It ain't necessarily so on sea rise

Because CH4 in the atmosphere oxidizes to CO2 over a period of 12 years and for decades the concentration of CH4 in the atmosphere has been either stable or rising. In other words, CH4 has been and is entering the atmosphere at a rate which over short periods is equal to and over longer periods is higher than the rate of its loss due to the photochemical process resulting in its conversion to CO2. Because CH4 is being released as a result of permafrost degradation and ocean warming at an increasing rate, we know that its future concentration in the atmosphere will continue to rise and the rate may accelerate.

Accordingly at any point in time the GWP of CH4 is more accurately its GWP during its lifetime of ~12 years rather than the 100 year span most frequently cited. There is a political imperative but no scientific basis for selecting a 100 year span. The 5AR calculates the GWP as 84 over a 20 year period is much closer to the lifetime of CH4 in the atmosphere, yet is rarely used.

Carbon Emissions

None of the climate models used by the IPCC factors in the permafrost feedback.

The 5AR asserts that CH4 emissions associated with Arctic permafrost degradation have remained unchanged since 1980 and constitute <1% of global methane emissions – Table 6.8 (pdf). Indeed, the Bottom-Up measure shows that total natural emissions declined by 8 gigatonnes in the decade 2000-09 compared to the decade 1980-89. But can this be true given that Arctic permafrost is degrading and contains vast quantities of biota and methane gas?

Offshore, the Arctic continental shelf is estimated to contain over 2,200 gigatonnes of carbonincluding 500 gigatonnes in permafrost covered seabed sediments and 700 gigatonnes in gaseous form in the hydrate stability zones.

Water over the Siberian continental shelf is warming resulting in permafrost degradation. Seabed sediments at a depth of over 50 meters beneath the seabed have been found to be free of permafrost, permitting CH4 gas on and under the continental shelf to supersaturate and percolate through covering seawater.

Seawater covering the Siberian Continental Shelf is ≤ 40 meters deep so seabed emissions have no chance of being oxidized and enter the atmosphere as CH4 and this is occurring at increasing levels. CH4 in the atmosphere above the shelf has been measured at concentration regionally reaching ~8ppm compared to a global average of ~1.8 ppm.

Onshore permafrost is estimated to contain ~1,500 gigatonnes of carbon largely in the form biota which, with permafrost degradation, could result in release to the atmosphere of up to 160 gigatonnes by 2100. It is estimated that >95% will be in the form of CO2 with the balance as CH4.

Onshore estimates of the rate of permafrost degradation and CH4 release are likely to be underestimates because (a) the former excludes the warming effect of bacterial activity and phytoplankton, accelerating methanogen activity and permafrost melting and: (b) release of CH4 to the atmosphere is likely to be much higher than an estimated ≤5% of total emissions for three reasons.

1. Archea and other methanogens are active and able to produce CH4 from biota in sub-zero conditionsas well as at higher temperatures. It is unclear that bacteria (methanotrophs) can convert CH4 to CO2 in oxic conditions on or near the land surface at temperatures below 0°C.

2. CH4 gas is converted to CO2 when it percolates from anoxic production conditions into those where oxygen is abundant and bacteria can oxidize it. It is unlikely that bacteria would be able to oxidize a very high quantum of CH4 (in excess of 95%) before much of it escapes to the atmosphere – particularly in the absence of sphagnum moss (uncommon on permafrost land) with which methanotrophs have a symbiotic relationship and act most efficiently.