Every year the world wastes about a third of the food we produce. That wasted food, according to a United Nations report released this week, translates into billions of tonnes of greenhouse gases, when one takes into account the energy, land and chemicals used to produce and dispose of it.

The UN Food and Agriculture Organisation estimates that the carbon footprint of the world’s wasted food is equivalent to 3.3 billion tonnes of carbon dioxide (3.6 billion tons) every year. That’s more greenhouse gas emissions than any country produces overall, aside from China and the United States. The report asserts that countries are missing not only a chance to improve food security—hundreds of millions still go hungry every year—but an opportunity to lessen the environmental impact of global food chains.

One place to start would be rice in Asia. Of the regional commodities analyzed by the UN, cereals produced in Asia are the biggest contributor to food waste’s carbon footprint. (Others were meat in Europe; vegetables in North America and Oceania, and so on.) Rice makes up over half of wasted cereals in Japan, China and South Korea, and 72% of lost or discarded cereals in South and Southeast Asia—a total of 149.7 million tonnes, according to the UN. That wasted rice emits greenhouse gas emissions equivalent to 610.5 million tonnes of carbon dioxide a year. Mathilde Iweins, project coordinator for the UN’s Food Wastage Footprint program, says that most of the region’s rice carbon footprint happens during the agricultural production. That’s because decomposing leaves, stalks and other organic matter decompose in rice paddies, giving off methane. Degrading rice in landfills also contributes to emissions.

Why does all this rice go to waste? Poor processing, transportation or storage result in rice being spilled or spoiled before getting to consumers. Some waste also happens on the consumer side as people simply throw uneaten rice away. The UN estimates that 80 kilograms of cereals, mostly rice, are wasted per person in the region every year.

As populations surge in developing Asia and Africa where rice is a staple, even more rice will be produced as well as wasted. And rice’s carbon footprint may get worse. According to a study last year, the presence of more carbon dioxide in the air combined with rising temperatures in the coming decades could double the amount of methane that results from producing a kilo of rice.