How Increased Carbon Dioxide Levels Influence the Human Diet

The UN has announced record average levels of CO2. So states the annual flagship report released October 30 by its World Meteorological Organization. The average levels measured using ships, aircraft and land stations have reached over 400 parts per million (ppm), prompting the authors and other scientists to urge strong action.

That climate change will affect food production is intuitive. Rising global temperatures and the consequent extreme weather events and changes in climate patterns impact production, distribution and potential for spoilage. Some of the worst hurt will be people in a broad tropical belt of countries in Africa, Asia and the Americas. And ever more severe hurricanes and typhoons will do their damage to coastal areas.

The levels of CO2 have been rising steadily since the industrial revolution. In the nearly 60 years since 1958, they have increased from 316 ppm to the latest figure of 406.58 ppm measured on January 22, 2017. It is the highest figure in human history. A Harvard study predicts CO2 to increase in the range 500-700 ppm for 2050-2100. Meanwhile, the US Global Change Research Program projects CO2 levels to reach anywhere from 540-958 ppm by 2100 — the latter figure a truly disconcerting scenario.

But there is another effect related to rising CO2 levels: Higher CO2 concentration stimulates plant growth. Plants are larger, producing more carbohydrates, but this fast growth lowers the concentration of protein and essential minerals. As this also affects food crops like rice, wheat, potatoes and vegetables, it is likely to impact negatively on nutrition and health.

As CO2 rises, plant stomata (pores that facilitate gas exchange) close up. Less water transpiring through the stomata results in less water from the roots, and less minerals brought up to build the proteins and vitamins.

The Harvard study reports that under elevated concentrations of CO2 (eCO2) as projected for 2050-2100, protein contents decreased as follows: rice (7.6 percent), wheat (7.8 percent), barley (14.1 percent) and potatoes (6 .4 percent). It estimated an additional 148 million of the world’s population could risk protein deficiency. Plant-based diets (such as those prevalent in India) increase vulnerability in the population. The study also projects that a billion-plus mothers and 354 million children could be affected by a dietary drop in iron and subsequent anemia.

Vegetables too, are not immune. The United States Department of Agriculture (USDA), in studying the food content of 43 garden crops, found significant decline in nutrients. They found statistically reliable declines in protein, calcium, phosphorous, iron, riboflavin and ascorbic acid, ranging from 6 percent for protein to 38 percent for riboflavin. To maintain health, humans will have to supplement their diet with vitamins and minerals. It is a prospect not very feasible in the less developed countries, leaving those populations exposed to malnutrition and early death.

Irakli Loladze noted the effects of speeded up growth on plant nutrients while pursuing a Ph.D. at Arizona State University. The subject was green algae, and how, when they were bombarded with light, they grew faster. Yet the plankton that fed on it, and had now more than enough to eat, began to struggle to survive. The cause was soon evident. Speeded up growth had so reduced the nutritional content that the plankton could not eat enough to thrive.

Another way growth speeds up is through increased levels of atmospheric CO2, and that also increases levels of carbohydrates through plant sugars, thereby diluting other nutrients. Loladze had moved to a post-doctorate position at Princeton, and while there, published his findings as “Rising CO2 and Human Nutrition: Towards Globally Imbalanced Plant Stoichiometry.” It was the first to propose that rising CO2 levels cause a change in plant quality, reducing essential minerals and protein, thus affecting human nutrition. A later article backed up his assertions with solid research.

Many researchers are now involved in the area. Thus, a paper by Swedish and German academics published this year examined wheat crops under elevated levels of CO2. Its findings confirm increasing yields but decreasing nutrients, including significant reductions in the dietary important elements N, Fe, S, Zn and Mg.

If humans are impacted, then surely other species are as well. Lewis Ziska, a noted researcher with the USDA, planned an experiment to allay another concern: that of plant breeding and its effect on nutrients. He chose the goldenrod, a wild flower for which there is a long history. The Smithsonian has in its archive samples dating back as far as 1842. Since no human plant breeding is involved in the goldenrod, it afforded the Ziska team a clear path to look at environmental effects. They discovered the protein content had reduced by a third through increasing CO2.

It also happens the goldenrod is critical to bees. It flowers late and the protein in its pollen is an important source of nutrition for bees as they build themselves up to weather the winter. Thus, a drastic drop like a third of protein content could easily contribute to the serious decline in bee populations around the globe. Now with its own acronym, CCD for Colony Collapse Disorder, it continues, although thankfully has declined from a high of 60 percent in 2008 to 31.1 percent in 2013, as reported by beekeepers to the Environmental Protection Agency. Moreover, strenuous replenishment efforts by beekeepers have helped to stabilize somewhat these domesticated colonies. Of course, wild bee losses are another matter. Bees are critically important as they pollinate over 80 percent of cultivated fruit, vegetable and grain crops, not to mention nuts, herbs, oils, forage for dairy and beef cattle, and medicinal plants.

One final sobering thought: The nutrient content of food is expected to continue to fall as CO2 levels increase this century. There is no doubt that this decline will impact a wide range of species, including us.