Methane map

Glob. Biogeochem. Cycles doi:10.1029/2008GB003299 (in the press)

Credit: PHOTOMORPHIC/ISTOCKPHOTO.COM

Methane emissions from rice paddies may have been previously overestimated, according to a new study. The concentration of atmospheric methane — a major greenhouse gas — has nearly tripled since the industrial revolution, but the contribution from individual sources has remained unclear.

Now Xiaoyuan Yan of the Chinese Academy of Sciences and his colleagues have generated a global map of methane emissions from rice paddies for the year 2000, using country-specific estimates of rice harvest area and data on agricultural practices. They calculate that methane emissions totalled 25.6 million tonnes over the entire year and mostly came from monsoon Asian countries. The authors say that the reason their calculation is at the lower end of earlier estimates, which range from 25 to 170 million tonnes per year, is probably because it takes account of farming practices.

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 per cent annually.

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Armstrong, A. Methane map. Nature Clim Change 1, 42 (2009). https://doi.org/10.1038/climate.2009.27

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