This Earth Day, as America’s motor city faces perhaps its darkest hour, Arnold Schwarzenegger rode in yesterday and (to mix a cinematic metaphor) made Detroit’s day.

The region’s troubles aren’t the automakers’ fault, he said, but due to a lack of consistent government policy to promote higher fuel economy and the use of alternative fuels.

Two years ago, when California was still fighting the Bush administration over greenhouse-gas emissions limits, a Michigan Representative running for reelection reportedly erected billboards around Detroit that read: “Arnold to Michigan: Drop Dead.”

While the California governor denies he ever said that, he did tell automakers last year to “Stop whining,” and start producing more alternative fuel cars.

Schwarzenegger was interviewed on Monday at the Society of Automotive Engineers World Congress by CNBC correspondent Phil LeBeau.

There he said that U.S. presidents since Dwight Eisenhower have talked about energy independence, but that policies keep changing with the price of gas. “We cannot make policy according to where the oil price is at any given time,” he said.

He insisted that California will stick with its target of reducing greenhouse gas emissions to 1990 levels by 2020 regardless of who occupies the governor’s mansion in Sacramento. The state wants to “be an inspiration to the rest of the country…to go in the same direction” and to be “a good example for India, for China, for Brazil, and for other developing nations,” he said.

“That we are the biggest polluters in the world is unacceptable. We can do better than that…I think it is embarrassing that the United States still has only 2.8 percent of renewables [sic],” when some European countries get up to 20 percent of their energy supplies from renewable sources.

As a fan of American cars (and Hummers, in particular; the governor has a Hummer converted to fuel-cell power, and one converted to run on biodiesel), the Governator says he supports aid to the Detroit automakers. “For anyone to say…don’t help is a huge amount of nonsense talk,” he said.

In the end, he says, “The car industry is saying: ‘I’ll be back!”

--Eric Evarts