It may be delicious, but the evidence is accumulating that meat, particularly red meat, is just a disaster for the environment — and not so great for human beings, either.Agriculture today accounts for for one-third of global greenhouse gas emissions — posing one of the biggest challenges to countries desperately trying to curb the emissions that promote global warming. And half of those agriculture emissions come from livestock, which produce large amounts of methane, a short-lived but powerful greenhouse gas.