As carbon dioxide levels rise, staple grains could lose some nutritional value

Southwestern researcher and former students publishes paper.

By Asher Price
AMERICAN-STATESMAN STAFF
Monday, January 21, 2008

It started with a seemingly off-the-wall question in a 2004 global change biology class at Southwestern University. The discussion was about how increases in carbon dioxide, a contributing cause of global warming, lead to a decline in the amount of proteins in some plants.

"How would rising CO2 levels affect the Atkins diet?" asked Holly Allen, then an undergraduate majoring in environmental studies. The Atkins diet, still en vogue then, emphasizes proteins over carbohydrates.

Searching for the answer led to a study, to be published in an upcoming issue of the journal Global Change Biology, that provides a serious answer:

Protein levels in staple foods like rice and wheat could decline by as much as 15 percent by the year 2100.

Those results could have far-reaching consequences for nutrition, especially in developing countries.

"Wheat and rice are really major ingredients of the food aid we deliver worldwide in some 80 countries," said Bettina Luescher, a spokeswoman for the United Nations' World Food Program.

Protein is a key source of nourishment, according to the World Food Program.

Climate-change scientists say the carbon dioxide concentrations in the atmosphere, currently about 380 parts per million, could jump to between 540 and 958 parts per million by the year 2100.

Allen, a classmate and Southwestern biology professor Max Taub pored over more than 200 previously published studies to determine how the higher carbon dioxide would affect nutrient levels, winnowing out studies that relied on carbon dioxide levels above or below the 2100 predictions.

"One study that looked at space missions and the possibility of growing plants on Mars had concentrations of 10,000 parts per million," Taub said.

"We'll never see that on Earth."

They found that protein concentrations could decline by 10 percent to 15 percent in wheat, barley and rice; by 14 percent in potatoes; and about 1.4 percent in soybeans.

"Patterns aren't apparent until someone does this," Taub said of their analysis.

Other reports have suggested that more carbon dioxide in the atmosphere will help plants thrive, even if, assuming the Southwestern paper bears out, they're less nutritious.

"In general, plant growth is increased by elevated CO2 levels," Taub said. "But it's a complicated story. While any plant's growth will increase on its own, when plants are competing together, they may be dealing with bigger competitors."

asherprice@statesman.com; 445-3643