So for the average American, buying local every day of the year would cut their carbon foot print by only around 4 per cent or 400 kg of CO2eq per year. By comparison, shifting just one day a week from eating red meat and dairy to either chicken, fish, eggs or vegetables lowers your emissions by between 252 kg and 400 kg of CO2eq. ~ Source: New Scientist - What is Your Dinner Doing to the Climate?
And if you're one of those people who's having trouble making the jump from vegetarian to vegan, here's an interesting tidbit...
333 grams of CO2eq is emitted to make one hard-boiled egg. Compare that with a bowl of cereal with milk: 1224 grams of CO2eq - equivalent to driving a typical SUV 6 km. The main culprit in the bowl isn't the cereal, it's the milk. That's because the most emissions-intensive foods are red meat and dairy products. In general, red meat emits 2.5 times as much greenhouse gas as chicken or fish, since rearing cows and other livestock requires a lot of energy. It takes 2.3 kilograms of grain to make every kilo of chicken meat, 5.9 kg of grain for a kilo of pork, and 13 kg of grain plus 30 kg of forage for a kilo of beef. Worse still, they produce methane and their manure releases nitrous oxide. ~ Source: New Scientist - What is Your Dinner Doing to the Climate?
(Note: the science of calculating the carbon footprint of food items is not an exact science as it does not necessarily take into account the manner in which foods are produced regionally. What's been used here is a specific formula not based on generalized data.)