The hybrid car has been touted as the green savior of the automobile industry. A decade after the Toyota Prius debuted worldwide, issues like climate change and energy security have helped push the popular hybrid's sales numbers past the two million mark -- nearly half of them sold in North America [source: Autoblog].
Americans don't buy the Prius for its style or speed. They buy it to save money on gas and to shrink their carbon footprint. In most American cities, the personal automobile is the largest overall polluter, spewing millions of pounds of greenhouse gases like carbon dioxide, nitrous oxide, carbon monoxide and sulfur oxide into the atmosphere and into our lungs [source: EPA]. Eco-conscious consumers see the Prius and other hybrids as an investment in the environment and in our collective future.
But are hybrids really as green as they seem? How much is marketing hype and how much is scientific fact? Because hybrids have a second electric motor, they burn less fuel than conventional cars and emit lower levels of greenhouse gases during operation. That's great, but what about the hybrid manufacturing process? In 2007, a report commissioned by an auto industry trade group insisted that when you factor in the waste generated during production, the notoriously gas-guzzling Hummer is actually greener than the Prius [source: Slashdot]. While this report was largely discredited by environmental groups, it did raise an important question: does the pollution created during hybrid production offset the benefits of "green" driving?
The answer might surprise you. According to an in-depth study by the U.S. Department of Energy's Argonne National Laboratory, hybrid cars do, in fact, require more energy to produce than conventional cars, emitting more greenhouse gases and burning more fossil fuels during the manufacturing process. The production of hybrid batteries, in particular, requires much more energy than producing a standard car battery and results in higher emission levels of gases like sulfur oxide [source: Burnham et al].
But do the environmental impacts of hybrid vehicle production outweigh the long-term benefits of driving a cleaner running automobile? That answer is a resounding "no." If you drive both a conventional and hybrid car for 160,000 miles (257,495 kilometers), the conventional vehicle requires far more energy to operate and emits far more greenhouse gases over its lifetime, significantly canceling out any imbalance during the production stage [source: Burnham et al].
Keep reading as we break down the statistics for both hybrid production emissions and hybrid driving emissions and learn what "green" really means.

Pollution Caused By Building a Hybrid Car

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.

Hybrid Car Air Pollution Statistics

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.

Lots More Information

Sources
  • Autoblog. "Worldwide Toyota Prius sales crack 2-million mark, 10-year anniversary celebration planned." October 8, 2010http://www.autoblog.com/2010/10/08/worldwide-toyota-prius-sales-crack-2-million-mark-10-year-annive/
  • Bradsher, Keith. "Earth-Friendly Elements, Mined Destructively." The New York Times. December 25, 2009http://www.nytimes.com/2009/12/26/business/global/26rare.html?_r=2
  • Burnham, A.; Wang, W.; Wu, Y. Energy Systems Division, Argonne National Laboratory. "Development and Application of GREET 2.7 - The Transportation Vehicle Cycle Model." November 2006.http://www.transportation.anl.gov/pdfs/TA/378.PDF
  • California Energy Commission. "Full Fuel Cycle Assessment: Tank to Wheels Emissions and Energy Consumption." February 2007.http://www.energy.ca.gov/2007publications/CEC-600-2007-003/CEC-600-2007-003-D.PDF
  • Elgowainy, A. Energy Systems Division, Argonne National Laboratory. "Well-to-Wheels Analysis of Energy Use and Greenhouse Gas Emissions of Plug-in Hybrid Vehicles." June 2010.http://www.afdc.energy.gov/afdc/pdfs/argonne_phev_evaluation_report.pdf
  • Green, Jeff; Ohnsman, Alan. "Toyota Expects 20,000 U.S. Plug-in Prius Sales." Bloomberg Businessweek. September 14, 2010http://www.businessweek.com/news/2010-09-14/toyota-expects-20-000-u-s-plug-in-prius-sales.html
  • Moon, Paula. Center for Transportational Research, Argonne National Laboratory. "Vehicle-Cycle Energy and Emissions Effects of Conventional and Advanced Vehicles." 2006http://www.transportation.anl.gov/pdfs/TA/381.pdf
  • Samaras, Constantine; Meisterling, Kyle. "Life Cycle Assessment of Greenhouse Gas Emissions from Plug-in Hybrid Vehicles: Implications for Policy." Environmental Science and Technology, 2008.http://pubs.acs.org/doi/abs/10.1021/es702178s
  • Strickland, Eliza. "Isn't It Ironic: Green Tech Relies on Dirty Mining in China." Discover. December 28, 2009http://blogs.discovermagazine.com/80beats/2009/12/28/isnt-it-ironic-green-tech-relies-on-dirty-mining-in-china/
  • U.S. Energy Information Administration. "Electric Power Monthly." November 2010http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html
  • U.S. Environmental Protection Agency. "Automobile Emissions: An Overview"http://www.epa.gov/oms/consumer/05-autos.pdf
  • Williams, Stephen. "Toyota Engineers Flowers to Offset Production Pollution." The New York Times. November 3, 2009http://wheels.blogs.nytimes.com/2009/11/03/toyota-engineers-flowers-to-offset-production-pollution/