Life Cycle Emissions to Help Quantify ‘Green’

Recent media coverage of electric vehicles has featured claims of high environmental impact due to the production and disposal phases of the vehicle life cycle. ACEEE’s Green Book, which evaluates such impacts for real vehicle models, helps put this issue into perspective.

Among model year 2012 vehicles, production and disposal emissions were about 30 percent higher for EVs than for comparably-sized conventional vehicles, due to relatively high per-pound battery production emissions. And while these ‘embodied’ emissions accounted for 22 percent of total vehicle impacts on average, they were just above half for EVs.

Nonetheless, EVs received very high Green Scores, reflecting low environmental impact, not a surprise given their zero in-use emissions. And of course, their scores will climb further if and when the ‘upstream’ emissions associated with electricity generation decline.

More broadly, as vehicles’ in-use emissions and energy consumption fall, production and disposal will indeed be increasingly important determinants of environmental impact. Material substitution to reduce vehicle weight, which in turn allows downsizing of vehicle systems and further weight reduction, is already a key strategy to boost fuel economy. Production of advanced, lightweight materials can be energy-intensive, and net impacts will reflect this, together with material recyclability and the fuel savings these materials enable. But careful analyses of these considerations to date have shown a clear net reduction in energy use and GHG emissions from the use of high-strength steel and aluminum, for example.

The recent light-duty vehicle fuel economy and GHG emissions rule provoked a lively discussion of the possibility of standards based on full life cycle emissions. At present, this would be quite a challenge, given the paucity of data on the content and production of individual models and differing views on life cycle analysis.

And for now, fuel economy remains the undisputed heavyweight in vehicle environmental impacts. But we should prepare for a time when, thankfully, that will no longer be the case.

 

Therese Langer is Transportation Program Director of the American Council for an Energy-Efficient Economy, www.ACEEE.org