Conclusions

It is now though time to reflect on all that we have touched on and to form 10 concise, take-away conclusions and lessons learned...

My 10 key points to take away for the future!

Here we go...

1. Today Methane is the 2nd most significant GHG, it is presently responsible for 53% as much radiative forcing as CO2 provides

2. Methane's ability as a GHG is many times stronger than CO2 (about 120 times as great) yet its residence time is significantly shorter - at present thought to be about 12 years. This means warming from methane is much sharper, yet shorter lived than warming from CO2.

3. Methane's GWP has been significantly raised since it was first cited as having a 100 year GWP of 21 in AR2. Despite the fact this number is significantly erroneous it is still widely utilised today, including in emissions trading schemes.

4. Today we contribute 330Tg/year of anthropogenically produced methane to the atmosphere. It is thought natural production is about 280Tg/year, unsurprisingly methane levels have risen significantly since the rise of man and are now at their highest level for at least 800,000 years.

5. Of this anthropogenic methane emission 50% is created by agriculture

6. There is now 1,800ppb methane in the atmosphere, about 1/200th of the amount of CO2 that there is. CO2's growth rate of 60% compared to pre-industrial times is insignificant compared to methane's standing at 150%. Despite a pause in growth methane's growth appears to have accelerated again significantly in the past few years.

7. 90% of methane is metabolised by the unusual OH radical which is an important agent in breaking down other GHGs too. It has sensitive requirements for its creation that limit its rate of production. Measuring the abundance of this molecule in the atmosphere is hard, despite this it is thought though that its abundance could be in decline.

8. If OH levels are becoming depleted this means the residence time of methane is increasing. This could have significant consequences for the GWP of methane.

9. Scientists are keen to draw parallels between the global warming being experienced today, and for the coming decades to past warming events to try to predict the responsiveness of the earth's methane stores to a warming climate.

10. Methane hydrates and permafrost are though to pose the largest risks for the future. Knowledge into the stores is limited though and the many reports contradicting of each other. Despite this the current academic consensus is that rapid, large scale methane releases are unlikely in coming decades however could take place in the future if predicted potential global warming paths are realised.

There we are! 14 weeks, 14 posts and 7,200 thousand words of analysis, critique and comment later we have arrived at the end of our journey! For those that have followed me throughout this project I hope you've learned as much as I have. Thank you too for those who have got involved; I've enjoyed our discussions on different matters along the way!

Very best,

Rob

A word cloud image; the size of a word indicates its frequency of use in the blog

(Graphic courtesy of worditout.com)

Risks for the future 2: Methane Hydrates

Methane Clathrates: the scare factor

Over the last decade there have been several publications citing methane hydrates(also known by methane clathrates) as being cause of utmost concern in the coming century, having even been nicknamed as the source of 'artic methane apocalypse or 'arctic methane catastrophe'. The Arctic Methane Emergency Group are certainly gravely concerned (http://ameg.me for more), the following taken from a summary of reasons for action needing to be taken immediately:

Source: Arctic Methane Emergency Group

There are clearly many big claims here, the last though has been the subject of intense debate over the past few years - the suggestion that 'a 50 gigaton methane burst is possible at any time'. 

(Source: Authors own)

As the figure above highlights - this really is a release of enormous scale and if it were to happen on anything but a multi century-scale timeframe would certainly have very major consequences for humanity. So, what are the chances of this happening and where does the figure of 50Gt come from?

Plume of methane from methane hydrates being emitted from ocean floor

Source: Ruppel (2011)

Well... It originally appeared in a short paper by Shakova et al. published in 2008 (full paper available here). Since then there has been intense to-ing and fro-ing in the scientific community with various skeptic groups trying to outprove the other as to the likelihood of a 50Gt release in particular, but also the chances of any significant release this century. If you're interested in learning more about this a summary article published by the Guardian is available here.

At present, I would conclude it remains hard to nail down a genuinely substantiable statistic as to the likelihood of a methane burst from stored hydrates. The conclusion by the IPCC in 2013 that:

Source: Carbon and Other Biogeochemical Cycles in IPCC AR5, 2013

Appears true today also - I struggled to find any new evidence since 2013 substantiating the likelihood of the burst any more solidly than prior to 2013. An article in the New Scientist (23 May 2015: p38-41) came to the same conclusion with their investigation which coined their front-cover headline "It's not grim up north - arctic safe from methane apocalypse" along with the concluding statement 

"There is, then, no solid evidence to back the idea of a methane bomb and past climate records suggest there is no cause for alarm."

For the sake of the planet and of mankind let's hope Anil Ananthaswamy from New Scientist is right on this one and that conclusions like hers and like Ruppel's (2011) are indeed correct; 

"Catastrophic, widespread dissociation of methane gas hydrates will not be triggered by continued climate warming at contemporary rates (0.2ºC per decade; IPCC 2007) over timescales of a few hundred years."

References:

Ananthaswamy, A. (2015). The methane apocalypse. New Scientist, pp.38-41.

Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Cli- mate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 

Ruppel, C. D. (2011) Methane Hydrates and Contemporary Climate Change. Nature Education Knowledge 3(10):29

Risks for the future: Melting permafrost

First off... Melting permafrost and methane release

A changing climate and accelerated warming in polar regions is causing grounds traditionally held in a permafrost state to transition into a sporadically frozen or even fully defrosted state. 

Permafrost - The tipping time bomb

As the video above explains this enables the carbon rich organic matter held in the soil to continue its natural decomposition stalled for as long as it remains frozen. When this decomposition place in the absence of oxygen methane is produced. This can happen in big, explosive and very clear releases leaving craters on the landscape (as documented in this article from the Siberian times).

Methane explosion in Siberia

Source: Siberian Times

More commonly however it is an ongoing, discrete and gradual release of methane that is detectable via analysis of air compositions such as displayed in the following product from NOAA clearly showing high emissions from Siberia in this animation of methane levels in August 2007.

Source: Carbon Tracker-CH4 (available here)

The potential risks to permafrost defrosting and the subsequent methane production is undeniably massive if it were to happen on a significant scale. This is due to the enormous store of carbon held in permafrost, thought to be in the region of about 1,700GT. 

What continues to be the focus of debate is the chance of a major, rapid methane release occurring from the defrosting of permafrost and hence also, what climatic changes are needed to induce such a change. Some academics have suggested that the chance of a significant permafrost melting soon is quite likely. A paper titled 'Speleothems reveal 500,000 year history of Siberian Permafrost' by Vaks et al. (2013) used dating of "periods of speleothem growth in a north-south transect of caves in Siberia to reconstruct the history of permafrost in past climate states" their resounding conclusion is that "global climates only slightly warmer than today are sufficient to thaw significant regions of permafrost"- a harrowing conclusion if their conclusions are correct and major regions of permafrost are at risk of defrosting. Indeed already, as the video makes out and as Rachold et al. (2007) concluded there is now evidence that "continuous permafrost is actively thawing in many circum‐Arctic regions".

Despite lots of doom and gloom suggesting studies showing the modelling impacts methane releases from permafrost melting there still remains a vast uncertainty as to what extent, when and if we are to see dangerous methane releases from to be ex permafrost regions in coming decades:

Source: Isaksen et al., 2011

Conclusion on permafrost; easy to sensationalise but hard really to predict; predictions remain wooly despite the potential risks!

In light of length of this discussion here on the risks of methane from defrosting permafrost regions we'll touch on clathrates next week!

Hope to see you back soon!

Methane flaring in Siberia

References:

Vaks, A., Gutareva, O., Breitenbach, S., Avirmed, E., Mason, A., Thomas, A., Osinzev, A., Kononov, A. and Henderson, G. (2013). Speleothems Reveal 500,000-Year History of Siberian Permafrost. Science, 340(6129), pp.183-186.

Isaksen, I., Gauss, M., Myhre, G., Walter Anthony, K. and Ruppel, C. (2011). Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions. Global Biogeochem. Cycles, 25(2), p.n/a-n/a.

Rachold, V., D. Y. Bolshiyanov, M. N. Grigoriev, H.‐W. Hubberten, R. Junker, V. V. Kunitsky, F. Merker, P. Overduin, and W. Schneider (2007), Nearshore Arctic subsea permafrost in transition, Eos Trans. AGU, 88(13), doi:10.1029/2007EO130001. 

O'Connor, F., Boucher, O., Gedney, N., Jones, C., Folberth, G., Coppell, R., Friedlingstein, P., Collins, W., Chappellaz, J., Ridley, J. and Johnson, C. (2010). Possible role of wetlands, permafrost, and methane hydrates in the methane cycle under future climate change: A review. Rev. Geophys., 48(4).

Höglund-Isaksson, L.: Global anthropogenic methane emissions 2005–2030: technical mitigation potentials and costs, Atmos. Chem. Phys., 12, 9079-9096, doi:10.5194/acp-12-9079-2012, 2012.