Rising levels of carbon dioxide and global climate change may be responsible for lowering nutrition in crops. According to new research, crops that provide most of the essential iron and zinc consumed by humans may lose much of their nutritional value by 2050. 

As many as two billion people worldwide suffer from a deficiency of one or both of these essential minerals. This gives this problem significant importance for global health. According to the study, this may be the greatest direct threat to human health directly caused by global warming. 

The research was conducted by researchers from the Harvard School of Public Health (HSPH).

"This study is the first to resolve the question of whether rising CO2 concentrations - which have been increasing steadily since the Industrial Revolution - threaten human nutrition," Samuel Myers, from the Department of Environmental Health at HSPH, said.  

Research has been conducted before, searching for possible links between rising concentrations of carbon dioxide and the mineral levels in crops. However, early experiments could only raise levels of the gas in an enclosed area. Because of this, the studies were criticized for growing plants indoors. 

New technology called free air carbon dioxide enrichment (FACE) allows researchers to grow crops outdoors, while still being able to control the amount of carbon dioxide the plants experience. In recent studies, this system has become standard testing equipment. 

More than 40 types of legumes and grains were studied by the group. Plants were grown at FACE facilities all across the globe, in atmospheres containing between 546 and 586 parts per million of carbon dioxide. After the plants had matured, they were sent for testing of nutrient levels. 

Wheat and rice lost significant levels of protein, as well as zinc and iron, between 5.1 and 9.3 percent. While legumes did not lose measurable amounts of proteins in the crops, both minerals were negatively affected by the greenhouse gas. Increased carbon dioxide levels had little impact on either sorghum or maize. 

Somewhere between two and three billion people receive 70 percent or more of their zinc and iron from crops affected by rising levels of the greenhouse gas, according to the researchers. 

Interestingly, rice showed significant variances in its tolerance for increase carbon dioxide levels in the atmosphere. This may make it possible to selectively breed or genetically engineer rice varieties that will not be impacted by growing concentrations of carbon dioxide. 

Study of the role global warming may play in future mineral deficiencies in crops was profiled in the journal Nature.

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