This story was originally published on Civil Eats.
As the climate crisis progresses, the planet is becoming less inhabitable — not only for humans and other animals, but also for plants.
Farmers know first-hand how climate disasters, pollinator loss, heat waves, flash floods, and diminishing water supplies can make growing crops harder and less predictable. Yet many questions remain when it comes to how exactly crops are responding across cultivars and varying landscapes.
A new review paper, published in Advances in Nutrition, draws together the existing science of how climate change threatens staple grains, fruits, vegetables, and nuts across the world, while also underscoring the significant need for further research. The team of public health researchers from John Hopkins Bloomberg School of Public Health and the Children’s Investment Fund Foundation in London conclude that climate change — including the combined impacts of rising temperature and carbon dioxide, rising sea levels, and climate disasters — will cause crop yields, or the amount of food we can produce on the planet, to fall. The authors project that this could trigger increased spikes in food prices, deepening food insecurity and micronutrient deficiencies.
“The paper shows very clearly that production will definitely be diminished,” said Martin Bloem, the director of the Johns Hopkins Center for a Livable Future and an author on the review. The researchers found that foods rich in micronutrients — particularly vitamin A, zinc, and iron — will see decreased yields, especially threatening the staple food and nutrient supply of low- and middle-income countries. While unable to draw more nuanced conclusions, Bloem says “there’s enough evidence that we need to [turn to] solutions.”
Already, over 2 billion people, or 30 percent of the global population, suffer from micronutrient deficiencies, a major cause of death and disease, and the authors project this will likely worsen.
Richard Semba, the review’s lead author and a professor at the School of Public Health, hopes the paper will draw attention to this urgent but often overlooked aspect of the climate crisis.
“We’re watching this disaster unfold,” he said. “People who work in international health and nutrition need to start pointing out the changes that are going to come with rising temperature, atmospheric carbon dioxide, and sea level rise.”
This growing health burden is an environmental justice issue, given that it will not be shouldered equally throughout the world. “The countries that are likely to feel the brunt of this, like with so many of the consequences of climate change, are those in the developing world — those that are already on the brink of nutritional deficiency and rely most heavily on the foods affected by this,” said Matthew Smith, a research scientist at the Harvard T.H. Chan School of Public Health. “That’s a huge part of the story.”
The potential for micronutrient deficiencies comes with far-reaching public health consequences, explains Smith. “Zinc deficiency, especially in children, makes you a lot more susceptible to severe cases or dying from respiratory infections, diarrheal diseases, [and malaria],” said Smith, who wasn’t involved in the paper. Iron deficiency, he explained, “can cause anemia, lower IQ and cognitive ability, reduce work capacity, and increase mortality for mothers and their children.”
Both iron and zinc are found in legumes, nuts, and grains, which the authors expect will see critical drops in yields. Rice, a staple crop for 3.5 billion people, is increasingly threatened by coastal erosion and rising temperatures. Climate change is predicted to bring major drought to over 60 percent of areas that grow wheat, another important source of nutrition and energy. As the review notes, beans, grown by smallholders in western Malawi, northern Mozambique, Zambia, Zimbabwe, and Tanzania will likely no longer be cultivated in the region by 2050, due to worsening drought.
The review also looked at vitamin A, commonly found in leafy green vegetables and yellow and orange fruit. Like zinc, vitamin A is important for immunity and decreasing the risk of infections; a deficiency can also lead to vision problems, including night blindness. The authors highlight how mangos, an important source of vitamin A, are sensitive to shifts in rainfall and temperature. In some countries, their cultivation is already moving to higher elevations and latitudes, more conducive to their growth and flowering, to adapt to climate change.
The Research Is Just Beginning
While the authors project overall production declines, they provide far from a complete picture of how climate change disrupts crop growth. In researching the paper, Semba says he was surprised by the “considerable lack of standardization” across studies and consistent data needed for more nuanced conclusions. “Luckily, there were enough studies done where you could paint broad strokes,” he added.
The authors are hopeful that the review will help serve as a jumping off point for more detailed research. “There are so many gaps,” said Bloem. “I do feel that the paper is just the beginning of a whole series of papers, looking at different gaps.”
One murky area is the existing body of research on how micronutrient levels within individual plants are affected by rising temperatures and atmospheric carbon dioxide. Many of the studies from the past 30 years were conducted with a technology known as Free-Air Carbon Dioxide Enrichment (FACE), which was developed to study how plants respond to more carbon dioxide in an open-setting under natural conditions and doesn’t account for rising average temperatures. But the review also brings in emerging studies that rely on a new technology, known as T-FACE, which combines the existing FACE set-up with infrared heaters to allow scientists to study warmer temperature and carbon dioxide levels at the same time.
When rising carbon dioxide is studied on its own, the results show that plant growth tends to be stimulated. Yet the review notes that this fast growth often leads to lowered concentrations of micronutrients in the plants. However, when rising temperature and elevated carbon dioxide are looked at together in T-FACE studies, some initial data suggests that the micronutrient levels in individual plants remain high even as yields go down. And that decrease in crop yields, the paper’s authors say, will likely be the most significant threat to micronutrient access.
In addition, climate impacts such as extreme weather events are wiping out entire fields, lowering yields, and disrupting the food supply chain, while ground-level ozone pollution (which gets worse when the temperature rises) is already diminishing the growth of staples, like rice, wheat, soybean, and potatoes. Rising oceans are eroding and inundating coastal farm ecosystems. And climate change is one of the factors driving the decline in pollinators, which are essential for many crops.
Experts unaffiliated with the review paper also emphasized that T-FACE technology is still in its infancy with limited data.
“The number of studies that needed to be assembled in order to find a consistent signal for strict FACE experiments was quite a few,” said Harvard’s Matthew Smith. “If you look at the review’s studies, there’s [only] a handful that have used T-FACE to find results. But often they’re either looking at a single cultivar or under a single growing season.”
Based on the recent addition of T-FACE research, Smith is not ready to draw any firm conclusions just yet. However, he considers the study of the combined impacts of carbon dioxide and temperature to be an important new direction for the field. “It is important to know how they work in concert,” he said.
Lewis Ziska, a plant physiologist and professor at Columbia’s Mailman School of Public Health who has extensively studied the impacts of rising carbon dioxide on crops, describes the recent review as a “good primer” on the issue. But he also emphasized the limited body of T-FACE research. Ziska says how micronutrient levels within crops will be impacted by climate change is “an area that needs a lot more work and a deeper dive.” He notes that there is other research that suggests that carbon dioxide’s main impact on plants will be on their nutritional quality, regardless of temperature for some plants. “That’s still an open question,” said Ziska.
Carbon Dioxide is More Than ‘Plant Food’
The review and existing body of research clearly show that rising CO2, often thought of solely as plant food, isn’t beneficial to plants in the broader context of the climate crisis. And Ziska believes this misguided notion may partially explain the research gaps.
“This is an issue that does not get any of the attention that it deserves,” he said. “When you see carbon dioxide as [only] stimulating the growth of plants, that’s a very simplistic meme of what CO2 actually does.” Ziska, who left a role at the U.S. Department of Agriculture after the Trump Administration attempted to bury his paper on carbon dioxide’s impacts on rice, has been working to bring the full impacts of CO2 to the forefront.
For example, Ziska points to grains like wheat and rice, which are described as “self-fruiting.” At higher temperatures, that process stops working right due to sterile pollen, which can be worsened by elevated carbon dioxide. By stimulating plant growth, CO2 leads the plant to require more water. To conserve water, the plant will often close its pores, known as the stomata, to prevent evaporation. However, this also makes it harder for the plant to cool itself down, similar to sweating for humans, and can increase the risk of sterile pollen.
This idea that elevated CO2 levels is a net positive for plants has been touted by the fossil fuel industry in climate disinformation campaigns. In a 2000 Exxon advertisement, published in the New York Times, the oil and gas company argues that climate change will help plant growth, pointing to how “many academic studies and field experiments have demonstrated that increased levels of carbon dioxide can promote crop and forest growth input.” (This advertisement was republished by Greenpeace’s PolluterWatch.)
It’s nearly impossible to account for the full array of impacts that the climate crisis could have on crop production and nutrition levels. The review, for instance, didn’t mention how climate change is leading crop pathogens and invasive species to migrate to warming regions, potentially compromising the safety of crops, or the role of soil health, which also influences crop nutrient content and yields.
With the exception of nitrogen, all of the essential nutrients plants require for growth only come into the plant through the soil. However, climate change can also lead soil to degrade. “So, both wind and water erosion may be accelerated [by climate change] and impact the productivity and water retention capacity of the soil,” said Rattan Lal, a professor of soil science at Ohio State University and recipient of the Japan Prize and the World Food Prize for his work on soil and climate change. As soil degrades, it lacks the micronutrients essential for its health and human health. “Soil degradation and depletion is a cause of human malnutrition,” said Lal.
Protecting and restoring soil is an important way to prevent deepening malnutrition as climate change accelerates, added Lal. Healthy soil has been gaining more attention as a climate solution, though it’s still lacking broad incentives in the U.S. and elsewhere. The review also points to other solutions, such as developing staple crops, which are better able to tolerate a changing climate and applying zinc and iron to the soil and foliage to increase its uptake. As more immediate solutions, they recommended national micronutrient supplement programs and enriching foods by adding essential vitamins and minerals.
It’s clear there remains an immense amount of work ahead when it comes to deepening the understanding of how plants respond to climate change—and helping crops and food systems remain resilient. The review’s authors are hopeful that it can contribute to a more foundational shift in the way we produce what we eat.
“We need to change the food system,” said Bloem. “We need to do it fast and we need to do it with everyone.”
• Could Climate Change Make Food Less Nutritious? [Civil Eats]