If I butcher a steer for my food, and that steer has been raised on grass on my farm, I am not responsible for any increased CO2. The pasture-raised animal eating grass in my field is not producing CO2, merely recycling it (short term carbon cycle) as grazing animals (and human beings) have since they evolved. It is not meat eating that is responsible for increased greenhouse gasses; it is the corn/soybean/chemical fertilizer/feedlot/transportation system under which industrial animals are raised.
This is an important distinction to understand.
