“Humanity now stands at Peak Farmland, and the 21st century will see [the] release of vast areas of land, hundreds of millions of hectares, more than twice the area of France, for nature,” declared Jesse Ausubel, director of the Program for the Human Environment at Rockefeller University, in a December lecture. Ausubel was outlining the findings of a study he and his collaborators had reported in the Population and Development Review Supplement that month. Unlike other alleged resource “peaks,” peak farmland reflects not the exhaustion of resources but the fruits of human intelligence and affluence.

The trend toward reducing farming’s impact on nature took off with the Green Revolution of the 1960s. That leap in agricultural productivity was sparked by plant breeder Norman Borlaug and his colleagues, who created high-yield varieties of wheat and rice, an effort so successful that Borlaug received the Nobel Peace Prize in 1970.

While Borlaug was working to avert famines, others were declaring them inevitable. “The battle to feed all of humanity is over,” Stanford biologist Paul Ehrlich declared in his best-selling 1968 dystopian screed The Population Bomb. “In the 1970s the world will undergo famines—hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now.” The epicenter of Ehrlich’s alarm was impoverished India.

In 1960 India’s population was 450 million, and the average Indian subsisted on a diet of just over 2,000 calories per day. Indian farmers wrested those meager calories from 161 million hectares (400 million acres) of farmland, an area a bit more than twice the size of Texas. By 2010 the Indian population was more than two and half times as big, national income had risen 15-fold, and the average Indian ate one-sixth more calories. Yet the amount of land devoted to crops rose just 5 percent, to 170 million hectares. 

Had wheat productivity in India remained the same as it was in 1960, Ausubel and his colleagues calculate, farmers would have had to plow up an additional 65 million hectares of land, an area one and a half times the size of California. Instead, as people abandoned the land for cities, Indian forests expanded by 15 million hectares—bigger than the area of Iowa.

This trajectory of rising agricultural productivity has also been seen in post-Mao China. During that period, China’s population doubled, and its GDP rose 45-fold. While the amount of land harvested for corn also doubled, each acre produced 4.5 times as much as it did in 1960. Ausubel and his colleagues calculate that rising Chinese corn productivity spared 120 million hectares from the plow. 

In the United States, corn production grew 17-fold between 1860 and 2010, but more land was planted with corn in 1925 than in 2010. (The area planted in corn has started increasing again, thanks to the federal government’s biofuels mandates and subsidies.) Today U.S. forests cover about 72 percent of the area that was forested in 1630. Forest area stabilized in the early 20th century, and the extent of U.S. forests began increasing in the second half of the century.

If global crop yields had remained stuck at 1960 levels, Ausubel noted in his lecture, farmers around the world “would have needed about 3 billion more hectares, about the sum of the USA, Canada, and China or almost twice South America.” Plowing down this amount of the world’s remaining forests and grasslands would have produced what Ausubel calls “Skinhead Earth.”

So where are these trends heading? The researchers offer a 50-year forecast via their ImPACT equation, which calculates how much land will be used for crops (Im) by multiplying population trends (P), affluence (A) as measured by GDP per capita, consumption (C) as calories demanded per unit of GDP, and technology (T) as crop productivity per hectare. The U.N. expects population growth to continue slowing, global affluence to increase at around 1.5 percent per year, people to spend a smaller share of their incomes on food as their incomes rise (a phenomenon known as Engel’s Law), and the amount of crop per hectare to rise by 2 percent annually. (In aggregate, farmers today can produce nearly three times the food they did in 1960 on the same amount of land.) The authors also take into account the growing global desire for meat, which means growing more grains to feed animals, and the diversion of crops into nonfood products such as biofuels.

American corn farmers currently average about 180 bushels per acre, and the world average is around 82. Ausubel and his colleagues assume a modest 1.7 percent annual increase in corn yields between 2010 and 2060, which implies that “the average global yield in 2060 would resemble the average U.S. yield in 2010.”

One concern is that farmers may be approaching the biological limits of photosynthesis, which would constrain crop yields. But the authors note that the winners of the annual National Corn Yield Contest currently produce nonirrigated yields of around 300 bushels per acre, nearly double average U.S. yields. Ausubel suggests that the difference between the global average of 82 bushels and contest-winning 300 bushels per acre yields means that “much headroom remains.”

Cranking various population, economic growth, and yield trends through the ImPACT equation, the authors conservatively conclude that in 2060 “some 146 million hectares could be restored to Nature, an area equal to one and half times the size of Egypt, two and half times France, or ten times Iowa.” Under a slightly more optimistic scenario—one in which population growth slows a bit more, people choose to eat somewhat less meat, agricultural productivity is modestly higher, and there’s less demand for biofuels—an additional 256 million hectares would be spared from the plow. That would mean nearly 400 million hectares restored to nature by 2060, an area almost double the size of the United States east of the Mississippi River.

As Ausubel notes, sparing land usually also means sparing water, which would lessen pressure on the world’s fresh water supplies. Crops need nitrogen to grow, but excess nitrogen fertilizer runoff pollutes streams and is responsible for algae blooms that produce low-oxygen dead zones in many coastal regions. Researchers are hard at work producing biotech varieties that require far less nitrogen.

For example, researchers at Cornell University reported in January that efforts to dramatically boost the photosynthetic efficiency of staple grain crops are moving forward, prompting them to make the optimistic conjecture that “farmers could grow wheat and rice in hotter, dryer environments with less fertilizer, while possibly increasing yields by half.” Currently about 40 percent of the world’s grain is fed to livestock to produce meat. In the ultimate move toward what Ausubel calls “landless agriculture,” the biotech company Modern Meadow hopes to use tissue engineering and 3D printers to make meat. Obviously, such breakthroughs would free up even more land.

“Now we are confident,” the authors conclude, “that we stand on the peak of cropland use, gazing at a wide expanse of land that will be spared for nature.” Now that’s a real Green Revolution!