October 23, 2012
Rice Paddies Accelerate Global Warming
April Flowers for redOrbit.com - Your Universe Online
A new study led by the University of California, Davis finds that more carbon dioxide in the atmosphere, coupled with rising temperatures, is making rice agriculture a larger source of the potent greenhouse gas methane.Relatively simple changes in rice cultivation, according to the study, could help reduce methane emissions.
"Together, higher carbon dioxide concentrations and warmer temperatures predicted for the end of this century will about double the amount of methane emitted per kilo of rice produced," said Chris van Kessel, professor of plant sciences at UC Davis. "Because global demand for rice will increase further with a growing world population, our results suggest that without additional measures, the total methane emissions from rice agriculture will strongly increase."
Rice is the world's second-most produced staple crop, making rice paddies one of the largest man-made sources of methane. The team gathered findings, mostly from Asia and North America, from 63 different experiments on rice paddies. Using a technique called meta-analysis, which is a statistical tool for finding general patterns in a large body of experimental published data, the team mined the findings of the previous studies.
The experiments they used measured how rising temperatures and extra carbon dioxide in the atmosphere affect both rice yields and the amount of methane released by the rice paddies.
"Our results show that rice agriculture becomes less climate-friendly as our atmosphere continues to change," said Kees Jan van Groenigen, research fellow at Trinity College Dublin.
The data showed that rice plants grow faster as more carbon dioxide enters the atmosphere. In turn, this growth ramps up the metabolism of the microscopic organisms that live in the soil beneath rice paddies and produce methane, pushing more methane into the atmosphere.
The analysis revealed that increased carbon dioxide in the atmosphere boosted rice yields by 24.5 percent. It also showed a rise in methane emissions by 42.2 percent, increasing the methane emitted per kilo of rice.
Conversely, rising temperatures were found to have only a small effect on methane emissions. Warming does decrease rice yields, however, effectively increasing methane emissions per kilo of rice.
Several options are available to reduce methane emissions from rice agriculture, according to the study. Management practices like mid-season drainage or alternative fertilizers have been shown to reduce methane emissions. Switching to more heat-tolerant rice cultivars and adjusting sowing dates shows that yield declines due to temperature increases can be prevented.
Professor Bruce Hungate from Northern Arizona University says that the study's findings underscore the importance of securing the global food supply while keeping greenhouse gas emissions in check.
The results of the study were published in the journal Nature Climate Change.