Methane emissions from rice paddies may have been about 3 times overestimated, according to a new study carried out by researchers of the Chinese Academy of Sciences (CAS).
Total emission amount of world's atmospheric methane a major greenhouse gas from rice paddies in 2000 is 25.6 million tonnes, instead of previously estimated 80 million tonnes. And the emission of rice paddies in China is only 25% of the estimated amount, according to the new study.
The British science journal Nature reported about the achievement in early April.
Concentration of atmospheric methane has nearly tripled since the industrial revolution, but the contribution from individual sources has remained unclear. "Rice plantation has been regarded culprit of all causes, which put high pressure on China's rice farming," said Yan Xiaoyuan, researcher with the Institute of Soil Science, CAS, who carried out the research.
The Intergovernmental Panel on Climate Change (IPCC) published guidelines for estimation of methane emission from rice paddies in 2006 and recommended to its member countries as one and only method. And this is the right method that Yan and his colleagues use.
Using country-specific estimates of rice harvest area and data on agricultural practices, Yan and his colleagues calculated that methane emissions totalled 25.6 million tonnes over the entire year and mostly came from monsoon Asian countries.
The study found that the release of methane was highly dependent on management techniques: emissions were reduced by 4.1 million tonnes per year if fields were drained at least once during the growing season, and a further 4.1 million tonnes if rice straw was applied off season. They estimate that if both practices were implemented, emissions could be reduced by 30 percent annually.
Contact Yan Xiaoyuan:
Tel: 025-86881530
Fax: 025-86881000
E-mail: yanxy@issas.ac.cn
