Given California’s infinite diversity and its maddeningly diffused governmental apparatus, it’s rare for the state’s politicians to undertake a comprehensive change of public policy.

The decades-long stalemate on water, the state’s perpetual budget crisis and the failure of Gov. Arnold Schwarzenegger’s health care plan are merely three examples of the political system’s chronic inability to act decisively and effectively.

Even on those rare occasions when major new policies are adopted, they tend to fall well short of their purported benefits, a sterling example being the unanimous approval of electric energy “deregulation” in 1996 that became a colossal failure a few years later.

California used to undertake big and visionary projects, such as its famous freeway network, or its once-unmatched system of public higher education. But that was then, and this is now. California has changed immensely from those halcyon days.

We should, therefore, be somewhat skeptical of California’s latest foray into high-concept politics, Schwarzenegger’s crusade to sharply reduce the state’s dependence on fossil fuels that will both curb global warming and spark an economic renaissance.

Two years ago, the Republican governor and Democratic legislators passed Assembly Bill 32, which authorized the state to promulgate an extensive set of new regulations aimed at reducing carbon dioxide emissions. On Thursday, the administration unveiled a “scoping plan” that outlines how the state would cut greenhouse gases 10 percent from current levels by 2020 and 80 percent by 2050.

Not coincidentally, as the draft plan was released in Sacramento, the governor was in Florida (having flown there on his private, oil-consuming jet) to complain that the United States is “so addicted to oil it will take years to wean ourselves from it.” He touted the bill as “something the world will be watching very closely” as the state allocates responsibility for reducing carbon emissions to various segments of society and the economy — with the greatest effect being on cars and other forms of personal transportation.

Are Californians ready to become the point of the global-warming spear, shouldering the financial costs and potential inconveniences that will be involved and, in effect, exchanging the expansive California lifestyle for something different?

Schwarzenegger cites a poll by an outfit called Next 10, purporting to prove Californians are eager for that change, but the poll didn’t fully lay out the trade-offs that going green may require for the ambitious goals for carbon reduction to be met. As with energy deregulation, there is a tendency among advocates to hype the upside without exploring the downside. And we can be certain there will be a downside.

Finally, there is the risk that even if we do everything the governor wants us to do to reduce our “carbon footprint,” it will have very little real world impact. If China, India and other “emerging economies” remain exempt from global emission standards, California’s effort may turn out to be an exercise in political symbolism signifying nothing.

By the time we know one way or the other, Schwarzenegger will be long gone from Sacramento.

(Walters writes for the Sacramento Bee.)