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November 1, 2011

Carbon Counting

Why the evolving science of measuring life cycle emissions is both helpful and flawed.

Maybe you thought that buying a lightweight, eco-friendly hybrid would be your way of fighting global warming. Fewer emissions, great gas mileage, a relatively small carbon footprint.

Then some environmental experts come around saying that manufacturing the weight-reducing materials that go into the carbon fiber hatch door on your car puts beaucoup amounts of greenhouse gases (GHGs) into the environment—much more than the standard steel part. The environmental experts probably come armed with “life cycle assessments” (LCAs), or detailed accounts of the energy that goes into producing a product—and the emissions that come out.

Manufacturers have used life cycle assessments since 1969, when Coca-Cola ran a study to determine the comparative energy and resource costs of various types of containers. Other manufacturers, particularly in Europe, followed suit, using these detailed “cradle-to-grave” studies to make choices about the materials that went into their products. In those days, the emphasis was on energy use. For example, how much electrical power went into producing the glass, plastic or metal in one of those Coke bottles.

Now, with their numbers expanding geometrically, LCAs are fast becoming one of society's primary defenses against environmental deterioration. A mountain of new studies are being commissioned every year by corporations, government regulators and environmental groups, as worries about sustaining Earth's resources have gone global. Everything from the carbon impact of ethanol fuels to the structural capabilities of various metals in cars, from the disposal of used engine oil to the relative merits of different clothing fabrics, is being given the rigorous LCA treatment.

The results have sometimes been startling. Products that are marketed as “green” turn out, under the LCA lens, to have merely shifted environmental impact from one part of the supply chain to another. Take, for example, the “zero emissions vehicles,” or ZEVs, entering the market. “From a life cycle perspective, zero-emissions vehicles should be called emissions-somewhere-else vehicles, since they typically shift the environmental burdens from vehicle use to fuel production,” says Roland Geyer, professor of industrial ecology at University of California, Santa Barbara. The so-called ZEV cars don't emit greenhouse gases, but the production of the electricity or hydrogen that fuels them put out ample GHGs.

THE EVOLUTION OF LIFE CYCLE STUDIES

Nobody is keeping track of the total number of LCA studies that are produced every year, but LCA practitioners say they now number in the hundreds. In recent years, the United Nations Environment Programme has joined the Society of Environmental Toxicology and Chemistry to launch a program promoting a global “life cycle initiative,” and the European Environment Agency began requiring LCAs to back up labeling claims on manufactured products. The U.S. Environmental Protection Agency does not generally require LCAs, but it maintains an archive of environmental studies.

Since 1997 life cycle studies have been elevated to the realm of scientifically validated research, with their own set of ISO standards (developed by the International Organization of Standardization) complete with the requirement of peer review.

Not all LCAs aim for environmental improvement, of course. LCAs are often commissioned by manufacturers to pitch their products or, if the results are not positive, to be filed away as proprietary information. Mercedes-Benz now issues an LCA, with fuel consumption, emissions and recyclability data, for each new car it sells. Both the steel and aluminum industries frequently refer to LCAs that purportedly show the environmental superiority of their own products. With heightened scrutiny from regulatory agencies, the same is happening in other industries.

AN EXEMPLARY ASSESSMENT

Experts sometimes cite a 2010 study of aluminum beverage cans, the first such study in 17 years, as an exemplary life cycle assessment, adhering to ISO standards. The report was produced by PE Americas, a joint venture of the German firm PE International and the U.S. firm Five Winds International, which have since merged to become the largest producer of LCAs and LCA software in the world. The detailed study, commissioned by the Aluminum Association, considered raw materials extraction, fuel usage, processing materials (like chemicals and solvents), the conversion of raw materials (from bauxite to alumina to rolled aluminum), transportation to various processing centers and recycling. Collectively, it produced a blizzard of data on everything from energy and resource inputs to emissions outputs and final products.

PE Americas researchers delved into the costs of extracting bauxite from mines in countries as diverse as Brazil (North America's largest supplier at about 3.2 million metric tons, nearly a third of the total) and Australia (232,000 metric tons). They calculated the costs of shipping the raw material to processing centers, either in the United States or elsewhere, and the fuel expenses of converting it to alumina—the intermediary substance created when powdered bauxite is mixed, heated and refined in a slurry with a cocktail of sodium compounds.

It takes about 2.7 metric tons of bauxite to produce a metric ton of alumina, the PE Americas report says, adding, “This is a global representative average that has been adopted to model the alumina production process in North America.”

Once the bauxite has been turned into alumina, it's shipped to an aluminum manufacturer. The process is, of course, energy intensive, with more than 15,500 kilowatt hours of electricity expended for each metric ton of primary aluminum. And it is heavy on GHG emissions, with the entire bauxite-to-aluminum course producing 9.7 metric tons of carbon dioxide per metric ton of aluminum; most of it, about 7.5 metric tons, comes from the electrolysis process. (Steel produced in an electric arc furnace puts out only a ton of CO2 per ton of finished product.)

The PE Americas study measures energy inputs and emissions outputs for every mining center, shipping and trucking operation, factory, power plant and processing site along the way. Among other things, it found that about 122 kilograms of CO2 is produced for every 1,000 aluminum cans turned out. It also found that nearly 68% of used beverage cans and scrap from the production process is recycled—the highest of any beverage package material, the Aluminum Association says.

Though the richly detailed report does not draw comparisons between aluminum cans and those made from other materials, like glass or plastic, the Aluminum Association has used it freely to pitch the environmental superiority of its product. The association has turned over the LCA results to Wal-Mart, for use in its scorecard of comparative costs of beverage cans, and to the U.S. Environmental Protection Agency. (Wal-Mart is still compiling data from all of its suppliers and has not made a decision on which beverage container will eventually go on the shelves of its stores.) A press release from the association about the PE Americas study notes that, compared with beverage cans produced 17 years ago (when another LCA was performed), aluminum has reduced its carbon footprint by 44%, its energy usage by 30% and its package weight by 15%.

RELIABLE DATA?

Is there a potential weak spot for LCAs? For example, don't bauxite ores vary in yield, depending on the country they came from or even on the mine that produced them within a particular country? Without exact numbers, particularly when dealing with undeveloped countries, researchers must employ industry averages, possibly undermining the precision of their findings, critics have said. “Life cycle assessments are very diverse and very complicated,” says National Resources Defense Council senior scientist Allen Hershkowitz. “They don't give the last-word accurate assessment. They're estimates—though estimates that have to comport with accurate analytical protocols.” In other words, by sticking to ISO standards, the results are valid in a general, if not in a particular or “site-specific” sense.

But Nuno Da Silva, PE International's life cycle solutions product manager, insists the goal of the beverage can study was to produce a general picture of beverage can production rather than to focus on a specific manufacturer of aluminum cans. “If you want to make an LCA on a type of product, like aluminum cans, you have to use average data,” he says. “There's no way around it.”

The data improves year by year, LCA practitioners say. With increasing concerns globally about environmental issues, many more countries are starting to monitor their own industries, they say. “Are we at a state where the precise characteristics of every process in the world is at the same level of quality and completeness? No,” says Bruce Vigon, scientific affairs manager for the Society of Environmental Toxicology and Chemistry and an LCA specialist. Nevertheless, he adds, developing countries like China and Brazil are now providing useful data of their own to sharpen the findings of LCA researchers. “These data sets are more and more available to us,” Vigon says.

CONSIDER ALL THE FACTS

While the carbon footprint is often the most remarked upon finding of an LCA, environmentalists stress that valid life cycle studies should go far beyond simple measurements of GHG emissions. “Just measuring for carbon gives you a very limited picture,” says Hershkowitz. He adds that some companies have “narrowed the boundaries” of their life cycle assessments “to make their product look a little better.”

In fact, different LCAs can appear to come to contradictory conclusions about the same products. It all depends on how a study is framed, LCA practitioners say.

Last year, LCA specialists completed a report sponsored by Canadian, Chinese and American governmental agencies on magnesium front-end auto parts, showing the relative benefits of steel, aluminum and lightweight magnesium in automobile engineering. This LCA compiled the environmental performance of steel, magnesium and aluminum front-end parts, using the Cadillac CTS as its model. Again, researchers went “cradle-to-grave,” including mining of primary materials, pre-fabrication production, manufacturing of auto parts, assembly, transportation and end-of-life recycling, as well as the all-important period when the car is actually being driven.

By using structural magnesium in the front end, the car sheds 55 kilos compared with the standard steel, while the aluminum-intense car slimmed down by 21 kilos. Less weight means better mileage, so both magnesium and aluminum have an advantage there over steel. But there's a catching point. When the production phase is taken into account, magnesium, with its heavy electricity requirement during manufacturing, starts to lose its low-carbon advantage. Steel still has the edge in terms of production efficiency, with aluminum a distant second. (The report says that GHGs emitted in manufacturing magnesium auto parts are about two-and-a-half times those produced by aluminum and approximately six times those for steel.) Cradle-to-grave, though, aluminum comes out on top, the report contends.

“Overall large magnesium structural parts can provide environmental benefits in terms of energy use and GHG emissions vis-à-vis steel within the expected life of the car,” the researchers say. “But overall, the aluminum design is still better at achieving the break-even distance from energy use and GHG emissions perspectives within the vehicle life.”

All of which leaves steel proponents sputtering. Advanced high strength steel, they say, is not only a low-emissions product but, because of its comparative strength, it is now being used in “lightweight” cars, producing less bulky parts with the same strength and toughness.

OUR WORD AGAINST THEIRS

Representatives of the American Iron and Steel Institute pull out another report by WorldAutoSteel, this one purporting to show the superior advantages of steel. In a mass reduction study performed by Lotus Engineering and funded by the U.S. Energy Foundation, researchers compare three versions of the 2009 Toyota Venza. One model is made with mostly conventional steel, another with advanced high-strength steel (AHSS) and a third with an array of weight-saving materials like magnesium, aluminum and fiber-reinforced plastic.

In this case, there's a dead heat between the two experimental cars, at least in the cradle-to-grave GHGs contest. The lightweight model, with its costly alternative materials, may weigh in a svelte 218 kilos lighter than the AHSS model, but the GHGs emitted through the lifetime of each are virtually the same. Add a hybrid engine to the steel-intensive body, though, and steel wins hands down, with an emissions load of almost 3,000 fewer kilos.

So how do researchers explain the differing results? Steel industry experts say that the magnesium front-end study went wrong when it focused on just one section of the Cadillac CTS. “You can't break it up by percentages of components,” says Jody Shaw, U.S. Steel Corporation's director of technical marketing. “You have to look at the impact of the entire vehicle.” On the other hand, aluminum industry experts say the Venza study undervalues the recyclability of aluminum. “The energy required to recycle aluminum is less than that for recycling steel,” says Ken Martchek, director of life cycle and environmental sustainability for Alcoa Inc. “For that reason, the front-end study gives aluminum a higher credit.” He contends that the Venza study is biased in favor of steel.

But Roland Geyer, who is involved in automotive and steel life cycle studies at the University of California, Santa Barbara, says the definitive study has yet to be done. “I would say that it's still up in the air,” Geyer says. “I don't think any one material has made its case conclusively.”

LCA practitioners acknowledge that LCAs often don't answer all questions. “Some people get frustrated because LCAs don't come back with clear answers,” Geyer says. “Rather than say the study was wrong, you have to say, OK, maybe we didn't ask the right questions.”

Flawed or not, LCAs will be an increasingly important presence in manufacturing and public policy, Geyer and others say. The LCA is the only technique that gives both a big-picture view and detailed close-ups of products as they progress from raw material to marketable item to recyclable leftover. Says Geyer: “It's my personal belief that we're going to see increasingly that environmental regulation and corporate and public policy will be based on life cycle thinking.”