U.S. Carbon Dioxide Emission Trends and the Role of the Clean Power Plan, April 11, 2016.

摘要

U.S. greenhouse gas (GHG) emission levels, particularly from carbon dioxide (CO2), remain a topic of interest among policymakers and stakeholders.1 Recent international negotiations and domestic policy developments have generated increased attention to current and projected U.S. GHG emission levels. An understanding of GHG emission source data and the underlying factors that affect emission levels might help inform the discussion among policymakers regarding GHG emission mitigation. In June 2013, President Obama stated his commitment to reduce U.S. GHG emissions by 17% below 2005 levels by 2020 if all other major economies agreed to limit their emissions as well.2 In November 2014, President Obama announced an additional interim goal to reduce U.S. GHG emissions by 26% to 28% below 2005 levels by 2025 in the context of negotiations toward an agreement applying to all countries to address climate change beyond 2020.3 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.4 Whether the United States ultimately achieves the 2020 and 2025 targets will likely depend, to some degree, on GHG emission levels from electric power plants—one of the largest sources of U.S. emissions. The Environmental Protection Agency (EPA) promulgated standards for CO2 emissions from existing fossil-fuel-fired electric power plants on August 3, 2015.5 EPA cites Section 111(d) of the Clean Air Act (CAA) as the authority to issue its final rule.6 The rule, known as the Clean Power Plan (CPP), appeared in the Federal Register on October 23, 2015.7 The CPP is the subject of ongoing litigation. A number of states and other entities have challenged the rule, while other states and entities have intervened in support of the rule. On February 9, 2016, the Supreme Court stayed the rule for the duration of the litigation. The rule therefore currently lacks enforceability or legal effect, and if the rule is ultimately upheld, at least some of the deadlines would likely be delayed.8 A question for policymakers is whether U.S. GHG emissions will remain at current levels, decrease to meet the President’s 2020 and 2025 goals, or increase toward former (or even higher) evels. Multiple factors—including economics, technology, and climate policies—may impact GHG emission levels. This report examines recent trends in U.S. GHG emissions, particularly CO2 emissions from electricity generation, and the factors that impact emission levels in that sector. In addition, this report examines the degree to which CPP implementation (or lack thereof) may impact CO2 emission levels from electric power plants. The first section provides an overview of various sources of GHG emissions in the United States. This includes an overview of CO2 emissions from fossil fuel combustion and a closer look at CO2 emissions from electricity generation, which account for the largest percentage of CO2 emission from fossil fuel combustion. The second section examines projections of CO2 emissions in the electric power sector, with a particular focus on the role of the CPP and other factors. The final section highlights the challenges in making CO2 emission projections with a comparison of actual CO2 emissions with prior emission forecasts.