A steak at a market sells at an explicit price per pound. But it also has a much higher implicit price: It took energy, land, and water to grow the feed that nourished the cow. As that cow grew, it belched methane, an extremely potent greenhouse gas. Still more emissions arose from shipping the meat to market.
With an ever-expanding population—and a ballooning middle class consuming more meat—humanity is spewing ever-more planet-warming gasses in its quest to feed itself. A new estimate shows just how bad it could get: By the year 2100, the global food system alone could contribute almost a degree Celsius of warming. For context, humanity has already warmed the planet 1.1 degrees since the dawn of the Industrial Age. The Paris Agreement’s goal is to limit warming to 2 degrees above preindustrial levels, or ideally just 1.5 degrees. Agricultural emissions alone could push us past 2 degrees—and food systems are just a fraction of overall global emissions.
Even worse, the authors of the new study, which was published today in the journal Nature Climate Change, caution that their calculation is likely an underestimate. “We’re just considering, essentially, for our baseline scenario: How much additional warming could we expect if the entire global population ate exactly the same as it does today?” says lead author Catherine Ivanovich, a climate scientist at Columbia University and the Environmental Defense Fund. “That’s not necessarily considering if that’s a realistic future, or if that’s really what the world is going to look like in 2100. But it gives us this very simple baseline that we can work off of.”
Ivanovich and her colleagues arrived at the estimate by gathering previous data on the emissions associated with 94 food items, including fruits, vegetables, and animal products like meat and dairy. Producing these creates three key greenhouse gasses that the researchers considered. Agricultural machinery, like tractors, and the trucks, trains, and planes that transport crops to consumers all emit carbon dioxide. Ruminants like cows and goats burp up methane—which is 80 times as potent a greenhouse gas—thanks to the fermenting plant material in their guts. Methane also comes from the practice of flooding fields to grow rice, which allows bacteria to proliferate and spew the gas as a byproduct. And nitrous oxide, which is 300 times as potent as CO2, comes from synthetic fertilizer, which farmers use to give plants the nitrogen they need to grow.
With data for so many different kinds of foods, Ivanovich’s team could then factor in population growth—basically, how many more people will be consuming these foods by the year 2100. They then plugged the emissions data into a climate model that calculated how much warming the food system alone would produce: nearly 1 more degree Celsius.
Critically, though, the modeling can’t say how food habits might change as the human population grows—particularly, how much more meat an expanding middle class might consume. Previous research, though, has suggested that demand for ruminant meats like beef, lamb, and goat could grow 88 percent between 2010 and 2050. “The projection for the rates of ruminant meat demand, and animal products more broadly, far exceeds that of population growth,” says Ivanovich. “We think that our estimations are probably underestimates of the actual future warming associated with global dietary consumption.”
As people’s incomes rise, they tend to switch from “starchy staples” like grains, potatoes, and roots to meat and dairy products. “You’d think there would be big cultural differences across human populations in these patterns,” says Thomas Tomich, a food systems economist at the University of California, Davis, who wasn’t involved in the new paper. “There are some, but it is surprising how almost universal this shift is: how increasing income, especially going from poor to middle class, really affects people’s consumption of livestock products.”
Yet cattle and milk products are especially critical to the climate conversation because they are such massive sources of methane emissions. Ivanovich’s modeling shows that by 2030, ruminant meat alone could be responsible for a third of the warming associated with food consumption. Dairy would make up another 19 percent, and rice a further 23 percent. Together, these three groups would be responsible for three-quarters of warming from the global food system.
There’s a silver lining, though: The team thinks we can avoid half of this warming by improving our food system and diets. That starts with eating fewer cows and other ruminants—the fewer fermenting stomachs out there, the better. New food technologies can certainly help, such as plant-based meat imitations like the Impossible Burger or meats grown from cells cultured in labs, also known as cellular agriculture. Researchers are also experimenting with feed additives for cows that reduce the methane in their burps.
Out in the fields, rice growers can significantly reduce methane emissions by switching between wetting and drying paddies, instead of leaving the plants flooded. Researchers are also developing crops that fix their own nitrogen, in a bid to reduce nitrous oxide emissions. (Legumes do this automatically, thanks to symbiotic bacteria living in their roots.) One team has made rice plants that grow a biofilm to act as a home for nitrogen-fixing microbes, thus reducing the need for synthetic fertilizers. Making such fertilizers is extremely energy-intensive, so reducing reliance on them will further reduce emissions.
But Ivanovich stresses that rich nations certainly can’t force methane-conscious diets on economically developing ones. In some parts of the world, a cow is simply food and milk, but to a subsistence farmer, it may be a working animal, or currency. “It’s really essential that no changes to dietary composition are made without being culturally relevant, and supportive of local production practices and how they contribute to economic livelihoods,” she says.
Ivanovich’s 1-degree figure is an estimate, not a prophecy. For one thing, she can’t intricately model how new food and farming technologies might reduce emissions in the decades ahead. And environmental scientist Adrian Leip, a lead author of last year’s IPCC report on climate mitigation, points out that while these technologies are promising, it’s not clear when—or how rapidly—people will adopt them. “At a certain point in time, one of those technologies—I don’t know whether it will be cellular agriculture or whether it will be plant-based analogs—will be so cheap. It will be so tasty and nutritious that people will start thinking: Why on Earth did I ever eat an animal?” says Leip, who wasn’t involved in the new paper. “I believe it must happen, because I really don’t see good reasons not to happen. And so if the social norms start to shift, it can go really quick.”
Further complicating matters is an additional feedback loop: As the food system raises global temperatures, crops will have to endure more heat stress and ever fiercer droughts. “This is really a dynamic interplay of two-directional change,” says Ivanovich, “where our agriculture that we produce affects our changing climate, and our changing climate really affects how well we’re able to produce crops and support our global population.”
But she does offer a note of hope: Methane abates rapidly once people stop producing it. It disappears from the atmosphere after a decade, whereas CO2 lasts for centuries. “If we reduce emissions now, we experience those reductions in future warming quite quickly,” she says.
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