The Carbon Footprint of a Cheeseburger ...

How much carbon does your cheeseburger habit create?

At 2.85-3.1 kg of CO2 (equiv) per burger, then, that's 428-465 kg of greenhouse gas per year for an average American's burger consumption.

Follow the link, it's an interesting read.
For a real education you must read the 34 odd 'blog reactions' or comments. See the bottom right of the post in question - green text.