Global warming and empty calories

High CO2 crops could be low on nutrition

Posted by Maywa Montenegro (Guest Contributor) at 9:12 PM on 14 Aug 2007

Read more about: climate | climate change impacts | agriculture | food

One of the silver linings of climate change, some have argued, is that high carbon dioxide levels will mean increased crop yields, which will, in turn, be good for combating global hunger (the logic, I suppose, being that if we're frying fifty years from now, at least we won't be hot and hungry). But some underpublicized studies, reported this month in Nature, cast a long shadow on this sunny assertion. (Sorry! It looks like the the article is subscription only, so I'll be as descriptive as possible.)

In the 1980s, Bruce Kimball, a soil physicist with the USDA in Arizona, began conducting scientific experiments simulating a high-CO2 environment (using a system called "free air carbon dioxide enrichment," or FACE). He found that crop yields were elevated -- plants imbibing large quantities of CO2 had more starch and more sugar in their leaves than those on a normal carbon diet. But because they also took up less nitrogen from the soil, they made less protein.

High-CO2 plants, one theory goes, skimp on nitrogen uptake because with so much CO2 around, they no longer need as much protein machinery to "fix" this gas into sugar. Kimball, however, said he wasn't too worried about the reduced nutrition. "As far as crops go, I think higher CO2 is definitely a benefit. Yes, a little less nutrition than before, but we get more food ... The farmer in the future would have to be sure and apply ample fertilizers to keep protein quality up," he said. But others aren't so sanguine.

Arnold Bloom, a plant biologist at the University of California in Davis, thinks that the reduced nitrogen levels seen in high-CO2 conditions is not just the result of plants needing less protein. He believes they actually become less able to absorb nitrates from the soil -- in which case, dumping extra fertilizer on fields won't be of much help.

So just how much of a protein difference are we talking about? Measuring bread flour, Herbert Weiser, head of cereal proteins at the German Research Centre for Food Chemistry, found that normal-CO2 wheat produced flour with 9.1 grams of protein per 100 grams, while high-CO2 wheat produced flour with only 7.8 grams of protein per 100 grams -- about a 14 percent difference. While this won't amount to much in the average American diet (or that of most developed nations, for that matter, where protein intake is far greater than necessary), it could certainly have an impact on the developing world.

It's not just humans, of course, that consume plants. A nitrogen-impoverished plant world will have effects all along the food chain, from the grubs that feed on corn to the birds that eat those grubs to the snakes that eat those birds (you get the picture).

Meanwhile, other FACE research has shown that crops grown in high-CO2 environments have diminished calcium and zinc levels (between 10 and 20 percent). The take-home message? In a warming world, quality of nutrition will probably go down, even as quantity of food goes up.

For story: Global warming and empty calories
4 Comments | Post a Comment

Don't count on the quantity either

I would not advise counting on the quantity of food continuing to rise and match population growth. Collapses have been associated with declining quantities and qualities of food sources, both of which affect health, disease and political stability.

An interesting article on Peak Phosphorus and the relationship between phosphorus production, peak oil, agricultural production and population growth:
http://www.energybulletin.net/33164.html
"Phosphorus may be the real bottleneck of agriculture."

by justlou at 6:40 AM on 15 Aug 2007

Common sense would suggest

that plants evolved to grow in a given CO2 environment will be compromised when that environment changes. The plants will eventually evolve and adjust to the new levels but that will take stable levels and a few centuries.

In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

by biodiversivist at 7:57 AM on 15 Aug 2007

Temperature and crops

Another major consideration is the increase in both maximum and minimum temperatures.

Higher maximum temperatures increase the chances of crop failure, especially among plants that use C3 photosynthesis. Higher minimum temperatures in winter can assist the spread of pests, as the current situation in British Columbia's pine forests amply demonstrates.

a sibilant intake of breath

by sindark at 8:17 AM on 15 Aug 2007

Other Factors

Many of the crop experiments testing the influence of higher carbon dioxide levels on photosynthesis and yield were conducted in very controlled, growth chamber like environments. In the real world production will be affected by many environmental factors that are not controllable. Higher temperatures during grain fill will reduce the number of days that grains are being filled, decreasing yield potential. Higher night temperatures will increase respiration rates, decreasing grain fill. Plus warming will be associated with extremes of drought and flooding which can reduce production. Other biological factors affected by temperature and CO2 include weed, disease and insect pests also enter into the equation.

Can the gene jockeys keep ratcheting up the biotechnology to compensate for all the potential negatives associated with warming and higher CO2? Very unlikely.

Food vs. energy production is also a key determinant. As is our continuing destruction of prime farmland in the US.

by justlou at 9:02 AM on 15 Aug 2007

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