According to the U.N. Food and Agriculture Organization, livestock agriculture contributes more to global warming than all transportation sectors (cars, trucks, planes, ships, trains) combined.

There are four times as many fowl and three times as many cows and pigs as there are people on the planet.

The global livestock population has increased 60 percent since 1961 according to the Worldwatch Institute.

The Environmental Protection Agency reports that U.S. factory farms generated 1.4 billion tons of animal waste, which pollutes American waterways more than all other industrial sources combined.
 
Producing a single hamburger patty uses enough fossil fuel to drive 20 miles and causes the loss if five times its weight in topsoil.
 
It's going to get worse. The FAO expects global meat consumption to more than double by 2050.

According to the FAO, livestock grazing is also among the top contributors to other environmental problems like deforestation, water pollution and species loss.

Tropical forests are cleared for pasture land. In both 1993 and 1994, the U.S. imported over 200,000,000 pounds of fresh and frozen beef from Central American countries. Two thirds of these countries' rainforests have been cleared, primarily to raise cattle whose cheap meat is exported the U.S. food industry. -Rainforest Action Network.

Because of deforestation to create grazing land, each vegetarian saves an acre of trees per year.

Beef production alone uses more water than is used in growing the nation’s entire fruit and vegetable crop.
 
Meat production wastes resources. The water required to produce one pound of California beef, according to the University of California Agricultural Extension Department, is 5,214 gallons. (Producing one pound of grain takes 250 gallons.) You could save more water by not eating a pound of beef than by not showering for six months.  

According to the University of Chicago, cutting meat from your diet does more to help the planet than switching from a gas guzzler to a hybrid car.

Facts from “Ecological Cooking” by Joanne Stepaniak and Kathy Heckler unless otherwise noted.