<b>Marcotullio<b>, P. J., L. Bruhwiler, S. Davis, J. Engel-Cox, J. Field, C. Gately, K. R. Gurney, D. M. Kammen, E. McGlynn, J. McMahon, W. R. Morrow, III, I. B. Ocko, and R. Torrie, 2018: Chapter 3: Energy systems. 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. 110-188, https://doi.org/10.7930/SOCCR2.2018.Ch3.
The North American energy system is a net source of carbon emissions to the atmosphere. Recently, however, this system has undergone dramatic changes. Since 2007, energy use and CO2e emissions have decreased despite population and GDP per capita increases. This decrease accompanied a regional transition to greater reliance on natural gas energy sources and an increase in deployed renewable energy capacity. Early in the economic recession of 2007 to 2008, most of the decreases in energy use and CO2e emissions were due to changes in behavior, including a slowdown in the consumption of goods and services. However, post-recession, a number of other factors have emerged that have kept emissions levels low. Growing energy efficiency and changes in regional carbon intensity were observed across all energy sectors, facilitated by new technologies and changes in the fuel mixture, particularly the increase in natural gas and renewables and the decrease in coal for electricity production, as well as industrial processes and a variety of lower carbon–intensity technologies. These dynamics have been influenced by relative changes in the price of fuels, slow growth in electricity demand, the growing importance of electricity demand for electronics, and a history of policies that promoted technology development for energy efficiency and clean energy. In Mexico, the recent Reforma Energética and strong leadership on environmental issues underpin energy restructuring that is prompting changes in energy use, energy intensity, and that nation’s fuel mix. Across North America, state and subnational governments are increasingly involved in carbon management decisions. The result of all these influences has been a decline in CO2e emissions and a restructuring of the North American energy system.
Whether this trend will continue depends on both the continuation of energy system change and energy and economic policies. Furthermore, despite the decrease in GHG emissions experienced over the recent past and the recent decoupling of emissions from economic growth, all studies suggest that further efforts are needed to meet the 2°C trajectory and that these added reductions can come about only with policy intervention. Key methods for lowering carbon emissions from the North American energy system include 1) increasing energy efficiency across all sectors; 2) upgrading, modernizing, and standardizing the aging energy infrastructure; 3) reducing the use of carbon-intensive fuels and technologies; 4) transitioning to low-carbon energy sources and further developing scalable carbon sink technologies; and 5) generating public acceptance and policy effectiveness for decarbonization, whether at the national or subnational levels. In general, whether the current patterns in energy use and carbon emissions will follow historical trends and rebound to higher levels than 2007 by the early 2020s, or whether the restructuring of the energy system currently underway will be enough to change the energy use and CO2e emissions pathways, remains an open question. Notwithstanding these uncertainties, studies suggest policy change and infrastructure investment across a wide variety of technologies can put the North American energy system on a 2°C trajectory by 2050 (80% reduction in emissions relative to 2005 levels). The costs of energy system changes in the United States are estimated to be around $1 trillion to $4 trillion by 2050, with this investment offsetting some or all of expected costs without mitigation of approximately US$170 billion and $206 billion (US$ 2015) annually by 2050.
Much is already understood about the North American energy system and its role in the carbon cycle, but significant knowledge gaps remain. Most importantly, four areas stand out that need further examination and research. First, the governance and institutional needs in the transition to a low-carbon society are not well understood. As identified herein, studies have examined the potential costs of mitigation, but much more detail is needed on the governance structures and institutions required to support navigation through the future energy transition. Second, the potential feedbacks associated with changes in the energy system in combination with climate change, exogenous and endogenous system changes, and the impacts of those feedbacks on the energy system are not clear. Third, studies have identified the potential extent of CH4 emissions from natural gas extraction and use, putting into question the role of natural gas as a “bridge fuel.” Also, the amount of gas that escapes as leakage and fugitive emissions has yet to be measured accurately. The effectiveness of policies that increase energy efficiencies, reduce carbon intensity, and reduce emissions, while also maintaining social benefits such as environmental equity and economic growth, needs to be more fully documented. Finally, detailed comparable data for end-use energy, emissions, and projections across North American economies have yet to be compiled, and, as noted, end-use data across economies differ due to a number of factors, and thus better data could help inform evidenced-based regional policies regarding carbon management.
The North American energy system, although varied across economies, has developed into a vast, complex infrastructure and set of institutional arrangements that have consistently provided for the economic growth and well-being of the regional population. Yet, the workings of this system contribute significantly to the carbon cycle. This system may be able to continue to provide the reliable and consistent energy demanded by increasing regional activities with decreasing contributions of CO2e to the atmosphere in the near future. Research suggests that the emissions-level targets that secure populations from predicted impacts of climate change and the potential impacts of energy system internal change cannot be met in the absence of policy drivers.
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