Atmospheric methane levels continued to increase in 2009, the World Meteorological Organisation’s annual Greenhouse Gas Bulletin (summary PDF) confirmed this week. Methane averaged 1803 ppb over the year, up 5 ppb on 2008, and now contributes 18.1% of the radiative forcing caused by current greenhouse gas levels. The Bulletin suggests that “likely causes were above average wetland methane emissions due to exceptionally warm temperatures at high northern latitudes in 2007 and heavy precipitation in tropical wetlands in 2007 and 2008. However, it cautions that the reasons for the recent increases are not yet fully understood.”

A hint that the rise might be continuing this year is contained in this rather striking graph of methane levels recorded recently at the Mt Zeppelin recording station (a misty mountain?) in Ny Ã…lesund, Svalbard…

The graph comes from NOAA’s Earth System Research Labs Global Monitoring Division’s new data visualisation web page here (you’ll see a CO 2 graph first, but click on the menu to the left of the graph to get the methane version). The readings for the last year are preliminary, and shown in brown. The last five data points are so far off the chart that they are almost certainly going to be rejected as being caused by local contamination. That’s happened before — the green dots show when — and at the moment other Arctic sites are not showing a similar rise. However, Svalbard is close to sea floor methane hydrate deposits that are known to be venting gas.

Another way to appreciate the elevated levels of methane in northern high latitudes is to take a look at the ESRL’s Globalview-CH4 page, which features a nice (but large) animation of monthly methane levels by latitude from 1997 to 2009. There’s a clear hemispheric imbalance as well as an obvious seasonal cycle. Mesmerising viewing.

This recent AP article explores why Arctic methane levels are worth watching. Russian scientist Sergey Zimov, director of the Northeast Science Station near Chersky on the Kolyma River in Siberia is shown doing a Katey Walter in the pictures accompanying the text. It’s a good overview of the state of play in a region where, as Zimov says, “total carbon storage is like all the rain forests of our planet put together”, and where there’s a lot of sea floor methane hydrate bubbling away…

Methane hydrates are also plentiful under the sea floor around New Zealand, and evidence is emerging that huge amounts of the gas might have erupted during glacial/interglacial transitions. A new paper, Gas escape features off New Zealand: Evidence of massive release of methane from hydrates by Bryan Davy, Ingo Pecher, Ray Wood (all of GNS Science), Lionel Carter (VUW) and Karsten Gohl (Alfred Wegener Institute) [Geophys. Res. Lett. (2010) vol. 37 (21) pp. L21309] looked at sea floor scans of 20,000 km2 of the Chatham Rise, which lies to the east of the South Island. They found thousands of distinct of gas escape features, from numerous small “pockmarks” about 150m across to ten of the largest such structures yet found — 8 to 11 km across, twice the size of the largest recorded to date. The team estimate that one structure of that size could release as much as 7 x 1012g methane, equivalent to about 3% of current natural emissions. The paper suggests that methane hydrate decomposition could have been stimulated by the reduction in sea floor pressure caused by the 120 m fall in sea level during glacial periods, and by periodic incursions of deeper warm water. You have to hope we don’t see too many of those things going pop in the near future…

[Richard Thompson, John Kirkpatrick, Cropredy 1980]

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