Modelling past and future permafrost conditions in Svalbard

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Background and objectives
Changes in the spatial extent and temperatures of permafrost are generally taken as indications of climate change (e.g.Lachenbruch and Marshall, 1986).Permafrost is continuous in the parts of the high-arctic archipelago Svalbard not covered by glaciers (75-82 • N) (e.g.Humlum et al., 2003;Liestøl, 1977).The location of Svalbard in the northern part of the warm North-Atlantic ocean current makes its climate especially sensitive to atmospheric and oceanic changes (e.g.Aagaard and Carmack, 1989).Accordingly, a 4-6 • C warming and +5% precipitation increase are projected by Global Circulation Models (GCM) for Svalbard by 2100 according to the SRES A1b emission scenario (Benestad, 2005;ACIA, 2005).Since permafrost inhibits prominent groundwater flow and stabilizes frozen, unconsolidated sediments, the degradation of permafrost is likely to have wide influences on the processes shaping the physical and Introduction

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Full human environment (e.g.Williams and Smith, 1989;French, 1996).Temperature profiles through the permafrost reflect to some extent the history of the ground surface temperature, which, however, is closely coupled to air temperature and snow cover (e.g.Lachenbruch and Marshall, 1986;Goodrich, 1982).A Svalbard ground surface temperature reconstruction, based on a heat conduction inversion model, indicated a warming of the permafrost surface of 1.5 • C ± 0.5 • C over the last 6-8 decades (Isaksen et al., 2000) in the bedrock-dominated site of Janssonhaugen.Between 1999 and 2009 the permafrost has warmed there by 0.9 • C at 20 m depth.Significant warming is detectable down to at least 60 m depth, and the present decadal warming rate at the permafrost surface (c. 2 m depth) are on the order of 0.07 • Ca −1 , with indications of accelerated warming during the last decade (Isaksen et al., 2007b).
In this paper, we used ground temperatures collected in five boreholes, which were mainly established during the International Polar Year project TSP-Norway (Thermal state of permafrost; Christiansen et al., 2010) to calibrate a 1-D heat conduction model and establish statistical relationships between local ground surface temperatures (GST) and surface air temperature (SAT) at a nearby meteorological station.This framework enables the reconstruction of borehole temperatures since 1912 using a historical record of air temperature.Further, we assess the possible future permafrost conditions and the related uncertainties, by using downscaled air temperature projections from an ensemble of GCMs for the 21st century (Benestad, 2008).

Permafrost and air temperature observations
We used four locations studying five boreholes, situated in the central and western part of Spitsbergen, and covering an roughly west-east transect from the most maritime west-coast at Kapp Linn é to the inland in the Longyearbyen/Adventdalen area (Fig. 1, Table 1).An overview over location, landforms, stratigraphy and detailed instrumentation of these sites is given by Christiansen et al. (2010).Site information particularly relevant for this study is given below and in Table 1.Three boreholes were Introduction

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Full drilled in bedrock with little (some cm) sediment cover and thin snow cover (Janssonhaugen, Kapp Linn é borehole, BH 1), whereas the other boreholes have a considerable sediment cover consisting of 1 m regolith at Gruvefjellet, a solifluction sheet with 6-7 m diamicton (Endalen) and beach ridge sandy to pebbly sediments at Kapp Linn é BH 2.
The two boreholes at Kapp Linn é are less than 100 m apart from each other, differing only by the amount of sediment cover.At all boreholes ground temperature is recorded automatically, usually in 1 or 6 h intervals, with the longest series from Janssonhaugen (Isaksen et al., 2000).On-site meteorological observations are available from Janssonhaugen, Kapp Linne and Gruvefjellet.

Historical meteorological data
West Spitsbergen has three official meteorological stations with longer time series, Svalbard Airport (close to Longyearbyen), Isfjord Radio (Kapp Linn é) and Ny-Ålesund (Fig. 1).Mean annual air temperature (MAAT) for the standard normal period 1961-1990 for Svalbard Airport is −6.7 • C, and mean annual precipitation is 190 mm.The Isfjord Radio station shows slightly more maritime conditions, having higher precipitation and means surface air temperature is 1.6 • C higher.The temperature variability is highly correlated between the three stations (r 2 > 0.9), with the largest differences between Svalbard Airport and Isfjord Radio.The homogenised monthly temperature series of Svalbard Airport (1912 -present) (Nordli and Kohler, 2004) is a composite of several shorter series of measurements carried out at a few nearby sites (Fig. 2).MAAT has again increased.The main characteristics of Svalbard's air temperature development since the end of the Little Ice age is the two cold decades in the 1910s and 1960s and the warm spell around the 1930s and the 1950s.Since 1990 a significant positive trend is seen.Inter-annual variations are large, and are mostly driven by variations in winter temperatures, while summer temperatures exhibit little variation.This pattern clearly demonstrate the maritime setting of the archipelago (cf.Førland and Hannssen-Bauer, 2003).

GCM scenario data for Svalbard Airport
For Svalbard Airport monthly air temperatures covering the 20th and 21st Centuries are available (Fig. 2) based on empirically statistically downscaling an ensemble of GCM scenarios (Benestad, 2008).Large-scale monthly mean surface air temperature (SAT) was used as predictor to derive the local monthly temperature for Svalbard Airport.The calibration of the downscaling models was based on the 40 year reanalysis of the European Centre of Medium-range Weather forecast (ERA40; Uppala et al., 2005) and the station climate archive of the Norwegian Meteorological Institute.The calibration and projection were carried out for each of the calendar months separately, and subsequently assembled for the whole year.This set of global climate model simulations is from the multi-model World Climate Research Programme (WCRP) Coupled Model Intercomparison Project (CMIP3; Meehl et al., 2007) of the most recent Special Report Emission Scenario (SRES) A1b (in which atmospheric CO 2 reaches 720 ppm by 2100) reported for the Intergovernmental Panel on Climate Change (IPCC) Assessment Report 4 (AR4; Solomon et al., 2007).A common framework of empirical orthogonal functions was used to ensure that similar large-scale spatial patterns in the GCMs as in the ERA40 were used to predict the local temperature for Svalbard Airport (Benestad, 2001).
The Arctic Climate Impact Assessment (ACIA, 2005) provided more detailed analysis on the Arctic, for which an enhanced greenhouse gas warming is expected to be more pronounced than elsewhere on the planet.Introduction

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Ground temperatures
The ground temperatures in the boreholes vary mainly according to elevation, distance to sea, land form types, and by variations in snow cover and near surface ice-and water content.In the year from summer 2008 to summer 2009, boreholes had mean ground temperatures (MGT) at 15 m depth ranging from −3.2 • C at the west coast at Kapp Linn é and in the valley bottom of Endalen to −5.4 • C and c. −6 • C further inland and at higher elevation at Janssonhaugen (Fig. 3e-h).The Endalen borehole has higher ground temperatures, which is related to the snow cover, and moister summer ground conditions due to receiving runoff from upslope areas (Christiansen et al., 2010).The active layer thicknesses (ALT) varied between around 2 m in the bedrock sites of Kapp Linn é and Jannsonhaugen to close to 1 m in the Endalen site and Gruvefjellet sites (Christiansen et al., 2010).
On each site ground surface temperature (GST) is measured, either by a separate data logger in c. 5 cm depth or by the first thermistor located at 0 m depth in the borehole.The records from Kapp Linn é, Gruvefjellet and Janssonhaugen reveal a relatively close coupling between GST and SAT, while at Endalen, coupling is complicated by more pronounced snow and vegetation covers and their associated insulating properties (Fig. 3d).We calculated the ratios of annual sums of freezing or thawing degree days of GST to those of SAT, referred to as n-factors n T and n F , respectively (e.g.Smith and Riseborough, 2002).For the non-vegetated sites, the thawing n-factor n T ≥ 1 (Kapp Linn é 1.00, Gruvefjell 1.18, Janssonhaugen 1.13), symptomatic for equal or warmer summer conditions at the ground surface than at screen level (2 m above ground).At the Endalen site, n T was considerable lower (0.83), equivalent to lower summer GST than summer SAT.The freezing n-factor (n F ) depends mainly on snow cover, with n F < 1 indicating a weak coupling between GST and SAT due to the insulating effect of the snow cover.The Endalen site showed lowest n F with 0.78, while at all the other sites n F was between 0.95 and 1. Introduction

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Full These n-factors were then used to derive GST series for each site from the long-term SAT series  and from the multi-model ensemble SAT scenarios  for Svalbard Airport.This was achieved by first adjusting the SAT from Svalbard Airport to the elevation of the considered site utilizing a simple regression to the sites with meteorological information (Kapp Linn é, Janssonhaugen, Gruvefjellet), with a r 2 > 0.9, or a lapse rate (Endalen).Subsequently, we applied n-factorization.The r 2 > 0.75 was achieved for all sites during the calibration period (Fig. 3a-d).

Heat flow model
The subsurface temperature distribution was simulated by numerically solving the transient 1-D heat equation for non-constant coefficients (see also Farbrot et al., 2007 for more details): (Williams and Smith, 1989).As boundary conditions, we prescribe time series of GST and the geothermal heat flux Q geo = 65 mW m −2 at depth.The thermal properties of the ground are described by density ρ, thermal conductivity k and heat capacity c.
The presence of water in the substrate has a twofold effect on the thermal properties.First, the thermal properties of water and ice are different to those of the matrix, and we consider effective values as a linear mixture of values for the substrate and the corresponding ones for the volumetric content of water or ice, depending on the temperature conditions.Secondly, the water content affects the thermal properties during the phase transitions.During freezing or thawing, the latent heat associated with these phase changes is released or consumed, respectively.In our model runs, we apply an apparent heat capacity to consider the change of latent heat L due to phase changes of the pore water within a small temperature interval of ± 0.1 Full Further, any effects of heat advection related to water flow in the active layer are neglected in our modelling.The heat conduction equation (Eq. 1) was discretized along the borehole depth using finite differences and subsequently solved by applying the method of lines.

Calibration and model initialisation
To achieve a first impression of the parameter space, the mean apparent thermal diffusivity (κ a ) was determined for the different layers at the borehole locations following Williams and Smith (1989): where m is the slope of a linear fit to the natural logarithm of the maximum amplitude A(z) versus depth, assuming that the period p is one year.Effective diffusivities ranged from around 0.7-2.6 × 10 −7 m 2 s −1 in the surface sediment layers to 10-19 × 10 −7 m 2 s −1 in sedimentary bedrock (Table 1).
All borehole models in this study were calibrated to closely reproduce measured ground temperatures (Fig. 4).Each calibration was started from the observed distribution of ground temperatures, at least one month after drilling, when thermal disturbance from the drilling was assumed to be negligible.The model domain was 150 m discretized in constant steps of 0.1 m.For thermal conductivity and bedrock density literature values were used and fine-adjusted during calibration (Table 1).Main calibration parameter was the water content, influencing the effective damping and retardation of the temperature signal.The calibration period was between 500 and 680 days (see Table 1).The calibrated models show good correspondence between observed and modelled temperatures yielding r 2 -values of above 0.9 (Fig. 4).However, the Gruvefjellet site is the most weakly constrained one because of coarsely-spaced sensors and lacking information from depth below 5 m.Introduction

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Full  4).The model performed well in closely reproducing measured temperature time series at various depths as well as the active layer thickness (Fig. 4).
To reproduce a realistic temperature distribution at depth below the lowermost sensor (Jansonhaugen 100 m, otherwise ∼ 5-40 m), the models were initialised using colder conditions than today.For all boreholes we used SATs derived from the mean MAAT 1912-1922 from Svalbard Airport (−8 • C) and superimpose a harmonic function to mimic the seasonal variation of SAT.The amplitude of that variation was derived from the observed variations of the respective SAT records (typically r 2 > 0.8).The models were then spun up over 200 years or until steady state was reached.

Past development
Janssonhaugen is the best calibrated and validated series, as data on deeper ground temperatures is available below 50 m.Our model was forced using site-specific GST series (Fig. 3a-d) which in turn were derived from the instrumental record from Svalbard Airport (Fig. 2).Model results show for all sites a 1-3 • C permafrost temperature increase over the last century at 10 m depth; at 50 m depth ground temperatures have increased by < 1 • C (Fig. 5a-b), and at 100 m depth only minor variations were modelled.The largest changes were modelled at Kapp Linn é BH1, presumably because of the assumed low water content and the associated low thermal buffering capacity (Fig. 5).At all sites the modelled ALT shows some inter-annual variation but no clear trend between c. 1920 and c. 1990, later more substantial warming have led to an increase in ALT (Fig. 5c-d).The simulated ALT increase since the 1990s is between 1.25 cm a −1 (Gruvefjellet) to 3 cm a −1 (Kapp Linn é BH1 and Janssonhaugen).For the Introduction

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Full sediment-rich locations Endalen and Kapp Linn é BH2, the change rates in ALT were similar with 1.25 cm a −1 and 2.2 cm a −1 , respectively (Fig. 5c).

Future development
All together 32 individual SAT scenarios derived from downscaling a multi-model GCM ensemble were used to further derive GST series for the individual borehole locations, which in turn provided the surface boundary conditions to drive the ground heat conduction models.For Janssonhaugen, the model was initialised from observed January 2000 temperatures, and the others were started from the end of the subsurface temperature reconstruction described above.The uncertainty of the future evolution is demonstrated by the spread of the individual SAT scenarios within the ensemble (Figs. 2 and 6).Here, we present the median of the different results to provide a balanced picture of the potential future development of the ground thermal regime along with the 10% and 90% percentiles to indicate the uncertainty for two of the sites (Figs. 5  and 6).The climate scenario forcing revealed the following major effects of the permafrost thermal state: 1.The expected SAT warming during the 21st century will result in a significant warming in the near-surface layers (Figs. 5 and 6).
2. The spread of the individual scenarios at the depth of zero annual amplitude (ZAA) varies between 5 • C and 2.5 • C, depending on ice/water content and distance to the 0 • C isotherm (Fig. 6).at Gruvefjellet (+0.7 m), Endalen (+1 m), Kapp Linn é BH2 (+2.5 m) and Janssonhaugen (+2 m), the increase is more pronounced at Kapp Linn é BH1 (+8 m) and may lead to the development of taliks.The spread of ALT for the individual scenarios increases towards the end of the period and depends on assumed water/ice content (Fig. 5c).Apart from Gruvefjellet, taliks develop at all other sites for GST scenarios above the 75% percentile.
6. Model results show degradation of permafrost in bedrock sites at low elevations.Contrarily, at sediment sites with a high water content, modelled ground temperatures increase to close to 0 • C, but permafrost conditions still remain stable until 2100.
7. During 2000 and 2009 we have an overlap between scenario and instrumental data at the Janssonhaugen site.The ALT modelled based on the scenario median slightly overestimates modelled ALT when using observed GSTs (Fig. 5d).

Sensitivity to changes in temperature
A sensibility analysis was conducted for the study sites, addressing the effect of temperature changes in different seasons.This was achieved by attenuating the amplitudes above and below 0 • C, respectively, of the GST by a factor between 0 and 1, and extracting the associated ground temperature at 15 m depth and the active layer thicknesses (Fig. 7).The results suggest for a given temperature change that an increase of winter temperature and/or increase of snow cover has a major effect on warming the permafrost, while an increase in summer temperature mainly affects the ALT.However, also the warming during winter affects the ALT.The bedrock sites had a more rapid response both with respect to ALT and ground temperature because of a low water content, with especially quick reactions in the Kapp Linn é BH1 site.Introduction

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Uncertainties and sensitivity
The major uncertainties for this study are related to (1) deficits of the heat conduction model, (2) the spread of the SAT-scenario ensemble and (3) the validity of the statistical relationships between SAT at Svalbard Airport and the GST at the borehole sites.
The heat flow model used in this study does not account for annual or interannual variations of water content in the upper layers, like other model approaches do (e.g.Zhang et al., 2003;Burn and Zhang, 2009).However, only few measurements are available that address these effects at the borehole sites, and the model performed well during calibration, even in the ice-rich site of Endalen.This behaviour is probably related to the generally low water content in the relatively coarse sediments above bedrock and pure bedrock at the borehole sites.Over the period 1912-2000, precipitation has increased (Førland andHanssen-Bauer, 2000, 2003) and a further ∼ 5% increase is expected based on the GCM scenarios (Benestad, 2008;Hanssen-Bauer, 2007).Such an increase in precipitation would furthermore increase the water content of the near-surface, depending on snow re-distribution.However, thicker active layers would release water from thawing of the transient layer (Shur et al., 2005), which is icerich.On the other hand, an increase in ALT and thawing of ground ice may decrease the water content.It is obvious that the drying of the active layer may lead to non-linear responses of the thermal regime, typically intensifying the increase in temperature, as already observed in mountain sites in southern Norway (Farbrot et al., 2010;Isaksen et al., 2010).In our study this is demonstrated for the two Kapp Linn é sites, which show a different response for the ALT projections due to differences in assumed water content.Thus, our estimates here are considered as rather conservative.
Large uncertainties are related to the spread between the individual SAT scenarios.Introduction

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Full variability of the individual scenarios contain information about the thermal responses in the ground, reflecting soil properties and moisture conditions.At sites where temperatures approach 0 • C, the spread is reduced due to the consumption of latent heat associated with thawing, e.g. the Endalen site.This is in accordance with observed warming trends recently published e.g. by Romanovsky et al. (2010a) and Smith et al. (2010) from Russia and North America, respectively.The coupling between SAT at Svalbard Airport and GST at the individual sites depends strongly on snow conditions in terms of snow cover thickness and duration.Here, we have derived GST series from SAT using n-factors, implicitly assuming unchanged snow conditions over the considered period.This may seem somewhat unrealistic given the pronounced warming, especially during winter.A general reduction in snow cover duration would lead to a reduced warming of the ground since the heat loss of the ground would be enhanced during the cold period.Recent studies highlight the effect of snow cover thickness and duration on ground temperatures (e.g.Luetschg et al., 2008), while Engelhardt et al. (2010) showed that differences in the timing of a thick snow cover have a similar influence of ground temperature than different forcing climate scenarios.Recently, Christiansen et al. (2010) and Romanovsky et al. (2010b) demonstrated the large differences of near-surface ground temperatures between two adjacent boreholes with different snow cover in Svalbard.Deeper ground temperatures in turn will tend to be similar because of lateral heat transfer.In our study, however, the values of the n F -factors are close to 1 besides for the Endalen site, indicating little influence of snow on the SAT-GST coupling.Further, the anticipated warming trend would change vegetation towards a larger abundance of higher plants like bushes and thereby alter n T -factors.Those plants are known to trap snow, potentially increasing the GST during winter considerably, even if summer temperatures would decrease somewhat because of increased shading (e.g.Blok et al., 2010;Sharkhuu et al., 2007;Hinzman et al., 2005).
Finally, the SAT-GST relationships employed here assume a constant lapse rate between Svalbard Airport and the study sites.However, lapse rates are not constant Introduction

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Full over time and especially at arctic sites highly depending on sea ice conditions and the general circulation pattern.Svalbard Airport is situated close to the coast, and its temperature especially during winter covaries with sea ice cover.The Svalbard Airport is highly sensitive to the coupled sea ice-ocean-atmosphere system (Benestad et al., 2002) and recently observed shrinkage in Arctic sea-ice cover (Vinje, 2001;Stroeve et al., 2007) suggests that larger differences may be expected further inland e.g. at Endalen, Gruvefjellet and Janssonhaugen today than previously (O.Humlum, personal communication, 2010).In summary, different uncertainties draw in different directions, and the importance of each factor is difficult to quantify or even unknown.We believe, however, that our results provide a fairly realistic picture of consequences of future CO 2 -emissions as specified in the A1b scenario.

Trends and consequences
According to the model the warming since the start of the last century has resulted in a low-gradient temperature profile, which corresponds well with the measured values.
We model a c. +0.5 • C difference between modelled and measured GT at 20 m depth for the Janssonhaugen site, while the overall gradient fits well.The offset is probably due to two main reasons.First, the initial temperature distribution is somewhat speculative and temperature may have been too low, as the former ground temperature history is not known.Secondly, lapse rates may have differed during earlier parts of the last century as mentioned above.For all sites the modelled active layer thicknesses correspond to the measured values from the boreholes within c. ± 0.3 m.
During the last 100 years only minor changes occurred in the modelled ground temperatures, apart from the period since the mid 1990s which were the warmest since the instrumental record started.The last 10-15 years warming can explain almost 50% of the simulated warming in the uppermost 50 m of the permafrost.We clearly see the warm year of 2006/2007, described and analysed in Isaksen et al. (2007a), with a considerable increase in ALT at all sites apart from Gruvefjellet.Individual warm 1890 Introduction

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Full events like that in spring 2006 are important, as the system needs time to recover, as e.g.demonstrated for the Alps after a similar event in 2003 (c.f.Hilbich et al., 2008;Gruber et al., 2004).In general, the active layer change during the recent years, and especially during the last decades is similar to observations in other parts of the world (Romanovsky et al., 2010a;Smith et al., 2010;Zhao et al., 2010;Christiansen et al., 2010).
In Svalbard the temperature variability during summer and winter is different.While summer temperatures are fairly constant between years, the variability of winter temperature is high (Førland et al., 2009).The trends for the entire instrumental SAT record at Svalbard Airport  show that temperatures have increased significantly during spring (MAM, +0.044 • Ca −1 ), winter (DJF, +0.015 • Ca −1 ) and autumn (SON, +0.014 • Ca −1 ), whereas summer (JJA, +0.009 • Ca −1 ) temperatures were more constant during the last century (Førland et al., 2009).Our sensitivity study suggests that the increase of winter temperatures leads to a substantial warming of the permafrost, while the relatively constant summer temperatures have only a minor influence and mainly on the active layer thickness.An exception is the bedrock site at Kapp Linn é BH1, which shows a somewhat faster response also in ALT when winter temperature increases.This explains the low variability of the modelled ALT during large parts of the last century.
For the future development, the ground thermal regime stays relatively stable for reasons discussed above.However, sites close to sea level are modelled to undergo permafrost degradation and to develop taliks.The major effect is the warming of the permafrost, where temperature are modelled to rise to above −2 • C at 20 m depth in the more continental sites and above −1 • C at the lower sites like Endalen and Kapp Linn é.
Such temperature conditions are currently observed within the discontinuous mountain permafrost in e.g. the high mountains of the Norwegian mainland (Christiansen et al., 2010;Farbrot et al., 2010).
Major permafrost changes are mainly to be expected by the end of the 21st century along the coast lines and in the outer parts of the large glacial valleys of

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Full Nordenski öldland (Fig. 8) below 100 m a.s.l., where the permafrost is warmest and where the local settlements are located.These areas are characterized by the presence of mainly marine, raised beach sediments, fluvial and glaciofluvial sediments, partly overlain by eolian, colluvial or alluvial deposits, having a relatively fine matrix (Christiansen et al., 2010).Those sediments are ice-rich, and associated periglacial landforms such as ice wedges, pingos and solifluction sheets or lobes are wide-spread (Christiansen, 2005;Harris et al., 2009;Ross et al., 2007).Addressing the consequences of climate change on certain periglacial processes remains a challenge.The possible thaw of the ice-rich layers in the transitions zone on the top of permafrost has received considerable attention (B üdel, 1982;Shur et al., 2005;Murton et al., 2006).
On one hand, this effects buffers ground warming, on the other hand it may cause a non-linear response if completely thawed.Resulting increases in ALT may in certain areas of Svalbard be associated with unprecedented thaw settlement as ice-rich soils if the upper permafrost layer thaws (Nelson et al., 2001), and in consequence, a marked increase in slope instability (Harris et al., 2001(Harris et al., , 2009;;Davis et al., 2001;Gruber and Haeberli, 2007).An important geomorphological consequence for bedrock in coastal areas is coastal erosion.The coastal sections within the study areas have a large frequency of rock cliffs (e.g.Etzelm üller et al., 2003;Ødeg ård et al., 1987) formed in sedimentary bedrock.Those are heavily shattered by frost weathering, and probably an important source for material transport and erosion into the sea (e.g.Ødeg ård et al., 1995;Ødeg ård and Sollid, 1993).Such sites would be highly susceptible to proposed changes, supposing that many cliffs are stabilized by permafrost.

Conclusions
From this study the following conclusions are drawn: -The substantial warming of ground temperatures and associated active layer thickening observed in recent years on Janssonhaugen was successfully reproduced by our model.

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Full There was little variation in modelled ALT over these 100 years although there was substantial variability of air temperature.MAAT changes were mainly caused by the increase of winter temperatures and thus have less influence on ALT.
-A similar pattern is valid for future development, with a general warming of permafrost, but limited changes in ALT at least at ice-rich sites.
-The sensitivity analysis shows that GT is more sensitive to changes in winter temperatures than to changes in summer temperatures for sites with sediment cover.
Changes in summer temperatures have a direct impact on ALT whereas ALT is only indirectly affected by changes in winter temperatures through the general influence on GT.
-Permafrost degradation can be expected at low elevation, e.g.close to the coast below c. 100 m a.s.l. in well-drained and dry sites (e.g.bedrock), where the development of taliks is likely.From this analysis a major degradation of permafrost is not expected on Svalbard during the next c.50 years for areas with no ground disturbances by human activity.

TCD Introduction
Full  Full   et al., 2000).The gray lines denote the contours from above.The area below 50 m is mainly consisting of marine sediments, beach deposits, fluvial infilling, slope sediment such as gelifluction colluviums, alluvial fans and some singular bedrock outcrops, mainly in steep rock walls or coastal cliffs.
Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | All shorter series are adjusted to the current Svalbard Airport meteorological station (established in 1975).The beginning of the series coincides with the end of the Little Ice Age in Svalbard (Fig. 2).Since 1912 annual mean temperatures have changed by about 4 • C, from c. −8 • C at the end of the last century to −4 • C today.Temperature varied between −8 • C and −5 • C (Fig. 2) between 1920 and c. 1960.Since the late 1980s Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | For Janssonhaugen, ground temperature is measured since May 1998, and local meteorological records are available since spring 2000.At this location we divided the dataset into a calibration (May 2000-May 2005) and a validation period (June 2005-April 2009) (Fig.
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3.
Warming rates are efficiently reduced where the temperature is close to 0 • C and where ice is present due to the consumption of latent heat for 4. The median ground temperatures at the depth of ZAA is suggested to increase by 2-4 • C over the period 2000-2100.5.Over the same period, ALT increases at all sites, the magnitudes of the modelled increase depend on GST and ground characteristics.While ALT roughly doubles Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

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Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Since the end of the Little Ice Age on Svalbard (mid to end of 19th century) and until 1990, permafrost has warmed up by around 1• C and since then by 0.5-1• C.
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Fig. 1 .Figure 5 Fig. 5 .
Fig. 1.Location of the studied borehole sites in Svalbard in the Nordenski öldland Permafrost Observatory (Juliussen et al., 2010).The selected sites for this study on Nordenski öld peninsula are Endalen (a), Janssonhaugen (b), Gruvefjellet (c) and Kapp Linn é (d).The blue circles show borehole location, while the "T "s indicate locations for ground surface temperature monitoring.The blue boxes in the inlet map are defined permafrost regions on Svalbard, where monitoring is carried out.

Fig. 8 .
Fig. 8. (a) Hillshaded map of the Adventdalen area and surroundings.The two violet colours denotes the 50 m and 100 m contour line, respectively.Large areas within the valley bottoms draining to Isfjorden are lying within this zone.(b) Geomorphological map over the area around Longyearbyen (based on Tolgensbakk et al., 2000).The gray lines denote the contours from above.The area below 50 m is mainly consisting of marine sediments, beach deposits, fluvial infilling, slope sediment such as gelifluction colluviums, alluvial fans and some singular bedrock outcrops, mainly in steep rock walls or coastal cliffs.

Table 1 .
Calibration parameters used for ground temperature modelling