{ "id": "R45453", "type": "CRS Report", "typeId": "REPORTS", "number": "R45453", "active": true, "source": "EveryCRSReport.com", "versions": [ { "source": "EveryCRSReport.com", "id": 589503, "date": "2019-01-07", "retrieved": "2019-01-08T18:07:35.204547", "title": "U.S. Carbon Dioxide Emissions in the Electricity Sector: Factors, Trends, and Projections", "summary": "International negotiations and domestic policy developments continue to generate congressional interest in current and projected U.S. greenhouse gas (GHG) emission levels. In December 2015, delegations from 195 nations, including the United States, adopted an agreement in Paris that creates an international structure for nations to pledge to abate their GHG emissions, adapt to climate change, and cooperate to achieve these ends, including financial and other support. Pursuant to that agreement, the United States pledged (in 2015) to reduce GHG emissions by 26-28% by 2025 compared to 2005 levels. In 2017, President Trump announced his intention to withdraw from the Paris Agreement, but under the provisions of the agreement, this cannot be completed before November 4, 2020.\nGHG emissions are generated throughout the United States from millions of discrete sources: vehicles, power plants, industrial facilities, households, commercial buildings, and agricultural activities (e.g., soils and livestock). Of the GHG source categories, carbon dioxide (CO2) emissions from fossil fuel combustion account for the largest percentage (76%) of total U.S. GHG emissions. Among the sectors, transportation contributes the largest percentage (36%) of CO2 emissions from fossil fuel combustion, with electric power second at 35%.\nRecent changes in the U.S. electricity generation portfolio played a key role in the CO2 emission decrease. The electricity portfolio affects CO2 emission levels, because different sources of electricity generation produce different rates of CO2 emissions per unit of electricity (zero in the case of some renewables). The figure below illustrates the changes in electricity portfolio between 2005 and 2017. Highlights include:\nCoal\u2019s contribution to total electricity generation decreased from 50% to 30%;\nNatural gas\u2019s contribution to total electricity generation increased from 19% to 32%; and \nNon-hydro renewable energy (wind and solar) generation increased from 2% to 10%.\nIn recent years, several groups have prepared projections of CO2 emission levels in the electricity sector. The results generally indicate that the 2015 Clean Power Plan would have an impact on CO2 emission levels from electricity generation. In addition, reference case scenarios in more recent studies (2018) project lower emissions by 2030 when compared to reference cases from earlier studies. \nPercentage of Electricity Generation by Source: 2005-2017\n/\nSource: Prepared by CRS; data from EIA, Electric Power Monthly, Table 1.1, http://www.eia.gov/beta/epm/. Renewable sources include wind, utility scale solar, wood fuels, landfill gas, biogenic municipal solid waste, other biomass, and geothermal. Petroleum includes petroleum liquids and petroleum coke.\nMultiple factors will likely impact electricity sector CO2 emissions levels, including the electricity generation portfolio, the relative prices of fossil fuels, federal and/or state policy developments, economic impacts, and improvements in demand-side energy efficiency. Accurately forecasting future CO2 emission levels is a complex and challenging endeavor. A comparison of actual CO2 emissions between 1990 and 2017 with selected emission projections illustrates this difficulty. 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