Methane concentrations in the atmosphere have been rising rapidly for the last decade but the last two years have seen a significant uptick. Scientists aren't sure where it's coming from. Most likely from agriculture in the tropics but also "scientists are now seeing large plumes of methane escaping from the shallow seas north of Siberia. These emissions, and those from the thawing tundra, are contributing to the sudden rise in methane concentrations." - which would be a worrying signal of a potentially powerful positive feedback loop in the climate system strengthening. Conclusion is that more attention should be paid to methane emissions relative to carbon dioxide.