The EPA says [1] 9% of the US's GHG emissions are from agriculture, so there's an upper limit. However, the more relevant consideration is how much more GHG comes from ruminants compared to other protein sources [2].

[1] https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emis...

[2] https://www.businessinsider.com.au/the-top-10-foods-with-the...