Mary Lou Peter

MANHATTAN, Kan. - Plenty has been written about concerns over elevated
levels of carbon dioxide in the earth's atmosphere, but a Kansas State
University researcher has found an upside to the higher CO2 levels. And it's
been particularly relevant in light of drought that overspread the area in
recent months.

"Our experiments have shown that the elevated carbon dioxide that we now
have is mitigating the effect that drought has on winter wheat and sorghum
and allowing more efficient use of water," said K-State agronomy professor
Mary Beth Kirkham.

Kirkham, who has written a book on the subject, "Elevated Carbon Dioxide:
Impacts on Soil and Plant Water Relations," used data going back to 1958.
That's when the first accurate measurements of atmospheric carbon dioxide
were made, she said.

"Between 1958 and 2011 (the last year for which scientists have complete
data), the carbon dioxide concentration has increased from 316 parts per
million to 390 ppm," she said. "Our experiments showed that higher carbon
dioxide compensated for reductions in growth of winter wheat due to drought.
Wheat that grew under elevated carbon dioxide (2.4 times ambient) and
drought yielded as well as wheat that grew under the ambient level carbon
dioxide and well-watered conditions."

The research showed that sorghum and winter wheat used water more
efficiently as a result of the increased levels of carbon dioxide in the
atmosphere, Kirkham said. Because elevated carbon dioxide closes stomata
(pores on the leaves through which water escapes), less water is used when
carbon dioxide levels are elevated.
Evapotranspiration is decreased.

Studies done subsequent to the early work confirmed the findings.

Over the past few months, the researcher said she's heard people comparing
the dry summer of 2012 with the Dust Bowl years of the 1930s and the drought
of the mid-1950s in Kansas.

The first accurate measurements of CO2 levels were made in 1958, so while
scientists do not know what the concentration of CO2 was in the 1930s,
Kirkham said, she used the data that she and her students collected to
calculate how much the water use efficiency of sorghum has increased since
1958, which was about the time of the middle of 1950s drought.

"Due to the increased carbon dioxide concentration in the atmosphere, it now
takes 55 milliliters (mL) less water to produce a gram of sorghum grain than
it did in 1958," she said. "Fifty-five mL is equal to about one-fourth of a
cup of water. This may not seem like a lot of water savings, but spread over
the large acreage of sorghum grown in Kansas, the more efficient use of
water now compared to 1958 should have a large impact.

"The elevated carbon dioxide in the atmosphere in 2012 ameliorated the
drought compared to the drought that occurred in the mid-1950s."

At the basis of Kirkham's book are experiments that she and other
researchers conducted in the Evapotranspiration Laboratory at K-State from

"They were the first experiments done in the field in a semi-arid region
with elevated carbon dioxide," Kirkham said. The lab no longer exists, but
the work continues.

More information about Kirkham's research is available at