According to a United Nations report, cattle are "responsible for 18% of greenhouse gases, more than cars, planes and all other forms of transport put together." But why are cattle so bad? And are other sources of meat equally bad? There are about 1.3 billion cattle occupying 24% of the world’s entire land area.
Cattle consume more than a third of the world’s grain. Producing one kilogram of steak requires almost 20,000 litres of water. Not eating 500 grams of steak would save more water than not showering for a year. In regard to greenhouse gases, the problem with cattle is that they are ruminants.
Ruminants regurgitate their food as cud in order to slowly break it down for digestion. This process produces methane which is 21 times more potent than carbon dioxide as a greenhouse gas. Animals which do not chew their cud may need just as much feed and water, but they do not produce anything like as much greenhouse gas.
Almost all common sources of meat, other than fish and fowl, are ruminants like cattle. The major exceptions are pigs and kangaroos. The huge part which beef plays in our diet is a very modern phenomenon.
Eating beef has actually been rare in most societies throughout history. The prohibition on eating beef in most of India is well known. For 2,000 years, eating beef was taboo for most Chinese who used cattle for ploughing. Beef was not eaten in Japan until the late 19th century because of the Buddhist prohibition on killing. In Europe until modern times, cattle were regarded as too valuable for milk and as beasts of burden to be killed for food. Beef cattle were not introduced into America in significant numbers until the railways opened up the western plains in the 19th century.
The exception to the almost universal prohibition on eating beef was the religions (Judaism and Islam) which follow dietary laws based on the Old Testament. These laws are believed to have arisen in pre-Biblical times as a way of distinguishing the hill-dwelling ancestors of the Israelites, who were sheep and goat herders, from the coastal Caananites, who ate pigs and shellfish. Under these laws only ruminants can be considered "clean" – precisely the opposite of what would be sensible from a greenhouse gas production point of view.