The linked references (& associated articles) indicates that evidence for the risks of significant GHG emissions from permafrost degradation is increasing:
Donatella Zona. Biogeochemistry: Long-term effects of permafrost thaw, Nature (2016). DOI: 10.1038/537625ahttp://www.nature.com/nature/journal/v537/n7622/full/537625a.html
Abstract: “Carbon emissions from the Arctic tundra could increase drastically as global warming thaws permafrost. Clues now obtained about the long-term effects of such thawing on carbon dioxide emissions highlight the need for more data.”
Min Jung Kwon et al. Long-term drainage reduces CO2 uptake and increases CO2 emission on a Siberian floodplain due to shifts in vegetation community and soil thermal characteristics, Biogeosciences (2016). DOI: 10.5194/bg-13-4219-2016http://www.biogeosciences.net/13/4219/2016/
Abstract. With increasing air temperatures and changing precipitation patterns forecast for the Arctic over the coming decades, the thawing of ice-rich permafrost is expected to increasingly alter hydrological conditions by creating mosaics of wetter and drier areas. The objective of this study is to investigate how 10 years of lowered water table depths of wet floodplain ecosystems would affect CO2 fluxes measured using a closed chamber system, focusing on the role of long-term changes in soil thermal characteristics and vegetation community structure. Drainage diminishes the heat capacity and thermal conductivity of organic soil, leading to warmer soil temperatures in shallow layers during the daytime and colder soil temperatures in deeper layers, resulting in a reduction in thaw depths. These soil temperature changes can intensify growing-season heterotrophic respiration by up to 95 %. With decreased autotrophic respiration due to reduced gross primary production under these dry conditions, the differences in ecosystem respiration rates in the present study were 25 %. We also found that a decade-long drainage installation significantly increased shrub abundance, while decreasing Eriophorum angustifolium abundance resulted in Carex sp. dominance. These two changes had opposing influences on gross primary production during the growing season: while the increased abundance of shrubs slightly increased gross primary production, the replacement of E. angustifolium by Carex sp. significantly decreased it. With the effects of ecosystem respiration and gross primary production combined, net CO2 uptake rates varied between the two years, which can be attributed to Carex-dominated plots' sensitivity to climate. However, underlying processes showed consistent patterns: 10 years of drainage increased soil temperatures in shallow layers and replaced E. angustifolium by Carex sp., which increased CO2 emission and reduced CO2 uptake rates. During the non-growing season, drainage resulted in 4 times more CO2 emissions, with high sporadic fluxes; these fluxes were induced by soil temperatures, E. angustifolium abundance, and air pressure.
Anna K. Liljedahl et al. Pan-Arctic ice-wedge degradation in warming permafrost and its influence on tundra hydrology, Nature Geoscience (2016). DOI: 10.1038/ngeo2674http://www.nature.com/ngeo/journal/v9/n4/full/ngeo2674.html
Abstract: “Ice wedges are common features of the subsurface in permafrost regions. They develop by repeated frost cracking and ice vein growth over hundreds to thousands of years. Ice-wedge formation causes the archetypal polygonal patterns seen in tundra across the Arctic landscape. Here we use field and remote sensing observations to document polygon succession due to ice-wedge degradation and trough development in ten Arctic localities over sub-decadal timescales. Initial thaw drains polygon centres and forms disconnected troughs that hold isolated ponds. Continued ice-wedge melting leads to increased trough connectivity and an overall draining of the landscape. We find that melting at the tops of ice wedges over recent decades and subsequent decimetre-scale ground subsidence is a widespread Arctic phenomenon. Although permafrost temperatures have been increasing gradually, we find that ice-wedge degradation is occurring on sub-decadal timescales. Our hydrological model simulations show that advanced ice-wedge degradation can significantly alter the water balance of lowland tundra by reducing inundation and increasing runoff, in particular due to changes in snow distribution as troughs form. We predict that ice-wedge degradation and the hydrological changes associated with the resulting differential ground subsidence will expand and amplify in rapidly warming permafrost regions.”
Extract: “"The authors report that the net effect of draining in their study is an increase in the amount of CO2 emitted to the atmosphere, which will ultimately magnify climate change," Zona wrote in her commentary.
Zona published a study about the effects of drainage in permafrost earlier this year in the journal Nature Geoscience. Additionally, she and fellow SDSU ecologist Walt Oechel, along with colleagues at several other institutions, published another study last year showing that the emission of methane, another greenhouse gas, is highest in the Arctic during the region's cold season. That was surprising, as most scientists thought little if any greenhouse gases escaped the frozen soil during the cold season.”
T. Schneider von Deimling, G. Grosse, J. Strauss, L. Schirrmeister, A. Morgenstern, S. Schaphoff, M. Meinshausen, and J. Boike (2015), “Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity”, Biogeosciences, 12, 3469–3488, 2015 www.biogeosciences.net/12/3469/2015/
Abstract: “High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrams of carbon (Pg-C) (68 % range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 PgC (68 % ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40 % of total permafrost-affected radiative forcing in the 21st century (upper 68 % range). We infer largest CH4 emission rates of about 50 TgCH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03–0.14 ◦C (68 % ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 ◦C (68 % range) to simulated global mean surface air temperatures in the year 2300.”
Extract: “What’s happening today really started about 22,000 years ago, when the world began to warm at the end of the last Ice Age.
None of the permafrost thawing beneath millions of lakes across the Arctic is accounted for in global predictions about climate change—it’s “a gap in our climate modeling,” says Katey Walter Anthony, a University of Alaska Fairbanks researcher who studies permafrost thaw across Alaska and Siberia.
But according to the latest estimates, published last year in Biogeosciences, thawing beneath lakes in yedoma permafrost—the oldest, most carbon-rich type of permafrost found in Alaska and Siberia—could, by 2100, increase the amount of methane accumulated in the Earth’s atmosphere by as much as 2.6 billion metric tons. By 2300, that could spike to 10 billion metric tons. Before 2000, yedoma permafrost hadn’t thawed enough to begin forming these methane lakes. Now there’s no looking back. “It’s like the food for microbes has been locked away in the freezer for 30,000 years,” Walter Anthony says, “and now the freezer door is open.” The degree of warming that implies is catastrophic. “The methane causes climate warming, which causes more permafrost to thaw, which causes more gas to be produced, which causes more warming, so you get a positive feedback loop.” “