Quantification of active-layer thickness (ALT) over seasonally frozen terrains is critical to understand the impacts of climate warming on permafrost ecosystems in cold regions. Current large-scale process-based models cannot characterize the heterogeneous response of local landscapes to homogeneous climatic forcing. Here we linked a climate-permafrost model with a machine learning solution to indirectly quantify soil conditions reflected in the edaphic factor using high resolution remote sensor products, and then effectively estimated ALT across space and time down to local scales. Our nine-year field measurements during 2014-2022 and coincident high resolution airborne hyperspectral, lidar, and spaceborne sensor products provided a unique opportunity to test the developed protocol across two permafrost experiment stations in lowland terrains of Interior Alaska. Our developed model could explain over 60% of the variance of the field measured ALT for estimating the shallowest and deepest ALT in 2015 and 2019, suggesting the potential of the designed procedure for projecting local varying terrain response to long-term climate warming scenarios. This work will enhance the National Aeronautics and Space Administration's Arctic-Boreal Vulnerability Experiment's mission of combining field, airborne, and spaceborne sensor products to understand the coupling of permafrost ecosystems and climate change.

Permafrost degradation poses serious threats to both natural and human systems through its influence on ecological-hydrological processes, infrastructure stability, and the climate system. The Arctic and the Third Pole (Tibetan Plateau, TP hereafter) are the two northern regions on Earth with the most extensive permafrost areas. However, there is a lack of systematic comparisons of permafrost characteristics and its climate and ecoenvironment between these two regions and their susceptibility to disturbances. This study provides a comprehensive review of the climate, ecosystem characteristics, ground temperature, permafrost extent, and active-layer thickness, as well as the past and future changes in permafrost in the Arctic and the TP. The potential consequences associated with permafrost degradation are also examined. Lastly, possible connections between the two regions through land-ocean-atmosphere interactions are explored. Both regions have experienced dramatic warming in recent decades, characterized by Arctic amplification and elevation-dependent warming on the TP. Permafrost temperatures have increased more rapidly in the Arctic than on the TP, and will likely be reinforced under a future high emission scenario. Near-surface permafrost extents are projected to shrink in both regions in the coming decades, with a more dramatic decline in the TP. The active layer on the TP is thicker and has substantially deepened, and is projected to thicken more than in the Arctic. Widespread permafrost degradation increases geohazard risk and has already wielded considerable effects on the human and natural systems. Permafrost changes have also exerted a pronounced impact on the climate system through changes in permafrost carbon and land-atmosphere interactions. Future research should involve comparative studies of permafrost dynamics in both regions that integrate long-term observations, high-resolution satellite measurements, and advanced Earth System models, with emphasis on linkages between the two regions.

The Qinghai-Tibet Plateau (QTP) is characterized by its extreme climate and dominated by periglacial processes. Permafrost conditions vary greatly, and the recent changes on the QTP are not well known in the hinterland. Here, we examine the changes in climate and permafrost temperatures in several different regions. Climate data were obtained from three weather stations from 1957 to 2019. Annual mean air temperature (T-a) has gradually increased at .031 degrees C/yr-.039 degrees C/yr. Climate warming has been more rapid in the past two decades, particularly during the cold season (November to February). Precipitation has also been slowly increasing during the instrumental record. However, there is pronounced heterogeneity in the seasonal distribution of precipitation, with very little falling between October and April. Ground temperatures and active-layer thickness (ALT) have been investigated over similar to 20 years at five sites representative of the hinterland of the QTP. These sites are located along the Qinghai-Tibet Highway, which crosses the permafrost zone and traverses the mountainous area and basin areas. Annual mean ground temperatures within the active layer (T-al similar to 1 m depth) indicate recent ground warming at all sites, at rates near .05 degrees C/yr. The ALT at five sites has been increasing steadily by 2-9 cm/yr, with an average of 4.6 cm/yr. The temperature near the permafrost table (T-ps) has been increasing at .01 degrees C/yr and .06 degrees C/yr, with an average of .03 degrees C/yr. Permafrost temperatures at 15 m depth (T-g) have been increasing by about .01 degrees C/yr-.02 degrees C/yr. The southern boundary (AD site) of the permafrost has warmed the least among the five locations. In high mountainous areas where permafrost temperatures are low (e.g., KLS site), the annual mean T-g has increased by nearly .02 degrees C/yr. The rate of permafrost warming at a basin site (BLH), with relatively high ground temperatures, was approximately .01 degrees C/yr. The GIPL2.0 model simulation results indicate that the annual mean permafrost temperature at 1 m depth at these sites will increase by .6 degrees C-1.8 degrees C in the next 100 years (to 2100) and that ALT will increase by similar to 40-100 cm. We also discuss the impacts of permafrost changes on the environment and infrastructure on the QTP. This study provides useful information to understand observed and anticipated permafrost changes in this region, under different shared socioeconomic pathways, which will allow engineers to develop adaptation measures.

The observed global warming has significant impacts on permafrost. Permafrost changes modify landscapes and cause damage to infrastructure. The main purpose of this study was to estimate permafrost temperatures and active-layer thicknesses during the Holocene intervals with significantly warmer-than-present climates-the Atlantic (5500 years BP), Subboreal (3500 years BP) and Subatlantic (1000 years BP) optimums. Estimates were obtained using the ready-to-use models derived by G.M. Feldman, as well as mathematical modeling taking account of the paleogeography of the Holocene warm intervals. The data obtained were analyzed to reveal the regional patterns of warming impacts on different permafrost landscapes. The study results will be useful in predicting future permafrost changes in response to climate warming.

The relevance of the problem under review is explained by the need to study the thermal response of permafrost to the modern climate change. Evolution of the thermal state of grounds has been studied with a view to evaluate the effects of modern climate warming on permafrost in Central Yakutia. The leading method to study this problem is the arrangement and performance of long-term monitoring observations of the permafrost thermal state that enable quantitative evaluation of the thermal response of upper permafrost layers to climatic fluctuations of recent decades. The analysis of long-term records from weather stations in the region has clearly revealed one of the highest increasing trends in the mean annual air temperature in northern Russia. Quantitative relationships in the long-term variability of ground thermal parameters, such as ground temperature at the bottom of the active layer, at the bottom of the annual heat exchange layer, and active thaw depth, have been established. The thermal state dynamics of the annual heat exchange layer under climate warming indicates that both warm and cold permafrost are thermally stable. Short-term variability of the snow accumulation regime is the main factor controlling the thermal state of the ground in permafrost landscapes. The active-layer thickness is characterized by low interannual variability and exhibits little response to climate warming, with no statistically meaningful increasing or decreasing trend. The results of ground thermal monitoring can be extended to similar landscapes in the region, providing a reliable basis for predicting heat transfer in natural landscapes.

Soil properties such as soil organic carbon (SOC) stocks and active-layer thickness are used in earth system models (ESMs) to predict anthropogenic and climatic impacts on soil carbon dynamics, future changes in atmospheric greenhouse gas concentrations, and associated climate changes in the permafrost regions. Accurate representation of spatial and vertical distribution of these soil properties in ESMs is a prerequisite for reducing existing uncertainty in predicting carbon-climate feedbacks. We compared the spatial representation of SOC stocks and active-layer thicknesses predicted by the coupled Model Intercomparison Project Phase 5 (CMIP5) ESMs with those predicted from geospatial predictions, based on observation data for the state of Alaska, USA. For the geospatial modeling, we used soil profile observations (585 for SOC stocks and 153 for active-layer thickness) and environmental variables (climate, topography, land cover, and surficial geology types) and generated fine-resolution (50-m spatial resolution) predictions of SOC stocks (to 1-m depth) and active-layer thickness across Alaska. We found large inter-quartile range (2.5-5.5 m) in predicted active-layer thickness of CMIP5 modeled results and small inter-quartile range (11.5-22 kg m(-2)) in predicted SOC stocks. The spatial coefficient of variability of active-layer thickness and SOC stocks were lower in CMIP5 predictions compared to our geospatial estimates when gridded at similar spatial resolutions (24.7 compared to 30% and 29 compared to 38%, respectively). However, prediction errors, when calculated for independent validation sites, were several times larger in ESM predictions compared to geospatial predictions. Primary factors leading to observed differences were (1) lack of spatial heterogeneity in ESM predictions, (2) differences in assumptions concerning environmental controls, and (3) the absence of pedogenic processes in ESM model structures. Our results suggest that efforts to incorporate these factors in ESMs should reduce current uncertainties associated with ESM predictions of carbon-climate feedbacks. (C) 2016 The Authors. Published by Elsevier B.V.

Wilhelm et al. (2015) employed the widely used Stefan and Kudryavtsev equations to predict the maximum active-layer thickness (ALT) on Amsler Island, Western Antarctic Peninsula. Their predictions far exceed the observations of ALT reported from other parts of the region. Here, I demonstrate that the values of ALT are significantly overestimated by the predictive equations because the authors incorrectly assumed that little or no latent heat of phase change is absorbed during thawing. Although the area is the warmest in the Antarctic Peninsula region, with a rapid increase in air temperature and permafrost temperatures close to 0 degrees C, the active layer is likely to be substantially thinner than values predicted by Wilhelm et al. (2015). Copyright (c) 2016 John Wiley & Sons, Ltd.

Active-layer thickness (ALT) is one of the most robust measures used to assess the impact of climate change on terrestrial permafrost. Testing of a handheld dynamic cone penetrometer showed that it was capable of measuring ALT with the same level of accuracy as conventional methods in boreal and tundra sites in eastern Siberia. The penetrometer also characterised the vertical structure of ground hardness within the active layer. The vertical profile of penetrometer measurements corresponded closely with soil plasticity and the liquid limit in high-centred polygons produced by thermokarst subsidence in dry grassland areas at a boreal site at Churapcha. The ALT was markedly deeper (>70cm) at gravelly slope points adjacent to a wet tundra plain (<50cm) in a CALM grid (R8) at Tiksi. Overall, the penetrometer is considered to provide an accurate and informative proxy for rapidly assessing the spatial heterogeneity and interannual changes in ALT. Copyright (c) 2016 John Wiley & Sons, Ltd.

Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6cm) promoted increased ALTs, whereas deeper soil moisture (11-16cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate.

Between 2002 and 2012, daily soil temperature measurements were made at 10 sites within five alpine ecosystems in the Beiluhe area of the central Qinghai-Tibet Plateau. Changes in freeze-thaw occurrence, active-layer thickness and near-surface permafrost temperature in barren, desert grassland, alpine steppe and alpine meadow ecosystems indicate that alpine ecosystems are sensitive to climate variability. During this time, the average onset of spring thawing at 50-cm depth advanced by at least 16 days in all but the barren alpine settings, and the duration of thaw increased by at least 14 days for all but the desert grassland and barren ecosystems. All sites showed an increase in active-layer thickness (ALT) and near-surface permafrost temperature: the average increase of ALT was similar to 4.26 cm/a and the average increase in permafrost temperatures at 6 m and 10 m depths were, respectively, similar to 0.13 degrees C and similar to 0.14 degrees C. No apparent trend in mean annual air temperature was detected at the Beiluhe weather station. However, an increasing trend in precipitation was measured. This suggests that the primary control on the ALT increase was an increase in summer rainfall and the primary control on increasing permafrost temperature was probably the combined effects of increasing rainfall and the asymmetrical seasonal changes in subsurface soil temperatures. (C) 2014 Elsevier B.V. All rights reserved.