26th January 2011.
A major new study published in Reviews of Geophysics* in December 2010 puts the spotlight on methane emissions from natural sources and asks the question, how might they both affect and be affected by future climate change.
The authors conclude, based on a comprehensive review of recent literature, that ‘significant increases in methane emissions are likely, and catastrophic emissions cannot be ruled out’.
Major uncertainties surround the impact and timescale of several important feedback processes in the global methane cycle. How will natural methane emissions from wetlands, permafrost areas and methane hydrate deposits respond to climate change? At the most extreme, one can envisage a scenario in which permafrost melts, the carbon-rich wetland areas increase and the methanogens up their rate of production in response to greater warmth, which in turn promotes release of biogenic volatile organic compounds, these additional BVOCs reduce the potential for atmospheric oxidation of methane by competing for OH radicals, and finally, under further warming, hydrates become unstable and release their vast store of methane, as may have happened at the Palaeocene-Eocene Thermal Maximum.
In reality, the authors acknowledge that this ‘perfect storm’ of methane emissions is likely to be countered by negative feedback processes such as the drying out of some wetlands and reduced BVOC emission efficiency. But the point remains that the strength and relative timing of both positive and negative feedbacks are currently poorly understood and the potential for significant increases in methane emissions exists.
When asked which gaps in current knowledge he considered the most important, co-author Olivier Boucher of the Met Office listed “…wetland processes and their sensitivity to climate change, permafrost dynamics and its interactions with vegetation, fire and hydrological processes, the transient aspects of marine hydrate destabilisation and the fate of methane emitted in the ocean”.
*O’Connor, F.M., Boucher, O., Gedney, N., Jones, C.D., Folberth, G.A., Coppell, R., Friedlingstein, P., Collins, W.J., Chappellaz, J., Ridley, J. & Johnson, C.E. 2010, “Possible role of wetlands, permafrost, and methane hydrates in the methane cycle under future climate change: A review”, Reviews of Geophysics, vol. 48, no. 4.