Say you’re faced with buying what you suspect will be your last gasoline-powered car. Do you buy into the green option, and what, exactly, does that mean anyway?

There are several schools of thought. One says you should use less gas by employing a hybrid gas-electric engine. Popular models suggest this option is an immediate stop-gap, getting the technology model into the market in some quantity while the battery technology improves into its next stage. At this moment it is conspicuous green consumption, a kind of taking-one-for-the-team venture that if you can afford, you should, and one not without social redemption. But using less fuel, greater per gallon economy - a key goal - is achievable with the hybrid.

Tangential to the hybrid gas-electric is the straight plug-in electric that, while not yet widely available, promises to change the basic model of transportation and wean us from our dependence on dreaded foreign oil. Many of the Silicon Valley VC are betting on this angle, although the currently available options from companies like Tesla are entirely high-end, two-seater sport coupes. Whether these are green depends on two things: how much energy is required to make these vehicles, and where the electricity to power them comes from. Right now, our plug-in electricity mostly comes from coal. So, then the question becomes one of emissions. As fossil fuels, petroleum and coal both contribute to the inventory of greenhouse gases in the atmosphere, though not equally.

To offer a criminally brief summary, burning gas (a hydrocarbon) releases some energy into the generation of water vapor in addition to CO2; burning coal, everything goes into generating CO2. Thus a coal-powered car is not green. Electric cars powered by solar energy or any carbon-free power, on the other hand, would be. Perhaps the electric car makers are building the infrastructure in reverse - paving the way for how we use carbon-free power before we properly know how to capture it. You could support this effort with your late-2008 car-buying, and that intention would be in the direction of green even if driving around in a coal-powered car isn’t. In this model, wait-and-see becomes take a hit in the short term in support of a future infrastructure for carbon-free power.

Another point on the continuum of existing models is buying a diesel. Though not widely available in the U.S., diesel engines have become terrifically efficient, using less fuel, emitting less CO2 and lasting longer than gasoline engines. Additionally, the development of biodiesel and other alternative fuels will make these vehicles popular, if not more environmentally friendly over the short run. The bad news is that this is yet another crowded sidewalk the Big Three decided to collectively moon, so the best diesel engines are idling in fancy BMW and Benz models, including SUVs, effectively out of reach to most people.

By now the endeavor seems sufficiently complicated that you consider just sticking with your old clunker. But that’s not really an option, and while you can barely afford to consider the nightmare that would be taking on a huge car payment in this economic environment, you’ve got to find some way around $5–$9/gallon gas (it is coming) and the non-existent train to Atlanta.

A friend did an amazing thing the other day - he bought a new truck from GM. “You want to do something patriotic?” the salesman baited him. “Buy a new truck from the General.” He laughed in the re-telling, as an addendum to his purchase of a product from a company about to not exist. President Obama suddenly has some serious leverage over the Big Three; we should know in the next month or so whether he might exchange our bailout billions for an ultimatum: within five years be manufacturing a car that uses no gas or we’ll take your asses into receivership.

Being sustainable on an individual level is different from being able to counteract the effects of greenhouse gas emissions; yet between them is more than correlation. What you can do right now counts; at the end of one era, we can create assumptions about the beginnings of another. At the end of WWII, Germany was decimated by its self-inflicted horrors - money, resources and fuel were all so scarce that four-wheel vehicles were all but prohibited. But people still needed to get around, and companies like BMW were determined to eke out an existence. Thus began the golden age of the microcar, super-stylized, often three-wheeled models that made the most of resource scarcity to get Europe moving again. You can enjoy the art and innovation of hundreds of these beauties just down the road in Madison, Georgia at the Bruce Weiner Microcar Museum, which houses the world’s largest collection of microcars. It is with some misgiving that I suggest a fill-up for such an excursion; but it might just avail a glimpse of the future.