Impossible to say, since there are so many factors involved and metrics to consider. In terms of raw GHG emissions? Lots. But we should consider that animal agriculture is the largest contributor to deforestation, which has an enormous carbon output in addition to reducing the Earth’s ability to offset and sequester future emissions. Also, considering factors like ocean eutrophication, zoonotic diseases and antibiotic resistance, ditching animal agriculture may be one of the best things we could do for humans, the planet, and of course animals.