Climat‍‍‍e change is already causing major problems- flooding, drought, and life-threatening storms, to name only some; the wrath of hurricanes Irma, Jose, and Maria in the Caribbean and along the gulf coast, along with recent extreme monsoon flooding in India, Bangladesh, and Nepal attest to this.

We know too that, beyond what we are able to predict, there may be a host of unforeseen consequences from climate change, particularly as the earth’s global average surface temperature creeps past 1.5 deg. C.

Can we guess, for instance, what might be happening to some of our main food sources as this global experiment continues? We know that climate change alters plant-ecosystem interactions, and that crop production is highly dependent on things like soil quality, water availability, temperature stability, pollinating insects, and carbon dioxide (CO2) concentration in the atmosphere. Striking a healthy balance between these resources is very important.

Iron, Zinc, and Protein

In an attempt to better understand the impact of rising greenhouse gas concentrations on major food crops like wheat, rice and soy, scientists at Harvard University studied the nutritional makeup of plants grown at higher carbon dioxide (CO2) levels. In other words, they wanted to know whether key nutrients within these crops (elements like iron and zinc, but also protein) would be impacted if the plants were grown at CO2 levels that are expected here on earth by the year 2050.

As you might be able to guess, carrying out an experiment like this requires a controlled environment. Plants may either be grown in chambers or in fields- applying methods to enrich the air with carbon dioxide; in this case, the latter approach was taken, and different varieties of crops were cultivated outdoors, while extra CO2 was blown over the site by ducts encircling the growing area (a method known as Free-Air ‍‍‍CO2 Enrichment, or FACE).

Is Climate Change Making Plant Foods Less Healthy?

Planetary H‍‍‍ealth

©  2016, Plant Based Living Initiative

©  2016, Plant Based Living ‍‍‍Initiative‍‍‍



Follow our blog

Unfortunately, we simply cannot fully anticipate how plants will ‘adapt’ to stressors brought on by climate change; some plant yields could increase, at least for a time, while others could drop dramatically.  Growth modelling has been helpful, but not insightful enough, when it comes to guessing at how the quantity (or quality) of food crops might be affected by climate change‍‍‍, but more must certainly be done.

‍‍Researchers analysed 41 strains of 6 different food crops- wheat, rice, maize, soybeans, field peas, and sorghum, which were grown in 7 (geographically diverse) experimental locations scattered across Australia, Japan, and the US. In all locations, they compared crops grown at ambient (i.e. current) CO2 levels of 363-386 parts per million (ppm), with those grown at levels of 546-586 ppm (i.e. anticipated 2050 levels; it’s worth noting that these levels are expected to occur even if governments around the world achieve significant emissions reductions targets in the meantime).

The findings were obvious: nutrient concentrations within the edible parts of these crops were reduced when grown at higher CO2 levels. Concentrations of iron and zinc dropped significantly in wheat, rice, and soybeans (in wheat, concentrations went down, on average, by 9% and 5% respectively). The majority of crops showed reductions in key nutrients, although maize and sorghum fared better.

Interestingly, protein content in this study was also shown to fall by 6.3% and 7.8%, o‍‍‍n average, in wheat and rice grains grown at higher CO2 levels- a revelation that could (in the not so distant future) turn out to be especially problematic in (poorer) parts of the world with populations reliant on plant proteins for human nutrition. Other studies, done in either chamber or open-field settings using the FACE approach, have shown similar findings: reductions in protein content range from 7-15% in the edible portion of wheat, rice, barley, and potatoes.‍‍‍‍‍

These findings help us to better understand how climate change directly affects the nutritional quality of our food. We know that quantities of key micronutrients in many of the world’s staple crops will be diminished, and that even higher CO2 levels in our atmosphere will only worsen the situation.  

Carbohydrate Overload?

Although nutrient concentrations in staple crops show an obvious decline in response to rising CO2 levels, the internal mechanisms(s) behind this shift are still not fully understood.

Researchers point to a process called ‘carbohy‍‍‍drate dilution’- essentially an overload of starch (carb) production in response to more CO2, which then literally affords less room for other nutrient-rich parts of the grain to develop (i.e. things like protein, iron, zinc and other nutrients get ‘stamped out’).

While carb dilution does indeed take place, some studies suggest that this alone does not quite explain the phenomenon and that other effects might also be at work, such as declines in nutrient uptake from soils by plant roots, and other damaging processes.

‍‍‍‍‍‍Nutrient Deficiencies and the World's Poor

As usual, the world’s poor will bear the brunt of the impact, as it is they who rely most on staple crops like rice, wheat, corn and soybeans for energy. In 2010, for example, 2.3 billion people consumed at least 60% of their iron and/or zinc from rice, wheat and legumes; another 1.9 billion took in at least 70% of one or both of these nutrients from these same crops.

Deficiencies of zinc and iron are already a massive global public health issue, affecting 2 billion people and equating to a loss of 63 million life-years (i.e. years lost to pre-mature death) annually. In fact, about 138 million more people are anticipated to zinc deficient by 2050, while existing deficiencies will worsen among billions.

The situation may be particularly grim for pregnant women and children: zinc deficiency raises a woman’s risk for premature delivery, which can have lifelong consequences (due to poor weight gain and growth) for children; it also worsens immune system functioning, which leads to difficulties in fighting off infections (100,000 children already die each year from pneumonia or diarrhoea).

In many countries, iron deficiency is responsible for high rates o‍‍‍f anaemia (defined as a low blood haemoglobin level or fewer working red blood cells).

Outcomes, again, are worse for some- particularly young women and children aged 1-5: an anaemic pregnant woman is at greater risk of death during the perinatal period, and there may be negative impacts during pregnancy and delivery; physical, mental, behavioural, and/or social-emotional health and development of infants might also be compromised.

As CO2 concentrations continue to rise, the ability of certain crops to provide crucial dietary nutrients is expected to worsen. Overall, hundreds of millions of people are anticipated to be placed at further risk of essential micronutrient and/or protein deficiency.


‍‍‍Scientists have also recently been interested in climate impacts on selenium (an essential nutrient that serves as an antioxidant in the human body and that plays important roles in thyroid‍‍‍ and immune system functioning). Good plant sources include whole grains, garlic, sunflower seeds and Brazil nuts.

Having pieced together a world map using an abundance of data from across the globe, researchers found that the impact of climate change on soil (and therefore on plant) selenium content was extremely important. Arid land, as a rule, can be expected to have a lower concentration, while woodlands can be expected to retain the element.  

This study applied ‘moderate climate change projections’ in order to predict future losses of selenium from soils, and found that, considering croplands alone, an average loss of 8.7% could be expected in 66% of modelled areas between 2080 and 2099. Given that soils are set to become increasingly acidic due to higher atmospheric CO2 concentrations, the problem of soil selenium losses in the face of CC is likely to be worsened still (i.e. soil pH and soil selenium are inversely related).

Other research has shown that a CO2 concentration of 550 ppm equates to a 3-11% drop in zinc and iron in both cereal grains and legumes, while 5–10% decreases in the concentration of phosphorus, potassium, calcium, sulphur, magnesium, iron, zin‍‍‍c, copper, and manganese across a wide range of crops may occur under even higher (and not unrealistic) CO2 concentrations (e.g. 690 ppm).  

The researchers also considered impacts on phytate- a natural component of most plants that inhibits, albeit to a limited extent, the absorption of zinc in the human digestive system. Most crops grown at elevated CO2 levels in this study did not show significant drops in phytate content coincident with drops in other nutrients, prompting the authors to point out that this could serve to worsen the issue of zinc deficiency.  

Can Technology Prevail?

Some plant varieties, of cours‍‍‍e, could be expected to fare better than others in response to rising CO2 levels. In response, it has been suggested that breeding programmes might allow us to tackle the issue. It’s important to remember, however, that this is not likely to work as a cure-all solution, especially in poor countries where affordability is a barrier.

Other potential draw-backs include lower yields and diminished performance, and there could also be issues with things like taste and marketability. Researchers themselves have noted that: ‘such breeding programmes will not be a panacea for many reasons including …the numerous criteria used by farmers in making planting decisions…’

Can We Eat Our Way Out of This?

Despite some hope for growth spurts and high crop yields in the face of climate change, this has proven to be mostly fantasy.

The Intergovernmental Panel on Climate Change (IPCC), in a 2014 report, laid these hopes to rest:

“Assessment of many studies covering a wide range of regions and crops shows that negative impacts of climate change on crop yields have been mor‍‍‍e common than positive impacts (high confidence).” -IPCC

‍‍‍IPCC- projected crop yield change (wheat, maize, rice and soy), due to climate change over the 21st century.

Global food demands continue to rise as the earth’s population grows, and by 2050, ~50% more food will have to be produced as compared to present day. Is it even possible to meet people’s requirements, globally, for energy and essential nutrients, given the trends that are being observed in response to rising CO2 levels?

Can we simply eat more food in order to meet our nutrient needs? Can we obtain what we need through commercial supplements and/or biofortification? Where does this leave us?

“For wheat, rice and maize in tropical and temperate regions, climate change without adaptation is projected to negatively impact production for local temperature increases of 2°C or more above late 20th century level‍‍‍s… -IPCC

Global temperature increases of ~4°C or more above late 20th century levels, combined with increasing food demand, would pose large risks to food security globally (high confidence).” -IPCC

Common sense tells us that these options are simply not available to the world’s poor, who often do not get enough to eat (hence the term ‘protein-energy malnutrition’) and who already suffer micronutrient deficiencies at extremely disproportionate rates.  This plight may not seem as relevant for affluent societies like NZ, England, or Canada, for instance, where alternative strategies are likely to be much more feas‍‍‍ible, and where the vast majority of people do not rely entirely, or even substantially, on staple plant crops for energy.

Consider, though, that livestock may also have trouble obtaining the nutrients they need from rangeland grasses, particularly here in NZ where the majority of cows and sheep are raised outdoors. Although impacts are not entirely clear, there is evidence that nitrogen uptake is weakened and that protein content of grasses consumed as forage is lowered in the face of rising CO2 levels.  

We must remember, too, that plant-based eating patterns are essential in the fight for planetary health: certainly, one of the ways in which we will effectively combat climate change is by substantially decreasing livestock production around the world, while increasing our collective intake of whole plant foods. Ruminants, or animals that ‘chew the cud’ (cows, sheep, goats), emit a considerable amount of greenhouse gases- primarily methane- through the process of enteric fermentation and belching.  

As a society, we need plant foods for optimal health, and to reduce our risk of acquiring common chronic conditions like type 2 diabetes, heart disease, and cancer. We most definitely should not consider animal foods to be a viable substitute or solution when it comes to the problem of nutrient depletion in the face of rising CO2 levels.  

Now, more than ever, we must turn to (whole) plant foods.

One, perhaps somewhat practical, future effort co‍‍‍uld involve the increased consumption of so-called ‘C4’ plant crops like corn, sorghum, millet, and amaranth, which might perform somewhat better in the presence of increased CO2 levels. Encouragingly, soybeans have also been shown to fare better at CO2 levels in line with 2050 expectations. We must remember that little is known for sure about longer-term outcomes, particularly at much higher CO2 levels, or about how societal adaptations may eventually come about. FACE experiments should no doubt be repeated using protein-rich crops in particular (i.e. legumes- beans, peas, lentils) so as to better understand how plants are impacted.

Inequities and socio-economic constraints are set to worsen around the world due to climate change, as is food insecurity. We must now anticipate and prepare for various outcomes, and policy and programme development is essential in both poor and rich nations around the world.

For related reading, click here.‍‍‍

Author: Anna DeMello

Anna is the founder of PBLI and is registered as a dietitian in Canada.‍‍‍ She holds a Masters degree in Human Nutrition from McGill University, and is currently an Assistant Research Fellow at the University of Otago, Dunedin.