What climate change means for agriculture: Less food, more emissions todayheadline

New research spotlights the challenge of growing food on a warming planet. 

Two recent studies — one historical and the other forward-looking — examine how rising temperatures have made and could continue to make agricultural production less efficient, fundamentally reshaping the global food system as producers try to adapt to hotter growing seasons.

The findings illuminate the bind that farmers and consumers find themselves in. Agricultural production is a driver of climate change; it’s estimated to be responsible for somewhere between a quarter and a third of global greenhouse gas emissions. But it is also hampered by the changes in weather patterns associated with climate change. While producers struggle to harvest the same amounts of food in the face of droughts, heat waves, and hurricanes, shoppers are more likely to face climbing food prices.  

The forward-looking study, published June 18 in Nature, analyzes the impact of warming temperatures on the caloric output of agricultural production. Researchers at the University of Illinois Urbana-Champaign and the Stanford Doerr School of Sustainability found that for every additional degree Celsius of warming above the 2000-2010 average, the global food system will produce roughly 120 fewer calories per person per day.

In a scenario where the Earth experiences 3 degrees Celsius of warming by the end of the century, that’s the equivalent of everyone on the planet missing out on breakfast, said Andrew Hultgren, lead author of the study.

Hultgren and his colleagues compiled a massive dataset on the production of six staple crops in more than 12,000 regions spread out over 54 countries. They then modeled how different warming scenarios might impact crop production; they also factored in how farmers around the world are adapting to higher temperatures. What they found is that, even with adaptation, global warming is associated with an “almost a linear decline in caloric output,” said Hultgren, who is also an assistant professor of agricultural and consumer economics at the University of Illinois Urbana-Champaign.

Measuring agricultural adaptation and its impact on output was important, said Hultgren, because research often assumes that farmers either adapt perfectly to global warming or not at all. The reality is that adapting to any growing season challenges comes at some cost, and farmers are constantly weighing the business benefits of implementing new techniques.

For example, one tool that corn farmers in the U.S. Midwest have to prevent hot days from thwarting their harvest is planting crop varietals that mature relatively quickly. “Corn is very sensitive to extreme heat,” said Hultgren, “so one very hot day can actually be bad for your entire growing season yield.”

But fast-maturing varietals also often produce lower yields overall, meaning these farmers likely can’t sell as much corn as they would have under cooler weather conditions, said Hultgren. “So there’s literally a cost of avoiding that extreme heat,” he said. 

A drop in the global supply of crops will also lead to an uptick in food prices. But Hultgren noted that the impacts of reduced agricultural output won’t be evenly distributed. In wealthier countries such as the U.S., for example, those who can afford higher food prices will likely eat the cost. In poorer countries, these shifts could worsen food insecurity. 

Additionally, rising temperatures will impact producers unevenly; the study estimated that in a high-warming climate scenario, corn farmers in the U.S. will experience 40 to 50 percent losses in yield by the end of the century. Based on these projections, “you wonder if the Corn Belt continues to be the Corn Belt,” said Hultgren. Meanwhile, other regional producers — like rice farmers in South and Southeast Asia — will see yields grow in the same time frame.  “There are absolutely regional winners and losers in this global aggregate,” he said.

The historical study, published June 20 in Nature Geosciences, looks at one of the ways agricultural production contributes to global warming: land clearing. When farmers want to cultivate new cropland, they often start by removing the plants that are already growing there, whether that’s grass, shrubs, or trees. When land clearing happens in carbon-rich regions in the Global South, like the Amazon rainforest, it increases deforestation and carbon emissions, said Jessica Till, the study’s co-lead author. 

“Deforestation in tropical areas is one of the most urgent issues and biggest areas of concern,” said Till, a research scientist at the University of Illinois Urbana-Champaign. (Till and Hultgren were not involved in each other’s studies.) “The more land you clear, the more forest you remove to create cropland, that’s going to have a negative effect on the climate.”

Till and the other study authors examined this feedback loop between agriculture and the environment: When crop production becomes less efficient due to extreme weather and heat, farmers must acquire and clear more land to boost production. That expansion in croplands then in turn results in higher greenhouse gas emissions, which exacerbates warming and makes crop production even less efficient. 

They found that, even with improvements in agricultural productivity (due to technological improvements like new seed varieties and precision fertilizer application), climate change was responsible for 88 million hectares, or 217 million acres, in cropland expansion globally — an area roughly twice the size of California — between 1992 and 2020. 

They also determined that this expansion was led by major agricultural producers, including the United States, India, China, Russia, and Brazil. Unsurprisingly, these countries were also the top five highest emitters of greenhouse gas emissions stemming from climate-driven expansions in cropland. 

Both Till and Hultgren noted that these shifts can also influence global trade. When certain regions see a decline in agricultural productivity, said Till, other regions will gain a competitive advantage in the international market for agricultural commodities. 

Erwan Monier, co-director of the Climate Adaptation Research Center at the University of California Davis, said he was not surprised by either studies’ findings, and said they contribute to the growing body of research on climate impacts on agriculture. 

But he added that both come with caveats. Monier noted that the Nature study on caloric output fails to consider possible future advances in technologies like genetic editing that could make crops much more resilient to climate change. He said the paper demonstrates that “in order to really limit the impact of climate on our ability to grow food, we’re going to need a scale of innovation and adaptation that is really substantial, and that’s going to be a real challenge.”

Referring to the Nature Geosciences paper on the feedback loop between agriculture and climate, Monier said that it similarly does not take into account how farmer behavior might change in response to global warming. 

“The fact is we have an ability to change what grows where,” said Monier. In the U.S., for example, where corn and soy production reign, farmers could choose to plant different crops if they see yields fall consistently. These growers will not “continue growing corn with very low yields and invest more capital and land with very, very low returns,” said Monier. “Farmers are going to move away to something that actually is more valuable and grows well” — and that, in turn, could reduce the need to clear more land.

Monier acknowledged that the latter study might come across as quite pessimistic. But, he said, it underscores the importance of having difficult conversations now about how to grow enough food to feed the world’s population as temperatures climb. 

In order to avoid serious losses in agricultural production, he said, climate researchers and institutions must work hand-in-hand with farmers, helping them understand the risks of global warming and seek out new ways of adapting. This work should be “bottom up,” said Monier, rather than “top down.” “We need to engage the people who are going to be actually growing the food.”

He added that this will involve work that extends beyond the academic sphere. “I don’t know if publishing in Nature and Nature Geoscience is the way to really drive the bottom-up adaptation at the scale that is necessary.”