Does hybrid car production waste offset hybrid benefits?

Building a hybrid car is almost exactly the same as building a conventional car, requiring high-tech and highly automated assembly lines. This type of manufacturing process requires tremendous inputs of energy, particularly the forging of materials like steel, aluminum, glass and plastic. Interestingly, lightweight vehicles can sometimes be more energy-intensive to build than heavier cars because lighter metals like aluminum are harder to forge than stainless steel [source: Moon]. Experts estimate that 10 to 20 percent of a vehicle's total lifetime greenhouse gas emissions are released during the manufacturing stage alone [source: California Energy Commission].

Toyota admits that the production of its lightweight Prius requires more energy and emits more carbon dioxide than the production of its gas-only models [source: Williams]. The major reason is because hybrids like the Prius include more advanced components than a conventional car, including a second electric motor and heavy battery packs.

Batteries are an essential component of hybrids. Regenerative braking lets hybrids generate and store their own energy to power the vehicle at low speeds and while idling. Unfortunately, both nickel-hydride batteries and the newer lithium-ion batteries rely on the mining of nickel, copper and so-called rare earth metals. The production of lithium-ion batteries account for 2 to 5 percent of total lifetime hybrid emissions and nickel-hydride batteries are responsible for higher sulfur oxide emissions, roughly 22 pounds (10 kilograms) per hybrid compared with 2.2 pounds (about 1 kilogram) for a conventional vehicle [sources: Samaras and Burnham et al].

There are additional environmental concerns related to those rare earth metals, like those used in the magnets of hybrid batteries. In recent years, rare earth metals like lithium have been imported almost exclusively from China, which was able to lower its prices enough to monopolize the industry [source: Strickland]. One of the reasons China could sell lithium so cheaply was because it widely ignored environmental safeguards during the mining process. In the Bayan Obo region of China, for example, miners removed topsoil and extracted the gold-flecked metals using acids that entered the groundwater, destroying nearby agricultural land. Even the normally tight-lipped Chinese government admitted that rare earth mining has been abused in some places. A regulator at the Ministry of Industry and Information Technology in China went so far as to tell The New York Times, "This has caused great harm to the ecology and environment" [source: Bradsher].

Although hybrid vehicle production is more energy-intensive and results in higher production emissions, hybrid vehicles are still the greener choice overall. Read more about hybrid lifetime emissions on the next page.

Since hybrid cars burn regular gasoline, they emit the same greenhouse gases as conventional cars. But since hybrid cars are much more fuel efficient than conventional vehicles -- the U.S. Energy Information Administration sets the average mileage for a hybrid at 38.7 miles per gallon (16.5 kilometers/liter) compared with 26.7 (11.4 kilometers/liter) for a gas-only vehicle -- they require far less gas to cover the same distance.

If every gallon of gasoline contains 20 pounds (9 kilograms) of carbon dioxide, then a hybrid car will emit 51.6 pounds (23.1 kilograms) of carbon dioxide every 100 miles (161 kilometers), while a conventional car will emit 74.9 pounds (34 kilograms). If you multiply those numbers over the lifetime of a vehicle, hybrids more than make up for their heavier production footprint. Let's look at some more lifetime emissions numbers.

The Argonne National Laboratory ran a side-by-side comparison of hybrid and conventional vehicles over their entire life cycle, which includes vehicle production, vehicle operation and the energy required to produce fuel for both cars. If you assume that both vehicles travel 160,000 miles (257,495 kilometers) over their lifetime, the conventional vehicle requires 6,500 Btu of energy per mile compared to 4,200 Btu per mile for a hybrid. That higher energy input results in far greater lifetime greenhouse gas emissions for conventional vehicles compared to hybrids, more than 1.1 pounds (500 grams) per mile compared to 0.75 pounds (340 grams) per mile [source: Burnham et al].

But there is an interesting side note to the hybrid vs. conventional debate. Hybrid carmakers like Toyota are set to release a new breed of plug-in hybrids. Equipped with a bigger battery pack, these hybrids can be plugged into the wall like an electric car, giving an extra 10 to 20 miles (16 to 32 kilometers) of zero emissions driving before the gas engine kicks in. Toyota expects to sell 20,000 to 30,000 units of its 2011 Plug-in Prius -- and more in the coming years [source: Green].

The trouble with plug-in hybrids (and electric cars, too) is that electricity isn't always cleaner than gasoline. More than 45 percent of electricity in the U.S. is generated by coal-powered plants [source: EIA]. According to another Argonne National Laboratory report, if a plug-in hybrid charges from coal-generated electricity, it could be responsible for emitting up to 10 percent more greenhouse gasses than a conventional vehicle and up to 60 percent more than a standard hybrid [source: Elgowainy].

For lots more information about hybrids, electric cars and the world of alternative-fuel vehicles, see the links on the next page.