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The fistfight between steel and aluminum for a greater share of the automotive market is not just about making vehicles lighter and more fuel-efficient, it’s about which material offers a net benefit to the planet. Both sides claim they win in a full life-cycle assessment.

The life cycle of a vehicle has three parts: production, drive time and end-of-life disposal. Boosting mileage while reducing tailpipe emissions is the primary goal, but the environmental drawbacks of metal production and the environmental benefits of post-use recycling are important considerations, as well. On that, both sides agree. But that’s where the agreement ends.

The Steel Market Development Institute maintains that producing primary aluminum ingot in North America, which requires a lot of electricity, generates at least four times the emissions of producing steel. There is a huge pool, about 80 million tons of steel, available for recycling each year, which greatly reduces the need for primary production. In comparison, only about 200,000 tons of automotive aluminum sheet is scrapped and available for re-melting each year. Therein lies aluminum’s Catch-22. To create a sufficient amount of automotive aluminum for recycling in the future would require producing larger quantities today. Fortunately for the environment, claims SMDI, the combination of advanced high-strength steels and new engine technology is sufficient for the auto industry to meet most fuel economy targets.

Heidi Brock, president and CEO of the Aluminum Association, strongly disputes the steel industry claim that, when all vehicle life-cycle phases are considered, use of AHSS produces a smaller total carbon footprint than aluminum. She points to a U.S. Energy Department report that concludes: “A full life-cycle analysis confirms that—when compared with both traditional and advanced steels in the areas of cumulative energy demand, potential ozone depletion and other likely factors in climate change—aluminum rises to the top as the best choice for the environment.”

The steel industry’s life-cycle assessment is premised on old data, which overstates aluminum’s carbon footprint by nearly 20 percent, she argues. Current data confirms a nearly 40 percent reduction in carbon emissions for North American primary aluminum production since 1995. The steel industry significantly downplays mass reduction achievable with aluminum, and overplays mass reduction achievable with AHSS. It wrongly assumes auto body mass reduction potential of 25 percent for AHSS and 35 percent for aluminum. Production design studies from automakers have found mass reduction potentials of 20 percent for AHSS and 40 percent for aluminum, she claims.

Without a Ph.D., it’s impossible to vet the positions of both camps. They each make a strong case for their product. With auto sales forecast to grow for the seventh year in a row, producers and distributors of both metals promise to be winners, at least in 2016.