Our best predictions of earth’s response to anthropogenic warming are continually changing, with famous mechanisms such as the ice-albedo feedback and modification of oceanic circulation patterns dominating the literature and media. The greatest threat, however, might seem less exotic, less dramatic and less striking although it is likely the most ominous, sinister and menacing of all. I am alluding to the melting of the earth’s permafrost (frozen ground)…
Perhaps it is due to its less than spectacular appearance that it is one of the lesser known climate dangers. It changes slowly, it is dull in appearance and does not inspire urgency; however, far from being as benign as it looks, the permafrost is a looming catastrophe.
The permafrost is a huge storage unit for carbon, but only so long as it stays frozen. Biomass and organic material trapped in frozen ground cannot contribute to atmospheric carbon concentrations, however, once it thaws and starts to rot, heterotrophic microorganisms respire using the organic material and release carbon dioxide as a waste product, just like we do when we breathe. This is worrying enough, but anaerobic bacteria are also hard at work in thawing permafrost, and the waste product of their metabolic activity is not carbon dioxide, but methane.
Carbon dioxide and methane are both greenhouse gases that occur naturally in earth’s atmosphere, and both have been supplemented by anthropogenic (human) activity, especially in the past century, a process which is largely to blame for contemporary climate warming (IPCC, 2007). Methane, however is a far more potent greenhouse gas than carbon dioxide – it has been estimated that methane has a warming effect at least 25 times greater than an equal mass of carbon dioxide (Shindell et al, 2009). In northern Sweden the melting of permafrost has actually led to a reduction in carbon emissions, because newly released water has prevented air from reaching the buried organic matter. However, although emissions have reduced by 13%, the resultant warming has increased by 50% due to anaerobic bacteria releasing methane in place of aerobic bacteria providing carbon dioxide (Johansson et al, 2006).
Right now there is approximately 850 Gigatonnes of carbon in the atmosphere, and current estimates of the volume of carbon in the permafrost put it at around 1400 Gigatonnes (NSIDC, 2013). This doesn’t necessarily mean that all of this carbon is going to rot and become incorporated into the atmosphere, but it illustrates a huge reserve of carbon that could potentially contribute catastrophically to the greenhouse effect. The permafrost IS melting, and the result IS increased carbon dioxide and methane emissions into the atmosphere. It will only require a few percent of the stored carbon from the permafrost to equal our current anthropogenic emissions and cause climate chaos.
The potential for extreme feedbacks is clear – more warming could cause permafrost to melt, release carbon in the form of carbon dioxide and methane and result in further warming. As we stand, the Arctic is a net carbon sink (it absorbs more carbon than it releases), but how far are we from the tipping point beyond which it slides unstoppably towards net carbon release? My own research has shown that microbes on glacier surfaces contribute significantly to absorbing atmospheric carbon (Cook et al, 2010; 2012), however with enhanced melt these organisms may be washed from the glacier surface to an uncertain fate in the proglacial zone (Stibal et al, 2012).
All of this emphasises the importance of the cryosphere in climate science, and supports the cause to protect, preserve and study the earth’s ice in order to understand as deeply as possible its responses to and forcing of the climate. It also reiterates yet again that our knowledge of climate change is full of uncertainties and unknowns – we don’t know how close we are to irreversible, disastrous changes – many think we are already there (Lovelock, 2009)- but we do know for sure that we are heading in that direction and that it is largely our own fault.
Cook, J; Hodson, A.; Telling, J.; Anesio, A.; Irvine-Fynn, T.; Bellas, C. 2010. The mass-area relationship within cryoconite holes and its implications for primary production. Annals of Glaciology, 51 (56): 106-110
Cook, J.M., Hodson, A.J., Anesio, A.M., Hanna, E., Yallop, M., Stibal, M., Telling, J., Huybrechts, P. 2012. An improved estimate of microbially mediated carbon fluxes from the Greenland Ice Sheet. Journal of Glaciology, accepted for publication July 2012
Johansson et al. 2006. Decadal vegetation changes in a northern peat land, greenhouse gas fluxes and net radiative forcing’ Globaql Change Biology, 12: 1-18
Lopez, B. 2007. Coldscapes. National Geographic, http://ngm.nationalgeographic.com/2007/12/permafrost/barry-lopez-text.html
Lovelock, J. 2009. The vanishing face of Gaia: a final warning. Penguin, ISBN: 0141039256
NSIDC (2013). All about frozen ground: methane and frozen ground. http://nsidc.org/cryosphere/frozenground/methane.html
Stibal, M, Telling, J, Cook, J., Mak, K. M., Hodson, A. & Anesio, AM. 2012. Environmental controls on microbial abundance and activity on the Greenland ice sheet: a multivariate approach. Microbial Ecology, 63: 74-84