Table Of Contents

    The landmark 2007 U.S. Supreme Court case, Massachusetts v. EPA, paved the way for the U.S. Environmental Protection Agency (EPA) to regulate greenhouse gases (GHGs) under the Clean Air Act (CAA). The case began in 2003 when the EPA said it lacked authority under the CAA to regulate GHGs and even if it did have that authority, that it would not set GHG standards for vehicles. A group led by 12 states sued the EPA, arguing that carbon dioxide and other GHGs should be regulated under the CAA, as these gases contribute to climate change, which can cause harm to public health and welfare. Despite the case’s focus on vehicle GHG emissions, the Court’s decision triggered EPA to also begin work on GHG regulations for stationary sources, including power plants. The following timeline shows EPA’s major actions and related court rulings regarding carbon emissions from stationary and mobile sources that have taken place in the seven years since the Massachusetts v. EPA decision. This fact sheet excludes EPA regulatory actions aimed primarily at fluorinated GHGs, including hydrofluorocarbons (HFCs).

    Items with a * indicate that more information can be found at the end of the fact sheet.


    Timeline of EPA Actions on GHGs


    April 2, 2007

    The U.S. Supreme Court ruled 5-4 in Massachusetts v. EPA that GHGs are air pollutants covered by the Clean Air Act. EPA may regulate GHGs if they are determined to be a danger to human health.

    December 18, 2008

    EPA issued a memorandum entitled, “EPA’s Interpretation of Regulations that Determine Pollutants Covered by Federal Prevention of Significant Deterioration (PSD) Permit Program” (also known as the “Johnson Memo”).

    December 7, 2009

    EPA issued its “Endangerment Finding,” which finds that current and projected levels of six GHGs threaten the health and human welfare of current and future generations. The final rule was published on December 15, 2009.

    January 14, 2010

    EPA’s Endangerment Finding went into effect.

    March 29, 2010

    EPA issued the final “Timing Rule” which stated that the earliest that GHGs could be subject to regulation is January 2, 2011, and that the Agency will continue to use the guidance outlined in the “Johnson Memo” of 2008. The final rule was published in the Federal Register on April 2, 2010.

    April 1, 2010

    EPA and the National Highway Traffic Safety Administration (NHTSA) issued the Corporate Average Fuel Economy (CAFE) standards for new light-duty vehicles for model years (MY) 2012–2016 (known as the “Tailpipe Rule”).* The final rule was published May 7, 2010.

    May 13, 2010

    EPA issued its “Tailoring Rule,” which limited air permitting guidelines under Title V of the Clean Air Act to the largest stationary sources of GHGs, exempting smaller facilities that emit less than 75,000-100,000 tons of GHG per year. The result was a more manageable rule that targeted power plants and other large emitters. The final rule was published on June 3, 2010.

    December 1, 2010

    EPA finalized a rule requiring that new, large facilities (or those making expansions on existing facilities) must obtain a New Source Review Prevention of Significant Deterioration (PSD) to control GHG emissions.

    January 2, 2011

    The Tailoring Rule phase-in for the Title V and PSD programs began, subjecting large facilities to GHG permitting requirements if they were already required to obtain PSD permits for non-GHG pollutants.

    June 20, 2011

    The U.S. Supreme Court ruled 8-0 in American Electric Power Company v. Connecticut that corporations cannot be sued to reduce GHG emissions under federal common law because common law is superseded by EPA regulatory authority granted under the Clean Air Act.

    July 1, 2011

    EPA finalized a three-year deferral of GHG permitting for facilities that use biomass and other biogenic sources. The final rule was published on July 20, 2011.

    July 6, 2011

    EPA finalized the Cross-State Air Pollution Rule (CSAPR) which requires states to reduce power plant emissions that contribute to ozone and fine particle pollution.

    August 9, 2011

    EPA and NHTSA issued GHG emissions standards for medium- and heavy-duty engines and vehicles for MY 2014–2018.* The final rule was published on September 15, 2011.

    March 27, 2012

    EPA proposed carbon pollution standards for new power plants that would require power plants to reach a maximum emissions rate of 1,000 pounds of CO2 per megawatt hour. The proposed rule was published on April 13, 2012, but withdrawn on January 8, 2014, and replaced with a new proposed rule on September 20, 2013 (see below).

    June 5, 2012

    EPA issued the final set of minor adjustments to CSAPR; published in the Federal Register on June 12, 2012. Previous adjustments had been issued on February 7, 2012 (published February 21), parts of which were revoked in May 2012.

    June 26, 2012

    The U.S. Court of Appeals for the D.C. Circuit upheld all four GHG regulations made by EPA thus far, including EPA’s “Endangerment Finding” and carbon pollution limits for passenger vehicles, in Coalition for Responsible Regulation v. EPA.

    August 28, 2012

    EPA and NHTSA issued a joint rule to extend GHG and fuel economy standards for light-duty passenger vehicles for MY 2017–2025.* The final rule was published October 15, 2012.

    June 25, 2013

    President Obama announced his Climate Action Plan*, which directs the EPA through memorandum to set carbon pollution standards for new and existing power plants.

    September 20, 2013

    EPA proposed modified carbon pollution standards for new power plants. The new draft rule was published on January 8, 2014. The comment period closed on March 10, 2014.

    March 28, 2014

    The White House announced its Strategy to Reduce Methane Emissions, an extension of the Climate Action Plan. The plan includes steps to improve methane data quality and update standards on emissions from landfills, coal mines, and the oil and gas sector. The plan also expands voluntary programs to reduce methane from the agricultural sector.

    April 29, 2014

    The Supreme Court upheld EPA’s Cross-State Air Pollution Rule (CSAPR) in EPA v. EME Homer City Generation, L.P. with a 6-2 decision.

    June 2, 2014

    EPA proposed the Clean Power Plan* for cutting carbon pollution from existing power plants, as directed by the president’s Climate Action Plan.

    June 23, 2014 In Utility Air Regulatory Group v. EPA, the U.S. Supreme Court found 5-4 that EPA cannot regulate a power plant solely due to its GHG emissions, striking down the Tailoring Rule. However, a separate 7-2 ruling found that EPA has the authority under the Clean Air Act to regulate GHG emissions from new power plants, provided the source is regulated for other air pollutants. The case marked the third major decision from the Supreme Court confirming EPA authority to regulate GHGs.

    Looking Ahead


    December 1, 2014

    Public comments are due on EPA’s proposed Clean Power Plan rule, extended from the original October 16 cut-off date. More information on how to submit a comment is available here.

    January 2015

    EPA is expected to issue its final rule regulating carbon emissions from new power plants.

    March 2015

    EPA and NHTSA are expected to issue proposed rulemaking for fuel efficiency and carbon pollution standards for medium- and heavy-duty vehicles for MY 2019 and later.

    June 2015

    EPA is expected to issue its final rule for the Clean Power Plan to regulate carbon pollution from existing power plants.

    June 30, 2016

    State Implementation Plans (SIPs) for regulating carbon pollution from existing power plants are due from states as part of the Clean Power Plan. States needing additional time must submit an initial plan and reasons for the delay by this date.

    June 30, 2017

    States that were granted extensions and are not part of a multi-state plan must submit their complete Clean Power Plan SIPs.

    June 30, 2018

    States that that were granted extensions and are participating in a multi-state approach must submit their complete Clean Power Plan SIPs.


    The first year for interim carbon reduction goals under the Clean Power Plan.

    Further Information


    Vehicle Fuel Economy Standards

    In April 2010, the Obama administration finalized fuel efficiency standards and tailpipe emission limits for light-duty vehicles and trucks for model years (MY) 2012-2016 in President Obama’s first major initiative to reduce GHG emissions. The joint ruling from the National Highway Traffic and Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) set estimated corporate average fuel economy (CAFE) standards at 35.1 miles per gallon by MY 2016 and required tailpipe emissions to be less than 250 grams carbon dioxide (CO2) per mile. EPA estimated that the ruling will eliminate the equivalent emissions of 50 million cars and light trucks and conserve 1.8 billion barrels of oil over the lifetime of the regulated vehicles. In August 2012, the Obama administration finalized an extension of light-duty CAFE standards through MY 2025, when the standard will hit 54.5 miles per gallon. EPA estimates that the new standards will save 163-170 billion gallons of fuel and generate more than $450 billion in net economic benefits.

    The Obama administration finalized fuel efficiency and GHG emission standards for medium- and heavy-duty vehicles (including buses and semi-trucks) in August 2011. The standards, covering MY 2014-2018, were the first such federal rule for large vehicles. EPA estimates that the standards will reduce oil consumption by approximately 530 million barrels and reduce CO2 pollution by 270 million metric tons over the life of the affected vehicles. The White House initiated a second round of fuel efficiency standards for large vehicles in February 2014, directing EPA and NHTSA to issue a draft rule for MY 2019 and beyond by March 2015.


    President Obama’s Climate Action Plan

    President Obama announced his Climate Action Plan (CAP) on June 25, 2013. The CAP included a memorandum to the EPA to set carbon pollution standards for new and existing power plants, which account for 38.7 percent of U.S. carbon emissions. The goal outlined in the CAP follows Obama’s 2012 pledge to reduce U.S. emissions 17 percent below 2005 levels by 2020. The CAP sets three pillars to guide U.S. actions to meet this goal: cut carbon pollution, prepare the U.S. for climate impacts, and lead international efforts to combat climate change on the global level and help the world prepare for its impacts. The first pillar, largely focused on carbon pollution from power plants, led to EPA releasing the Clean Power Plan the following year.


    Clean Power Plan

    The Clean Power Plan (CPP) was introduced by the EPA in draft form on June 2, 2014, and published in the Federal Register on June 18. The CPP implements EPA’s authority under Clean Air Act section 111(d) (42 U.S. Code § 7411 section (d)) to regulate carbon emissions from existing power plants. The CPP will provide a 30 percent cut in the carbon emission rate (pounds of CO2 per net megawatt hour (MWh)) from the U.S. power sector compared to 2005 levels by 2030. The regulation requires different percentage cuts from each state and gives states the flexibility to determine their own emissions reduction plan. EPA determined each state’s target reductions for 2030 (and annual interim goals beginning in 2020) by analyzing opportunities within the state to reduce emissions, the carbon policies the state is already using, and the unique structure of each state’s energy system.

    The plan has four “building blocks” which the states can use to achieve reductions, including: improve the heat efficiency of fossil fuel power plants, substitute lower emissions power generation (i.e. natural gas combined cycle plants) whenever possible, install more zero emissions power generation (i.e. renewable and nuclear energy), and increase end-use energy efficiency. The final CPP is expected in June 2015. Under the proposed rule, states have until June 30, 2016, to submit their CPP State Implementation Plans (SIPs) or to submit an initial plan and request an extension. States granted extensions have an additional year (if developing an independent SIP) or two years (if developing an SIP in coordination with other states) to submit their plans.

    EPA estimates that for every dollar invested in this rule, there will be a $7 return in health benefits. For more information, see the EESI article on the rule.


    Author: Jenifer Collins

    Editor: John-Michael Cross -