California Republican Gov. Arnold Schwarzenegger (search) is warning that global warming is a threat to the world's future. And, at a recent U.N. conference on the environment, he laid out his plan for curbing it.

"I say the debate is over. We know the science. We see the threat. We know the time for action is now," Schwarzenegger told an audience last week attending the World Environment Conference in San Francisco, the first time the United Nations has held the event in the United States.

Calling global warning an "imminent threat," Schwarzenegger did not specify how he would meet the goal of reducing emissions in 2010 to less than those produced in 2000. Through the voluntary program, which Schwarzenegger planned to introduce through executive order, greenhouse gases (search) — carbon dioxide, methane and nitrous oxide — would also hit 1990 levels by 2020 and 80 percent below 1990 levels by 2050.

Representing the world's seventh-largest economy and one-eighth of the nation's population, the governor's message is a broad pledge, but not one that everyone believes he will fulfill.

"It looks a little like taking advantage of an opportunity and going to a friendly audience and telling them what they want to hear without doing anything to make people mad. So it's like having your cake and eating it too," said Mary Nichols, a board member on the California League of Conservation Voters.

"It is political, and the first question ought to be if he means to put his policies where his mouth is," said Chris Horner, a senior fellow at the Competitive Enterprise Institute.

Schwarzenegger isn't a stranger to environmental issues. Last September, his state became the first to adopt regulations to curb greenhouse gas emissions from automobiles. Schwarzenegger also has introduced a "hydrogen highways" program to install hydrogen fueling stations across the state and a "million solar roofs" program that aims to subsidize the installation of solar power equipment in homes.

"The governor is sincere in his desire to do good by the environment, we've seen him make good appointments," said Nichols. "The problem we have with this initiative is it looks a little too slick."

Critics of the governor charge that the reduction in carbon emissions would cost California consumers and businesses billions in taxes and fees to fund investment in clean energy, something a pro-business Republican might be reluctant to do.

"If he means this and believes what he says, which I doubt, but if he moves from cheap virtues into energy rationing, which is what is required [with what] you're talking about ... he is not going to be elected to anything," Horner said.

Schwarzenegger's executive order leaves it up to various state agencies to hammer out the details of his plan, but in time-honored gubernatorial tradition, while the governor may take credit for setting noble goals, the challenge of reaching them will be left to future generations.

Click in the box near the top of the story to watch a report by FOX News' William La Jeunesse.

The Associated Press contributed to this report.