Keywords: GHG emissions. Industrial-scale food animal production. Extensive animal agriculture systems. Highlights of this report or guidance memo: *Scientific literature on greenhouse gas emissions of various forms of animal agriculture systems are synthesized. *Explains the complexities of models used to generate estimates of GHGs in these scientific literature, and the reasons why they are not very robust and they contain errors that often go unreported. *Points out that high-quality measurements that do exist consistently demonstrate that industrial animal agriculture's emissions are actually higher than typically estimated. Therefore the claim held by many experts and policy-makers that intensifying animal agriculture significantly limits global GHG emissions is unjustified. *Cautions about not jumping to the conclusion that extensive, pastoral systems is the perfect answer.