Is Your Half-Eaten Lunch Harming the Planet.

• Author: Bubar, Joe

Food waste is a bigger driver of climate change than many people realize. What will it take to solve the problem?

The yogurt that's past its "sell by" date. The banana in your lunch that turned brown. The leftovers in the fridge that you forgot to eat. For most people, all that food goes right into the trash.

Americans throw out 40 percent of the food produced in the U.S. each year, according to the environmental group Natural Resources Defense Council (N.R.D.C.). Worldwide, 1.3 billion tons of food goes to waste each year, worth nearly $990 billion, the United Nations (U.N.) estimates.

Experts say that food could go a long way toward solving world hunger. But they also point out that there's another, less obvious reason to be concerned about food waste: It's one of the top drivers of climate change.

Eight to 10 percent of global greenhouse gas emissions are related to food waste, according to a report released in August by the U.N.'s Intergovernmental Panel on Climate Change. In fact, global food waste accounts for more greenhouse gas emissions than any country aside from China and the U.S.

A Big Waste

Many environmental experts say that throwing away less food is a crucial personal habit people can adopt to help the planet.

"There's been a lot of focus on energy," says Paul Behrens, a professor in energy and environmental change at Leiden University in the Netherlands. "But climate change is as much a land issue and a food issue as anything else."

When most people think of the drivers of climate change, they think of gas-guzzling vehicles and coal-burning power plants. But while transportation and energy account for more than half of all carbon emissions in the U.S., experts say that throwing out food is also a lot more wasteful than it might seem.

"When you throw away an egg or a sandwich," says Yvette Cabrera, food waste deputy director at the N.R.D.C., "you're also throwing away all the resources that went into producing those things."

That includes not only all the water, land, and fertilizer that went into producing that food, but also the massive amounts of fossil fuels used to power the farms, transport the food, and create the packaging.

Then there's the issue of what happens to food after it's thrown out. More food ends up in U.S. landfills than any other type of trash. Food rotting in landfills emits methane, a greenhouse gas that's roughly 25 times more powerful at trapping heat in the atmosphere than carbon dioxide, which is...