I wish I could find the blog post again, but someone did the math and found that for their commute, driving actually emitted less CO2 than biking if the extra c

I wish I could find the blog post again, but someone did the math and found that for their commute, driving actually emitted less CO2 than biking if the extra calories came from meat. I think it still works out positive if the extra calories come from vegetarian sources, but the delta is much smaller than I'd hope. Of course, there are lots of other benefits to not using vehicles, but it was interesting to think about.