Summer hydrographic data (1920–2009) show a dramatic warming of the bottom water layer over the eastern Siberian shelf coastal zone (<10 m depth), since the mid-1980s, by 2.1°C. We attribute this warming to changes in the Arctic atmosphere. The enhanced summer cyclonicity results in warmer air temperatures and a reduction in ice extent, mainly through thermodynamic melting. This leads to a lengthening of the summer open?water season and to more solar heating of the water column. The permafrost modeling indicates, however, that a significant change in the permafrost depth lags behind the imposed changes in surface temperature, and after 25 years of summer seafloor warming (as observed from 1985 to 2009), the upper boundary of permafrost deepens only by ~1 m. Thus, the observed increase in temperature does not lead to a destabilization of methane-bearing subsea permafrost or to an increase in methane emission. The CH4 supersaturation, recently reported from the eastern Siberian shelf, is believed to be the result of the degradation of subsea permafrost that is due to the long-lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent Arctic climate changes. A significant degradation of subsea permafrost is expected to be detectable at the beginning of the next millennium. Until that time, the simulated permafrost table shows a deepening down to ~70 m below the seafloor that is considered to be important for the stability of the subsea permafrost and the permafrost-related gas hydrate stability zone.

Several authors report that impacts of climate change on infrastructure in the Arctic are already evident. Damage to infrastructure and engineering structures in permafrost regions are often linked to observed increase in air temperature over the last 10 to 20 years. However, these reports do not show in detail how the change in air temperature may affect the active layer thickness and permafrost temperature at specific sites and for specific structures in the Arctic. This paper presents the results of a study of the impact of climate change on Arctic infrastructure based on historical meteorological records. The temperature data are used together with a numerical model to evaluate the possible warming of permafrost at depth, and theoretical impacts on pile foundation capacity at specific sites in the Arctic. Results from permafrost model forced by several GCM-based climatic projections are used to construct the predictive map indicating threats to infrastructure due to potential weakening of the frozen ground.

The permafrost regions currently occupy about one quarter of the Earth’s land area. Climate-change scenarios indicate that global warming will be amplified in the polar regions, and could lead to a large reduction in the geographic extent of permafrost. Development of natural resources, transportation networks, and human infrastructure in the high northern latitudes has been extensive during the second half of the twentieth century. In areas underlain by ice-rich permafrost, infrastructure could be damaged severely by thaw-induced settlement of the ground surface accompanying climate change. Permafrost near the current southern margin of its extent is degrading, and this process may involve a northward shift in the southern boundary of permafrost by hundreds of kilometers throughout much of northern North America and Eurasia. A long-term increase in summer temperatures in the high northern latitudes could also result in significant increases in the thickness of the seasonally thawed layer above permafrost, with negative impacts on human infrastructure located on ice-rich terrain. Experiments involving general circulation model scenarios of global climate change, a mathematical solution for the thickness of the active layer, and digital representations of permafrost distribution and ice content indicates potential for severe disruption of human infrastructure in the permafrost regions in response to anthropogenic climate change. A series of hazard zonation maps depicts generalized patterns of susceptibility to thaw subsidence. Areas of greatest hazard potential include coastlines on the Arctic Ocean and parts of Alaska, Canada, and Siberia in which substantial development has occurred in recent decades.

The Circumpolar Active Layer Monitoring (CALM) program, established in the early 1990s, was designed to observe temporal and spatial variability of the active layer, near-surface permafrost parameters, and their response to changes and variations in climatic conditions. CALM is the world’s primary source of information about the active layer. Auxiliary information includes air temperature, soil moisture, soil temperature at different depth, snow cover, soil composition, and landscape characterization and frost heave and thaw subsidence. Metadata include detailed site descriptions and photographs for each site. Several groups of sites have been used to create regional maps of activelayer thickness. CALM data are distributed through the program’s website (www.udel.edu/Geography/calm), and are also archived in and distributed through the Frozen Ground Data Center at the University of Colorado. This paper provides details about the nature, availability, and uses of data from the CALM network

Active layer monitoring is an important component of efforts to assess the affects of global change in permafrost environments. In this study we used data from 13 (1995-2007) years of spatially oriented field observations at a series of 16 representative Circumpolar Active Layer Monitoring (CALM) sites in northern Alaska to examine temporal and spatial trends in active-layer thickness and its relation to climatic, surface, and subsurface conditions. The observation strategy consisted of measuring active-layer thickness on regular 1 ha and 1 km2 grids representative of environmental conditions on Alaska’s North Slope. The measurement program also involves continuous air and soil temperature monitoring, periodic frost heave and thaw subsidence using Differential Global Position System (DGPS) as well as landscape, vegetation, and soil characterization. This paper showcases CALM observation procedures and analysis designed to monitor processes and detect changes not anticipated in the original CALM protocol of the early 1990s.

Several model-based assessments predict a discernible increase in the depth of seasonal thawing and circumpolar-scale warming of permafrost by the mid-21st century. Quantitative estimates of the environmental and socioeconomic impacts of changing climate in northern regions require robust projection of changes in permafrost, which in turn depend on the availability of appropriate models and forcing data. We examined four high-resolution, hemispheric-scale gridded sets of monthly temperature and precipitation constructed using different interpolation routines and reanalysis of data from a large number of weather stations. At many of 455 Russian weather stations, the four data sets depart from empirical mean annual air temperatures averaged over the 15-year period by 1–2 °C and in cumulative daily positive temperature sums (degree days of thawing) by more than 200 °C days. A permafrost model, forced with the gridded climatic data sets, was used to calculate the large-scale characteristics of permafrost in northern Eurasia. We analyzed zonal-mean air and ground temperatures, depth of seasonal thawing, and area occupied by near-surface permafrost in Eurasia north of 45 °N. The 0.5–1.0 °C difference in zonal-mean air temperature between the data sets translates into a range of uncertainty of 10–20% in estimates of near-surface permafrost area, which is comparable to the extent of changes projected for the following several decades. We conclude that more observations and theoretical studies are needed to improve characterization of baseline climatic conditions and to narrow the range of uncertainties in model-based permafrost projections.

Large amounts of soil carbon deposited in permafrost may be released due to deeper seasonal thawing under the climatic conditions projected for the future. An increase in the volume of the available organic material together with the higher ground temperatures may lead to enhanced emission of greenhouse gasses. Particular concerns are associated with methane, which has a much stronger greenhouse effect than an equal amount of CO2. Production of methane is favored in the wetlands, which occupy up to 0.7 million km2 in Russian permafrost regions and have accumulated about 50 Gt of carbon (Gt C). We used the permafrost model and several climatic scenarios to construct projections of the soil temperature and the depth of seasonal thawing. To evaluate the effect of such changes on the volume of the seasonally thawing organic material, we overlaid the permafrost projections on the digitized geographically referenced contours of 59 846 wetlands in the Russian Arctic. Results for the mid-21st century climate indicated up to 50% increase in the volume of organic substrate in the northernmost locations along the Arctic coast and in East Siberia, where wetlands are sparse, and a relatively small increase by 10%–15% in West Siberia, where wetlands occupy 50%–80% of the land. We developed a soil carbon model and used it to estimate the changes in the methane fluxes due to higher soil temperature and increased substrate availability. According to our results, by mid-21st century the annual net flux of methane from Russian permafrost regions may increase by 6–8 Mt, depending on climatic scenario. If other sinks and sources of methane remain unchanged, this may increase the overall content of methane in the atmosphere by approximately 100 Mt, or 0.04 ppm, and lead to 0.012 ?C global temperature rise.

The permafrost regions occupy about 25% of the Northern Hemisphere’s terrestrial surface, and more than 60% of that of Russia. Warming, thawing, and degradation of permafrost have been observed in many locations in recent decades and are likely to accelerate in the future as a result of climatic change. Changes of permafrost have important implications for natural systems, humans, and the economy of the northern lands. Results from mathematical modeling indicate that by the mid-21st century, near-surface permafrost in the Northern Hemisphere may shrink by 15%–30%, leading to complete thawing of the frozen ground in the upper few meters, while elsewhere the depth of seasonal thawing may increase on average by 15%–25%, and by 50% or more in the northernmost locations. Such changes may shift the balance between the uptake and release of carbon in tundra and facilitate emission of greenhouse gases from the carbon-rich Arctic wetlands. Serious public concerns are associated with the effects that thawing permafrost may have on the infrastructure constructed on it. Climate-induced changes of permafrost properties are potentially detrimental to almost all structures in northern lands, and may render many of them unusable. Degradation of permafrost and ground settlement due to thermokarst may lead to dramatic distortions of terrain and to changes in hydrology and vegetation, and may lead ultimately to transformation of existing landforms. Recent studies indicate that nonclimatic factors, such as changes in vegetation and hydrology, may largely govern the response of permafrost to global warming. More studies are needed to better understand and quantify the effects of multiple factors in the changing northern environment.