I heard recently someone declare, on CBC radios 'crosscountry checkup' (mp3 of that program on the proposed carbon tax), that a meat eating bicycle commuter produces more carbon emissions than a vegetarian SUV commuter. Turns out its not quite true according to this calculation investigating the exact same claim. However it is quite shocking how energy intensive a omnivorous diet actually is in this day of industrialized agriculture. Basically a full vegan diet saves about 1.5 tonnes of carbon emissions, while an SUV can produce over 3 tonnes of carbon emissions. So it's actually close enough that it depends on how long your commute actually is. I guess this leaves the question, could you do both? Probably not since vegetarians are so notoriously physically weak. I have yet to see one on UFC.
BTW check out how great a site New Zealand has for consumer information about choosing a good vehicle with safety, fuel economy and emissions as criteria. Compare this to the only equivalent Canadian site I could find.