Projections that climate change during the 21st century could benefit agriculture may be off target, two new studies show. The studies, which tested the effects of higher CO2 and ozone levels in open fields of soybeans, suggest models of future crop production are missing important factors.
For the coming decades, most climate change models forecast increasing pollution, shifting zones ideal for agriculture, and possibly more extreme weather, all of which could hurt agricultural yields. But estimates from the U.N.-sponsored International Panel on Climate Change (IPCC), the closest thing in the field to a scientific consensus, suggest such effects would be largely countered by the benefits of mild rises in temperature and CO2. These would aid growth by making photosynthesis more efficient and helping plants retain water. But the IPCC estimates did not include direct effects of ground-level ozone, which can hurt plant growth. Also, most studies of the gases' effects have taken place in greenhouses or enclosures, which make the climate inside warmer and more humid, thus confounding results.
Now two new open-field studies suggest climate change could cause grave losses in food production. The studies, led by environmental physiologist Stephen Long of University of Illinois at Urbana-Champaign, used Free-Air gas Concentration Enrichment (FACE) technology, which spews gases over crop plots. Like a thermostat keeping temperatures constant, sensors in the field monitored the gases, allowing the researchers to control the concentration of ozone or CO2 over 300-square-meter plots. The researchers used the technology to simulate climate conditions expected around the year 2050.
One of the studies, to be published in an upcoming issue of Environmental Pollution, shows that a 20% increase in ground ozone would slash soy yields by 20%. The other experiment, to be published in an upcoming issue of Global Change Biology, indicates that an atmospheric increase to 550 parts-per-million of CO2 would boost soy yields by about 15%, a third less benefit than seen in previous studies. And the harm from ozone would more than cancel out this benefit.
The two studies' results are consistent with other open-field studies of corn, maize, and rice, which overall suggest that by 2050, the gases could push down staple crop yields by 10-15%, Long noted yesterday at Royal Society meeting in London. "We shouldn't be as confident about the global food supply as the IPCC assessment might suggest," Long said.
"These results are very serious," says Julia Slingo, climate scientist at the University of Reading in the United Kingdom, who attended yesterday's meeting. "Food security is much more insecure than we had thought."