Going green is no longer just about saving the planet. Now it’s about saving the other kind of green. From rising fuel prices to the old-fashioned “turn the lights off!” admonishment from Mom, the lousy economy could do more for the environment than the spotted owl and Ralph Nader combined.

There’s an historic shift underway. It started in low (a year ago, I mentioned the greening of both major political parties), then it started to grow (Americans began driving less and … horrors!!! … driving more slowly). Now even the environmental Grinches are going green.

Cash, or lack of it, is driving this engine of change.

I live in a planned community in Arizona where you see the occasional golf cart on the street amid a slew of SUVs. Disdain for greenies is as thick as a desert dust storm here. But now just about everyone wishes they had a golf cart, and some are acting. A woman who lives in a very expensive home (which for all I know she’s about to lose because of the mortgage crisis) said to me yesterday she and her husband made a decision specifically to save hundreds of dollars a month: “We just bought a golf cart,” she said excitedly. “It costs pennies a day to run. We’re going to park one of our cars and reduce the insurance on it.” And, she didn’t say, emit a lot less CO2.

Another sign of the times: Toyota can’t meet the demand for hybrid cars because it can’t make enough batteries. Meanwhile, it won’t be long and you’ll be able to buy 100 mpg hybrid cars, either direct from manufacturers or from 3rd-party vendors, both of whom can easily see the potential for green in the red sea of economic data these days.

Other people are making small changes to save cash, from eating out less to buying more frugally at the grocery to cutting back on unnecessary purchases. Any reduction in consumption cuts down on a person’s overall environmental footprint … of course it’s only really useful if the changes stick in the long run.

For those who already leaned green, the new and sudden shift could be seen as a huge “I told you so.” But for others who ranged from lacking motivation for green initiatives to being downright hostile to any of “that environmental crap,” change in our collective purchasing and consumption habits is coming as sure as change will appear in the next Obama speech. The big question is whether we can afford all the change and emerge with a robust, technologically grown-up economy.

[A footnote: Earlier this year, I suggested that the red ink of the economy and fuel shortages might supplant green efforts, in particular fueling a resurgence of coal, which is dirty. That remains a concern, but what I didn't think of then is how tighter household budgets and tighter energy supplies would force Americans to simply use less fuel. Millions of us now (regardless of our beliefs or views) must trim fuel consumption, one way or another.]