"My thoughts on what has or hasn't been the cause of climate change have nothing to do with the decisions I make to advance the cause of General Motors," he wrote.

Lutz said GM was continuing development of the battery-powered, plug-in Chevy Volt and other alternatives to traditional internal combustion engines.

As part of a campaign against higher fuel economy standards, Lutz wrote in a 2006 blog posting that forcing automakers to sell smaller cars would be "like trying to address the obesity problem in this country by forcing clothing manufacturers to sell smaller, tighter sizes."

In December, President George W. Bush signed a law mandating a 40 percent increase in fleetwide fuel economy by 2020, the first substantial change in three decades.