The article is about how soon-to-come plug-in autos such as the Nissan Leaf and Chevy Volt may put more carbon in the atmosphere than regular hybrids like the Toyota Prius, depending on what region of the country it is operated in. The plug-ins will either be all-electric (the Leaf) or will have gasoline-powered motors that start up to help charge their battery in a pinch (the Volt). Both types will have to be recharged, mainly or exclusively, by plugging into a power outlet in the owner's garage, though the Volt and other "hybrid" plug-ins can add to their per-charge range by burning gasoline in their gas-powered motors as needed.
At first blush, the less gasoline the plug-ins consume — those that consume any at all, that is — the cleaner and greener they would seem. An all-electric would seem greenest of all. But wait, says the article. Drawing electric power can cause more carbon pollution at the electric power generating facility than the cars save by burning less (or no) gas.
The Scientific American article says that there is wide variation among the regions of the United States as to the mix of energy sources used to make electricity: coal, natural gas, oil, renewables, etc. Depending on the mix, driving a plug-in in a particular region may actually put more carbon in the air than an entirely gasoline-powered hybrid like the Prius.
The same is true with respect to oil consumption, in that oil, or petroleum, is of course the source of gasoline. Even though a plug-in nominally consumes little or no gasoline, in regions where petroleum is used to generate electricity, the saving is again problematic.
As it turns out (see the graphic above) plug-ins do save on oil consumption in every region, vis-à-vis standard hybrids, but the saving is very slight in one particularly populous region: New York.
Meanwhile, the plug-ins' comparative carbon "footprint" varies from one region to the next. In no region is the carbon saving huge for either type of plug-in, but then again in no region do the plug-ins, of either type, put hugely more carbon in the air, either. In two regions, the Upper Midwest and the Mid-Atlantic, hybrid plug-ins help reduce carbon emissions, while all-electrics add to emissions. But in other regions, all-electrics are preferable to hybrid plug-ins, and in most of these, both are preferable to standard hybrids that don't plug in to electrical power sources at any time.
Of course, we can expect the mix of energy sources from which electricity is derived to change over the next several years. If climate-change legislation, via a carbon tax or a cap-and-trade system, puts a price on carbon, then electricity generators will gradually switch away from oil, coal, and natural gas to (say) wind farms and nuclear reactors. That would redraw the Scientific American map over time. A Leaf bought in 2011 may get a whole lot greener by, say, 2020.
Be that as it may, we all need to be aware that there is no such thing as a zero-emission car — not now. Decades from now, maybe.
