Increasing carbon dioxide levels in the atmosphere is causing a loss of nutrients like zinc, iron, and certain proteins in plants, especially C3 plants.
Climate change stimulates our apocalyptic imagination. The mind leaps to anxious images of glaciers melting, erratic weather patterns and increasing average global temperatures. These visible effects are only one part of the climate change picture; many other pieces are hidden from plain sight.
One such “hidden” piece is how plant metabolism affects the increasing CO2 in the air. Evidence from research conducted in the last decade has shown that climate change is causing our food to become less nutritious.
A study published by Nature in 2014 drew the public’s attention about how climate change affects our food. Until that point, the dialogue had revolved around GMOs, the wasteful use of pesticides and fertilizers, and unpredictable weather degrading food quality. These are changes that humans are directly causing to plants.
Aside from the level of CO2 indirectly leading to food insecurity, there was very little discussion about how this would directly affect plants. From the gamut of urgent issues, this one just wasn’t enough of a concern for the general public.
That changed in 2014 when a collaborative effort across countries—headed by Dr. Samuel Myers, principal researcher of the paper—caught the media’s eye. The media coverage finally made the public aware that CO2 can change the nutritional characteristics of life. The increasing levels of CO2 are actually messing with plant nutrients.
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How is food becoming less nutritious?
School taught us that photosynthesis is the process by which plants make food from basic chemical ingredients powered by the energy in sunlight. These starting ingredients are CO2 (from the air) and water (from the soil), which ultimately form a variety of carbohydrates.
Logically, if we increase the amount of ingredients, we should get more of the product. The more CO2 that is available in the air, the more of it there is for plants to make sugars. This sounds great until you consider its effects on other nutrients in the plant.
Research, including the 2014 Nature paper mentioned above, have found that the amount of carbohydrates increase in many crops with an increase in atmospheric CO2 levels. However, these studies also show that the plants studied had less protein, as well as lower levels of zinc and iron, two essential micronutrients for life.
This effect was more significant in C3 plants than C4 plants. The difference between C3 and C4 plants are the different roads they take to make their sugars. C3 plants have a direct path—CO2 enters through open stomata, which is picked up by the enzyme rubisco to start the carbohydrate synthesis. Energy can be wasted in C3 plants when rubisco uses an O2 molecule instead of a CO2 molecule.
To overcome this inefficiency, C4 plants take a circuitous route to carbohydrate synthesis as an adaptation in warmer climates. About 85% of the plant world, including crops like rice and wheat, takes the C3 pathway, with only 3% taking the C4 path. The more pronounced effect of CO2 levels on C3 plants are concerning. Why the effect was more significant in C3 compared to C4 is not certain.
Junk food effect
Irakli Loladze, a biomathematician and quantitative ecologist, called this the “junk food effect”. This high-carb, low-protein food would be plentiful, and even appetizing, but would lack the good and healthy stuff upon which life thrives. Scientists haven’t yet figured out why this is happening. One theory floating around is that the excess carbs simply dilute other nutrients in the plant. A more molecular explanation has yet to surface.
Humans get most of their nutrient requirements—60% of protein, 70% of zinc and 80% of iron from plant sources. The world’s population is poised to reach 9.8 billion by 2050. With plants losing nutrients, the pressure to satisfy the nutritional needs in every one of those 9.8 billion people is daunting.
Average global CO2 levels in the month of August, 2019 was 410 ppm and this figure is projected to reach 550 ppm in the next 30 to 80 years. Myers noticed a 3-17% decrease in zinc and iron in C3 crops and legumes when they were grown under the projected C02 levels.
Using this data, Smith and Myers estimated that about 175 million more people could suffer from zinc deficiency in 2050. Zinc is an indispensable nutrient for all cells, especially when it comes to growth and mounting an immune response. Furthermore, hemoglobin is responsible for oxygen transport, and requires iron. Iron deficiency would severely impact women and children under 5.
The increase in greenhouse gases is not an isolated event with a narrow range of effects. It occurs in conjunction with erratic rainfall, temperature fluctuations, and pests developing resistance to the current arsenal of pesticides. Some researchers postulate that these effects, in combination, could lead to an overall decrease in crop yields.
In August, the United Nations released a report warning the world about the precarious circumstances of food stability. In light of rampant deforestation, the Amazon fires, and the growing lifestyle demands of an expanding population, the forecast is truly frightening. Without immediate intervention and change in governmental attitudes, the picture for humanity looks undeniably bleak.