Cropland has gobbled up over 1 million square kilometers of Earth’s surface | Science

Farmland is overtaking much of the planet. That’s the conclusion of a new satellite map, which finds that fields of corn, wheat, rice, and other crops have eaten up more than 1 million additional square kilometers of land over the past 2 decades.

The study highlights how Earth’s land is becoming, in essence, a unified global farm, with wealthier countries increasingly outsourcing crop production to poorer regions. Half of the new fields have replaced forests and other natural ecosystems that stored large amounts of carbon, threatening efforts to conserve Earth’s increasingly precarious biodiversity and avert catastrophic climate change.

“The inexorable march of the human footprint is just brutal,” says study author Matt Hansen, a geographer at the University of Maryland (UMD), College Park.

Many organizations and governments map farmland locally and regionally but getting a worldwide view has proved difficult. The Food and Agriculture Organization of the United Nations (FAO), for example, compiles cropland statistics from member nations whose methods and definitions vary widely, yielding a patchy global picture.

To stitch together a broader view, Hansen and colleagues mapped cropland using data from the U.S. Geological Survey/NASA Landsat program, which has launched a series of satellites designed to continuously monitor the planet’s surface. For decades, the imagers have periodically photographed every spot on Earth with pixels roughly the size of baseball diamonds. Getting computers to recognize crop fields in satellite data presented challenges, however, because plants such as corn, rice, and soybeans look very different from one another. Fields also come in many shapes and sizes, and crops typically grow for only part of the year.

To validate and train the algorithms the researchers used to create their map, they visited farms around the world and used high-resolution commercial satellite photos available from Google, which are sharper than Landsat images but do not cover the entire globe.

“The idea of the satellite is that we’re using a consistent signal, a consistent method,” Hansen says. “You can get a global story; you can also tell the story of [a single nation such as] Cambodia.”

The global cropland footprint increased 9% over the study period, which covered 2000 to 2019. The new fields amount to roughly twice the area of Spain, and the increase is several times higher than FAO’s estimate of a 2.6% growth in “arable land,” the authors report today in Nature Food. (FAO did not respond to a request for comment.)

South America led the world in relative cropland expansion per land area. That’s thanks largely to a booming soybean industry supplying livestock farmers in China and elsewhere, which boosted the continent’s cropland by nearly 50% during the study period. Meanwhile, Africa saw the largest total area of new farm fields, most of which were created to feed a fast-growing population. Forty percent of Africa’s cropland appeared in the past 2 decades, and the rate is accelerating.

Farmland also swelled in several South Asian nations and North America’s Great Plains. And although the conversion of rainforests like the Amazon to agriculture often gets the headlines, new crop fields took a bigger bite out of less heralded biodiversity hot spots, such as dry forests and savannas, says study co-author Peter Potapov, also at UMD. In South America, for example, important dry ecosystems known as the Chaco and Cerrado took major hits. “They will disappear completely very soon,” Potapov says.

When forests or savannas are converted to farm fields, large amounts of carbon that was stored in trees and soil is often lost to the atmosphere, accelerating climate change. Such land clearing causes roughly one-eighth of humans’ total carbon emissions, researchers have estimated.

Crops didn’t gain ground everywhere. In large swaths of the former Soviet Union, for example, farmers abandoned unproductive areas. But the analysis shows that at the global scale, far more cropland is being created than abandoned, says Tim Searchinger, a senior fellow at the World Resources Institute in Washington, D.C., who was not involved with the work. This indicates, he says, that the carbon and biodiversity lost from natural ecosystems is not being compensated for by restoration of former farmland elsewhere. Moreover, the analysis didn’t account for new livestock pastures and tree plantations, he notes, which can also destroy natural ecosystems and cause carbon emissions.

The study did reveal some hopeful trends. The plant biomass growth rate in croplands increased by 25%, and per capita crop area decreased by 10% over the study period, suggesting humanity may be continuing to find ways to squeeze more food out of a given hectare. The researchers did not pinpoint which crops grew where, however; they hope to do that in the future.

The map is sharper and more up to date than many currently in use, says Amy Molotoks, a geographer at the Stockholm Environment Institute. She and her colleagues “are highly likely to use it in the future” to determine where agricultural products are being grown on farms that have replaced forests or other natural ecosystems, she says.

To put the data into action, researchers will need to make clear to consumers how their food choices drive farmland expansion. As U.K. consumers have learned that large tracts of South American forest are cleared to grow soybeans for animal feed, for example, more have turned toward vegetarian and vegan diets, Molotoks notes.

And to prevent more land from being cleared for crops in Africa, scientists must also help farmers there produce far more food on land they currently farm, Searchinger adds; that continent’s crop yields are the world’s lowest.

“If the world wants to solve climate change, from a purely self-interested standpoint, it needs to support Africa in solving its land use challenge, and that includes much higher yield growth and food security,” Searchinger says.