It simply takes too much water to grow a steak. In a new report, leading water scientists say the human population would have to switch to an almost entirely vegetarian diet by 2050 to avoid catastrophic global food and water shortages.
"There will not be enough water available … to produce food for the expected 9 billion population in 2050 if we follow current trends," Malin Falkenmark and colleagues at the Stockholm International Water Institute stated in the report. By their estimation, there should be just enough water to go around if humans derive just 5 percent of their calories from animal-based foods by midcentury, instead of the 20 percent of calories that they currently get from meat, eggs and dairy.
It's a simple numbers game: Cattle, for example, consume a shocking 17 times more grain calories than they produce as meat calories. All that lost grain (which humans could have eaten) requires water. "Producing food requires more water than any other human activity — and meat production is very water-intensive," Josh Weinberg, the institute's communications officer, told Life's Little Mysteries.
The fixed amount of water on Earth indicates people must reduce their meat consumption to avoid shortages. But with so many meat lovers around, will people actually do it?
They'll be forced to eat less meat, experts say. But not by government intervention or their own inner moral compasses. For most people, the choice between a juicy, medium-rare sirloin steak and a humble plateful of soybeans won't turn on which one is sucking wells dry in Texas. It will hinge on the contents of their wallets.
In fact, meat eating is already on the decline in the United States. It reached its peak in 2007. According to Janet Larsen, director of research at the nonprofit Earth Policy Institute, Americans collectively consumed 55 billion pounds (25 billion kilograms) of meat that year. This year, consumption will total about 52 billion pounds (22 billion kg). Beef eating has dropped off the most.
One driver, Larsen said, is health; another is environmental concerns, because meat production contributes greatly to greenhouse gas emissions and thus global warming. But the primary reason meat-eating has fallen is the rising price of meat, especially beef, Larsen said. And that reflects the increasing price of the corn used to feed livestock.
"Incomes aren't rising nearly as fast as corn prices, and people end up filling their carts with less meat," Larsen told Life's Little Mysteries. She thinks the trend will continue. "We might go back to when Sunday night dinner was [the only time] when you had a chicken on the table."
In the past two years, corn prices have been driven up in the United States by droughts across the Southern Plains — a palpable demonstration that water is the ultimate deciding factor in the availability of meat. A fixed amount of water paired with a growing world population means something has to give (or if not give, at least become a luxury). And that something is meat eating.
"When you look at the absolute numbers of people on the planet and the amount of food that we're producing, you ask the age-old question: How many people can Earth support? We look at the question from the perspective of food-intake levels," Larsen said.
"People in India eat very little meat, so they consume about 200 kilograms [441 pounds] of grain per person each year. At that level of consumption, our total grain harvest could support 10 billion people on the planet. In the U.S., people are eating closer to 800 kilograms [1,768 pounds] of grain, and that's because much of our grain is being consumed indirectly through livestock. At that level, we could only support a world population of closer to 6 billion or less."
Humans stand at 7 billion strong partly because most people consume a fraction of the grain that Americans do. As the population presses upward, placing ever greater demand on the grain supply, fewer people will be able to afford the large quantity of grain that goes into each pound of meat. Wealthy populations will import grain to support their meat-eating, but at great cost.
Beef will probably end up as the priciest meat of all, Larsen said. In fact, although people in China, India and other rapidly modernizing countries are eating more meat, beef production is already leveling off globally, according to Larsen. "I don't think that the world will be able to produce much more beef," she said. Cows just eat too much.
"Not all animal-based foods are created equal," said Gidon Eshel, a statistician at Bard College in upstate New York who studies the energy cost of various agricultural practices. "Certainly beef is a huge contributor to unchecked water consumption that is hard to imagine continuing."
Eshel's research shows that beef has a "conversion efficiency" of just 6 percent: "So if you give a cow 100 calories of feed, it will produce 6 edible beef calories," he said. Chicken and turkey are four times more efficient, and pork falls in between poultry and beef. [How Much Water Is Used to Grow a Hamburger?]
The low conversion efficiency of the cow is partly due to its digestion, which starts in the rumen. "A ruminant supports itself as well as a couple trillion protozoa and fungi and unicellular organisms that also make a living in its rumen," Eshel said. "We humans also have a ridiculous amount of bacteria, but it is unique that for [cows and other ruminants] the bulk of those hitchhikers are involved in digestion — they mostly live in that oxygen-free chamber called the rumen." In this symbiotic relationship, the bacteria break down cell walls in plant matter and extract the useful material, some of which gets offered up to the host cow, and some of which they use for their own metabolism, Eshel said. "Without them, cows would be no more competent at digesting ruffage than we are."
Considering how much grain cows require to satisfy both themselves and their hangers-on, Eshel thinks beef is still pretty cheap. (In the United States, it's cheap enough to contribute to the obesity epidemic, he noted.) This is bound to change, whether the passionate meat lovers of the world like it or not. "I assume the ranks of 'passionate meat eaters' will thin dramatically," he said, "once it is expensive."
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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.