July 05, 2006
|CO2 Benefit To Crops Overestimated||Environment|
Global warming will rob soils of moisture, hurting crop yields. But some studies have seemed to show that increased CO2, which increases photosynthesis, will offset soil moisture effects. New research casts doubt on that conclusion, however, partly because of the damaging effects of ozone, which is also increasing. NASA:
Open-air field trials involving five major food crops grown under carbon-dioxide levels projected for the future are harvesting dramatically less bounty than those raised in earlier greenhouse and other enclosed test conditions — and scientists warn that global food supplies could be at risk without changes in production strategies.
The new findings are based on on-going open-air research at the University of Illinois at Urbana-Champaign and results gleaned from five other temperate-climate locations around the world. According to the analysis, published in the June 30 issue of the journal Science, crop yields are running at about 50 percent below conclusions drawn previously from enclosed test conditions.
Results from the open-field experiments, using Free-Air Concentration Enrichment (FACE) technology, "indicate a much smaller [CO2] fertilization effect on yield than currently assumed for C3 crops, such as rice, wheat and soybeans, and possibly little or no stimulation for C4 crops that include maize and sorghum," said Stephen P. Long, a University of Illinois plant biologist and crop scientist.
FACE technology, such as the SoyFACE project at Illinois, allows researchers to grow crops in open-air fields, with elevated levels of carbon dioxide simulating the composition of the atmosphere projected for the year 2050. SoyFACE has added a unique element by introducing surface-level ozone, which also is rising. Ozone is toxic to plants. SoyFACE is the first facility in the world to test both the effects of future ozone and [CO2] levels on crops in the open air.
Older, closed-condition studies occurred in greenhouses, controlled environmental chambers and transparent field chambers, in which carbon dioxide or ozone were easily retained and controlled. [...]
Older studies, as reviewed by the Intergovernmental Panel on Climate Change, suggest that increased soil temperature and decreased soil moisture, which would reduce crop yields, likely will be offset in C3 crops by the fertilization effect of rising [CO2], primarily because [CO2] increases photosynthesis and decreases crop water use.
Although more than 340 independent chamber studies have been analyzed to project yields under rising [CO2] levels, most plants grown in enclosures can differ greatly from those grown in farm fields, Long said. FACE has been the only technology that has tested effects in real-world situations, and, to date, for each crop tested yields have been "well below (about half) the value predicted from chambers," the authors reported. The results encompassed grain yield, total biomass and effects on photosynthesis. [...]
"The FACE experiments clearly show that much lower [CO2] fertilization factors should be used in model projections of future yields," the researchers said. They also called for research to examine simultaneous changes in [CO2], [O3], and temperature and soil moisture."
While projections to 2050 may be too far out for commercial considerations, they added, "it must not be seen as too far in the future for public sector research and development, given the long lead times that may be needed to avoid global food shortage." [Emphasis added]
It's too bad we were all raised on stories that ended, "And they all lived happily ever after." Maybe that's were we learned complacency. But down here in the real world, not all stories have happy endings. Much of real life is brutal and tragic. Nature is pitiless. If we continue our complacent inaction in the face of the mountain of scientific evidence on global warming, we'll deserve what we get. We cannot say we haven't been warned.