collaborating scientists are using a method called free-air concentration
enrichment to better predict how the future's increased CO2 levels could affect
crop yields. Click the image for more information about it.
New Crop-Yield Study Casts Doubt on a
Climate-Change Prediction By
Jan Suszkiw June
Leading crop-production models predict that higher temperatures and
dryer soils will diminish crop yields as a result of global climate change in
the year 2050. The models also predict that another anticipated climate-change
phenomenonthe yield-stimulating effects of elevated carbon
dioxidewill offset those losses. So nothing gained or lost, right? Not
quite, says a team of Agricultural Research Service (ARS), University of Illinois at
Urbana-Champaign (UIUC), and Swiss
In this week's issue of Science, the researchers contend that
today's simulation models overestimate the "CO2 fertilization effect," which
refers to the improved efficiency of some crops in using sunlight to convert
CO2 into sugars. The problem is, the models rely on data from enclosure
studies, say ARS plant physiologists
Ainsworth, UIUC scientists Stephen Long and Andrew Leakey, and Josef
Nösberger of the Institute of Plant
Science in Switzerland. According to their Science paper, trapped
heat, poor airflow, high humidity and other conditions inside greenhouses and
growth chambers skew plant responses to elevated CO2.
To avoid these problems, the researchers used free-air concentration
enrichment (FACE) to simulate the atmosphere of 2050 under actual field
conditions. The method continuously exposes crop plants within 66-foot-diameter
plots to 550 parts/million (ppm)the CO2 concentration predicted for 2050.
The current level is 380 ppm. Ort, who leads the ARS Photosynthesis Research
Unit in Urbana, monitored the growth and yield of corn and soybeans there with
his ARS and UIUC colleagues. In Maricopa, Ariz., an ARS collaborator monitored
wheat and sorghum; in Switzerland, Nösberger examined forage grasses.
After collecting FACE data for the crops, the scientists compared it
to earlier growth-chamber-based simulations. The difference was dramatic: CO2
fertilization-effect yield increases measured in the FACE experiments were 50
percent lower than the chamber simulations.
According to Ort, the finding warrants a reexamination of CO2's role
in forecasting future yields, especially in the presence of other
climate-change concerns such as ozone pollution, which is toxic to crops.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.