Crops Cotton to CO2

Published May 1, 2000

As petroleum prices continue to jump, high prices may cause petroleum-based synthetic fibers to fall out of fashion. Consumers and manufacturers alike may then rekindle their love of natural fibers, with cotton chief among them. After all, should atmospheric carbon dioxide (CO2) levels remain on the rise, studies show we’ll find ourselves in high cotton.

What better place to study this versatile fiber than in the South, where cotton is king? In 1998, K.R. Reddy and a group of botanists at Mississippi State University reported on a study in which they grew cotton at various temperatures under present and doubled CO2 levels. Their work showed that elevated CO2 increased the total weight of the plants by more than 30 percent, while the weight of the bolls increased by over 20 percent.

The plants grew taller and had more and longer branches, and their leaves grew bigger in the doubled CO2 chambers. That study proved that cotton plants benefit enormously from any increase in atmospheric CO2 levels.

A recent article in Crop Science provides even more membership privileges for the cotton club. Scientists in the southern state of North Carolina grew cotton in open-top chambers with varying levels of atmospheric ozone (O3) and varying atmospheric CO2 concentrations.

In the study, Heagle and colleagues noted that many others also had found plant stress for elevated ozone levels but enhanced growth and yield for elevated atmospheric CO2. The Heagle team, however, was particularly concerned with the interactions between ozone and CO2 in impacting the growth and yield of cotton. Furthermore, they varied the amount of nitrogen fertilizer applied to the plants. The cotton plants were grown over two seasons with various environmental conditions in the chambers.

Sure enough, CO2 enrichment generally stimulated growth and yield, whereas ozone exposure suppressed growth and yield. Specifically, the doubling of CO2 at medium nitrogen and low ozone concentration produced an increase in the number of bolls of 23.3 percent, seed-cotton weight (yield) of 11.4 percent, and shoot weight by 19.0 percent.

At elevated ozone levels, however, the CO2 doubling created even more amazing results. The doubling of CO2 at high ozone and medium nitrogen generated an increase in the number of bolls of 76.2 percent, seed-cotton weight (yield) of 96.4 percent, and shoot weight by 91.0 percent.

In conclusion, the authors simply stated that “stimulation induced by CO2 increased as O3 stress increased.”

One interpretation of their research, and the one favored by the Reddy team in North Carolina, is that atmospheric ozone monitoring is critical in evaluating how different levels of CO2 impact cotton growth and yield—as well as the growth and yield of many other plants susceptible to damage from elevated ozone levels.

Fair enough.

But another interpretation, and the one favored in Greening Up, is even simpler: Cotton and the rest of Nature’s wonderful plants are just plain better off when atmospheric CO2 levels are higher.

Robert C. Balling Jr., Ph.D. is director of the Laboratory of Climatology at Arizona State University and coauthor of The Satanic Gases.


Reddy, K.R., et al., 1998. Interactions of CO2 enrichment and temperature on cotton growth and leaf characteristics. Environmental and Experimental Botany, 39, 117-129.

Heagle, A.S., et al., 1999. Ozone stress, carbon dioxide enrichment, and nitrogen fertility interactions in cotton. Crop Science, 39, 731-741.