Kai Ryssdal: There are now, the United Nations tells us, 7 billion people on the planet. Sooner rather than later -- another 30, 35 years or so -- there's going to be more than nine billion. That's a whole lot of mouths to feed.

So today we're starting a year-long series about the global food system, and how we're going to feed those 9 billion people -- if we're going to be able to feed 'em at all.

We start at dinner.

Doorbell

You can think of the world's food system as a giant potluck dinner.

Woman: Hello, come in!

The first thing that strikes you is the abundance. There's a huge table, it's piled with food. And the smells --

Man: Magnifico!

Ryssdal: Wow, what is that?

Woman: It's goat stew. Try some!

Fifty years ago, people were eating a lot less on average, especially meat.

Man: Have a hamburger. It's delicious.

Back in the '60s and '70s, about a billion people -- one in every three human beings -- were hungry. Millions of people were dying in famines in China, Africa, Bangladesh. People worried there was no way to keep up with an exploding population.

But then came the Green Revolution. And over the course of just a couple of decades, global food production skyrocketed. Famines are now actually pretty rare. We're producing more food, and we're better at dealing with emergencies.

But even with that, things aren't exactly working. Down at this end of the room, there's a family sitting on the floor with a few grains of something, looks like millet. The number of chronically hungry people in the world is still around a billion. Granted that's one in seven of us -- not one in three -- but still, it's a lot.

And clearly something's out of whack, because there are also about a billion obese people worldwide. Actually, a lot of things are out of whack.

Back here in the kitchen, the water system's all messed up -- there's too much in some places, not enough in others. There's a big pile of rotting -- something -- over there, and man, it's getting hot. And crowded, too. There's hardly any room to move.

Here comes another busload of people -- and they look hungry, too.

Ryssdal: A question you might draw from such a scene setter is: Now what the heck do we do? More than nine billion people. So over the course of the next year, in collaboration with Homelands Productions and PBS NewsHour, we'll be looking at what we have do now to be able feed ourselves in the future.

Maybe one place to start is science. Can't we just research and develop our way out of this? It's worked before. Here's Jon Miller.

Jon Miller: I figured Mexico was a good place to go to take a look into the scientific pipeline. This is where farmers thousands of years ago transformed a grass called teosinte into what we now know as corn. It's also where scientists in the 1950s and'60s developed the semi-dwarf wheat varieties that launched the Green Revolution.

My first stop is where a lot of that work was done, at the International Maize and Wheat Improvement Center outside Mexico City. I'm here watching technicians clean and sort experimental corn seeds to go out around the world. I ask research director Marianne Bänziger if there's some big game-changer on the horizon. She says, basically, forget about it.

Marianne Bänziger: It is not just one solution. I mean, our action plans are 10 approaches. And the 10 approaches are not just breeding, they're about really looking at the whole livelihood of a farm family.

So the idea isn't just to increase the total amount of food the world produces. It's also to make life better for the two billion or so people who depend on farming for their food and livelihood. Because ironically, most of the world's poorest and hungriest people are in the food production business. If they can produce more, the thinking goes, everybody benefits.

Bänziger says for most crops, a good place to start is by closing what's known as the "yield gap." That's the difference between what farmers could be producing, using existing technology, and what they actually do produce.

Bänziger: In Africa, under the best conditions, you can get 10 times more yield than what farmers get today. On average, I would say in Africa we can increase production four or five times.

In Asia and Latin America, she figures output could double. Actually realizing those gains -- well, that's the challenge.

People speaking Spanish: Buenos días, hola, hola. Porfirio Bastida para servirles.

I go on a little field trip to see Porfirio Bastida, who farms just over an acre of corn near the Mexico City airport. The city's been creeping closer and closer, sucking up water and land.

People speaking Spanish: Esta bien. Buenos días. Pasenle!

For the last three years, Bastida has been practicing what's known as "conservation agriculture" -- he doesn't plow and he doesn't hoe and he lets the stalks and leaves of the corn plants stay in the field after harvest. American farmers have been doing this for decades to control erosion, but here it's a pretty radical departure from the way people normally farm.

Porfirio Bastida: Mire, en primer lugar, hemos visto que, pues, ya no tenemos suficiente agua.

Interpreter: Yeah, so basically Porfirio is saying that they decided to use conservation agriculture because they don't have much water available for their crops. When they keep all the organic material on the soil, that helps the field to retain humidity.

Bastida says he's using much less water now, and he's harvesting twice as much corn. Plus it's less work. Still, of all the farmers in this area, so far only he and his wife have adopted the method. Take-home message: It takes time for new things to catch on.

I spend the next day tromping around cornfields with Fernando Castillo, a Mexican geneticist who teaches at a nearby university.

Fernando Castillo: Que es lo que más le interesería?

Farmer: Primero las plagas.

Working with a tiny budget, he helps local farmers improve the way they select the corn they'll save for planting the next season. These are traditional varieties, not hybrids or GMOs, and since Mexico is where corn comes from, there's lots of genetic diversity in any given field. Castillo says with a little tutoring, Mexico's 2.8 million corn farmers can accomplish much more than a few plant breeders with Ph.Ds.

Castillo: Farmers have worked for years, and they have learned from their parents and grandparents the local conditions and the management. So most of it is based on local knowledge and local resources.

Castillo says the process could raise Mexican corn yields by 2 percent per year, which is just about what's needed to keep up with the demand. But he's been at this for 15 years, and he's still just working with a handful of farmers.

Around the world, thousands of scientists are hacking away at thousands of problems. Some are experimenting with "agro-ecological" methods -- mixing different crops and trees and animals to diversify diets and reduce the need for chemical fertilizers. Others are trying to breed crops that resist insects or diseases, or that tolerate flooding or drought. Some of this stuff is pretty ambitious.

Matthew Reynolds: This field contains the first experiment of the wheat yield consortium in Mexico.

Matthew Reynolds is a wheat specialist at the maize and wheat center. He's heading a global push to make wheat plants much more efficient at converting sunlight into grain. There's a parallel effort going on in rice.

Reynolds: This is actually a very interesting area, the spike photosynthesis, because no one has ever systematically tried to improve this photosynthesis of the spikes.

It's not just about the spikes -- those are the parts of the plants with the seeds on them -- it's about fundamentally changing the way the plant works. Reynolds says the research will take 20 or 30 years to bear fruit -- if it bears fruit at all. But it could increase wheat yields by 50 percent.

Reynolds: So what are the odds? The answer to that question is more: What are the consequences if we fail?

But no one is really counting on the project succeeding -- there are just too many scientific uncertainties. So the strategy for now is to keep working on as many fronts as possible.

With climate change, and another two or three billion people coming, I ask Marianne Bänziger if it'll be enough.

Bänziger: We can feed the world in 2050. Maize is the livelihood for 900 million poor people. Wheat feeds more than 1.2 billion poor people. So it is a little bit absurd to think that the resources are not there. They are there.

Still, everyone I talk to here says no matter how generous the funding, no matter how good the science, it won't make a difference if government policies aren't right. That means fair prices for farmers and help when crops fail. It means access to land and roads and warehouses and markets. It means education and nutrition programs and family planning.

But you can't just wait for all those things and then call in the scientists. Because if there's one resource scientists need more than anything, it's time.

In Texcoco, Mexico, I'm Jon Miller for Marketplace.

Ryssdal: Food for 9 Billion is a collaboration between Marketplace, Homelands Productions, PBS NewsHour and the Center for Investigative Reporting.