Long before the frenzy to "go green," the ferrous and nonferrous metal industries had made significant strides in reducing greenhouse gas (GHG) emissions. The question today is how much further they can cut emissions without the benefit of a step change in production technologies.

For the past two decades, aluminum and steel producers have been aggressively reducing GHG emissions—partly as a by-product of efforts to improve energy efficiency and slice fuel consumption. Since 1990, the aluminum industry has reduced overall GHG emissions by more than 50 percent, including lowering emissions of perfluorocarbons (PFCs) by about 90 percent, according to Robert Strieter, vice president of environment, health and safety at the Aluminum Association.

Over the same period, the U.S. steel industry has sliced its energy use per ton by 33 percent in a drive that also has resulted in a sizeable reduction in GHG emissions, mostly carbon dioxide, according to Larry Kavanagh, vice president of environment and technology at the American Iron and Steel Institute (AISI). While Kavanagh couldn't quantify the GHG reduction (the...