Meat production accounts for a staggering 14.5 percent of global greenhouse gas emissions. Though land use, feed production, and transport account for a portion of these, the animals themselves actually emit a fair amount of them just by existing.
Take cows, for example. They have a complex digestive system that splits their stomach into four compartments. One of these compartments, the rumen, actively ferments the cow's food as they chew. In the fermentation process, millions of stomach bacteria convert food into methane gas that is eventually released to the environment in burps and farts (on average, cows burp once a minute!). In this process, the average cow gives off 30 to 50 gallons of methane a day, and considering there are around 1.5 billion of them on farms today, these emissions can add up fast. Methane gas traps even more heat on the earth's surface than carbon dioxide, making it an important part of the climate change puzzle.