Forster et al (2007) comment that CH4 sinks are not well understood (related to complex atmospheric chemistry involving interaction and concentrations of hydroxyl radicals, ozone, and compounds which influence those), but nevertheless that many studies assume that there has not been any significant change in the sinks (which is questionable), instead assuming that anthropogenic emissions of CH4 have stabilised (which is perhaps even more questionable).

The bottom-up calculations of methane have been shown repeatedly to be inaccurate, and it is entirely possible that changes in other sources (perhaps non-anthropogenic) have produced the change in the balance between sources and sinks.

While this does not conclude anything about strategies for enteric CH4 mitigation which ought to be pursued, it does highlight the common fallacy of assuming correlation = causation, especially with regard to such complex systems in geoscience. Why should a correlation between the CH4 trend and ruminant numbers have influenced thinking with regard to the significance of enteric CH4 at all in the first place?

“Most carbon is in living trees, and tree mortality is not included in the models,” said David Hilbert of research organisation CSIRO at the Climate Congress in Copenhagen. “Trees grow faster with higher temperatures, but mortality goes up too. So despite higher tree growth and higher turnover of biomass, rainforests in a warmer climate have a reduced carbon storage capacity.”
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