U.S. crop harvests could suffer with climate change

Shifting climate patterns in North America could hit U.S. crop production hard, possibly even halving the production of corn by the end of the century, a new study finds.

Scientists believe that the spike in average temperatures that is widely predicted by climate models for North America could hurt its agriculture sector. As the number of days that are hotter than 30 degrees Celsius (86 degrees Fahrenheit) increases, they now predict, estimated future harvests of wheat, soybeans and corn could drop by 22 to 49 percent, depending on the variety of the crop.

“Projections tell us that in the U.S., these crops will suffer from hotter days. Since these days will get more frequent with climate change, there will be harvest losses,” said Bernhard Schauberger, lead author of the study, released by the Potsdam Institute for Climate Impact Research.

Schauberger and a team of scientists came to this conclusion by studying a series of computer simulations.

According to their estimates, corn and soybean plants can lose 5 percent of their harvest for every single day that is recorded above 30 C. Such crop losses could have huge repercussions for domestic food security and — given that the United States is one of the largest crop exporters in the world — affect prices in the international market.

There are multiple ways that higher temperatures could affect crop growth, and most of them come down to water stress, said Joshua Elliott, a research scientist with the University of Chicago and a co-author of the study.

Evaporation rates shoot up on hotter days, reducing the amount of moisture in the soil that's available to the plants. Moreover, plants tend to open their stomata — small pores on their leaves — to transpire water when temperatures increase, creating an additional source of stress. Certain studies have also suggested that high temperatures during a plant's flowering period could actually lead to a “sterilization” effect.
“Moreover, at very high temperatures, there can be direct damage to leaves and other organs of the plant — typically called wilting,” Elliott added.

Crops tend to respond to temperature changes in different ways. Some, like rice and cotton, can tolerate higher degrees of heat, but others, like corn and wheat, aren't as flexible.

Since a loss of water is the key problem that climate change could create for crops, the answer could lie in irrigation, something Elliott called a “key resiliency factor.” However, depending entirely on irrigation to curb crop losses could also be dangerous and unsustainable, he added.

“There are lots of irrigated parts of the world, like northern India, which are already starting to run out of resources. Some estimates say there will be widespread irrigation deficits in the next 20 years — and then you have a double-whammy effect, where temperatures are increasing and you don't have the water you need to irrigate your crops,” he explained.

The problem is exacerbated in areas like Kansas and West Texas that are entirely reliant on groundwater resources.

Moreover, irrigation can help protect crops until a certain temperature threshold — around 36 or 40 C, according to Schauberger — but not beyond.

The scarcity of water could be influenced by other consequences of climate change, like changes in precipitation patterns, as well as socio-economic factors like a higher demand for food, growth of the hydropower sector and population increase, said Erwan Monier, a principal research scientist with the Massachusetts Institute of Technology's Department of Earth, Atmospheric and Planetary Sciences.

“If there's no more water available for irrigation, the question becomes what would farmers do — they would either have to rely on rain-fed crops or move to a location where there's enough water for irrigation. If they shift to rain-fed crop management, there's going to be a significant decline in yield,” he said.

Some scientists are experimenting with ways to genetically modify crops that are more resilient to higher temperatures. However, this approach hasn't demonstrated significant results so far and, according to Elliot, contains restrictions in terms of how much the plants can be altered. He sees the most likely adaptation strategy as being a northward shift of traditional crop belts.

“It may very well be that in the next 50 to 100 years, the new Corn Belt is centered around North Dakota, Manitoba and Saskatchewan,” he said. “Parts of Iowa could be growing cotton and the Deep South — where cotton is currently grown — will probably be too hot to grow anything.”