Climate change agricultural impacts to heighten inequality: Study

Dramatic changes in crop productivity will be felt globally in the next 10 years — a decade earlier than previously thought — according to new computer simulations recently published in Nature Food.

The study projects major reductions in yield for crops such as soy and corn by 2100 if climate change continues unmitigated. Key breadbasket regions in the United States, the Middle East, Central Asia, China, and West Africa will see changes to agriculture emerging much sooner than previously thought, the study warns. The research effort was led by Jonas Jägermeyr at the NASA Goddard Institute for Space Studies in New York, in collaboration with researchers at Germany’s Potsdam Institute for Climate Impacts Research (PIK).

Scientists combined five new climate models from the World Climate Research Programme’s Coupled Model Intercomparison Project (CMIP), with twelve global crop models to create the largest and most accurate set of crop yield simulations to date. They simulated known processes in plant physiology and ecology to estimate corn, wheat, soy and rice yields under two different climate scenarios: a very high-emissions scenario (RCP8.5), and a climate mitigation scenario (RCP2.6). They found that corn (maize) — a staple crop in sub-Saharan Africa, Southeast Asia, and Latin America and the world’s most popular grain — could experience yield declines of up to 24% by the end of the century. Wheat might see a boost to productivity of as much as 17% over the same period.

Emergence of climate impacts

The researchers gauged how soon climate impacts on agricultural productivity might emerge in different regions using a statistical measure known as time of climate impact emergence (TCIE) — the year in which the average change in agricultural yield falls outside the historic range for a particular location. Jägermeyr explains: “The time of emergence [is] the year when mean changes leave the envelope of historical conditions, [and] we say OK, this is not normal anymore; this is the emergence of a signal that’s attributed to climate change.”

Using the period from 1983 to 2013 as a reference, the simulations confirm that in some subtropical regions, including the Middle East, Central Asia, parts of Mexico and the Western U.S., the TCIE has already occurred — climate change has already pushed agricultural productivity outside of the bounds of historical norms and into a new normal.

Other major breadbasket regions in North America, Europe, and Asia are projected to experience the TCIE in the next decade. “That’s alarming because it reduces the lead time for farmers, stakeholders, [and] policymakers, to really implement the adaptation pathways that are required,” Jägermeyr warned.

Increasing inequality

The research team found that tropical regions — where corn is heavily cultivated and climate change will be most severe — can expect to see larger yield losses, felt sooner, than in temperate regions.

“In higher latitudes, where crop cultivation is often operating in temperature-limited regions … additional warming can actually be beneficial for crop growth,” due to fertile zone expansion and a lengthening growing season, Jägermeyr explained. In contrast, “smallholder regions in lower latitudes, where agriculture is often a self-sufficiency measure, will feel these impacts most directly, with the strongest implications for food security, livelihoods, and equality.”

These latitudinal differences in climate impacts could be exacerbated by physiological differences between crops. Wheat, for example, is better equipped than corn to take advantage of higher atmospheric CO₂ levels which can fuel crop growth. According to the study, these combined factors will place the burden of climate change on developing nations, where financing for climate adaptation is often severely limited.

Last month, at the COP26 climate summit in Glasgow, Scotland, vulnerable nations made a plea for stronger international financial commitments to help adapt to global warming. But while an adaptation pledge of “100 billion dollars annually from developed to developing countries was … reaffirmed,” at the summit, that promise, first made in 2009, has yet to be fulfilled by high-income nations.

“There’s no question, [that] low-latitude farmers are at risk … in fact that’s a general truth about climate change,” said Robert Mendelsohn, a professor of economics at the Yale School of the Environment in Connecticut, USA, who was not involved in the study. He expressed concern for subsistence farmers, who “are among the most vulnerable,” to climate-driven food insecurity.

However, he added, “this [study] reaffirms the idea that the global [food] supply is not at risk,” because losses in low latitudes will largely be alleviated by gains in high latitudes, and because farmers will hopefully adapt to changes in local climate.

Adapting to a new climate reality

The study simulates changes in crop yield assuming that farmers make no changes to their current agricultural methods, in order to isolate the effect of climate. “This is critically important to understand and disentangle the complex climate change impact processes,” said Jägermeyr.

But there are measures farmers can take to minimize yield losses in tropical regions and to maximize gains in temperate areas. Some changes — such as sowing crops earlier or switching to heat-tolerant cultivars — are relatively inexpensive and simple to implement, while others, such as installing new irrigation systems, require financial investment, planning, and perhaps most importantly, time.

“In 74% of global corn-growing regions, we will see dramatic losses if we don’t act,” said Jägermeyr, concluding, “We need adaptation and we need it basically tomorrow.”

Mendelsohn is confident that farmers around the globe will adapt instinctively as the climate changes, as they have done so far, because “if they make those adjustments, they’ll earn more net revenue [so] the incentive is there already.”

Many climate crop adjustments won’t likely “require government intrusion; this is something individual farmers will do for their own sake,” he asserted. And taking those adaptations into account, “the [agricultural] outcome is going to be better than these [model] predictions.”

Jägermeyr acknowledged that “some of these measures are being implemented by the farmers already in an inherent way, [with] one example [being] the shift in planting dates.” However, other adaptation measures, such as breeding new cultivars, switching crops, changing land-use patterns, and investing in irrigation, “are not as simple and need incentives and dedicated policy support in line with local realities,” he said.

Locked-in changes

Importantly, shifts in agricultural productivity in regions around the globe over the next decade are largely locked-in, the authors say, as both the high- and low-emission scenarios produced similar trends.

However, humanity’s actions can still have a profound impact on the actual severity of those long-term agricultural productivity trends, the research shows. Action taken now to mitigate climate change could limit corn yield losses to just 6% by the end of the century, while maximizing gains in wheat productivity, according to the research. “There are huge gains to be made, huge risks to be avoided, if we manage to steer away from a business-as-usual, high-emission pathway,” Jägermeyr said.

The study results “confirm the importance of changing the climate trajectory we are currently on if we want to maintain agricultural progress,” said David Lobell, Professor of Earth System Science and Director of Stanford University’s Center on Food Security and the Environment in California, who was not involved in the study.

Mendelsohn described the new simulations as “helpful,” because they demonstrate that “if the climate scenario looked like RCP8.5 — with gigantic emissions and therefore gigantic changes in temperature — that will have very big effects on yield.” However, he feels that the high-emission scenario often cited as ‘business-as-usual,’ is too pessimistic, requiring an increase in the rate of global economic growth to move us onto that disastrous pathway.

The research team is currently running additional crop model simulations under a wider range of climate scenarios to gain a more complete picture. For the present study they chose “the most optimistic and the most pessimistic scenario available, to sample the range of potential climate change impacts,” Jägermeyr said.

What is clear in both modelled scenarios is that “agriculture is facing a new climate reality,” he warned. “In some parts [of the world] we need adaptation to exploit these gains, in other parts we need adaptation to avert negative changes, but the amount of change that’s coming is a lot and is surprising.”

“The spatial extent of these impacts are so widespread that deliberate adaptation measures, targeted, well-planned policies to implement adaptation, are critical and paramount,” Jägermeyr said.

Citation:

Jägermeyr, J., Müller, C., Ruane, A.C. et al. Climate impacts on global agriculture emerge earlier in new generation of climate and crop models. Nature Food 2, 873–885 (2021).

Banner image: Corn is a staple crop across Africa and Latin America, and the world’s most popular grain. Projected yield losses of up to 24% by 2100 threaten food security for subsistence farmers in the global south. Image courtesy of CIAT International Center for Tropical Agriculture on Visualhunt.

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