A new field test by researchers in California appears to confirm that humanity’s carbon dioxide emissions could decrease the nutritional value of crops, further threatening future food security.
Over the last two decades, agricultural research facilities in the United States and around the world have been running experiments in which a set up of pipes in a crop field pumps out carbon dioxide. The goal is to increase the concentration of carbon dioxide in the air immediately around the crops, thus simulating atmospheric conditions if humanity keeps burning fossil fuels and releasing large amounts of CO2.
The new study — done by researchers out of the University of California at Davis — took preserved wheat samples from those experiments and ran chemical tests on them that weren’t available at the time. It showed that the protein content of the wheat grown with increased atmospheric CO2 was lower than that of wheat grown under normal conditions. Protein, in turn, is a crucial part of a food crop’s nutritional value to humans. Wheat alone provides one-fourth of all the protein consumed in the global human diet.
In other words, if we were all living off crops grown under the higher CO2 levels, we’d have to eat more of them to get the same nutritional value we’re getting now.
“When this decline is factored into the respective portion of dietary protein that humans derive from these various crops, it becomes clear that the overall amount of protein available for human consumption may drop by about 3 percent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades,” said Arnold Bloom, a professor in the UC Davis Department of Plant Sciences, and the study’s lead author.
To explain the drop in protein and nutritional value: plants grow by taking in carbon dioxide from the atmosphere, then combining it with the nutrients they take in from the soil to create the building material for new growth. Oxygen is leftover by the process, and plants then release it back into the atmosphere. It’s a process called photosynthesis, and it’s led to claims that more carbon dioxide in the atmosphere would actually benefit plantlife and crop production by boosting growth.
Historical records show humanity’s emissions have already driven atmospheric carbon dioxide concentrations up by about 40 percent — and on their current path they could add another 40 to 140 percent by the end of this century. Meanwhile, the tests by Bloom and others did show a boost in plant growth of about 13 percent.
The catch is that the higher levels of carbon dioxide also changed the plants’ chemical processes. Assimilating more CO2 left less room for nitrogen, a key component in protein formation. Growth rates went up, but nutritional value went down.
Global warming and the resulting climate change already threaten global crops, thanks to changes in rainfall patterns, more droughts, more heatwaves, and stronger storms. So add changing plant metabolism to yet another way humanity’s carbon dioxide emissions could upend our food supplies over the course of this century.
Bloom said increased use of heavy nitrogen fertilizer could counteract the lack of nitrogen intake. But that solution comes with its own problems. It makes crop production more expensive, it can contaminate underground freshwater supplies, the nitrous oxide produced by the decay of excess fertilizer is a potent greenhouse gas in its own right, and fertilizer runoff causes other forms of environmental damage like the dead zone in the Gulf of Mexico.