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Beyond the Tailpipe to Considering Life Cycle Emissions
Historically, fuel economy regulations have been an effective mechanism for improving vehicle fuel economy and reducing greenhouse gas (GHG) emissions associated with fuel combustion. Through model years 2004 to 2014, CO2 emissions decreased by 95 grams per mile (g/mi), or 21 percent, and fuel economy increased by 5.0 mpg, or 26 percent.1 These improvements were achieved mainly through the development and implementation of new engine technologies. As regulations become even more stringent, however, automakers are looking to additional solutions, such as reducing vehicle weight. In anticipation of these requirements, the steel industry accelerated introduction of advanced high strength steels (AHSS) in the 2000s and continues to introduce new AHSS grades with improved properties. These new materials offer not only higher strength, but higher formability, both of which enable vehicle weight reduction. Importantly, these new materials have the advantage of "still being steel," meaning their production generates comparatively fewer GHG emissions than alternative materials and they are 100 percent recyclable across steel grades.
The life cycle of a vehicle has three parts (or phases): production, use (driving), and end-of-life disposal (recycling). The production phase accounts for up to about 30 percent of total GHG emissions for internal combustion engine and hybrid electric vehicles and as much as 47 percent for battery electric vehicles (BEVs).2 As fuel economy increases and as the share of alternate power train vehicles, such as BEVs, increases, production emissions will become more important.
Production emissions are an important environmental consideration because, in addition to the widespread adoption of AHSS, automakers are also considering aluminum, magnesium and carbon fiber. Producing primary aluminum ingot in North America currently generates at least four times the emissions of producing steel, (2.25 ton CO2eq/ton for steel vs. 8.94 ton CO2eq/ton for aluminum), even when using the aluminum industry's assertion that aluminum smelters in North America operate using 75 percent hydropower.3 Power accounting methods using regional grid information and/or recognizing imported aluminum ingots would skew production emissions even higher. Production of other materials can generate 20 times the emissions of steel.4
These emissions result in additional environmental impacts before a vehicle is ever driven and they are not accounted for in current fuel economy regulations or factored into most automotive design practices. Once emitted, GHGs immediately begin absorbing energy from the sun leading to warming of the atmosphere. Major GHGs remain in the atmosphere for decades (methane for example) to centuries (CO2 for example) after being released.5 Therefore, the timing of GHG emissions is an important consideration.
Looking Beyond the Tailpipe
As a result of economic and technological limitations, it is highly unlikely automakers will design for fuel economy targets above what the regulations require. Increasing a vehicle's fuel economy requires monetary investments, whether via materials, new engine technologies, improved aerodynamic design or other means. There is little reason for consumers to pay a premium for additional miles per gallon, especially when the cost of fuel is at a seven-year low and is expected to remain low for the foreseeable future. Currently, automakers are designing vehicles to meet future fuel economy targets—so vehicles in the same class will have essentially the same fuel economy, no matter what materials are used. With the same fuel economy, there will be little to no difference in their emissions during driving. Ultimately, since future use-phase emissions will be equivalent, production emissions play a more important role.
While production emissions are critically important, end-of-life disposal must also be recognized to consider a vehicle’s lifetime emissions. Steel from vehicles is consistently recycled at high rates because of the ease of magnetic separation following shredding. Steel can be continuously recycled, and unlike other metals requiring sorting and recycling to the same grade to maintain quality, steel can be recycled into any grade without loss of quality. Approximately 80 million tons of steel are available annually to be recycled into automobiles or any other new steel product.6 On the other hand only about 200,000 tons of scrap automotive aluminum sheet are currently available annually for recycling. This highlights the "Catch-22" concerning alternative materials: Use of recycled material could replace some primary production, lowering production emissions. Creating a sufficient pool of recycled alternative materials, however, means producing larger quantities of these materials now (and their associated high emissions) so they can be recovered 12 years or more in the future when vehicles using these materials reach end-of-life (12 years is the average vehicle life). Fortunately for the environment, the combination of AHSS and new engine technology is proving sufficient for automakers to hit the vast majority of fuel economy targets.
The time is right to begin looking beyond the tailpipe and instead consider the full life cycle emissions of vehicles. The trend is not unlike what has happened in the construction industry over the last several years. Initially, the focus of green building standards and rating programs were on operational energy improvement, as it was the dominant phase in the life cycle of buildings. As the use phase of buildings has become increasingly more efficient, however, the focus is now shifting to building materials and the construction process through the incorporation of new assessment methods. These methods include whole building life cycle assessment (LCA) and environmental footprinting. For example, the Material and Resources section in the latest version of the Leadership in Energy & Environmental Design (LEED) green building rating program (LEED v4) was significantly rewritten to include LCA-related credits for whole buildings and building products. Similarly in automotive design, regulators and engineers have been doing an excellent job improving fuel economy, but now need to consider the emissions from production of the materials that go into every vehicle, to lessen the automotive sector's impact on our environment with certainty.
1. U.S. Environmental Protection Agency, Office of Transportation and Air Quality (OTAQ). “Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 – 2015" website. Available online: http://www3.epa.gov/otaq/fetrends.htm
2. Derived from the peer-reviewed University of California, Santa Barbara Automotive Materials GHG Comparison Model V4, October 2013.
3. The Aluminum Association. "The Environmental Footprint of Semi-Finished Aluminum Products in North America: A Life Cycle Assessment Report." December 2013.
4.> Derived from the peer-reviewed University of California, Santa Barbara Automotive Materials GHG Comparison Model V4, October 2013.
5. U.S. Environmental Protection Agency. "Climate Change Indicators in the United States: Greenhouse Gases" website. Available online: http://www3.epa.gov/climatechange/science/indicators/ghg/
6. Steel Recycling Institute. "Goal: Steel, Our Most Sustainable Material" website. Available online: http://www.recycle-steel.org/sustainability.aspx