Alcoa has repeatedly supported stricter Corporate Average Fuel Economy standards and is a member of the U.S. Climate Action Partnership, a lobby for restrictions on greenhouse gas emissions. These policies act as energy taxes -- effectively taxing the weight of a car.
Absent such regulations, an aluminum car frame is much more expensive than a steel car frame. With these regulations, aluminum, which is lighter, becomes more desirable.
...Making aluminum car frames requires much more energy than making steel car frames. One stage in the process -- dissolving the alumina to get pure aluminum -- inherently gives off carbon dioxide and the far more potent greenhouse gasses hexafluoroethane and tetrafluoromethane.
But Alcoa makes its aluminum in Australia, where Washington's CAFE and climate policies can't touch it.
As Carney puts it, it's easy being green under Obama.