health & science

Carbon dioxide’s hidden hunger risk

Rising carbon dioxide levels could soon mean the vegetables on your dinner plate may not be as nutritious as they are today.

Many food crops grown in conditions with high carbon dioxide have reduced levels of zinc, iron and protein. A new study has estimated hundreds of millions more people could suffer nutrient deficiencies by 2050 as a result of the lower nutrient levels in plants.

The study points out most of the world gets iron and zinc from plants and even 63 percent of the protein eaten worldwide comes from plants: “Reducing the nutritional density of many of these sources—probably without a perceptible increase in hunger to motivate change—could increase the prevalence and severity of nutritional deficiency globally. This is particularly concerning as over two billion people are currently estimated to be deficient in one or more nutrient.”

Referred to as “hidden hunger”, micronutrient deficiency has become a global concern. Vitamin A deficiency is the leading cause of blindness in children. A lack of iodine can cause babies to be born with mental impairment, while iron deficiencies cause mothers to die during childbirth. Zinc deficiency can lead to increased rates of diarrhoea, premature births and reduced growth in children. Protein deficiency leads to malnutrition which can lead to stunted growth or death.

'Humans can only eat a certain amount of lettuce a day. If you’re eating a certain amount and that has a diluted concentration of important nutrients you will take in less."

University of Canterbury plant physiologist professor Matthew Turnbull said because plants take in carbon dioxide through photosynthesis, higher levels of it can act like a turbo-boost to growth.

“When plants are grown in elevated CO2 they take advantage of the carbon coming in, they grow a bit more quickly. In effect that dilutes the other content of the minerals and protein.

“That doesn’t greatly affect the plant but when we’re talking about human nutrition that’s a different story. Humans can only eat a certain amount of lettuce a day. If you’re eating a certain amount and that has a diluted concentration of important nutrients you will take in less.”

Unless drastic change occurs it is likely carbon dioxide, currently at 400 parts per million (ppm), will exceed 550ppm in 30 to 80 years.

Many crops grown under 550ppm carbon dioxide have protein, iron and zinc levels which are three to 17 percent lower than crops grown with the current level of carbon dioxide.

The study looked at 151 countries and 225 different foods to understand the likely risk faced by each country. It did not factor in any other effects climate change might have on food production, such as impacts of weather change, or possible increases in pest and disease.

Countries likely to bear the brunt of carbon dioxide caused by nutrient deficiencies are those heavily reliant on plants in their diets.

India, China, the Middle East, Africa and Southeast Asia will be the worst-affected areas due to their reliance on rice, wheat and legumes - all shown to be susceptible to rising carbon dioxide levels.

Maize, millet and sorghum, commonly eaten in Western and Central Africa, is not affected to the same level by carbon dioxide. Countries like the United States, Australia and New Zealand which currently eat large amounts of meat will also be likely to sidestep nutritional deficiency issues caused by the change in plant nutrition levels.

By 2050, the study’s authors say an additional 175 million people will be zinc deficient and an additional 122 million people will be protein deficient. They were unable to estimate how many people will be affected by the lack of iron, but said 1.4 billion women of child-bearing age and children live in areas where the commonly-eaten crops' iron levels could drop by more than 4 percent.

“There’s a ticking time bomb coming down the line and there is cause for concern. It’s not like a terrorist attack or a plane crash, these things are slowly creeping into our future.”

The obvious solution to the problem is to halt the rise of carbon dioxide. This will require a “redoubling” of effort, according to the study’s authors:

“In the absence of stringent mitigation efforts, atmospheric CO2 is expected to rise through at least 2100, with the upper limit of models predicting concentrations of nearly 940ppm by the end of the century

“Under the scenario most consistent with our current trajectory we anticipate reaching 550 ppm by the middle of the century.”

A more likely option is to breed plant cultivars which are less affected by carbon dioxide levels.

Turnbull said a possibility could be to reverting to heritage plants.

“We’ve now selected all these crops which grow quickly. It’s probably not surprising most of these crops are predicted to grow even more quickly under CO2. That’s a problem in some ways we may have partially created.

“The more conservative plants are the native plants, which haven’t had generations and generations of plant breeding to do more for us.”

Food fortification is another option. Folic acid is added to bread in some countries for example, and vitamin D to milk. This comes at a cost which may not be affordable for some of the countries most at-risk from nutrient deficiency. Increasing the variety of foods eaten is another solution, which could also be considered.

As a research scientist, Turnbull thinks more effort should be put into research around the impact of climate change. He worries the threat is not being taken seriously enough.

“There’s a ticking time bomb coming down the line and there is cause for concern. It’s not like a terrorist attack or a plane crash, these things are slowly creeping into our future.”

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