Cars affect the environment in a number of ways. In modern cars, tailpipe emissions of smog-forming chemicals--particular carbon monoxide, nitrous oxides, and unburned hydrocarbons--are now less than 1 percent of what they were before the first catalytic converters were fitted in 1975.
Now public attention has turned to cars' emissions of greenhouse gases, particularly carbon dioxide. Those vary directly with the fuel they consume. But contrary to popular myth, vehicle manufacturing is only responsible for a tiny part of the damage they cause. According to a study from the Massachusetts Institute of Technology, the gasoline or diesel fuel that your car burns--and the energy needed to locate, extract, refine, and transport it even before it reaches your car--accounts for the vast majority of its greenhouse-gas emissions. In other words, the lower your gas mileage, the worse your car is for the environment.
The data come from M.A. Weiss et al., in the MIT Energy Laboratory report they wrote called, On the Road in 2020: A Lifecycle Analysis of New Automotive Technologies. According to their models, 75 percent--or three-quarters--of the carbon emissions over the life of a vehicle come from the fuel it burns. And another 19 percent are due to the production of that fuel. On the mining and manufacturing side, though, extracting the various raw materials for the vehicle produces only 4 percent of lifetime emissions. And a miniscule 2 percent can be attributed to the assembly and manufacturing processes.
While hybrids and plug-in electric cars may have somewhat higher manufacturing emissions, due to the additional raw materials and assembly for the battery pack and electric machinery, the fuel they save far outweighs that difference.
Electric cars that can run some or all of their miles on batteries charged by plugging into the power grid are far less damaging to the environment. A lot of their impact depends on how your local electric utility generates power: Is it largely by burning coal, or is there cleaner natural gas plus a large portion of renewables like solar, wind, and hydro power?
But even on the dirtiest, most coal-heavy grids in the nation, an electric car's emissions of greenhouse gases is no worse than the best, most fuel-efficient non-hybrid vehicle (at around 35 mpg). In the best states--California, for instance, has a relatively clean grid--electric cars are definitively better than any car that burns petroleum-based fuel.