Rice and Global Warming
Rice is the most important grain with regard to human nutrition and caloric intake in the world, providing more than one fifth of the calories consumed worldwide by the human species. Without rice and the world will be a much different place. More carbon dioxide in the atmosphere, coupled with rising temperatures, is making rice agriculture a larger source of the potent greenhouse gas methane, according to a study published in Nature Climate Change by a research team that includes a University of California, Davis, plant scientist. The authors note that relatively simple changes in rice cultivation 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 and co-author of the study, published in Nature Climate Change.
"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 staple food of over half the world's population. It is the predominant dietary energy source for 17 countries in Asia and the pacific, 9 countries in North and South America and 8 countries in Africa. Rice provides 20% of the world’s dietary energy supply, while wheat supplies 19% and maize 5%.
Van Kessel and his colleagues gathered findings from 63 different experiments on rice paddies, mostly in Asia and North America. They used a technique called meta-analysis, a statistical tool for finding general patterns in a large body of experimental published data.
The experiments measured how rising temperatures and extra carbon dioxide in the atmosphere affect both rice yields and the amount of methane released by 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, and lead author of the study. As more carbon dioxide enters the atmosphere, rice plants grow faster, the experimental data showed. This growth, in turn, pumps up the metabolism of methane-producing microscopic organisms that live in the soil beneath rice paddies. The end result: More methane.
Overall, the rice paddy experiments indicated that increased carbon dioxide in the atmosphere boosted rice yields by 24.5 percent and methane emissions by 42.2 percent, increasing the amount of methane emitted per kilo of rice.
There are several options available to reduce methane emissions from rice agriculture. For instance, management practices such as mid-season drainage and using alternative fertilizers have been shown to reduce methane emissions from rice paddies.
For further information see Methane and Rice.
Rice Paddy image via Wikipedia.