thus, management decisions have to consider social drivers if the goal is to transition to low-carbon systems and make a substantial impact on the carbon cycle.
Social lifestyles and cultural backgrounds have been constrained historically by available resources, energy sources, and costs that have influenced the North American carbon cycle. For example, the proportional share of total continental fossil fuel emissions differs among the three North American countries (i.e., Canada, 11.9%; Mexico, 6.5%; and the United States, 81.6%); together these countries contribute 20% of global energy-related emissions (see Ch. 3: Energy Systems). Urban development has resulted in spatially concentrated sources of energy demand and consequently high anthropogenic carbon emissions (see Ch. 4: Understanding Urban Carbon Fluxes). Although the area of agricultural land for North America has remained constant in the last decade, regional carbon dynamics can be influenced by trends in food production and agricultural management (see Ch. 5: Agriculture). Differences between cultural backgrounds and current policies are evident in tribal lands. Ideologies, local practices, government land tenure, and agricultural and water policies create challenges for defining carbon management practices (see Ch. 7: Tribal Lands). Despite socioeconomic differences across North America, increasing demand for easily available energy has implications for the continental carbon cycle.
Regional carbon management decisions to mitigate CO2 emissions could benefit from sector-specific accounting, focusing efforts on reducing atmospheric GHG concentrations and identifying options for carbon sinks. Compiled from the chapters in this report, Table 18.1 summarizes a set of management activities and their relative contributions to potential reductions in GHG emissions across the various sectors of the North American carbon budget. For example, North American forests have significant potential as a carbon sink, so mitigation options for this sector could use a systems approach to assess large uncertainties in future land use and predict subsequent impacts on forests (see Ch. 17: Biogeochemical Effects of Rising Atmospheric Carbon Dioxide). These assessments will require quantifying changes in emissions associated with 1) forest ecosystems (e.g., changes in rates of land-use change), 2) harvested wood products and their substitution by high-emission products (e.g., steel and concrete), and 3) fossil fuels through the use of wood products (Kurz et al., 2016; Lemprière et al., 2013). The potential for changes to the carbon balance in the forest sector also will depend on societal drivers related to increases in urbanization and reduction of forested lands via land-use change. These processes could result in a loss of forest industrial capacity across North America that ultimately will limit the potential carbon sink of the forest sector. Therefore, socioecological factors could influence changes in emissions from different sectors, potentially requiring alternative practices to maintain the productivity of sector products (e.g., long-lived forest products) and ecosystems (i.e., carbon sequestration potential in long-term pools such as SOC).
Since SOCCR1, North American observational networks related to the carbon cycle (e.g., CO2 and CH4 stocks and fluxes from aquatic and terrestrial ecosystems) have increased (see Appendix C: Selected Carbon Cycle Research Observations and Measurement Programs). Thus, carbon management decisions could benefit from a high degree of interoperability among government, research, and civil sectors within the countries and across North America. Interoperability in this context is defined as an organized collective effort needed to foster development and implementation of carbon management decisions and actions. Furthermore, interoperability has the ultimate goal to maximize sharing and use of information by removing conceptual, technological, organizational, and cultural barriers (Vargas et al., 2017). For example, interoperability could be increased by defining inventory protocols (i.e., a conceptual barrier), using standardized instrumentation (i.e., a technological barrier), defining the specific roles of participants (e.g., researchers and governmental agencies), and being sensitive to cultural expectations (e.g., perception of data ownership). Although sector- and country-specific barriers exist, moving toward a high degree of interoperability will facilitate anticipation, recognition, and adaptation of management decisions to make a positive impact on the continental carbon cycle.
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