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A significant portion of the large amount of carbon (C) currently stored in soils of the permafrost region in the Northern Hemisphere has the potential to be emitted as the greenhouse gases CO2 and CH4 under a warmer climate. In this study we evaluated the variability in the sensitivity of permafrost and C in recent decades among land surface model simulations over the permafrost region between 1960 and 2009. The 15 model simulations all predict a loss of near-surface permafrost (within 3 m) area over the region, but there are large differences in the magnitude of the simulated rates of loss among the models (0.2 to 58.8 × 103 km2 yr−1). Sensitivity simulations indicated that changes in air temperature largely explained changes in permafrost area, although interactions among changes in other environmental variables also played a role. All of the models indicate that both vegetation and soil C storage together have increased by 156 to 954 Tg C yr−1 between 1960 and 2009 over the permafrost region even though model analyses indicate that warming alone would decrease soil C storage. Increases in gross primary production (GPP) largely explain the simulated increases in vegetation and soil C. The sensitivity of GPP to increases in atmospheric CO2 was the dominant cause of increases in GPP across the models, but comparison of simulated GPP trends across the 1982–2009 period with that of a global GPP data set indicates that all of the models overestimate the trend in GPP. Disturbance also appears to be an important factor affecting C storage, as models that consider disturbance had lower increases in C storage than models that did not consider disturbance. To improve the modeling of C in the permafrost region, there is the need for the modeling community to standardize structural representation of permafrost and carbon dynamics among models that are used to evaluate the permafrost C feedback and for the modeling and observational communities to jointly develop data sets and methodologies to more effectively benchmark models.

Permafrost is known to occur in high mountainous areas such as the Daisetsu Mountains in Japan, which are located at the southernmost limit of the permafrost distribution in the world. In this study, areas with climatic conditions suitable for sustaining permafrost in the Daisetsu Mountains are projected using bias-corrected and downscaled climate model outputs and statistical relationships between surface air temperatures and permafrost areas. Using freezing and thawing indices, the size of the area in the Daisetsu Mountains where climatic conditions were suitable for permafrost were estimated to be approximately 150 km2 in 2010. Under the RCP8.5 scenario, this area is projected to decrease to about 30 km2 by 2050 and it is projected to disappear by around 2070. Under the RCP2.6 scenario, the area is projected to decrease to approximately 20 km2 by 2100. The degradation of mountain permafrost could potentially affect the stability of trekking trails due to slope displacement, and it may also have deleterious effects on current alpine ecosystems. It is therefore important to accurately monitor changes in the mountain ecosystem environment and to implement measures to adapt to an environment that is projected to change significantly in the future. [ABSTRACT FROM AUTHOR]

The degradation of permafrost is a large source of uncertainty in understanding the behaviour and projecting the future impacts of Earth's climate system. The spatial distributions of soil organic carbon (SOC) and ground ice (ICE) provide essential information for the assessment and projection of risks and impacts of permafrost degradation. However, uncertainties regarding the geographical distribution and estimated range of the total amount of stored carbon and ice are still substantial. A numerical soil organic carbon–ground ice budget model, SOC-ICE-v1.0, that considers essential aspects of carbon and hydrological processes in above-ground and subsurface environments and permanently frozen ground (permafrost) and land cover changes (ice sheets and coastlines) was developed to calculate the long-term evolution of local SOC and ICE. The model was integrated to cover the last 125 kyr – from the last interglacial to date for areas north of 50 ∘ N at 1 ∘ resolution – to simulate the balance between accumulation and dissipation of SOC and ICE. Model performance was compared with observation-based data and evaluated to assess allogenic (external) impacts on soil carbon dynamics in the circum-Arctic region on a glacial–interglacial timescale. Despite the limitation of forcing climate data being constructed on the basis of a single Greenland ice core dataset, the simulated results successfully reproduced temporal changes in northern SOC and ICE, consist with current knowledge. The simulation also captured regional differences in different geographical and climatic characteristics within the circum-Arctic region. The model quantitatively demonstrated allogenic controls on soil carbon evolution represented by a key parameter that reflects climatological and topo-geographical factors. The resulting circum-Arctic set of simulated time series can be compiled to produce snapshot maps of SOC and ICE distributions for past and present assessments or future projection simulations. Examples of 1 ∘ resolution maps for the Last Glacial Maximum and mid-Holocene periods were provided. Despite a simple modelling framework, SOC-ICE-v1.0 provided substantial information on the temporal evolution and spatial distribution of circum-Arctic SOC and ICE. Model improvements in terms of forcing climate data, improvement of SOC and ICE dynamics, and choice of initial values are, however, required for future research. [ABSTRACT FROM AUTHOR]

To date, the treatment of permafrost in global climate models has been simplified due to the prevailing uncertainties in the processes involving frozen ground. In this study, we improved the modeling of permafrost processes in a state-of-the-art climate model by taking into account some of the relevant physical properties of soil such as changes in the thermophysical properties due to soil freezing. As a result, the improved version of the global land surface model was able to reproduce a more realistic permafrost distribution at the southern limit of the permafrost area by increasing the freezing of soil moisture in winter. The improved modeling of permafrost processes also had a significant effect on future projections. Using the conventional formulation, the predicted cumulative reduction of the permafrost area by year 2100 was approximately 60% (40–80% range of uncertainty from a multi-model ensemble) in the RCP8.5 scenario, while with the improved formulation, the reduction was approximately 35% (20–50%). Our results indicate that the improved treatment of permafrost processes in global climate models is important to ensuring more reliable future projections. [ABSTRACT FROM AUTHOR]

Permafrost is a large reservoir of soil organic carbon, accounting for about half of all the terrestrial storage, almost equivalent to twice the atmospheric carbon storage. Hence, permafrost degradation under global warming may induce a release of a substantial amount of additional greenhouse gases, leading to further warming. In addition to gradual degradation through heat conduction, the importance of abrupt thawing or erosion of ice-rich permafrost has recently been recognized. Such ice-rich permafrost has evolved over a long timescale (i.e., tens to hundreds of thousands of years). Although important, knowledge on the distribution of vulnerability to degradation, i.e., location and stored amount of ground ice and soil carbon in ice-rich permafrost, is still limited largely due to the scarcity of accessible in situ data. Improving the future projections for the Arctic using the Earth System Models will lead to a better understanding of the current vulnerability distribution, which is a prerequisite for conducting climatic and biogeochemical assessment that currently constitutes a large source of uncertainty. In this study, present-day circum-Arctic distributions (north of 50° N) in ground ice and organic soil carbon content are produced by a new approach to combine a newly developed conceptual carbon-ice balance model, and a downscaling technique with the topographical and hydrological information derived from a high-resolution digital elevation model (ETOPO1). The model simulated the evolution of ground ice and carbon for the recent 125 thousand years (from the Last Interglacial to the present) at 1° resolution. The 0.2° high-resolution circum-Arctic maps of the present-day ground ice and soil organic carbon, downscaled from the 1° simulations, were reasonable compared to the observation-based previous maps. These data, together with a map of vulnerability of ice-rich permafrost to degradation served as initial and boundary condition data for model improvement and the future projection of additional greenhouse gas release potentially caused by permafrost degradation. [ABSTRACT FROM AUTHOR]

GIS analysis of the French database of Pleistocene periglacial features allows an improved evaluation of the maximum extent of past permafrost. The distribution of typical ice-wedge pseudomorphs does not extend south of 47°N and therefore suggests that widespread discontinuous permafrost did not affect the regions south of the Paris Basin. The exclusive presence of sand wedges with primary infill between 45 and 47°N, mainly in the periphery of coversand areas, suggests that thermal contraction cracking of the ground occurred together with sand drifting in a context of deep seasonal frost or sporadic discontinuous permafrost, unfavourable for the growth of significant ground-ice bodies. The latitudinal variation of the wedge dimensions clearly shows that the sand wedges were located in the southern margin of the area affected by thermal contraction. The proposed map of Pleistocene permafrost in France partially reconciles field data with palaeoclimatic simulations. The remaining discrepancies may arise primarily from the time lag between the Last Permafrost Maximum ( c. 31-24 ka) and the Last Glacial Maximum (21 ka). Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

High-resolution maps of potential frozen ground distribution in South America have been produced for the present day (0 ka) and the Last Glacial Maximum (21 ka). Surface air temperature outputs from global climate models (GCMs) of the recent Paleoclimate Model Intercomparison Project were used for the reconstructions, and then downscaled from regional to local scales, with the help of a 1 arc-minute digital elevation model. Their validity was examined using fieldwork-based evidence and knowledge. The downscaled map for the present day successfully reproduces the presence of permafrost in the Andes, a task at which original coarse-resolution GCM output maps failed. The map also shows close correspondence with instrumental observations. Similarly, the downscaled distribution of 21 ka frozen ground shows overall consistency with geomorphological and/or palaeoenvironmental reconstructions. Areal coverage of potential permafrost for all of South America is estimated at 139 000 km2 for today and 435 000 km2 for 21 ka, mostly along the Andean mountain ranges. Regional inspections, however, show divergence from field-observed features, attributed to microclimatic effects and past permafrost conditions. For southern Patagonia, and especially the eastern lowlands, the diagnosed lower limit for permafrost is about 1000 m asl, whereas field evidence at lower altitudes indicates the presence of either permafrost or deep seasonal frost. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A high-resolution map of potential frozen ground distribution in NE Asia (90-150° E, 25-60° N) at the period of the Last Permafrost Maximum ( LPM, c. 21 000 years ago) was dually reconstructed by means of a statistical classification using air freezing and thawing indices and a topographical downscaling using a digital relief model ( ETOPO1). Background LPM climate data were derived from global climate model simulations of the Paleoclimate Model Intercomparison Project, Phase II ( PMIP2). The reconstructed LPM map shows the southward shift of the southern limit of climate-driven permafrost by 400-1500 km, with the greatest advance in the western sector (90-110° E), encompassing an area from central Siberia to most of the Altai area. The advance of environmentally conditional permafrost and seasonally frozen ground was greatest in the eastern sector (110-150° E), with an average shift of about 450 km. The descent of the lower limit of LPM alpine permafrost was in the range of 400-800 m. A comparison of the reconstructed map with published literature shows that this method, simplistically constructed yet effectively recognizing seasonality, continentality and topography, captures local features better than more elaborate methods. The sensitivity examination of a constant atmospheric lapse rate shows that altitudes of 2000-5000 m a.s.l. were most sensitive, though with only a limited effect on overall LPM distribution. [ABSTRACT FROM AUTHOR]

Permafrost is an important climate factor of the cold-region environments, known to evolve over a long timescale. Although direct observations are required for the exact determination of presence, this is difficult especially in remote areas. An indirect assessment of permafrost zonation can help in estimating the probable extents and providing an understanding of its spatiotemporal variability under different climate. In this paper, we adopt a previously defined indirect assessment method using freezing and thawing indices, which was revised and evaluated against new observation-based dataset. The revised method was applied to time-series of the circum-Arctic environment for the past 122 kyr constructed from a Greenland ice core, present-day reanalysis climatology, and a glacial isostatic adjustment model, and subsequently, examined in terms of the aggregation, persistence, and retreat of permafrost. Permafrost zones over exposed land varied between 9.11 million km2 (interglacial) and 26.7 million km2 (glacial); the maximum extent of subsea and subglacial permafrost was 7.7 million km2 and 0.5 million km2, respectively. The climatic sensitivity of its areal extent was examined for the meridional temperature gradient in the polar amplification (increase by 0.2 million km2 [ °C / 10 ° ]−1 when warming occurs) and the global mean annual temperature (decrease by 4.3 million km2 °C −1). [ABSTRACT FROM AUTHOR]

The Yedoma layer, a permafrost layer containing a massive amount of underground ice in the Arctic regions, is reported to be rapidly thawing. In this study, we develop the Permafrost Degradation and Greenhouse gasses Emission Model (PDGEM), which describes the thawing of the Arctic permafrost including the Yedoma layer due to climate change and the greenhouse gas (GHG) emissions. The PDGEM includes the processes by which high-concentration GHGs (CO2 and CH4) contained in the pores of the Yedoma layer are released directly by dynamic degradation, as well as the processes by which GHGs are released by the decomposition of organic matter in the Yedoma layer and other permafrost. Our model simulations show that the total GHG emissions from permafrost degradation in the RCP8.5 scenario was estimated to be 31-63 PgC for CO2 and 1261-2821 TgCH4 for CH4 (68th percentile of the perturbed model simulations, corresponding to a global average surface air temperature change of 0.05–0.11 °C), and 14-28 PgC for CO2 and 618-1341 TgCH4 for CH4 (0.03–0.07 °C) in the RCP2.6 scenario. GHG emissions resulting from the dynamic degradation of the Yedoma layer were estimated to be less than 1% of the total emissions from the permafrost in both scenarios, possibly because of the small area ratio of the Yedoma layer. An advantage of PDGEM is that geographical distributions of GHG emissions can be estimated by combining a state-of-the-art land surface model featuring detailed physical processes with a GHG release model using a simple scheme, enabling us to consider a broad range of uncertainty regarding model parameters. In regions with large GHG emissions due to permafrost thawing, it may be possible to help reduce GHG emissions by taking measures such as restraining land development. [ABSTRACT FROM AUTHOR]