Corrected 4/13/09: The Chicago Reader article cited in this blog overstated the prevalence of two-stroke engines in scooters. Four-stroke engines, which are more prevalent, run cleaner.
SUVs are bad, etc. etc.: this much we know. But could downgrading to a sleek scooter be worse for the environment than an SUV? This was a question posed to the Chicago Reader's Straight Dope column, on the basis that a two-stroke engine pollutes more in an hour than a car does all week. So should the smug Vespa-riding friend of the author give up and get a 4Runner? Not so fast.
Scooters do pollute more than cars. Straight Dope's Cecil Adams says they can legally emit "5.7 times more CO than cars, nearly 24 times more unburned hydrocarbons, and infinitely more NOx [Nitrogen oxides]--and real-world testing suggests they do run pretty dirty."