A significant increase in the use of aluminum to build aluminum-intensive vehicles would bring dire environmental impacts, says a steel executive at this spring's SAE Total Life Cycle Conference. "Our concern is carbon dioxide, including both the amounts released in automobile tailpipe emissions as well as the amounts released in the production of materials used in the manufacture of automobiles," says Peter Peterson of USX Corp. Citing findings of a Massachusetts Institute of Technology (MIT) study, the steelmaker notes that any improvements in powertrain efficiency and reduction in CO2 emissions will lengthen the time it takes to offset aluminum's initial CO2 burden. He argues that as cleaner automotive power sources become more prevalent, the need for expensive and difficult solutions, such as those provided by aluminum, diminishes, and steel solutions become attractive.