Studies investigating the amount of fossil-fuels it takes to grow, process and distribute our food suggest that a diet containing factory-farmed red meat really fleshes-out the spectre of global warming.

Since commercially raised fish are also transported over vast distances in fossil-fuel burning vehicles, pescatarians are not off the hook. Even vegans play their part when they buy processed foods in petroleum-based packaging. But overall, the greatest impact to global warming comes from a diet of factory-farmed animals and the totality of the system that sustains them. 

A meat-based diet also has a disproportionate effect on global water resources. Waste from factory farmed animals poison rivers, aquifers, and estuaries. Expanding grazing lands cause massive deforestation. The majority of the water we now use as a species goes to growing commercial grain. Since the animals the average western carnivore will consume in a year will have themselves consumed roughly one ton of grain (which takes roughly 1,000 tons of water to grow), carnivores are actually consuming about 1,000 tons of water annually just to maintain the meat in their diet.