Clean your plate. It could save the planet.

Americans and people the world over waste prodigious amounts of food — an estimated one-third of all that’s produced worldwide. Reducing that spoilage could help feed a growing global population while also reducing the greenhouse gas emissions that occur both when the food is produced and when it’s left to rot in landfills.

Even Pope Francis has been drawing attention to the problem: “The ‘throw-away’ culture produces many bitter fruits, from wasting food to isolating many elderly people,” he said recently on his Twitter feed.

Doing something about food waste is another matter.

Farmers and food companies, after all, are in business to sell more of what they produce, not less. Consumers throw away food needlessly if they’re not sure whether it’s safe to eat. Still, the waste issue is drawing attention of policymakers in Washington and industry leaders worldwide in a way it never has before:

The Obama administration this year mounted an effort called the U.S. Food Waste Challenge, signing up food retailers and manufacturers to take steps to reduce or recycle food waste. ConAgra Foods, maker of such brands as Healthy Choice and Hunt’s, says it’s educating employees on ways to cut waste. It’s also standardizing a corporate policy on donations to food banks.

“The United States enjoys the most productive and abundant food supply on earth, but too much of this food goes to waste,” Agriculture Secretary Tom Vilsack said in announcing the initiative.

Vilsack’s department is working with Cornell University to encourage changes in school lunchrooms to discourage kids from tossing out lunch items. Minor changes such as better lighting over a fruit bowl, or a catchy name like “X-ray Vision Carrots” can get kids to eat healthful foods instead of throwing them away, researchers found.

Meanwhile, the supermarket industry is working on ways to standardize the use of expiration dates on food labels.

The aim is to reduce consumer confusion about how long products are safe to eat. The Department of Agriculture and the Food and Drug Administration would be consulted on any label changes.

The U.S. Agency for International Development and major development donors such as the Bill and Melinda Gates Foundation also are trying to address the waste issue in poor countries, where subsistence farmers often lose precious crops to spoilage and pests because of lack of proper storage. On Wednesday, USAID announced it was soliciting bids from universities to study ways to cut back the spoilage of poor farmers’ crops.

The waste problem “is all along the food chain,” said Dana Gunders, a scientist following the issue for the Natural Resources Defense Council. “When you talk about reducing food waste, in some ways you’re just talking about making the food system more efficient. That means it’s a different type of problem in different parts of the food chain.”

The USDA estimates that 30 percent of the available U.S. food supply is lost at the retail and consumer levels. Americans wasted 36 million tons of food in 2011, and a lot of that wound up in landfills, producing methane, a powerful greenhouse gas, according to the EPA.

The United Nations’ Food and Agriculture Organization reported this fall that 1.3 billion metric tons of food is wasted globally each year across the food chain — one-third of all food that is produced, and enough to add 3.3 billion tons of greenhouse gases to the atmosphere.

In a stunning revelation last month, the British food giant Tesco estimated that 68 percent of bagged salad goes to waste, including 35 percent of what’s purchased by customers.

Among U.S. shoppers, confusion about expiration dates is a major cause of food waste, according to a study released this fall by the Natural Resources Defense Council and Harvard University’s Food Law and Policy Clinic. Researchers say consumers often think a product is no longer safe just because its “sell by” date has passed, even though such dates are primarily intended for managing inventory, with little relation to freshness.

The report called for establishing a more uniform, easy-to-understand labeling system that would differentiate between safety-based and quality-based dates. (“Safe if used by” would be more helpful to consumers than “use by,” for example.) “Freeze by” dates also could help discourage consumers from throwing out foods that are still safe to eat.

“The date labeling system in the U.S. is not a system at all, it’s a mess.” Gunders said.

Food manufacturers agree the dates aren’t based on safety. “These date declarations are intended to provide consumers with pertinent information about the product from a quality standpoint,” said a statement from the Grocery Manufacturers Association, suggesting that the issue needed to be addressed by international standards.

But the Food Marketing Institute, a trade group representing Walmart, Kroger and other supermarket chains, wants to work with manufacturers to address the date issue. The supermarket industry’s consumer experts believe there need to be two dates on products, one for retailers’ use and another telling consumers when the foods should be discarded, said David Fikes of FMI.

“We’ve got to get into conversation with the manufacturers and hear from them what is acceptable,” he said.

The USDA is developing a new Food Keeper app for smartphones and tablets that will allow consumers to find out what a food item’s shelf life should be. The FMI is supplying the data but couldn’t afford the development costs. The release date isn’t yet certain. The USDA is spreading the development costs over two fiscal years, Fikes said.

Restaurant chains, facing consumers’ growing interest in corporate sustainability practices, are wrestling with the waste issue, too, and are looking to local governments for help. A Duke University study done for the National Restaurant Association found that the biggest challenge restaurants face in reducing waste is a lack of affordable composting and recycling options.

Waste has long been a problem in school cafeterias as well, and some schools believe the problem has gotten worse since the USDA overhauled nutrition standards at the direction of Congress. Investigators with the Government Accountability Office recently visited some schools in a review of the standards and observed numerous students throwing away some or all of their fruits and vegetables.

The USDA knew kids might throw some of the more healthful foods away and commissioned Cornell researchers to provide advice on ways to make the new offerings more palatable, said Kevin Concannon, the USDA’s undersecretary for food, nutrition and consumer services. A new policy also allows kids to decline some items.

“Our goal is obviously to have the kid to consume the food that is being served to them,” said Concannon.

However, Jason Foscolo, a New York lawyer who advises small-scale food producers, sounds a note of caution on the effort to cut down on waste, especially on potential label changes.

“Preventing food waste is a noble goal, but it will be an additional burden for those new to the marketplace,” he said in a recent blog post. “With every aspect of a food label already controlled by federal regulation, adding another compliance requirement would disproportionately burden the small producer in particular.”