One of the world's major food crops could lose quality due to greenhouse gas emissions.
The results of a large study published yesterday in Science Advances suggest that rice plays a crucial role as food source for billions of people – is less nutritious when grown under higher carbon dioxide concentrations. Its reserves of protein, iron, zinc and some important B vitamins are decreasing.
That's a potential public health issue, say the authors, especially in poorer countries where rice is a big part of the diet.
These results suggest that the role of rising CO2 in reducing rice quality could be a fundamental but underestimated human health in the context of anthropogenic climate change, "write the authors, led by Chunwu Zhu of the Chinese Academy of Sciences Sciences.
The findings challenge a common argument amid doubts about accepted climate research ̵
Rep. Lamar Smith, a Texas Republican who runs the The House Committee on Science, Space and Technology is an outspoken advocate of the idea, arguing in an essay published in The Daily Signal last summer that more carbon dioxide will lead to increased plant growth, resulting in " a larger volume of food production and better quality of food "
Research and other studies published before this publication discredit these allegations.
"We have some rice varieties that show a stronger response to CO2 and can convert more CO2 into seeds, which can be good," said senior study author Lewis Ziska, a researcher at the Department of Agriculture. "On the other side of this coin, the quality of this seed is also reduced in response to CO2."
The new study looked at 18 types of commonly grown rice to see how they would respond to elevated levels of carbon dioxide. In the experiments, the researchers increased the carbon dioxide content of the environment to concentrations between 568 and 590 ppm. At present, carbon dioxide concentrations in the atmosphere are at around 410 ppm – but with the rate at which they are currently rising, by the end of the century they could reach the high levels used in the study if they are not contained.  Compared to the current concentrations, the nutrient contents of the rice crops suffered altogether from a higher carbon dioxide content. On average, protein levels dropped by about 10 percent, iron by 8 percent and zinc by 5 percent. The researchers also found that certain B vitamins decreased significantly, some by as much as 30 percent. Vitamin E was the only nutrient that increased with higher levels of CO2.
The study "confirms previous work showing that elevated levels of CO2 alter the protein, iron and zinc content of rice – and in the case of other staple foods, too," said Samuel Myers, a Harvard expert University for Climate Change and Human Health.
Myers, who was not involved in yesterday's research, co-authored earlier comparative studies Conclusions: Elevated levels of carbon dioxide cause nutrients in world-wide crops such as rice, wheat, barley and soybean to decline. While his work focuses primarily on protein, zinc and iron, the new study is one of the first of its kind to evaluate the impact of carbon dioxide on vitamins – and it appears that the results may be similar for some of them.  Overall, the growing number of research on crops and carbon dioxide levels shows that the future is not nearly as rosy as Smith and others suspect. While in some plants more carbon dioxide can increase growth and production – all other conditions are the same – there seem to be compromises. Bigger harvests are not necessarily useful for human societies if they are less nutritious.
In addition, some recent research suggests that growth could reach a plateau at a certain point due to higher carbon dioxide levels, Myers noted. And there are countless other climate-related factors, such as rising temperatures and changes in precipitation patterns – all caused by greenhouse gas emissions – that can also harm agriculture.
The idea that rising carbon dioxide levels are not good for global cultures is "sheer nonsense," Myers said.
The decline in nutrition raises an obvious interest in public health, especially when observed in global staple foods such as rice. Scientists are still investigating just how big the problem these nutrient decreases might be.
In previous studies, Myers and his colleagues used models to simulate the diet of people around the world, the nutrients they receive from these foods, and the decline in nutritional value as the level of CO2 increases. Some populations may experience nutrient deficiency in the future, some studies found. A high-profile study from 2015 in The Lancet suggested that by 2050, 140 million people around the world could suffer from zinc deficiency.
The new study took a more economic approach. Focusing on the ten largest rice-traveling nations in the world, rice consumption – and nutrient losses with higher CO2 – was compared to gross domestic product per capita. They found that people in countries with lower per capita GDP, where rice can make up more of their daily diet, will be most affected.
Still, "What's that impact on nutrition and health effects" remains to be seen, Ziska noted.
Myers warned that a more detailed modeling study – which looked at exactly how much of each nutrient a person derives from rice unlike other food sources – would fully assess the public health concerns raised by the new research.
In the meantime, Ziska hopes to investigate how the nutrient content of plants may have changed in previous decades in response to historical greenhouse gas emissions. He says there may be further insights into how crops respond to future carbon emissions.
"It is very important to understand this complexity and to understand these interactions," he said.
Reprinted with permission from E & E News of Climatewire. E & E provides daily coverage of key energy and environmental news at www.eenews.net.