Methane (CH4) is the 3rd most significant greenhouse gas after water vapour (H20) and carbon dioxide (CO2). Methane is present in the atmosphere in far lower concentrations than CO2 (approx. 1.8 parts per million (ppm) CH4 as opposed to 390+ ppm CO2) and persists for less time (CO2 takes approx. 100 years to degrade whereas CH4 degrades after approx. 20 years). Despite this, methane has a Global Warming Potential (GWP) 25 times higher than CO2 on a 100-year timescale (Forster et al., 2007), partly due to the fact that when it degrades, methane degrades into CO2...
Atmospheric methane concentrations for past centuries have been extensively reconstructed by analysing air bubbles trapped in polar ice sheets. Analysis of an ice core from Central Greenland confirms the pre-industrial levels of approx. 700 parts per billion (ppb) with the beginning of anthropogenic increases set between 1750 and 1800 (Blunier et al., 1993). Since that time, methane levels have more than doubled to well above 1800 ppb.
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Annual mean atmospheric CH4 concentrations in parts per billion (ppb), compiled from data gathered at the Mauna Lao station, Hawaii, between 1987 - 2008. The graph clearly shows a levelling off between 1999 & 2006 and a renewed increase of levels after 2007. |
Records show that in the late 90's the rapid increase in atmospheric methane concentration began to level off, so much so that between 1999 and 2006 there was almost no net increase. However, in 2007 methane levels began to rise once again (Rigby et al., 2008) and atmospheric scientists began the task of determining if this was a "return to normal" or a temporary spike.
If you retrieve data from the World Data Centre for Greenhouse Gases from the 10 stations with readings past mid-2010 it is possible to plot the average aligned values onto a composite graph:
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| Composite graph of averaged aligned readings from 10 stations recording atmospheric methane including data past the mid-point of 2010. -Credit: Open Mind |
There is a clear indication that the rise in atmospheric methane concentrations that resumed in 2007 is continuing at a rate comparable with that which pre-dates the levelling off period begun in 1999. This raises the obvious question of why? The industrial collapse of the former Soviet Union during the 1990's followed by improvements in industrial processes throughout Eastern Europe coupled with efforts to reduce methane emissions from landfill sites across Europe and North America could have been contributing factors in slowing the rise in CH4 concentrations. There was also a prolonged period of drying in natural wetlands from deliberate drainage and the effects of climate change and a reduction of natural gas flaring during oil production as gas became more important as a fuel in its own right, both of which will also have resulted in reduced methane emisions.
So, after a slight pause, the underlying trend of increasing atmospheric methane concentrations has returned, overcoming the stabilising factors of the early years of the new millennium. It is a well established fact that observed atmospheric surface temperatures of the Arctic have increased 2.5 times faster than the overall global surface air temperature, resulting in accelerating loss of sea ice and an increase in the albedo effect.
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| Melt-lakes in the Siberian "permafrost" |
Rising Arctic temperatures are also thawing vast tracts of permafrost from Siberia to Alaska, turning once frozen ground into lake riddled bogs in the summer months which bubble with releasing methane.
As the land warms, so do the oceans.
References
Blunier, T., J. A. Chappellaz, J. Schwander, J.‐M. Barnola, T. Desperts, B. Stauffer, and D. Raynaud (1993),
Atmospheric methane, record from a Greenland Ice Core over the last 1000 year, Geophys. Res. Lett., 20(20),
2219-2222.
Forster, P., Ramaswamy, V., Artaxo, P., Berntsen, T., Betts, R., Fahey, D.W., Haywood, J., Lean, J., Lowe,
D.C., Myhre, G., Nganga, J., Prinn, R., Raga, G., M., S., Van Dorland, R., 2007. Changes in Atmospheric
Constituents and in Radiative Forcing. In: S. Solomon et al. (Editors), Climate Change 2007: The Physical
Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental
Panel on Climate Change. Cambridge University Press, Cambridge, U.K.
http://tamino.wordpress.com/2011/05/28/methane-update/ (Accessed: 22/08/2011)
Rigby, M., et al. (2008), Renewed growth of atmospheric methane, Geophys. Res. Lett., 35, L22805,
doi:10.1029/2008GL036037.
