Get ready to eat differently in a warmer world | Science News for Students

Get ready to eat differently in a warmer world

Climate change is making crops less productive, foods less nutritious and farms weedier
May 23, 2019 — 6:45 am EST
a sack full of sorghum grain

With climate change, people may have to depend on grains such as the sorghum (shown here) that are not now commonly found on our plates.

Leonid Eremeychuk/iStock/Getty Images Plus

This is the final installment in a 10-part series about the ongoing global impacts of climate change. These stories look at the current effects of a changing planet, what the emerging science suggests is behind those changes and what we all can do to adapt to them.

In the late summer of 2016, wheat growers in France realized something was wrong. Their harvest was smaller than usual — much smaller. The farmers were used to their yields — the amount of crops produced in their fields — being very consistent. Wheat yields usually changed by no more than 5 percent from one year to the next. But this year was different.

It wasn’t obvious right away, though, what the problem was.

There had been an unusually warm spell that winter. Later in the year, some intense rains had fallen. These events led to unexpected issues. The heavy rains, for instance, leached nutrients out of the soil. The heat and damp increased the spread of diseases. None of these issues seemed too bad as they were happening. But when it came time to harvest the wheat, yields across France were one-quarter (25 percent) lower than normal. In some regions, they were just half (50 percent) of what they had been.

a photo of a shaft of wheat against a wheat field at dusk
Wheat grows in France. In 2016, a warmer than usual winter and a wet spring led wheat production in France to drop by an average of 25 percent.
Christophe Castronovo/iStock/Getty Images Plus

“That was amazing to me,” says Senthold Asseng. He’s works at the University of Florida in Gainesville, where he uses computers to analyze data and predict crop harvests. “It was a real warning that you don’t need to wait for a big shock like a heat wave or a drought. A shock to production could also come about by having three or four smaller changes that all come together in one season.”

France is a wealthy country. So it had other sources of grain and food. Other than the wheat farmers, few French people were affected. But in a poor country, such a huge drop in crop yields could worsen poverty — or even bring on a famine.

When people think about how their lives will be affected by climate change, they might imagine living in a world with shorter winters and longer summers. They might envision coastal cities losing ground to sea level rise. They might even expect more extreme weather, such as hurricanes or wildfires.

All of those effects have struck various parts of the world. But climate change is also affecting what we eat. With warmer temperatures and more pests, farms will produce less food. And farmers will have to work harder to grow what food they do bring to harvest. Some crops might even be less nutritious. We may eat less of foods that are vulnerable to climate change — such as wheat and corn — and more of those crops that can better tolerate drought. Think sorghum. (Mmmm … sorghum!)

Scientists are studying these issues and learning more about how climate change will affect food supplies. They’re also developing new crops and new growing techniques to help farmers adapt to the coming changes.

Turning up the heat

It’s hard to study how temperature changes will affect crops. Many factors influence crop growth. These include rainfall, sunlight, the quality of the soil, the amount of carbon dioxide in the air and the type of plants being grown. Scientists have been seeking ways to isolate the effect of temperature from all of those other factors. Some researchers do this with greenhouses or experimental fields of plants. Asseng, though, does this using a computer.

With a computer model, researchers can do experiments that would be difficult or impossible in real life. They can alter one factor, and keep all the others unchanged. They can go forward or back in time. Asseng helped develop a computer program to model the growth of plants. His team can now use this model to assess likely changes to crop yields on farms across the world.

Asseng and his team used this model to investigate how rising temperatures might affect harvests of wheat, rice, corn and soybeans. Worldwide, these four crops provide two-thirds of all calories that people eat.

Tweaking temperatures in the model turned up something very worrisome. A global warming of 1 degree Celsius (1.8 degrees Fahrenheit), his model showed, “leads to reductions in all the major crops.” Corn harvests would fall by 7 to 8 percent. Wheat would drop by 6 percent. Rice and soy yields would fall some 3 percent.

a photo of corn growing in a field with cracked dry earth
Hotter temperatures and drought are expected to lower the productivity of cereal crops, such as this corn.
no_limit_pictures/iStock/Getty Images Plus

To check these findings, Asseng and a group of other scientists compared their results to four other studies done by different scientists. Those studies included other computer models, math analyses and harvests of crops grown in test fields. “All these different methods came up with the same numbers,” he says. That made him confident that temperature really can and will play a big role in the size of future harvests.

But the impact of temperature on crops might not be obvious to most people, at least right away. That’s because other factors might be aiding crop production at the same time. Those benefits can hide any effect of warming temperatures — at least for a while.

Asseng says Egypt is a good example of this. Worldwide, crop yields have been rising steadily for the past 50 years. Better farming techniques are responsible. But in Egypt, harvests have leveled off in the last 10 years, even as its farmers have made the same farming improvements. Drought can’t be blamed. Egyptian farmers irrigate their fields, so the crops aren’t getting less water.

Asseng believes rising temperatures are responsible.

Slowing the growth of food production can make it hard to feed a world where the population is increasing. And world populations are rising rapidly. Today there are 7.6 billion people on Earth. The United Nations predicts there will be 8.6 billion by 2030, and 9.8 billion by 2050. That's a lot of mouths to feed.

“The changes are already there, but you often cannot see them,” Asseng says. “Yes, [crop] yields go up. But behind the scenes, someone is pushing the brakes,” he says. And in some places, such as Egypt, he argues, you can already see the impacts.

a photo of an Egyptian farmer carrying sugar cane
In Egypt, harvests have leveled off in recent years, despite farmers having made improvements that should increase yields.
benmm/iStock/Getty Images Plus

Changing soils

It’s not just temperatures and other features of climate that affect crop growth. Soil also plays a big role. “If you change the climate, you may also change the properties of the soil,” notes Lenny Winkel. An environmental geochemist, she works at ETH Zurich and at the aquatic research organization Eawag. Both are in Switzerland.

Wet, rainy areas have a lot of organic matter — largely carbon — in the soil. That’s because these wet places often have a lot of plants. When they drop leaves or die, their tissues break down in the moist environment. This adds compost — available nutrients — to the soil. But dry places have fewer plants. And as plant there die, they take longer to rot into compost.

If climate change leads some regions to become drier, she says, “you could also lose some organic matter in the soil.” That would lower the nutrients available to feed the next season’s crops.

Winkel studies the presence in soil of trace elements, such as selenium. Such elements show up in the environment in only tiny amounts. As an important micronutrient, selenium is something that people need in tiny quantities.

Not much is known about where selenium occurs naturally. So Winkel decided to try to map known amounts. From this she attempted to predict levels elsewhere in the world. Then her team looked to “find the link between [known] concentrations and environmental factors,” she says. “We found out that climate factors were really important.” That’s because one way selenium gets into the soil is through the breakdown of organic matter.

With this information, Winkel realized she could now predict how soil levels of selenium would change in a warming world. Using computer models of climate, she was able to add likely changes to her map that would reflect a warming environment. And, she now reports, “We saw that the change would be a loss of selenium in the soil.”

Of course, people don’t eat selenium out of the soil. The roots of plants mine it from the ground and carry it into their tissues. The next step to understanding this issue will be to study how a reduction of selenium in the soils affects levels of this micronutrient in food crops. “We can generally say that what happens in the soil is broadly reflected in the plants — but not in all cases,” Winkel says.

A coming flood of impacts

Another way climate change is affecting soil is through pollution. Joyce J. Chen works at Ohio State University in Columbus. There, she studies the economies of lower-income countries and tries to find policies and programs that can help them prosper. Her research has focused on how flooding can taint soils in Bangladesh.

This low-lying country on the eastern border of India is prone to flooding. As sea levels rise, storms and high tides can cause ocean water to surge inland, across coastal areas. Later, when low rainfall causes river levels to drop, more seawater flows inland from the mouths of rivers. This, too, floods these areas.

Saltwater floods contaminate drinking-water supplies. Even farm animals can sicken from drinking salty water. And salt can effectively poison farmland. Crops such as rice grow poorly in salty soils. So rice harvests fall where seawater flooding occurs. Many farm families respond, when this happens, by moving to cities. They try to seek work there when they can no longer raise crops on their salt-poisoned lands.

Such a situation “creates a double burden” for these people, Chen says. They not only need a new place to live, but their nation also suffers a potential reduction of food because fewer people are able to farm.

a photo of floodwaters covering a field in Bangladesh
Floodwaters inundate the land, here, in Bangladesh. When water from the sea floods coastal areas, it can make the land too salty to grow rice and other crops.
Sohel_Parvez_Haque/iStock/Getty Images Plus

Learning from weeds

Climate change doesn’t just bring rising temperatures. It also brings rising levels of carbon dioxide. That sounds like good news for plants, which absorb carbon dioxide, or CO2, from the air. They use the carbon to build tissues. But it’s not that simple, says Lewis Ziska. He’s a plant physiologist, someone who studies the biology of plant tissues. He works at the U.S. Department of Agriculture’s big research center in Beltsville, Md.

“Not all plants are going to respond the same way to that change [in CO2],” he says. Many will yield crops that are less nutritious when grown in higher levels of CO2. Their protein levels, especially, will likely fall. Crops also may lose vitamins and micronutrients. In experiments, crop plants such as wheat, soy and rice did not seem to grow better in a CO2-rich environment.

What did grow better? Weeds.

“Many of the worst weeds in agriculture are already responding to this change,” Ziska notes. Crop plants could grow to smaller sizes or produce smaller fruits and fewer seeds in a future where they have to compete with more weeds. More pests and diseases may also plague plants in a warmer world.

One thing contributing to the problem is the lack of genetic diversity in modern crop plants. While there are thousands of varieties of weeds, each with different traits, most foods today come from monoculture farming. That means farmers only grow one type of crop. And those crops all have pretty much the same traits, based on breeding that restricted the particular genes that they host.

a photo of hands holding a colorful selection of potatoes
Potatoes come in many varieties, but farmers tend to grow just one. If the variety they grow isn’t well-adapted to changing environmental conditions, their fields could be vulnerable to climate change.
Jupiterimages/Photodisc/Getty Images

Genes for thriving in warmer or drier environments may be gone. Breeders might have sacrificed them in favor of varieties whose genes produce bigger fruits, more seeds or stronger stems. But those varieties may now need a constant and very comfortable environment. Change the climate and those plants may become sick or puny.

For instance, most French fries today are made from a single potato variety. “That’s great if the climate is stable,” Ziska says, “but not so great if the climate is changing.” If farmers instead grew several different potato varieties, some of them might adapt, even if many others did not.

“The positive side of the coin is that we can learn from weeds and use that to improve our own varieties of major cereals,” Ziska says. Cereal plants are species like rice, wheat, and corn or maize.

Ziska and his colleagues looked at “weedy” relatives of cereal grains, such as wild rices. These aren't like the weeds that grow in your garden. They're ancient or wild varieties of grains that have been domesticated by humans. The researchers planted different varieties in test fields. The scientists could change growing conditions, making those fields warmer, drier or wetter. They could also expose them to higher than normal levels of CO2 — levels that mimic what’s predicted to occur in the future. The researchers monitored how the plants responded. Then they studied the genes in those plants that performed best.

Some rice turns “chalky” when it grows in warmer temperatures or breathes in more CO2, they found. Its cellular structure is changed, giving it a more opaque color, and causing it to be tougher and less sticky when cooked. These rice grains are a poorer quality. They're unappealing and don't taste as good as regular rice, which lowers their value. By testing different types of rice and looking at each plant’s DNA, scientists could find the genes affecting chalkiness. They can now avoid rice varieties that inherited these genes when farmers look for ones likely to produce better crops in a world that will be warmer and/or have higher levels of CO2.

a photo of Lewis Ziska and Martha Tomecek working with rice plants at the USDA
Lewis Ziska and Martha Tomecek, plant scientists at the U.S. Department of Agriculture, study how different varieties of rice respond to changes in temperature and carbon dioxide.
Peggy Greb/USDA Agricultural Research Service

“We think that literally the answer lies in the weeds,” Ziska says. The wild relatives of crop plants are already adapting to Earth’s changing climate. Learning how they are doing that offers hope that plant scientists can learn from these genes “to modify current crop lines and potentially make them more adaptive to the change.”

One solution might involve tinkering with the genetics of existing crops, such as rice, to insert the genes of some weedy, but resilient, cousins. Such plants are known as genetically modified organisms, or GMOs. Another alternative: Scientists could breed plant species together to create new hybrids that combine the best traits of both. But Ziska hopes that the foods of the future might already be hiding in plain sight.

“I have nothing against GMOs. But I also want folks to recognize that evolution has been doing this for a while. And the last time I checked, there were over 100,000 different lines of rice,” he says. “How about we go check those out first and see what we can use that’s already available before we go moving genes around?”

Adapting what we eat

It can take 10 or 20 years to develop a new variety of wheat. But people don’t have to wait that long to change how they grow food. “At the field level right now, farmers are recognizing that things are changing, and they’re adapting,” Ziska says.

“They’re planting earlier. Or they’re using a different method to plant faster," he says. They may be using different equipment in their fields or trying different methods to help crops grow.

The way Ziska sees it, we cannot stop climate change in our lifetimes. It’s got so much momentum, all we can hope to do is to slow it down. And even that may take a while to manage. “We’re not going to suddenly shut down the amount of CO2 going in the air,” he says. “We’ve got to adapt, and we’ve got to adapt quickly.”

The good news is that looking at the problem of food supplies could help more people understand the importance of climate change. Early in his career, Ziska noticed that most people were not interested when he talked about how climate change was affecting the environment. But when he showed them how it could affect food supplies, they suddenly sat up and listened.

“It went from 10 percent of the audience caring to 90 percent of the audience caring,” he says. “When it becomes personal, then you care. And I can’t think of anything more personal than food.”

Power Words

(more about Power Words)

agriculture     The growth of plants, animals or fungi for human needs, including food, fuel, chemicals and medicine.

aquatic     An adjective that refers to water.

breed     (verb) To produce offspring through reproduction.

calorie     The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food. The exception: when referring to the energy in food, the convention is to call a kilocalorie, or 1,000 of these calories, a "calorie." Here, a food calorie is the amount of energy needed to raise 1 kilogram of water 1 degree C.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon dioxide (or CO2)    A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

cereals     Plants in the grass family that provides an edible seed, which serves as a food staple (such as wheat, barley, corn, oats and rice).

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

colleague     Someone who works with another; a co-worker or team member.

compost     The end product in the breakdown, or decomposition, of leaves, plants, vegetables, manure and other once-living material. Compost is used to enrich garden soil, and earthworms sometimes aid this process.

computer model     A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

computer program     A set of instructions that a computer uses to perform some analysis or computation. The writing of these instructions is known as computer programming.

concentration     (in chemistry) A measurement of how much of one substance has been dissolved into another.

constant     Continuous or uninterrupted.

crop     (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers. 

develop     To emerge or come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.

developmental     (in biology) An adjective that refers to the changes an organism undergoes from conception through adulthood. Those changes often involve chemistry, size and sometimes even shape.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

drought     An extended period of abnormally low rainfall; a shortage of water resulting from this.

economy     Term for the combined wealth and resources (people, jobs, land, forests and minerals, for instance) of a nation or region. It is often measured in terms of jobs and income or in terms of the production and use of goods (such as products) and services (for instance, nursing or internet access).

element     A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

evolution     (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. 

factor     Something that plays a role in a particular condition or event; a contributor.

famine     A condition where many people go hungry because there is too little food. Droughts, flooding and other weather disasters often contribute to widespread crop failures causing famine.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

genetically modified organisms or GMOs     Organisms that people have altered, by tweaking their genes. In some instances, the genes may come from organisms totally unlike the species in which they end up.

genetic diversity     The range of genes types — and traits — within a population.

global warming     The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

hybrid     An organism produced by interbreeding of two animals or plants of different species or of genetically distinct populations within a species. Such offspring often possess genes passed on by each parent, yielding a combination of traits not known in previous generations. The term is also used in reference to any object that is a mix of two or more things.

infrastructure     The underlying structure of a system. The term usually refers to the basic physical structures and facilities on which a society depends. These include roads, bridges, sewers, drinking water supplies, electrical power grids and phone systems.

irrigation     An engineered supply of water to land or crops to help growth.

link     A connection between two people or things.

literally     A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

momentum     A forceful movement that is propelling something along.

monoculture     Large areas planted with a single type of crop.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

organic     (in chemistry) An adjective that indicates something is carbon-containing; a term that relates to the chemicals that make up living organisms.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

physiologist     A scientist who studies the branch of biology that deals with how the bodies of healthy organisms function under normal circumstances.

population     (in biology) A group of individuals from the same species that lives in the same area.

protein     A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells.

resilient     (n. resilience) To be able to recover fairly quickly from obstacles or difficult conditions. (in materials) The ability of something to spring back or recover to its original shape after bending or otherwise contorting the material.

sea level     The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.

seawater     The salty water found in oceans.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

taint     To contaminate something with an unexpected, unnatural or illegal substance.

tides     (adj. tidal ) The alternate rising and falling of the sea, usually twice in each lunar day at a particular place, due to the attraction of the moon and sun.

tissue     Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

variety     (in agriculture) The term that plant scientists give to a distinct breed (subspecies) of plant with desirable traits. If the plants were bred intentionally, they are referred to as cultivated varieties, or cultivars.

vitamin     Any of a group of chemicals that are essential for normal growth and nutrition and are required in small quantities in the diet because either they cannot be made by the body or the body cannot easily make them in sufficient amounts to support health.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

weed     (in botany) A plant growing wild in, around — and sometimes smothering over — valued plants, such as crops or landscape species (including lawn grasses, flowers and shrubs). Often a plant becomes such a botanical bully when it enters a new environment with no natural predators or controlling conditions, such as hard frosts. (in biology, generally) Any organism may be referred to as a “weed” if it enters an environment and begins to overwhelm the local ecosystem.

Citation

Journal: J. Chen. Coastal climate change, soil salinity, and human migration in Bangladesh. Nature Climate Change. Vol. 8. Oct. 22, 2018, p, 981. doi: 10.1038_s41558-018-0313-8.ris.

Journal: C. Zhao et al. Temperature increase reduces global yields of crops in four major estimates. Proceedings of the National Academy of Sciences. Vol. 114, Aug. 29, 2017, p. 9326. doi: 10.1073/pnas.1701762114.

Journal: G. Jones et al. Selenium deficiency risk predicted to increase under future climate change. Proceedings of the National Academy of Sciences. Vol. 114, March 14, 2017, p. 2848. doi: 10.1073/pnas.1611576114.

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