It's sad that the United States still isn't becoming a leader in reducing agricultural-based greenhouse gas emissions. We are still subsidizing global warming and doing nothing to stop it. Here is an excellent readable summary from The Lancet (possibly the most respected medical journal in the world):
Some key points:
* Agriculture accounts for 22% of global warming emissions (the #1 source) and it is projected to increase even further in the next 40 years.
* Human-raised livestock (cows and pigs in regards to the US) account for 80% of agricultural global warming emissions. Other sources make up the remainder: fertilizers, deforestation, land degradation, and marshy agriculture (mostly rice).
* Cattle (cows for beef and dairy) make up the vast majority of agricultural emissions -- beef cattle make up about 50%, dairy cattle about 15%, pigs (pork) about 15%, goats and sheep (including for wool) about 15%. Poultry (including turkey!), horses, camels, and buffalo cause very few emissions, relatively.
* The United States and Mexico are tied as the top livestock-consuming nations on the planet. Mexico was in the middle-of-the-pack as few as 15 years ago, but our western diet is spreading quickly. The United States should be a leader in reducing our livestock consumption, since we have been the leader in increasing global livestock consumption and are the current top offenders.
* Factory farms ("intensive systems") actually produce fewer greenhouse gases than traditional farms ("free-range" or "pastoral systems"), in absolute emissions and per-animal. However, adopting the most efficient technologies world-wide would reduce agricultural emissions by less than 20% if we don't reduce overall livestock production/consumption.
We need to reduce our beef, pork, and dairy consumption to as close as zero as possible. There are reasons to go vegan, but as far as global warming emissions go, chicken, fish, and eggs are not the culprits -- just beef, pork, dairy, and related livestock products like wool and leather.