If someone asks you to picture where greenhouse gases come from, images of smoggy traffic jams or billowing smokestacks are likely to spring to mind. But your dinner? Probably not so much.

Your dinner isn’t simply a delicious, innocent bystander. From the farm to your plate, there’s food waste at every step. And decomposing food isn’t just stinky; it releases potent greenhouse gases, mostly in the form of methane.

Even so, food waste should still be a relatively small issue, except that we needlessly waste food on such a massive scale that it adds up to a global problem. Just under 7 percent of greenhouse gas emissions come from food waste worldwide. To put that in perspective, if all the world’s food waste came together and formed a country, it would be the third-largest emitter of greenhouse gases, behind China and the US.

It might seem ridiculous to think of food waste as a country except as a thought experiment, but producing all of that unused food takes up real space — country-size space.

How much? According to a 2013 analysis by the United Nations’ Food and Agriculture Organization, the land devoted to producing wasted food would be the second-largest country in the world — smaller than Russia but considerably larger than Canada.

Imagine an area the size of Central America plus Mexico, plus the lower 48 states and a huge chunk of Canada, totally devoted to producing food we never even use.

There’s waste before food even leaves a farm; then food is shipped, stored, processed, sold in grocery stores, and served in restaurants or cooked at home, each step adding more to the food waste pile.

In the US, consumers are the biggest wasters. Nobody gets excited about throwing away food, so why are we doing it?

A lot of it comes down to little quirks of human psychology.

“One of the things we found in our research is that people are uncomfortable with white space when it comes to food,” said Dana Gunders, senior scientist at the Natural Resources Defense Council and author of The Waste-Free Kitchen Handbook. “We do not want to see empty space in our refrigerators, on our plates, in our grocery carts. In some subliminal way, we're just filling everything.”

And the things we fill with food have gotten larger. Dinner plates have expanded by 36 percent on average since 1960, refrigerators have grown by roughly 15 percent since the 1970s, and our perception of “normal” portion sizes has grown along with them.

On top of this, in places where food is abundant, people have a talent for finding ways to rationalize throwing away perfectly good food, whether it’s because their pear is lightly blemished or because their soup has passed some arbitrary “best by” date.

Compared with other climate change challenges, problems like these are relatively easy to fix, and are currently the focus of a lot of attention from both startups and regulators. For starters, new, clearer food labels are coming in the US.

“What we're seeing right now is a tremendous increase in attention and buzz on the topic of food waste, which is exciting,” said Gunders.

This buzz is leading to new, innovative food waste solutions that can help address both hunger and global warming at the same time.

Watch the video above featuring Dana Gunders and other researchers and entrepreneurs using both technology and human psychology to find solutions to food waste — and to get extra food onto the plates of people that really need it.

Find out more about new efforts to stop food waste and other climate change solutions at climate.universityofcalifornia.edu.