From cow burps to decaying food waste, agriculture is a major source of greenhouse gas emissions. Researchers estimate farms are responsible for about 13% of total global emissions, making it the world’s second-largest source, after energy production. And now that nations have committed to trying to hold global warming to no more than 2°C above preindustrial levels, researchers and policymakers are looking for practical ways to cut agriculture’s contribution to climate change.

Two recent developments could inform that search. Last week, officials in the United States—one of the world’s largest sources of agricultural products—released a progress report on U.S. efforts to promote “climate smart” agriculture. And this week, an international research team published a study that highlights the big changes in farm technology and human behavior that will be needed to achieve the worldwide farm-related cuts necessary to stay below the 2°C threshold.

U.S. building blocks

The U.S. road map for reducing agricultural emissions, released last year, takes aim at activities at farms, ranches, and forests that account for about 10% of total U.S. emissions. It rests on 10 “building blocks,” including efforts to promote renewable energy technologies, convert feedlot manure into fuel, and plant more trees to soak up carbon. Together, U.S. Department of Agriculture (USDA) analysts believe such steps could prevent emissions of 121 million to 136 million metric tons of carbon dioxide equivalent per year by 2025.

This week, ScienceInsider talked with U.S. Secretary of Agriculture Tom Vilsack about a 12 May progress report on the road map, as well as recent Obama administration efforts to implement the plan, including an initiative to spend some $72 million on efforts to promote farming practices that would promote carbon storage in soil and reduce fertilizer overuse. Climate-friendly practices—such as promoting the use of certain cover crops, and expanding the acreage under no-till management, which reduces plowing—can not only benefit the environment, Vilsack says, but also improve profits.

“This isn’t about feel-good, this is about doing good for yourself and your [farm] operation,” Vilsack says. “Certain practices can be quite effective in not only improving the climate, but also improving soil. The healthier your soil, the more productive your operation is going to be.”

What goes on at the farm is only one part of the total emissions from agriculture, Vilsack noted. One of USDA’s goals—separate from the building blocks—is to reduce the amount of food waste by 50% by 2030. Removing that organic waste from household trash streams would, for instance, help reduce landfill emissions of methane, a potent warming gas. (Landfill bacteria produce the gas as they break down the organic waste.)

New approaches needed

Such efforts, however, will have to be massively scaled up and combined with technical and policy solutions if we are to make a dent in global emissions from agriculture, concludes a study published 17 May in Global Change Biology. It examines what might be needed to meet the 2°C target—and lays out a preliminary, albeit ambitious, global goal: cutting 1 billion tons a year of non–carbon dioxide farm emissions, notably releases of methane and nitrogen oxides. But the researchers estimate that existing technologies and practices will get us just 21% to 40% of the way to that target—meaning many nations will need to become much more ambitious.

“Currently countries are setting goals according to what’s feasible, not what is needed to meet the 2° target,” says lead author Lini Wollenberg, a low emissions agricultural specialist with the CGIAR Research Program on Climate Change, Agriculture and Food Security in Burlington, Vermont.

The United States has made a good start with its plan to cut agricultural emissions, Wollenberg says. But other nations have yet to settle on firm strategies, and she sees big areas where technological fixes could have an immediate impact: raising livestock and systems for irrigating rice. Livestock such as cows and sheep produce a great deal of methane, she notes, so biological or chemical feed supplements that inhibit methane production, or even new low-emission livestock breeds, are worthy of pursuit. Similarly, paddies used to grow rice—one of the world’s major crops—produce a lot of methane under current farming practices. But changing the pattern of flooding and drying out the paddies could reduce the bacterial populations in soil that produce the gas.

“We need to consider more radical changes in the food system to meet these ambitious goals,” says her co-author, Pete Smith, a soils and global change researcher at the University of Aberdeen in the United Kingdom. For example, shifting what we eat could also play a profound role. “The biggest win” would be to curb meat eating, Smith says. Producing meat consumes a lot of energy, he notes, and the potential impact of “reducing demand for [the number of] livestock we need in the first place” is far greater than any tech fixes when it comes to reducing agricultural emissions.

As Smith notes, any official effort to reduce the demand for meat would be “an enormous lever [that] we’ve so far regarded as an infringement on freedom,” and would be “opposed by strong lobbies for meat consumption.” And calls to lower meat consumption, especially in developing nations, could quickly become a social justice issue. “It’s difficult to say to 7.3 billion people that this how we need to change collectively as a civilization,” he says. Still, Smith is “optimistic that social norms could change dietary practices.”

*Correction, 23 May, 12:35 p.m.: The emissions saved by the USDA plan has been corrected.