Al Gore, Leonardo DiCaprio, and others have brought the possibility of global cataclysm into sharp relief. What they have not been talking about, however, is the fact that all cars, trucks, planes, and other types of transportation combined account for about 13 percent of global warming emissions, whereas raising chickens, pigs, cattle, and other animals contributes to 18 percent, according to U.N. scientists. Yes, eating animal products contributes to global warming 40 percent more than all SUVs, 18-wheelers, jumbo jets, and other types of travel combined.

Al and Leo might not be talking about the connection between meat and global warming, but the Live Earth concert that Al inspired is: The recently published Live Earth Global Warming Survival Handbook recommends, “Don’t be a chicken. Stop being a pig. And don’t have a cow. Be the first on your block to cut back on meat.” The Handbook further explains that “refusing meat” is “the single most effective thing you can do to reduce your carbon footprint” [emphasis in original].

And Environmental Defense, on its website, notes, “If every American skipped one meal of chicken per week and substituted vegetables and grains … the carbon dioxide savings would be the same as taking more than half a million cars off of U.S. roads.” Imagine if we stopped eating animal products altogether.

If I lie in bed and never get up, I will burn almost 2,500 calories each day; that is what’s required to keep my body alive. The same physiological reality applies to all animals: The vast majority of the calories consumed by a chicken, a pig, a cow, or another animal goes into keeping that animal alive, and once you add to that the calories required to create the parts of the animal that we don’t eat (e.g., bones, feathers, and blood), you find that it takes more than 10 times as many calories of feed given to an animal to get one calorie back in the form of edible fat or muscle. In other words, it’s exponentially more efficient to eat grains, soy, or oats directly rather than feed them to farmed animals so that humans can eat those animals. It’s like tossing more than 10 plates of spaghetti into the trash for every one plate you eat.

And that’s just the pure “calories in, calories out” equation.  When you factor in everything else, the situation gets much worse.

With every stage comes massive amounts of extra energy usage — and with that comes heavy pollution and massive amounts of greenhouse gases, of course. Obviously, vegan foods require some of these stages, too, but vegan foods cut out the factory farms, the slaughterhouses, and multiple stages of heavily polluting tractor-trailer trucks, as well as all the resources (and pollution) involved in each of those stages. And as was already noted, vegan foods require less than one-tenth as many calories from crops, since they are turned directly into food rather than funneled through animals first.

All food requires water, but animal foods are exponentially more wasteful of water than vegan foods are. Enormous quantities of water are used to irrigate the corn, soy, and oat fields that are dedicated to feeding farmed animals — and massive amounts of water are used in factory farms and slaughterhouses. According to the National Audubon Society, raising animals for food requires about as much water as all other water uses combined. Environmental author John Robbins estimates that it takes about 300 gallons of water to feed a vegan for a day, four times as much water to feed an ovo-lacto vegetarian, and about 14 times as much water to feed a meat-eater.

Raising animals for food is also a water-polluting process. According to a report prepared by U.S. Senate researchers, animals raised for food in the U.S. produce 86,000 pounds of excrement per second — that’s 130 times more than the amount of excrement that the entire human population of the U.S. produces! Farmed animals’ excrement is more concentrated than human excrement, and is often contaminated with herbicides, pesticides, toxic chemicals, hormones, antibiotics, and other harmful substances. According to the Environmental Protection Agency, the runoff from factory farms pollutes our rivers and lakes more than all other industrial sources combined.

The World Bank recently reported that 90 percent of all Amazon rainforest land cleared since 1970 is used for meat production. It’s not just that we’re destroying the rainforest to make grazing land for cows — we’re also destroying it to grow feed for them and other animals. Last year, Greenpeace targeted KFC for the destruction of rainforests because the Amazon is being razed to grow feed for chickens that end up in KFC’s buckets. Of course, the rainforest is being used to grow feed for other chickens, pigs, and cows, too (i.e., KFC isn’t the only culprit).

Anyone who reads the news knows that commercial fishing fleets are plundering the oceans and destroying sensitive aquatic ecosystems at an incomprehensible rate. One super-trawler is the length of a football field, and can take in 800,000 pounds of fish in a single netting. These trawlers scrape along the ocean floor, clear-cutting coral reefs and everything else in their path. Hydraulic dredges scoop up huge chunks of the ocean floor to sift out scallops, clams, and oysters. Most of what the fishing fleets pull in isn’t even eaten by human beings; half is fed to animals raised for food, and about 30 million tons each year are just tossed back into the ocean, dead, with disastrous and irreversible consequences for the natural biological balance.Then there is aquaculture (fish farming), which is increasing at a rate of more than 10 percent annually. Aquaculture is even worse than commercial fishing because, for starters, it takes about four pounds of wild-caught fish to reap just one pound of farmed fish, which eat fish caught by commercial trawlers. Farmed fish are often raised in the same water that wild fish swim in, but fish farmers dump antibiotics into the water and use genetic breeding to create “Frankenstein fish.” The antibiotics contaminate the oceans and seas, and the genetically engineered fish sometimes escape and breed with wild fish, throwing delicate aquatic balances off-kilter. Researchers at the University of Stockholm demonstrated that the horrible environmental impact of fish farms can extend to an area 50,000 times larger than the farm itself.

Caring for the environment means protecting all of our planet’s inhabitants, not just the human ones. Chickens, pigs, turkeys, fish, and cows are intelligent, social animals who feel pain, just as humans, dogs, and cats do. Chickens and pigs do better on animal behavior cognition tests than dogs or cats, and are interesting individuals in the same way. Fish form strong social bonds, and some even use tools. Yet these animals suffer extreme pain and deprivation in today’s factory farms. Chickens have their sensitive beaks cut off with a hot blade, pigs have their tails chopped off and their teeth removed with pliers, and cattle and pigs are castrated — all without any pain relief. The animals are crowded together and given steady doses of hormones and antibiotics in order to make them grow so quickly that their hearts and limbs often cannot keep up, causing crippling and heart attacks. At the slaughterhouse, they are hung upside-down and bled to death, often while they are still conscious.

Is meat better if it doesn’t come from factory-farmed animals? Of course, but its production still wastes resources and pollutes the environment. Shouldn’t we environmentalists challenge ourselves to do the best we can, not just to make choices that are a bit less bad?

The U.N. report looks at meat at a global level and indicts the inefficiency and waste that are inherent in meat production. No matter where meat comes from, raising animals for food will require that exponentially more calories be fed to animals than they can produce in their flesh, and it will require all those extra stages of CO2-intensive production as well. Only grass-fed cows eat food from land that could not otherwise be used to grow food for human beings, and even grass-fed cows require much more water and create much more pollution than vegan foods do.

If the past is any guide, this essay will generate much hand-wringing from my meat-eating environmentalist colleagues and, sadly, some anger. They will prefer half-measures (e.g., meat that is “not as bad” as other meat). They may accuse PETA of being judgmental — simply for presenting the evidence. They will make various arguments that are beside the point. They will ignore the overwhelming argument against eating animal products and try to find a loophole. Some will just call the argument absurd, presenting no evidence at all.

But as Leonardo DiCaprio has noted, this is the 11th hour for the environment. Where something as basic as eating animals is concerned, the choice could not be any clearer: Every time we sit down to eat, we can choose to eat a product that is, according to U.N. scientists, “one of the … most significant contributors to the most serious environmental problems, at every scale from local to global,” or we can choose vegan — and preferably organic — foods. It’s bad for the environment to eat animals. It’s time to stop looking for loopholes.

Considering the proven health benefits of a vegetarian diet — the American Dietetic Association states that vegetarians have a reduced risk of obesity, heart disease, and various types of cancer — there’s no need or excuse to eat chickens, pigs, eggs, and other animal products. And vegan foods are available everywhere and taste great; as with all foods — vegan or not — you just need to find the ones you like.

You can find out more at GoVeg.com and get great-tasting recipes, meal plans, cookbook recommendations, and more at VegCooking.com.