There’s a paradox when you consider farming and climate change. Climate change may actually benefit some plants by lengthening growing seasons and increasing carbon dioxide, the lifeblood of anything that roots in the ground. Yet it’s important not to get distracted by these changes, which researchers think would be marginally beneficial at best. The other effects of a warmer world, such as more pests, droughts, and flooding, will be far less benign. A 2013 study published by Science magazine says, “The stability of whole food systems may be at risk under climate change because of short-term variability in supply.”

Trying to understand what that means for farmers requires an equation as complicated as the climate itself. So not long ago, I visited a typical American farm growing the most typical of all American crops: corn.

In Oakland, Iowa, A 78-year-old farmer named Mark Gardner drove me around his farm, explaining the ins and outs of commodity farming. Mark doesn’t grow designer corn that he sells at farmers markets or to high-end food stores. On his 1,000 acres, he grows the same corn (and some soybeans) as everyone around him and sells it for the same price as everyone else, determined by the commodity markets. He buys new seeds every year, plants it and harvests it with the help of a forest green combine. Then he hopes—or perhaps prays—that the sun shines and the rain pours enough to keep it growing, producing, decomposing, and then growing again.

Mark is a calm man; thoughtful, methodical, with a pace that suggests he long ago shed the anxieties inherent in farming. But in many ways, Mark isn’t special. Hundreds of thousands of people grow corn in the U.S. on 90 million acres. Corn is the world’s second biggest commodity (after sugar) and the U.S. is the biggest producer, to the tune of 26 percent of all corn grown on Earth. He knows this, and it’s the main reason he said he doesn’t stress about how growing conditions may change. They will, and the seed companies will fiddle in their labs to create better, more adaptable seeds, and Mark will fire up the combine for another season.

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But anyone who works at the behest of the weather knows the ending isn’t always happy. So I asked a group of researchers at the International Food Policy Research Institute to project what corn production might look like in 2050. Using an aggressive climate model known as HadGEM2, they say America’s corn output could drop by 20 percent. That’s only a slightly bigger loss than in Brazil, also a powerhouse producer, where corn production is expected to slide 16 percent. Globally, its projected to live 24 percent, which is the biggest drop predicted for the biggest commodity crops, including rice, potatoes, and wheat.

The reason that’s a problem is because, even if corn production goes down, consumption won’t. Prosperity around the world, particularly in developing countries, has increased pressure to grow more crops that are easy to scale, like corn and soybeans. Some of that is to feed people, although most of it is to feed cows, chickens, and pigs. The farm eggheads at IFPRI and the U.N. Food and Agriculture Organization think that corn consumption will double between now and 2050 as a result of booming and urbanizing populations. Some of that corn will feed those people, but most of it will feed their animals.

The question then becomes, if not in its traditional places, then where else will corn be grown? Places like Oakland, Iowa, may escape the worst effects of a warming planet. But while high heat and humidity will close off some areas, climate change will also open new areas to corn areas. Places like Europe, Asia, and the top of North America (which is to say, Canada) will see their crop land open up. There are signs it’s already happening. Even though the U.S. produces the most physical corn, China has become the global leader—by a lot—of seed production. The United Arab Emirates has some of the highest yields on Earth.

Clearly, the business of agricultural forecasting is imprecise and riddled with assumptions. That’s mostly because farming is an uncertain business, with contributing factors far beyond just the climate. But there are ways countries with arable land can set themselves up for stability and success, especially amid political shifts, changes in global demand, and swings in crop prices and farming costs. “The winners,” says crop modeler Ricky Roberts, “will be those supported by good policy and agricultural research to deal with the changing circumstances.”

If weather doesn’t keep Mark Gardner awake at night, the thing that does is what happens when he decides he’s done. At 78, he’s been farming for 62 years, most of it by himself. Without an obvious heir, odds are he will, like many aging farmers of his generation, sell his farm to a land conglomerate keen to exploit the economies of scale. Those companies work with large seed makers, and together, one wonders if they’re not better equipped to handle the changing demands, climate, and consumption markets for a crop like corn. Those seed-makers have a good track record. Gardner tells me proudly that since 1953, his corn yield has increased ten fold.

Learn more about climate change and other commodity crops in the November 2015 issue of National Geographic Magazine.