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For decades after World War II, global agricultural production outpaced population growth, driving down food prices and alleviating extreme poverty. Even after recent price spikes, food is quite cheap as a fraction of one’s income, says Wolfram Schlenker, the Ray A. Goldberg Professor of the Global Food System at Harvard Kennedy School and CID Faculty Affiliate.
But the growth rate of agricultural yields – particularly of the four commodities (corn, soybeans, rice and wheat) that comprise about 70 percent of the world’s diet (directly or indirectly through animal feed) – have started to slow in recent years.
Exacerbated by pandemic supply shocks, the war in Ukraine, more frequent and severe climate events, and protectionist trade policies, food inflation is at an inflection point – with profoundly uneven consequences. Many Americans are concerned about rising grocery costs, notes Schlenker, but most U.S. households can still afford food. For the over 700 million food-insecure people around the world, the effects are devastating.
The resurgence of global hunger led 150 Nobel and World Food Prize laureates to publish an open letter in January 2025, calling for a collective effort to ramp up food production and accessibility. We’re “not even close” to meeting the food needs of a global population expected to reach 9.7 billion people by 2050, the letter states. Among the drivers of food insecurity, it asserts, is a warming planet.
Schlenker, who works at the nexus of climate science, agriculture and economics, was among the first to identify on crop yields. While completing a doctorate in Agricultural and Resource Economics at U.C. Berkeley, he delved into “an ongoing debate on whether climate change would benefit or harm U.S. agriculture.” Some researchers argued it would lead to declines in crop yields, while others suggested warmer temperatures and higher carbon dioxide levels could lead to adaptations in certain climates. What stood out to Schlenker was the need “to capture the effect of extreme heat correctly.”
Most previous studies focused on average temperatures, overlooking the impact of extreme cold and heat, which plant biologists have long linked to plant distress. Schlenker and his co-author used fine-scale weather data, developing daily predictions of minimum and maximum temperatures to capture nonlinear weather effects for three U.S. crops (corn, soybeans and cotton) over precise growing locations countrywide.
They found that yields gradually increased up to a critical temperature (e.g., 29℃, or 84℉ for corn), then precipitously dropped above that threshold. “Being too cold or too hot is bad for the plant, but being too hot is far worse,” says Schlenker. “This means that as climate change shifts us to extreme heat, you could see a dramatic drop in agricultural output.” (This claim was corroborated in 2012 when a heat wave over the U.S. corn belt saw a 25 percent drop in yields.)
An economist and engineer by training, Schlenker grew up in a suburb of Stuttgart in southwestern Germany. With several physics professors in his family, he vowed not to become an academic. But a chance year abroad at Duke University’s newly launched Nicholas School of the Environment sparked a fascination for environmental economics that shifted his trajectory.
“I planned to come for a year, and liked it so much, I decided to stay for the rest of my life,” Schlenker recounts. At Duke, he was introduced to a framework for thinking about “the trade-offs between protecting the environment and the cost of regulation. ” It provided a way to rigorously quantify costs and benefits that had the potential to tangibly improve people’s lives while also keeping costs down for industry.
Over the last 20 years, Schlenker has studied the role of weather and climate on and , the impact of weather and the U.S. biofuel mandate on , and the effect of pollution on agriculture and . Time and again, he’s seen that “extreme heat drives everything; it always leads to big damages,” not just in agriculture, but in areas such as mortality, labor productivity, and energy consumption.
As the planet warms, poorer countries, which have contributed least to greenhouse gas emissions yet see the fastest rise in extreme heat as they are often warmer to begin with, will be disproportionately impacted. The U.S., meanwhile, is a puzzling outlier. It has not experienced the projected rise in extreme heat that has plagued other major growing regions, including in Europe, South America and Asia. This may be due in part to the cooling effects of large-scale irrigation practices, as Schlenker explored in a . His findings suggest that while “extreme heat impacts yields, agricultural practices can also impact climate, especially downwind.”
“Climate change is a threat multiplier,” he emphasizes. “But we can meet that threat. The challenge is convincing governments to not give in to beggar-thy neighbor policies that shift the burden of climate shocks to neighbors in the short term but lead to a less resilient food system in the longer term. A long-term global perspective is crucial.”
Despite Schlenker’s optimism about our capacity to craft innovative practices and policies, he cautions that the compound effect of weather shocks and protectionist trade policies could worsen inequality and geopolitical stability. “Free trade is especially important for agriculture because it mitigates weather shocks that, luckily, don’t hit all places in the same year,” Schlenker explains. “It works like a perfect hedging for risk,” incentivizing farmers with good harvests to export commodities to places with scarcer yields. But as countries turn increasingly protectionist, there are fewer ways to buffer against shocks, resulting in greater volatility. When India enacted an export ban to protect domestic wheat supply following a 2022 heat wave, for example, prices skyrocketed in neighboring countries.
There are very good economic and security reasons to heed the 2023 UN Climate Change Conference’s landmark call for “open, fair access to food,” Schlenker pointed out in an vlog podcast. The historical links between climate-related hardships and political disorder – from the food shortages preceding the fall of the Roman Empire to the three years of drought leading up to the conflict in Syria, to increased migration and asylum applications to Europe in the twenty-first century – signal a need for open international markets.
Citing a century of progress in the agricultural sector, global innovations in research, and, on an institutional level, “the building of expertise in the food space” at Harvard with the hiring of three new young professors, Schlenker remains sanguine.
“Climate change is a threat multiplier,” he emphasizes. “But we can meet that threat. The challenge is convincing governments to not give in to beggar-thy neighbor policies that shift the burden of climate shocks to neighbors in the short term but lead to a less resilient food system in the longer term. A long-term global perspective is crucial."
Image Credits
Main Photo by Lydia Rosenberg
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