The stability of arctic permafrost and the carbon it contains are currently threatened by a rapidly warming climate. Burial Lake, situated in northwestern arctic Alaska, is underlain by continuous permafrost and has a uniquely rich set of paleoclimate proxy data that comprise a 40-ka record of climate and environmental change extending well into Marine Isotope Stage (MIS) 3. Here, we examine the relationship between erosion, subsurface hydrology, and primary productivity from the Burial Lake sediments to improve our understanding of the links between climate, hydrology, sediment transport, and carbon mobility. The record is developed with radiocarbon (14C) age-offsets from two independent methods used to date the lake sediments: 1) 14 C measurements on paired bulk sediment and plant macrofossils from the same stratigraphic layer of lake sediment and 2) ramped pyrolysis- oxidation (RPO) 14 C analysis that separates fractions of organic carbon (OC) from a single bulk sediment sample based on thermochemical differences through continuous heating. As lakes capture and archive OC transported from the watershed, changes in the amount and relative age of permafrost-derived OC mobilized during past climatic variations can be documented by examining how age-offsets change over time. The Burial Lake sediment revealed higher age-offsets during the cold Last Glacial Maximum (LGM; 29-17 ka) than the comparatively warmer post-glacial ( 17 ka-present) and the MIS 3 interstadial ( 40-29 ka) periods. The relatively warm, wet climate of the post-glacial period promoted both terrestrial and aquatic productivity, resulting in increased OC deposition, and it likely favored transport via subsurface flow of dissolved OC (DOC) sourced from soils. This resulted in a greater flux of contemporary OC relative to ancient OC into the lake sediment, lowering the average age offset to 2 ka. In contrast, the low-productivity conditions of the LGM resulted in slow soil accumulation rates, leaving ancient OC in a shallower position in the soil profile and allowing it to be easily eroded in the form of particulate OC (POC). Although the amount of total OC deposited in the lakebed during the LGM is small relative to post-glacial deposition, the majority is ancient, which leads to a relatively high average age offset of 9 ka. Finally, climate and environmental conditions of the MIS 3 interstadial were intermediate between those of the post-glacial and the LGM. As with post-glacial sediments, a relatively large amount of OC is present; however, the vast majority of it is ancient (more similar to the LGM), and it produces an average age offset of 6 ka. The Burial Lake radiocarbon record demonstrates the complexities of the thaw and mobilization of permafrost OC in arctic Alaska, including the balance between production, transport, deposition, remobilization, and preservation. This record highlights the importance of considering factors that both enhance and inhibit erosion (i.e. vegetation cover, lake level, precipitation) and the mechanisms of OC transport (i.e. subsurface flow or erosion) in predictions of future permafrost response to changes in climate.

The state of the cryosphere in tropical regions is of great importance because the temperature around the glaciers, permafrost and snow cover always fluctuates near the melting point. These thermal conditions and their high sensitivity to climate change cause the accelerated disappearance of these elements; therefore, it is important to know the climatic factors that regulate them, as well as the physical characteristics of each cryospheric element. Unlike glaciers, permafrost and snow cover have not been widely studied. In recent decades, the study of the glacial and periglacial environment has been carried out in intertropical mountains. However, despite the altitude of their relief and the frequent occurrence of snowfall in tropical high mountains, the conditions that determine such events have been barely analyzed; and in the case of Mexico, the volume of snowfall and its thickness have not been quantified either, as well as their corresponding duration. Consequently, this work is aimed to analyze the temperature and precipitation conditions that determine the snowfall at the higher part of the Nevado de Toluca volcano; at the same time, the conditions of the cryotic climate and their possible implication on the surface are studied. The analysis of data from 1965 to 2016, using frequency statistics, allowed to realize that snowfall occurs with low intensity, its accumulation being less than 10 cm thick and 10 mm of snow water equivalent, which causes the snowpack to stay only a few weeks on average. At the same time, it was determined that there is a significant increase in the number of freeze-thaw cycles. Therefore, due to the climate conditions and their influence on the mountain surface, it is probable that the bedrock is subject to a greater gelifraction dynamics, and the unconsolidated soil surface increases; the combination of the above could cause a greater geomorphological dynamic over time, particularly due to debris flows, and by water and wind erosion of the surface. This work is intended to serve as a reference for the high mountain environment in the intertropical regions.

Using the daily snow cover data at 24-km resolution from the Interactive Multi-sensor Snow and Ice Mapping System snow cover analysis, this study describes the variability in Tibetan Plateau (TP) snow cover (TPSC) at multiple time scales with a focus on the intraseasonal time scale (10-90 days). TPSC demonstrates variability over a wide range of temporal scales, but the annual cycle is generally dominant. Synoptic-scale variability, seasonal variability and interannual and long-term changes make small contributions to the total daily variability in TPSC. Intraseasonal variability (ISV) is dominant over most of the central and eastern TP and explains 22-40% of the total variability and leads to obvious variations in TPSC over periods shorter than a season. The ISV of TPSC is more active in the cold season than in the warm season. Specifically, the ISV over the Changtang Plateau explains approximately 50% of the total variability of snow cover in the cold season and is even more dominant than the annual cycle. Possible influences of regional atmospheric circulations on TPSC are also examined. TPSC variability is highly correlated with regional surface air temperature (SAT) and precipitation at an intraseasonal time scale. TPSC and SAT tend to have a simultaneous relationship, while anomalous precipitation leads to subsequent TPSC variations with a lag of approximately 5 days and a positive relationship. Such relationships are the result of intraseasonal variations in regional atmospheric circulation. The anomalous adiabatic heating induced by vertical ascending motion leads to tropospheric temperature variations. Furthermore, the horizontal advection of moisture and apparent moisture sink, which are induced by anomalous moisture supply and snow evaporation anomalies, respectively, lead to anomalous moisture associated with changes in the TPSC.

The aim of this paper is to comprehensively evaluate the abiotic factors that influence changes in the annual growth rates of selected species of tundra plants (Saxifraga oppositifolia L and Salbc polaris Wahlenb.). The study was conducted in the area of the Fuglebergsletta coastal plain, in the vicinity of the Polish Polar Station (Wedel Jarlsberg Land, SW Spitsbergen). Relationships between the studied phenomenon and basic environmental factors and climate indicators were evaluated. The spatial variation of land surface temperatures (LST) was determined, as were the effects of the physical and chemical properties of soils and the spring melting of snow cover on growth rates. It has been argued that the spatial and seasonal variability of annual growth is determined by the rate at which snow cover disappears and by soil moisture, which determines plants' access to water. Soil moisture depends on soil particle size distribution and weather; it is regulated by the supply of snowmelt water and rainfall as well as by the depth of the top layer of permafrost (thaw depth), which determines the level of groundwater during the growing season. The spatial characteristics of the process of the disappearance of seasonal snow cover are co-determined by the morphology of the substrate and the physical properties of the soil. An important but destructive role is played by thawing episodes, which are increasingly frequent in the winter season, 'rain-on-snow' events, and glaze ice. The values of correlation coefficients indicate a positive role for precipitation and negative influence of temperature. The higher the temperature (along with low precipitation), the lesser the extent of plant growth. The observed trend towards warming in polar areas does not inevitably lead to an increase in biomass production. An increase in temperature during the growing season does not necessarily promote plant growth, but rather indicates drought stress caused by the lowering of groundwater levels related to the increase in thaw depth.

Heterogeneous Holocene climate evolutions in the Northern Hemisphere high latitudes are primarily determined by orbital-scale insolation variations and melting ice sheets. Previous inter-model comparisons have revealed that multi-simulation consistencies vary spatially. We, therefore, compared multiple model results with proxy-based reconstructions in Fennoscandia, Greenland, north Canada, Alaska and Siberia. Our model-data comparisons reveal that data and models generally agree in Fennoscandia, Greenland and Canada, with the early-Holocene warming and subsequent gradual decrease to 0 ka BP (hereinafter referred as ka). In Fennoscandia, simulations and pollen data suggest a 2 degrees C warming by 8 ka, but this is less expressed in chironomid data. In Canada, a strong early-Holocene warming is suggested by both the simulations and pollen results. In Greenland, the magnitude of early-Holocene warming ranges from 6 degrees C in simulations to 8 degrees C in delta O-18-based temperatures. Simulated and reconstructed temperatures are mismatched in Alaska. Pollen data suggest strong early Holocene warming, while the simulations indicate constant Holocene cooling, and chironomid data show a stable trend. Meanwhile, a high frequency of Alaskan peatland initiation before 9 ka can reflect a either high temperature, high soil moisture or large seasonality. In high-latitude Siberia, although simulations and proxy data depict high Holocene temperatures, these signals are noisy owing to a large spread in the simulations and between pollen and chironomid results. On the whole, the Holocene climate evolutions in most regions (Fennoscandia, Greenland and Canada) are well established and understood, but important questions regarding the Holocene temperature trend and mechanisms remain for Alaska and Siberia. (C) 2017 Elsevier Ltd. All rights reserved.

Multiple studies demonstrate Northwest Alaska and the Alaskan North Slope are warming. Melting permafrost causes surface destabilization and ecological changes. Here, we use thermistors permanently installed in 1996 in a borehole in northwestern Alaska to study past, present, and future ground and subsurface temperature change, and from this, forecast future permafrost degradation in the region. We measure and model Ground Surface Temperature (GST) warming trends for a 10 year period using equilibrium Temperature-Depth (TD) measurements from borehole T96-012, located near the Red Dog Mine in northwestern Alaska part of the Arctic ecosystem where a continuous permafrost layer exists. Temperature measurements from 1996 to 2006 indicate the subsurface has clearly warmed at depths shallower than 70 m. Seasonal climate effects are visible in the data to a depth of 30 m based on a visible sinusoidal pattern in the TD plots that correlate with season patterns. Using numerical models constrained by thermal conductivity and temperature measurements at the site, we show that steady warming at depths of similar to 30 to 70 m is most likely the direct result of longer term (decadal-scale) surface warming. The analysis indicates the GST in the region is warming at similar to 0.44 +/- 0.05 degrees C/decade, a value consistent with Surface Air Temperature (SAT) warming of similar to 1.0 +/- 0.8 degrees C/decade observed at Red Dog Mine, but with much lower uncertainty. The high annual variability in the SAT signal produces significant uncertainty in SAT trends. The high annual variability is filtered out of the GST signal by the low thermal diffusivity of the subsurface. Comparison of our results to recent permafrost monitoring studies suggests changes in latitude in the polar regions significantly impacts warming rates. North Slope average GST warming is similar to 0.9 +/- 0.5 degrees C/decade, double our observations at RDM, but within error. The RDM warming rate is within the warming variation observed in eastern Alaska, 0.36-0.71 degrees C/decade, which suggests changes in longitude produce a smaller impact but have warming variability likely related to ecosystem, elevation, microclimates, etc. changes. We also forward model future warming by assuming a 1D diffusive heat flow model and incorporating latent heat effects for permafrost melting. Our analysis indicates similar to 1 to 4 m of loss at the upper permafrost boundary, a similar to 145 +/- 100% increase in the active layer thickness by 2055. If warming continues at a constant rate of similar to 0.44 +/- 0.05 degrees C/decade, we estimate the 125 m thick zone of permafrost at this site will completely melt by similar to 2150. Permafrost is expected to melt by similar to 2200, similar to 2110, or similar to 2080, if the rate of warming is altered to 0.25, 0.90, or 2.0 degrees C/decade, respectively, as an array of different climate models suggest. Since our model assumes no advection of heat (a more efficient heat transport mechanism), and no accelerated warming, our current prediction of complete permafrost loss by 2150 may overestimate the residence time of permafrost in this region of Northwest Alaska. (C) 2016 The Authors. Published by Elsevier B.V.

Global warming as quantified by surface air temperature has been shown to be approximately linearly related to cumulative emissions of CO2. Here, a coupled state-of-the-art Earth system model with an interactive carbon cycle (BNU-ESM) was used to investigate whether this proportionality extends to the complex Earth system model and to examine the climate system responses to different emission pathways with a common emission budget of man-made CO2. These new simulations show that, relative to the lower emissions earlier and higher emissions later (LH) scenario, the amount of carbon sequestration by the land and the ocean will be larger and Earth will experience earlier warming of climate under the higher emissions earlier and lower emissions later (HL) scenario. The processes within the atmosphere, land, and cryosphere, which are highly sensitive to climate, show a relatively linear relationship to cumulative CO2 emissions and will attain similar states under both scenarios, mainly because of the negative feedback between the radiative forcing and ocean heat uptake. However, the processes with larger internal inertias depend on both the CO2 emissions scenarios and the emission budget, such as ocean warming and sea level rise.

Soil moisture dynamics and their temporal trends in the Czech Republic are forced by various drivers. The methodology of applying remotely sensed data with both high temporal and spatial resolutions provides detailed insight and objective quantification of the causes of changes in soil moisture patterns. Our analysis of temporal trends indicates that shifts in drought severity between 1961 and 2012 (especially in the April, May, and June period, which displayed a 50% increase in drought probability between 1961-1980 and 2001-2012) are alarming. We found that increased global radiation and air temperature together with decreased relative humidity (all statistically significant at the 0.05 level) led to increases in the reference evapotranspiration in all months of the growing season; this trend was particularly evident in April, May, and August, when more than 80% of the territory displayed an increased demand for soil water. This finding was shown to be consistent with the measured pan evaporation (1968-2012) that was characterized by increasing trends, particularly during the April-June period. These changes, in combination with the earlier end of snow cover and the earlier start of growing season (up to 20days in some regions), led to an increased actual evapotranspiration at the start of growing season that tends to deplete the soil moisture earlier, leaving the soil more exposed to the impacts of rainfall variability. These results support concerns related to the potentially increased severity of drought events in Central Europe. The reported trend patterns are of particular importance with respect to the expected climate change, given the robustness and consistency of the trends shown and the fact that they can be aligned with the existing climate model projections.