One-third of our greenhouse gas emissions come from agriculture

Fossil fuels is #1.

Livestock farting is #2.

Refrigeration is #3.

Fertilizers in agribusiness is #4 -- this must be what you are referring to.

https://en.wikipedia.org/wiki/Greenhouse_gas#Anthropogenic_greenhouse_gases

 

Being a vegetarian is no get out of carbon jail free card. If it makes you feel better and holier than thou by all means knock yourself out. As far as the almonds example goes, vegetarians have to get their protein somewhere and almonds is considered a "super food" so many vegetarian recipes call for them. At a gallon of water per nut that's a good example of doing more harm than good trying to lower your carbon footprint.

 

Forget about these issues today...think 100-500 years into the future...when planet Earth is home to perhaps 20-30-50 billion people? And factor in impacts from climate change. Is it even possible to feed this many people using animal and crop methods? And whatever food products we will have in the future, can our physiology change quickly or must our digestive systems evolve slowly?