Old carbon reservoirs were not important in the deglacial methane budget

M.N.Dyonisius, V.V.Petrenko, A.M.Smith, Q.Hua, B.Yang, J.Schmitt, J. Beck, B.Seth, M.Bock, B.Hmiel, I.Vimont, J.A.Menking, S.A. Shackleton, D.Baggenstos, T. K. Bauska,R. H. Rhodes, P.Sperlich, R. Beaudette, C.Harth, M.Kalk, E.J.Brook, H. Fischer, J.P.Severinghaus, R.F.Weiss

Explanation: We have found, using measurements of carbon-14 in atmospheric methane from air bubbles trapped in ice, that future large releases of methane from melting permafrost and marine methane hydrate is very unlikely.  The logic is that we found no signature of old methane in the atmosphere during the last major abrupt warming that the boreal region experienced (11,000 years ago).  But methane hydrates surely melted because the temperature increase was 5-10 C in just a few decades.  So the only explanation is that methane-eating microbes in the oxygenated upper few centimeters of the tundra consumed all the methane before it could make it out to the atmosphere.  We conclude that this is what will happen again during the anthropogenic warming.

So in a realm where bad news is everywhere, at least there is one small piece of good news.

Abstract: Permafrost and methane hydrates are large, climate-sensitive old carbon reservoirs that have the potential to emit large quantities of methane, a potent greenhouse gas, as the Earth continues to warm. We present ice core isotopic measurements of methane from the last deglaciation, which is a partial analog for modern warming. Our results show that methane emissions from old carbon reservoirs in response to deglacial warming were small (<19 teragrams of methane per year, 95% confidence interval) and argue against similar methane emissions in response to future warming. Our results also indicate that methane emissions from biomass burning in the pre-Industrial Holocene were 22 to 56 teragrams of methane per year (95% confidence interval), which is comparable to today.

Link to Paper: https://science.sciencemag.org/content/367/6480/907#:~:text=Our%20results%20show%20that%20methane,in%20response%20to%20future%20warming.

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