Garbage cans in South Korea weigh the amount of food thrown out. Grocers in London have stopped putting date labels on fruit and vegetables to make it easier to distinguish between good and bad food. California requires supermarkets to give away food that's unsold but still good to eat.

Efforts are being launched around the world to tackle hunger and climate change.

Methane gas is produced when food waste is deposited in a landfill. It is not easy to solve.

Which is where Vue Vang arrives. On a bright Monday morning recently, she pulled up behind a supermarket in Fresno, Calif., hopped off her truck and went to rescue as much food as she could under the state's new law.

There was a shopping cart that was laid out for her. There must be more. She persuaded the staff members to give her several crates of milk marked "best by" the next day, as well as a variety of food items. She asked them whether there were eggs.

That's a lot. Ms. Vang works with a charity that gives food to people in need.

Food waste is the largest source of material sent to landfills in the US. 8 to 10 percent of global greenhouse gas emissions can be attributed to food waste. That is enough food to feed a billion people according to estimates from the Food and Agriculture Organization of the United Nations.

Governments and entrepreneurs are coming up with ways to save food. In the United States, one start-up makes it easier for people to buy produce that is not perfect, and another has a plant-based coating that lasts longer. Farmers can use solar-powered refrigerators to store produce.

New mobile apps offer discounts on restaurant food that is about to be thrown out. China's top leader began a "clean plate" campaign last year, calling for an end to the "shocking and distressing" waste of food.

A lot of food is produced but not eaten in the modern world.

ImageA woman steps through the door of a walk-in refrigerator.
Ms. Vang on her rounds.Credit...Andri Tambunan for The New York Times
A woman steps through the door of a walk-in refrigerator.
ImageA row of men and women stand in front of boxes of produce, filling plastic bags with food.
Staff members from Centro La Familia, a neighborhood center in Fresno, sorting food brought by Ms. Vang to be distributed to people who need it.Credit...Andri Tambunan for The New York Times
A row of men and women stand in front of boxes of produce, filling plastic bags with food.
ImageA man driving a forklift loads a pallet stacked with boxes of food into the back of a truck.
Ms. Vang receiving 892 pounds of poultry in Fresno. “So much. So much goes to waste,” she said.Credit...Andri Tambunan for The New York Times
A man driving a forklift loads a pallet stacked with boxes of food into the back of a truck.

California's law is the most ambitious in the country. If grocery stores don't donate the maximum amount of food, they'll be fined. The organic waste that goes into landfills must be reduced by 75% by the year 2025.

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One of the highest rates of hunger in California can be found in the county where Ms. Vang lives. 26% of children in the county don't have enough to eat.

A store manager was stuffing garbage bags with milk as Ms. Vang left the store. She asked if the items were going to the trash. The people were. They had just stopped working.

ImageA large semi trailer full of garbage is being tipped, with the waste tumbling out in a colorful pile.
A Vacaville, Calif., landfill. The new state law requires cities and counties to reduce organic waste going to landfills by 75 percent by 2025.Credit...Andri Tambunan for The New York Times
A large semi trailer full of garbage is being tipped, with the waste tumbling out in a colorful pile.

It is a new problem in human history to throw away crops that have been grown. The stalks of a banana tree, vegetable peelings, and a carrot were all used for centuries by people.

31 percent of food grown is wasted.

There are many problems with food waste. Sometimes it is a refrigeration issue, strict supermarket standards, or poor human planning, and sometimes it is a giant portion at a restaurant. According to ReFED, a nonprofit focused on reducing food waste, 70% of restaurant food is thrown away.

According to the EPA, one-third of the US's food supply goes un eaten.

Food waste emissions are equivalent to 72 coal-burning power plants.

Several American states are trying to tackle one part of the problem with mandatory composting measures If California succeeds, it could take three million cars off the road. Compost is useful for improving soil, and there is a market for it in a state that is reeling from the effects of a long dry spell.

Some of Ms. Vang's rescued food. By one estimate, 70 to 90 percent of wasted food is edible.Credit...Andri Tambunen for The New York Times

Rachel Machi Wagoner is the director of CalRecycle. The goal is to turn waste into something useful.

That doesn't solve the whole problem. Compost orange peel and eggshells. The problem of the quarter sandwich left on a plate isn't solved by it. Dana Gunders, the executive director of ReFED, pointed out that that is a significant waste of water, land, fertilizers, diesel and refrigerants.

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She said it was better not to produce it if you knew it wouldn't be eaten. To do that, you need to redesign systems. Throwing something in the compost bin is easier.

Research shows that including date labels on produce leads people to discard perfectly good food. In Europe, France now requires supermarkets and large caterers to donate food that is still safe to eat, and a proposed law in Spain would require restaurants to provide doggy bags for un eaten food.

The campaign against throwing food away was born in South Korea in the late 1990s. The country had run out of space for landfills. The government said there would be no more food waste.

Most of the organic waste is turned into feed and compost. There is a cost for waste. Korean people pay for what they throw.

ImageA woman and a boy stand next to several recycling bins beneath a banner written in Korean.
An apartment complex in Seoul equipped with food waste recycling bins equipped with radio-frequency identification sensors.Credit...Chang W. Lee/The New York Times
A woman and a boy stand next to several recycling bins beneath a banner written in Korean.
ImageClose up of the inside of a bright yellow-orange trash bag showing plastic containers and other waste.
Nonorganic items in the apartment’s recycling bins.Credit...Chang W. Lee/The New York Times
Close up of the inside of a bright yellow-orange trash bag showing plastic containers and other waste.
ImageA man in a black-and-gray striped shirt stands next to a row of food-waste bins. The bins feature a touch pad and several glowing lights on a small control panel.
Suyeol Hong, a food waste campaigner, said the new bins had made the trash room less smelly.Credit...Chang W. Lee/The New York Times
A man in a black-and-gray striped shirt stands next to a row of food-waste bins. The bins feature a touch pad and several glowing lights on a small control panel.

The government has rolled out trash bins that measure how much food is thrown away each month. If people don't have sensor-equipped trash cans, they have to buy separate bags for food waste.

The sensors went to work in the trash room on a Sunday afternoon. A man emptied his bucket of slop after opening a bin and using a card. The woman said she didn't have to buy the special food-waste bags because of the high tech bins.

Suyeol Hong, one of the country's most prominent food waste activists, said the new bins had made the trash room cleaner. South Korea has a policy to divert food waste from landfills. Banchan, an assortment of side dishes served at no extra cost, is often left at the table at restaurants. People don't like the idea of making them pay for banchan.

Mr. Hong thinks it is hard to reduce food waste in Korea. He said there is always an extra rice cake from a holiday bound for the compost bin.

South Korea has improved. The amount of food waste dropped from 3,400 tons a day in 2010 to 2,800 tons a day in 2019.

A composting center in Vernalis, Calif., that processes some 1,200 tons of material per day.

Washington has a similar law that takes effect in 2025. State and local governments can use money in the U.S. farm bill to save food.

There are challenges in California.

Compost bins aren't always offered to households. People who have compost bins don't know what to put in it. The chicken bones are in good shape. When the poop is in a bag that isn't always composted, dog poop bags are not.

Ms. Wagoner is from CalRecycle.

Composting facilities are hard to build in urban areas. Sometimes compost can have a different effect. People are more likely to waste food if they know it will be composted.

ImagePortrait of a woman sitting on the rear bumper of a white van. The rear doors are open, showing a truck half-full of boxes of food.
Ms. Vang with a haul in a Fresno Metro Ministry food rescue van.Credit...Andri Tambunan for The New York Times
Portrait of a woman sitting on the rear bumper of a white van. The rear doors are open, showing a truck half-full of boxes of food.

Ms. Vang is the leader of the food share program. She is present in the back rooms of supermarkets.

She began saving food after a farmer called the ministry and said he couldn't sell his produce. The manager of the landfill called after the garbage truck came.

Ms. Vang only realized how much was being wasted when she looked at the mountains of food. She said that it hit her hard because so many of her neighbors couldn't afford it. A lot of people in the town don't eat well.

The needs have gone up a lot. The coronaviruses are the first reason. Inflation follows. People stop her when she drives by. A group of college students. People who work on farms. People with a hand.

She knows what she's talking about. Her four children are a mother of four. Ms. Vang knew. It's difficult to shop for groceries.

Two people from Beijing and one from South Korea contributed to the project.