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.