To feed a global population that's hurtling toward 10 billion people, the world's farms will have to increase output faster and more efficiently than at any point in history—or risk wiping out the world's forests, driving thousands of species to extinction and blowing past global goals for limiting temperatures.

In a sweeping study published Thursday, the World Resources Institute (WRI), along with the United Nations and other groups, outlines the challenges facing the world's farmers and prescribes a suite of solutions.

"If we want to both feed everybody and solve climate change, we need to produce 50 percent more food by 2050 in the same land area and reduce our greenhouse gas emissions from agriculture by two-thirds," the report's lead author, Tim Searchinger of Princeton University and WRI, told InsideClimate News. "That's a big job."

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The report stresses that succeeding will require acting quickly and in an integrated way. "Food production and ecosystem protection must be linked at every level—policy, finance, and farm practice—to avoid destructive competition for precious land and water," it says.

Agriculture has already converted giant swaths of the globe into crop and pasture land—nearly 70 percent of grassland and 50 percent of the tropical and subtropical plains—and continues to be the primary driver of deforestation. Factoring in this deforestation and land-use change for crop and pasture, agriculture is responsible for nearly one quarter of global greenhouse gas emissions.

The authors find that feeding the expected 9.8 billion people who will inhabit the planet in 2050 will require 56 percent more calories than were produced in 2010, and that nearly 600 million more hectares of cropland—an area about twice the size of India—will be needed in that same timeframe.

With agricultural greenhouse gas emissions currently on course to reach at least three times what's envisioned by the Paris climate agreement, staying within the agreement's global warming limits in the next few decades will require transformative changes, including reforestation on a grand scale, they said.

"We have to increase food production without expanding land and without adding more fertilizer and using more water," Searchinger said. "It's a big challenge, and it's a global challenge. We're on a path where agriculture alone will contribute 70 percent of allowable greenhouse gas emissions from human sources. And it's only 2 percent of GDP."

What to Do About Beef, Fertilizer and More

Production gains will have to come from a range of solutions, including higher-yielding plants, more efficient fertilizer and more nutritious forage for livestock, the report says.

Like other recent reports, it urges a reduction in meat consumption, specifically beef, which is especially resource-intensive and has an outsized carbon footprint relative to other proteins.

"We can't achieve a solution without big beef eaters eating less beef," Searchinger said, referring to the disproportionately high beef consumption rates in some developed countries, notably the United States. "In 2050, 2 billion out of 10 billion people will eat a lot of beef. We're among them. We need the average American to eat 50 percent less beef. That means one hamburger and a half instead of three hamburgers a week."

Better Farming to Reduce Emissions

Sustaining the global population will also mean cutting food loss and waste and avoiding more expansion of cropland for biofuels, the report says. At the same time, new farm technologies will be critical. These include new feeds that reduce methane emissions from ruminants, better fertilizers that reduce nitrogen runoff, improved organic preservatives that keep food fresh for longer periods and finding more plant-based beef substitutes.

"In the energy sector, everyone realizes that new energy technology is critical to solving climate change. Why shouldn't that be the case in agriculture?" Searchinger said. "When you count the opportunity costs of using land for food instead of using it for forests to store carbon, it turns out the greenhouse gas consequences of what we eat are as significant as the consequences of our energy use."

"Every acre of land that we devote to agriculture is an acre of land that could store a lot of carbon as forest," Searchinger added. "Reducing the amount of land we need for land has huge greenhouse gas benefits. That has been ignored over and over again."