But when it comes to sustainability, hybrids are another story.
Parts of the electric motor and batteries in vehicles such as the popular Toyota Prius contain rare earth metals, a little-known class of elements found in many consumer electronics.
Worldwide demand for rare earths is expected to exceed supply by some 40,000 tons annually in several years unless major new production sources are developed, according to a Reuters report.
That makes gasoline-electric hybrid cars such as the Prius, Honda Insight and Ford Focus vulnerable to a predicted supply crunch as China, the world's dominant rare earths producer, limits exports as global demand swells.
Of the 15 rare earths on the periodic table of elements, neodymium -- a key component of an alloy used in high-power, lightweight magnets for electric motors and generators for wind turbines -- is most at risk.
Another rare earth metal, lanthanum, is a major ingredient in hybrid car batteries.
As the green movement swells, production of hybrid cars and wind turbines is expected to increase sharply.
Our dependence on fossil fuels may become a dependence on individual elements.
For hybrid cars, the problem is that they use considerable amounts of these rare metals.
Each electric Prius motor requires 1 kilogram (2.2 lb) of neodymium, and each battery uses 10 to 15 kg (22-33 lb) of lanthanum. That number will nearly double under Toyota's plans to boost the car's fuel economy, he said.
Toyota plans to sell 100,000 Prius cars in the United States alone for 2009, and 180,000 next year. The company forecasts sales of 1 million units per year starting in 2010.
The scramble for lucrative oil reserves is turning into a scramble for rare earth reserves: Saudi Arabia and Iraq, meet Canada and Vietnam.
This post was originally published on Smartplanet.com