The earth is warming because of two main activities: the burning of fossil fuels, which creates too much CO2 in the atmosphere, and animal agriculture, which results in methane production. Methane has 25 times the global warming potential of CO2.
Animal agriculture is responsible for about 18% of global warming. Cows, For example, produce methane when they pass gas and from their manure. Trees, particularly in rainforests, are an important way the earth cools itself. Rainforest trees are being cut down to make grazing land for cattle and land to raise crops to feed cattle and other livestock.