What to do with all those SUV drivers? Should they be shamed? Mocked? Ostracized? Forced to wear a scarlet SUV across their chest? Greenpeace UK seems to think so.

There's no way around it: Your car is contributing to global warming. In fact, it's almost certainly the single most environmentally harmful component of your lifestyle. The transportation sector is responsible for nearly 40 percent of nationwide greenhouse gas emissions, not to mention plenty of ozone-damaging and smog-forming pollutants. The good news is that new clean-car technologies are emerging at a rapid pace – not just behind the scenes, but in the showrooms of car dealerships near you. Efficient hybrid-engine cars like the Toyota Prius and the Ford Escape SUV can't keep up with demand. Meanwhile General Motors and Ford are ramping up their development of flexible-fuel vehicles that can burn both standard gasoline and biofuels such as ethanol. So if you're in the market for a climate-saving, planet-positive vehicle, which should you choose -- better mileage or biofuel?