Not only are CO2 emissions important to consider, but the increasing scaricity of fresh water must also be considered. About 2/3rds of Chinese cities are short of fresh water!
Also, you must bear in mind that for most people, there are more CO2 emissions used to get the food to your table (including production, air miles, shipping miles, distribution miles, etc).
If you buy locally prodcued food as much as possible, minimise food waste, and go on to a vegan diet (not that I would suggest you to do this), these would all help you reduce your CO2 emissions as well as reduce the amount of “embedded water” – the water required to produce food items. See below for an example.
In the UK, many winter fruit and veg are flown in from the Andalucia region of Spain. This is a semi-desert environment. Part of this area has the largest area on the planet covered with plastic covered polytunnels. Irrigation water for the crops grown in the polytunnels is obtained from ground water sources. The ground water level is dropping, and is not replenished. When you fly tomatoes and other fruit and veg, you are mostly flying water from one part of the world to another, since they contain mostly water. The water taken to grow the crops is also effectively removed from the region!
I can’t remember the figures, but it takes a lot of kilos of water to grow a kilo of tomatoes (and other crops also).
The amount of water required to grow a kilo of beef (and other meat) is also enormous. It aslo takes about 7-8 kg of grain to produce a kg of beef. In terms of productivity, poultry is less damaging to the environment than beef prodcution.