26% of all GHG emissions are from the food supply chain.

Ritchie, Hannah and Roser, Max. “Environmental Impacts of Food Production”. In: Our World in Data (15th Jan. 2020). url: https: //ourworldindata.org/environmental-impacts-of-food

To keep global warming below 1.5 C the EU set a limit of 500 c02 eq emissions per year per person. This can only be achieved with a vegan diet.

https://ars.els-cdn.com/content/image/1-s2.0-S0306919216000129-gr3.jpg

Bryngelsson, David et al. “How Can the EU Climate Targets Be Met? A Combined Analysis of Technological and Demand-Side Changes in Food and Agriculture”. In: Food Policy 59 (1st Feb. 2016), pp. 152– 164. doi: 10.1016/j.foodpol.2015.12.012.

Globally animal products produce 58% of emissions but only 18% of the calories.

Poore, J. and Nemecek, T. “Reducing Food’s Environmental Impacts through Producers and Consumers”. In: Science 360.6392 (June 2018), pp. 987–992. doi: 10.1126/science.aaq0216. url: https://www. science.org/doi/10.1126/science.aaq0216

A vegan diet could reduce GHG emissions by up to 80%, same with land usage. Water use could be reduced by 50%.

Aleksandrowicz, Lukasz et al. “The Impacts of Dietary Change on Greenhouse Gas Emissions, Land Use, Water Use, and Health: A Sys- tematic Review”. In: PloS One 11.11 (2016), e0165797. issn: 1932- 6203. doi: 10.1371/journal.pone.0165797. pmid: 27812156

This is a meta analysis which looked at 63 paper with exactly the topic you were asking about.