FIGURE 1. Methane sources and sinks.

From the following article:

Global change: A green source of surprise

David C. Lowe

Nature 439, 148-149(12 January 2006)



Numbers are millions of tonnes of methane per year. a, Estimates8 and range of estimates2 of annual emissions of methane to the atmosphere from identified sources. b, Equivalent figures for methane sinks. The estimates from ref. 8 imply that atmospheric methane is decreasing because identified sources are smaller than the sinks, but this is not confirmed by current measurements of methane in the atmosphere5. The ranges in the right-hand column show the extreme values compiled by seven different research groups, as well as estimated total sources and sinks assessed by the Intergovernmental Panel on Climate Change2. Note that, for statistical reasons, the sum of the individual source and sink ranges is not the same as the estimated total source and sink ranges. The wide divergence in these figures shows just how ill-defined the methane source inventory and budget are. The new source identified by Keppler et al.1 — methane emitted by vegetation in oxic conditions — is estimated to produce between 63 million and 243 million tonnes per year, but potentially may double count sources listed above.