Inside these growth chambers, it’s the future. And Jerry Hatfield, an affable agronomist who heads the US Department of Agriculture’s National Laboratory for Agriculture and the Environment, doesn’t like what he sees.

“Either we’re going to change the crops that we produce or we’re going to have to think about how we genetically manipulate that plant to have a higher tolerance to higher temperature.”

Three years ago, Hatfield used the growth chambers to find out how local crops would perform under the temperatures predicted for the region in 2100, which are expected to rise roughly 4 °C on average, or about 7.2 °F. He simulated a growing season, from April 1 through October 30, for three different strains of corn used by farmers in the area. In one chamber, Hatfield started the temperature at just around 50 °F (10 °C) to mimic conditions in early April, raised it well above 100 °F (38 °C) to simulate the hot summer days (as high as 114 °F in the chamber with 2100 conditions), and then brought it back down again for autumn. In a second chamber, he simulated the region’s current, cooler climate norms.

The differences between the plants in the two chambers were stark. While the leaves looked the same, the impact of that extra 7.2 °F was far worse than projected by even the most pessimistic scientific literature. The number of corn kernels per plant plummeted, in some cases by 84%. Some plants produced no kernels at all.

Inside growth chambers like this one, plants will be grown under simulated conditions. Kathryn Gamble

It was just the first in a series of alarming results. In the months that followed, Hatfield and his colleagues simulated the rising temperatures and altered rainfall patterns expected to hit the wheat fields of Salina, Kansas, as soon as 2050. Yields fell as much as 30% with low precipitation and as much as 70% with the combination of high temperatures and low precipitation expected in the decades ahead.

To date, it’s been relatively easy for American farmers to shrug off climate change. After all, under the most optimistic models, projected US yields for corn and soybeans—which are grown on 75% of the arable land in the Midwest—are actually expected to increase through 2050, thanks to warmer weather that will benefit the relatively cool northern climes. But after that, if Hatfield is right, yields will fall off a cliff, devastating farmers and leaving much of the world hungrier.

By 2050, the world’s population is expected to grow to 9.7 billion. As living standards and diets also improve around the world, food production will have to increase by 50% at a time when climate change will help make both sub-Saharan African and East Asia unable to meet their own needs without imports. Already US corn and soybeans account for 17% of the world’s caloric output. The UN Food and Agriculture Organization projects that American exports of corn must almost triple by 2050 to meet the shortfall, while US soy exports would have to rise by more than 50%. All this extra food has to be grown without using significantly more land. That means it’s going to be all about yield—the productivity of the crop.

And that is what has Hatfield so worried. A growing body of scientific literature suggests that climate change is likely to decimate yields unless we can find new ways to help plants cope with the droughts, vast temperature fluctuations, and other extreme weather that’s likely to become commonplace in the decades ahead.

“If something isn’t done, we will see major drops in production across large areas of the corn belt and Great Plains,” Hatfield says. “Either we’re going to change the crops that we produce or we’re going to have to think about how we genetically manipulate that plant to have a higher tolerance to higher temperature.”

The end of Goldilocks

There is, of course, a familiar ring to the dire predictions. World leaders in the early 1970s were so worried that rising populations, increasing pollution, and soaring food prices would create an acute food crisis by the dawn of the 21st century that the UN convened a conference in Rome. “Time is short,” the member states declared after the conference, in 1975. “Urgent and sustained action is vital.”

In the years that followed, however, high-yield crops, a wider use of irrigation, farm mechanization, and the introduction of synthetic fertilizers and pesticides led to a “Green Revolution,” dramatically increasing agricultural production in many places around the globe.

Now the pace of growth has begun to slow. Water is short in many areas, limiting further expansion of irrigation. And it’s hard to imagine using even more fertilizers and pesticides. “It’s already an open question whether we will be able to keep inventing these new technologies and management practices that allow productivity to more than keep up with demand,” says Marshall Burke, a Stanford economist who focuses on climate change. “But climate is for sure going to make that a lot harder.”

What’s more, global warming is already making its effects felt. In 2011, Columbia University economist Wolfram Schlenker and Stanford ecologist David Lobell looked at what happened to crop yields as temperatures rose between 1980 and 2008. They found that global maize production (excluding the US) fell 3.8% and wheat production dropped 5.5% relative to what it would otherwise have been. The increase in hot days and nights explains about half of all variation in corn yield. Higher temperatures help up to a point, between roughly 50 °F and 84 °F, but hotter than that and yields plummet.

To get a sense of what this all might do to global food prices, Schlenker suggests looking at what happened in 2012, the last time the American Midwest experienced a summer with temperatures comparable to what climatologists project will become the norm by the end of the century. The region’s production of corn fell by 25% and soybeans by 10%. That constitutes about a 4% to 5% drop in total global caloric production—conditions under which we can expect food prices to spike by as much as 30%, he says.

Plants in the chamber will be closely monitored by a suite of sensors. The USDA scientists measure how each plant does under the varied conditions. Kathryn Gamble

Despite a few such bad years, however, Midwest farmers have enjoyed a decades-long rise in productivity, masking the worries about the future. There is a “Goldilocks” zone for temperature, humidity, and rainfall, and climate change has, for the most part, pushed the middle of the United States further into it, says Gene Takle, former longtime director of Iowa State’s climate science program. The largest change in Iowa to date has been increased rainfall in April, May, and June— it’s up by almost 25% over the last three decades. This extra rain, caused by the interaction of wind patterns with warming waters in the Gulf of Mexico, has forced farmers to spend more money on drainage tiles and the like to adapt, and it has shifted the planting season. But the combined result of technological advances and more favorable climate is that yields have risen 28% across the Midwest. “There’s pretty good agreement that climate change has been favorable to agriculture to this point,” Takle says.

These trends will reverse, though; where the experts disagree is on precisely when. Takle cites one model showing that the positive trend in productivity will turn around by 2035, undoing all the gains seen since 1981. And yields will only continue to fall from there. “We’re on the cusp right now,” he says.

On a recent day, he pushed a piece of paper across a table. It was full of colorful charts and bullet points, detailing the impact of climate change to date on local agriculture, with the positives spelled out in green and the negatives in red. Among the red points: more pests were surviving the winter, and waterlogged soil reduced the number of days farmers could work the fields. (In 2013, northwest Iowa had 700,000 acres—283,000 hectares—that couldn’t be planted for that reason.) But there was plenty of green, too.

Then he turned the page to show how things would look in 2050. There was no green on this page—only a long list of red. Intense spring rains will make field work early in the season harder, Takle expects. There will be more flooding; the warmest day will be 7 °F hotter. Every other year will see at least one five-day period when extreme heat will cause corn and soybean pollination to fail and vegetative growth to stall.

“We have a lot of problems coming down the pike,” he says.

New genetics

The job of Hatfield, the USDA agronomist, is to monitor the impact of environmental conditions on the country’s farmers and identify potential solutions. Sitting in his office on a recent day, he ticked off a long list of worries. The brown marmorated stink bug appeared in the US in the late 1990s, and as temperatures rise over the next 30 years, its range will expand all the way up to Canada, damaging a wide array of crops. The Palmer amaranth, an herbicide-resistant weed that lives in particular microclimates and has so far threatened mainly soybean and cotton crops in the South, will likewise spread northward and become ubiquitous.