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Greenhouse Gas Emissions Standards in the United States

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Greenhouse Gas Emissions Standards in the United States

            Without a doubt, Americans love to drive. Nationally, U.S. drivers travelled a total of 3.15 trillion miles in 2015 alone, equivalent to over 300 trips from Earth to Pluto and back. Driving has increased overall by about 35% since 1990, and greenhouse emissions from the transportation sector have increased substantially over this same period. [i] Mobile sources of air pollution are currently responsible for about one-third of total U.S. greenhouse gas emissions, with passenger cars and light trucks contributing the majority share of this carbon footprint.[ii]  Over the past decade, regulators combined independently-developed programs at the federal and state levels to form a cohesive system of vehicle greenhouse gas emission regulation.

            The transportation sector’s carbon footprint, second only to the electrical industry, is a major environmental issue that was all but ignored by federal regulators until 2007.  In that year, the Commonwealth of Massachusetts and several other plaintiffs sued the U.S. Environmental Protection Agency because the agency was not regulating greenhouse gasses emitted from motor vehicles.  The plaintiffs in Massachusetts v. Environmental Protection Agency[iii], claimed that the Clean Air Act required the EPA to create standards for motor vehicle emissions that could reasonably endanger public health or welfare.  Because scientific evidence had documented global climate change and related health and safety impacts of rising concentrations of greenhouse gasses in the atmosphere, the Massachusetts plaintiffs argued that the EPA was required to act.  The EPA countered that greenhouse gasses did not qualify as air pollutants under the Clean Air Act, and therefore the federal government was not able to regulate carbon emissions under the authority of this statute.  The majority of the Supreme Court decided in favor of Massachusetts and the other plaintiffs, and the EPA was required to act.

            The federal government responded to the Massachusetts v. EPA decision through legislative and administrative action.  Federal legislation specifically directed at curbing greenhouse gas emissions from vehicles began with the signing of the Energy Independence and Security Act of 2007.[iv]  The Energy Independence Act created a limited system of incentives for the development and use of vehicles with low or zero greenhouse gas emission levels.  Most significantly, however, the law increased mandatory fuel economy standards for new passenger vehicles by expanding the Corporate Average Fuel Economy (“CAFE") credit trading program established in the early 1970s.[v] 

The CAFE standards establish mandatory fuel efficiency minimums for vehicles sold in the United States and imposes financial penalties on auto manufacturers unable to meet the regulations.  The Energy Independence Act increased the CAFE standards for the first time since they were created, requiring a 40% bump in automobile fuel economy up to a mandatory 35 miles per gallon by 2020.[vi]  CAFE standards continue to ratchet upwards, with a mandatory 54.5 mile per gallon fuel efficiency and strict carbon dioxide emissions restrictions imposed upon new vehicles by 2025.[vii]

 America’s current system for controlling carbon emissions from vehicles has developed over time, and a single state – California – can be credited for paving the way for more effective vehicle emissions controls nationwide.  While the federal government limited its regulation of carbon emissions from motor vehicles by focusing on fuel efficiency, California has created its own system for regulating greenhouse gases.  The state is uniquely positioned to act, as California is the only state that has applied for and received a federal preemption waiver under a provision of the Clean Air Act that allows states to enforce their own air pollution regulations under certain circumstances. Further, the Clean Air Act waiver authorizes other jurisdictions to adopt California’s standards, placing the state in a unique position of national leadership.[viii] 

After securing this waiver, the California Air Resources Board (CARB) replaced the U.S. EPA as the agency responsible for establishing and maintaining air quality within the state. CARB operates a complex and progressive system of air quality regulation that has been adopted, at least in part, by a dozen other states. Following the Energy Independence Act’s legislative update to the CAFE standards, the EPA formally identified six greenhouse gasses – carbon dioxide, methane, sulfur hexafluoride, nitrous oxide, hydrofluorocarbons, and perfluorocarbons – as pollutants regulated under the Clean Air Act.  Immediately thereafter, the EPA initiated a formal partnership with CARB with the goal of collaborating on the development of new CAFE standards and other rules improving fuel efficiency and reducing greenhouse gas emissions.[ix]

The Clean Air Act and CAFE standards developed collaboratively between federal and state agencies now integrate greenhouse gas controls into the national system of motor vehicle air pollution regulation. However, CAFE does not set emissions standards for individual vehicles and as a result does not prevent the sale of carbon-intensive automobiles.  Rather, auto manufacturers may market and sell vehicles with low fuel efficiency and high carbon emissions so long as they offer plenty of clean, efficient vehicles to bring up the average footprint of the entire fleet. Such a policy begs the question of whether auto makers will actually make meaningful changes to overall vehicle design and efficiency, or whether large, gas-guzzling trucks and SUVs will remain the status quo.  Increasing production of hybrid and fully-electrical vehicles has been integral in the achievement of CO2 emissions targets thus far, and meeting the emissions targets required by 2025 will require an even greater deployment of non-gasoline vehicles.[x]  California’s existing zero-emissions vehicle program provides a policy framework for expanding the deployment of this important technology.  California recently collaborated with 7 other states and a consortium of international partners to implement policies that will accelerate the adoption of low and no emissions vehicles.[xi] 

The federal government began regulating greenhouse gas emissions from vehicles with a landmark Supreme Court case in 2007, but health and safety impacts from manmade climate change continue to be of concern.  Industry-wide greenhouse gas emissions from transportation are rising very quickly, and American travelers continue to consume fossil fuels in increasing amounts.[xii]  However, despite its late start, national regulation of vehicle greenhouse gas emissions have shown promising results. CO2 emissions from new personal vehicles are at record annual lows – an even more impressive achievement considering how recently the relevant policies have been developed. [xiii] In fact, 2016 marked the fourth consecutive year that U.S. automakers exceeded federal requirements for greenhouse gas emissions for passenger vehicles, a surprising turn of events considering the auto industry’s longstanding complaints that CAFE standards are too stringent.  Average automotive fuel economy is at a record high of 24.8 miles per gallon, and the post-2007 emissions regulations have prevented the release of 130 million metric tons of carbon dioxide into the atmosphere.[xiv]  State-level greenhouse gas regulation provides an important counterweight to the political pressures that often prevent such policies from being developed on the federal scale, and California’s continued leadership in this field creates space for optimism in the global fight against climate change.


[i] Kaenel, C. v. (2016, February 22). Americans Are Driving More than Ever. Retrieved from Scientific American: https://www.scientificamerican.com/article/americans-are-driving-more-than-ever1/

[ii] United States Environmental Protection Agency Office of Transportation and Air Quality. (2016). Fast Facts: U.S. Transportation Sector Greenhouse Gas Emissions 1990-2014. Retrieved from: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100ONBL.pdf

[iii] 127 S. Ct. 1438 (2007)

[iv] Energy Independence and Security Act of 2007, P.L. 110-140 (Dec. 19, 2007).

[v] Energy Independence and Security Act, Section 104 (2007).

[vi] Energy Independence and Security Act, Section 102 (2007).

[vii] United States Environmental Protection Agency. (2016, November 16). Regulations for Greenhouse Gas Emissions from Passenger Cars and Trucks. Retrieved from https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-greenhouse-gas-emissions-passenger-cars-and.

[viii] Environmental and Energy Study Institute. (2015, August 26). Fact Sheet: Vehicle Efficiency and Emissions Standards. Retrieved from http://www.eesi.org/papers/view/fact-sheet-vehicle-efficiency-and-emissions-standards

[ix] National Highway Transportation Safety Administration. (2010). NHTSA and EPA to Propose Greenhouse Gas and Fuel Efficiency Standards for Medium- and Heavy-Duty Trucks; Begin Process for Further Light-Duty Standards: Fact Sheet. Retrieved from https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/ld_hd_fe_factsheet.pdf

[x] United States Environmental Protection Agency. (2016). Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2016. Retrieved from  https://www.epa.gov/sites/production/files/2016-11/documents/420s16001.pdf

[xi] California Environmental Protection Agency Air Resources Board. (2017, January 18). Zero Emission Vehicle (ZEV) Program. Retrieved from California Air Resources Board: https://www.arb.ca.gov/msprog/zevprog/zevprog.htm

[xii] National Highway Transportation Safety Administration. (2010). NHTSA and EPA to Propose Greenhouse Gas and Fuel Efficiency Standards for Medium- and Heavy-Duty Trucks; Begin Process for Further Light-Duty Standards: Fact Sheet. Retrieved from https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/ld_hd_fe_factsheet.pdf

[xiii] United States Environmental Protection Agency. (2016). Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 Through 2016. 

[xiv] Sneed, A. (2016, December 1). Why Automakers Keep Beating Government Standards. Retrieved from Scientific American: https://www.scientificamerican.com/article/why-automakers-keep-beating-government-standards/