Cicerone 5-2002

The permafrost on Svalbard and in Norway is thawing

Temperature analyses from boreholes in the permafrost on Svalbard and in the alpine regions in mainland Norway show that the permafrost has warmed up over the last hundred years. Monitoring these changes can both identify societal vulnerabilities, particularly with respect to slope instability, and provide critical evidence of climate change over the next decades.

Av Ketil Isaksen og Johan Ludvig Sollid

As has also been reported in Siberia, Alaska and Canada, the permafrost on mainland Norway and Svalbard is warming up. A thawing of the permafrost can have serious consequences for society.

Damage to buildings and roads

Permafrost close to the melting point is particularly sensitive to a warmer climate, particularly where the frozen ground is ice-rich. A slight increase in ground temperature can create great instability, damaging roads, bridges, harbors, power lines, and pipelines. Thawing permafrost is currently the greatest geotechnical challenge facing engineers in arctic regions.

Svalbard in particular may be sensitive to such changes since the bulk of tourism, construction, and industrial activities take place near the shoreline, which is especially vulnerable to thawing of the permafrost due to slight temperature changes. The projected climate changes over the next 50–100 years will, in all likelihood, lead to additional changes in the permafrost.

Land- and rockslides

Changing climate in the mountain permafrost zone is likely to lead to a significant increase in both scale and frequency of slope failures (See Haeberli and Beniston, 1998). In the period 1905–1936, 175 people were killed in northwestern Norway from giant waves caused by large rockslides. Several other well-known major rockslides from the past in northwestern Norway may have been caused by thawing permafrost after the last ice age. The fjord bottom shows marks from a number of past slides, the cause of which is currently being investigated more closely (Blikra et al., 1999). Major rockslides are also recorded in Troms in northern Norway. Increased knowledge about the distribution pattern of the permafrost in the Norwegian mountain areas will help identify potential slide areas.

Permafrost on Svalbard and in Norway

The regional distribution pattern of permafrost is largely determined by air temperature and snow conditions; permafrost is normally formed in land regions that have an annual air temperature of -2 ^oC or below. As could be expected, Svalbard is covered almost entirely by permafrost, except for underneath the larger glaciers. The thickness varies; roughly speaking, the permafrost on Svalbard is about 100 meters thick in the coastal areas and 400–500 meters thick under mountainous regions (Liestøl 1976). It is perhaps less well known that the alpine regions in Norway also have an extensive amount of permafrost. Recent mapping in southern Norway shows that the lower boundary of permafrost, excluding sporadic occurrences and remnants from old (relict) permafrost, is about 1450 meters above sea level (m a.s.l.) in Jotunheimen, 1350 m a.s.l. in Dovrefjell, and 1100 m a.s.l. in Sølen close to Femunden (Ødegård et al. 1996; Etzelmüller et al. 1998; Isaksen et al. 2002; Heggem et al. submitted). Sporadic permafrost is found 300–400 m lower in the terrain, often in palsa bogs. Currently there is little field data on the lower altitudinal limits of mountain permafrost in western- and northern Norway.

Permafrost as a climate indicator

Monitoring changes in permafrost provides a valuable supplement to more traditional climate studies, and has been the subject of a three-year EU project called PACE (Permafrost and Climate in Europe), started in December 1997. Seven countries participated, including Norway. Seven boreholes more than 100 m deep were drilled in the permafrost in selected alpine areas from Svalbard in the north to Spain in the south. Identical instrumentation were used in all the holes to take systematic measurements of both long-term and short-term temperature changes in the permafrost. In Norway, The University of Oslo, the Norwegian Meteorological Institute, the University Courses on Svalbard (UNIS), and the Norwegian Geotechnical Institute (NGI) participated in the project.

Lachenbruch and Marshall (1986) aroused the interest of the scientific community by highlighting the potential for permafrost borehole temperature data to be used to reconstruct climate change. Because a major difficulty in identifying past climate signals has been to filter out the effects of random or very short-term temperature variations and to identify long-term trends, thermal monitoring of permafrost can provide a key research tool. Generally, heat advection by groundwater flow can be excluded in permafrost. Heat flow from the Earth’s interior towards its surface (geothermal flux) and the heat flux from the energy exchanges at the ground surface determine the temperature gradient in the upper crust of the earth. With homogenous bedrock and constant surface temperature, the gradient is linear with depth. Temperature changes at the surface become less marked as they move downward. The annual thermal cycle generally penetrates to a depth of 15–20 m (see Figure 2), but larger changes in surface temperature that take place over longer periods of time penetrate much deeper. Changes in the subsurface temperature gradient provide a record of recent ground surface temperature history: The depth of the temperature change shows when the change took place on the surface, and the shape of the perturbation is a function of the ground surface temperature history. Thus the temperature measurements in boreholes in the permafrost indicate the site’s current and past mean annual ground surface temperatures without having to use long meteorological series. Data from ground temperature measurements collected today to depths of 100 m or more can be used in inversion modeling to provide paleoclimatic information for the past one or two centuries.

The permafrost is becoming warmer

The PACE boreholes in the northern areas of Europe are located at Janssonhaugen in Adventdalen on Svalbard, at Tarfalaryggen in the Swedish area of Lappland, and at Juvvasshøe in Jotunheimen (Sollid et al. 2000). This is the first time in Norway and Sweden that such deep holes have been drilled in the permafrost with the aim of conducting climate research. The locations of borehole sites are selected to minimize possible influence on ground temperatures from undesired and non-climate-related sources, such as mining etc.

A reconstruction of the surface temperature at Janssonhaugen, Svalbard, from the borehole data indicates a temperature increase of 1.0–2.0 ^oC (Figure 3a) over the past 60–80 years (Isaksen et al. 2000). The temperature analyses from the borehole in Juvvasshøe indicate a temperature increase of 0.5–1.0 ^oC over the last 20–40 years (Figure 3b) (Isaksen et al. 2001). Although the temperature perturbations for this borehole are large, the energy imbalance at the Earth’s surface that produces the warming is very small compared to the solar flux that the surface absorbs and radiates in this region. This shows that ground temperatures, when properly integrated, are a very sensitive monitor of energy balances at the surface (see Lachenbruch and Marshall, 1986). The closest meteorological station to Janssonhaugen that has been keeping long temperature series is Svalbard airport, Longyearbyen. Here a homogenous temperature series was constructed back to 1912 (Førland et al. 1997). The series show that air temperature increased by about 4 ^oC from 1912 and up to the end of the 1930s. The temperature dropped about 2.5 ^oC up to the mid 1960s, and then increased by about 2 ^oC up to today. The linear trend for the entire period of 1912–1999 shows a temperature increase of about 1.2 ^oC.

The air temperature change measured by the meteorological stations in the region around Juvvasshøe in the 1990s show mainly the same trend as on Svalbard, but with less pronounced fluctuations. The air temperature increased by 1.1–1.3^oC from the beginning of 1900 to the 1930s, and dropped by 0.8–1.0^oC up to the mid 1960s, only to increase again by 0.7–0.9 ^oC up to the present. There are large inter-annual variations in the air temperature at the meteorological stations, particularly on Svalbard. This may complicate the analysis of the temperature trends. Permafrost, in contrast, functions as an excellent filter that preserves only the long-term trends of the temperature on the ground surface. Thus, long-term monitoring of ground temperatures at selected sites in permafrost regions will form a solid basis for the study of ongoing and future climate changes and contribute to a better understanding of the climatic changes in the past.

References

Blikra, L.H., Anda, E. and Longva, O. 1999. Fjellskredprosjektet i Møre og Romsdal: status og planer. NGU Report; 99.120. 21 pp.
Etzelmüller, B., Berthling, I. and Sollid, J. L. 1998. The distribution of permafrost in southern Norway: A GIS approach. Seventh International Conference on Permafrost, (Yellowknife, 23-27 June 1998), Collection Nordicana 57, 251-258.
French, H.M. 1996. The periglacial environment. (2nd edition) Longmann, London, 341 pp.
Førland, E.J., Hanssen-Bauer, I. and Nordli, P.Ø. 1997. Climate statistics & longterm series of temperature and precipitation at Svalbard and Jan Mayen. DNMI report, No. 21/97 Klima.
Haeberli, W. and Beniston, M. 1998. Climate change and its impacts on glaciers and permafrost in the Alps. Ambio 27/4: 258-265.
Isaksen, K., Vonder Mühll, D., Gubler, H., Kohl, T., and Sollid, J.L. 2000. Ground surface temperature reconstruction based on data from a deep borehole in permafrost at Janssonhaugen, Svalbard. Annals of Glaciology 31: 287-294.
Isaksen, K., Holmlund, P., Sollid, J.L., and Harris, C. 2001. Three deep alpine-permafrost boreholes in Svalbard and Scandinavia. Permafrost and Periglacial Processes 12: 13-25.
Isaksen, K., Hauck, C., Gudevang, E., Ødegård, R.S., and Sollid, J.L. 2002. Mountain permafrost distribution in Dovrefjell and Jotunheimen, southern Norway, based on BTS and DC resistivity tomography data. Norsk Geografisk Tidsskrift56: 122-136.
Lachenbruch, A. H. and Marshall, B. V. 1986. Changing climate: Geothermal evidence from permafrost in the Alaskan Arctic. Science 234: 689-696.
Liestøl, O. 1976. Pingos, springs and permafrost in Spitsbergen. In Norsk Polarinstitutts Årbok 1975, 7-29.
Sollid, J.L., Holmlund, P., Isaksen, K., and Harris, C. 2000. Deep permafrost boreholes in western Svalbard, northern Sweden and southern Norway. Norsk Geografisk Tidsskrift 54: 186-191.
Ødegård, R. S., Hoelzle, M., Johansen, K. V. and Sollid, J. L. 1996. Permafrost mapping and prospecting in southern Norway. Norsk Geografisk Tidsskrift 50: 41-53.

Sist oppdatert: 12.12.2002

<b>SVALBARD:</b> Monitoring changes in permafrost provides a valuable supplement to more traditional climate studies. (Photo: J.L.Sollid)

SVALBARD: Monitoring changes in permafrost provides a valuable supplement to more traditional climate studies. (Photo: J.L.Sollid)

What is permafrost?

Permafrost is defined as ground remaining frozen for more than one year. If the frost that is formed during the winter does not melt entirely during the warm summer months, permafrost will form. The upper layer that melts during the summer and re-freezes in the winter, the so-called active layer of the permafrost, ranges from 0.5 to 5 meters deep.

Today, about one-fourth of the Earth’s land surface is covered by permafrost (see Figure 1). It is found primarily in polar regions, but also in alpine areas at lower latitudes.

<b>Figure 1:</b> Distribution of permafrost in the Northern Hemisphere. A total of 24% of the world’s land area is covered with permafrost (after French, 1996).

Figure 1: Distribution of permafrost in the Northern Hemisphere. A total of 24% of the world’s land area is covered with permafrost (after French, 1996).

<b>Figure 2:</b> Four selected temperature series over 26 months from various depths in a borehole in the permafrost in Janssonhaugen, Svalbard. Note how the temperature signal from the surface becomes weaker with depth. Seasonal variations are evened out at a depth of 15–20 m. Monitoring the temperatures at these depths indicates changes in the ground surface energy balance with a time resolution of about 5–10 years. Long-term temperature changes at the surface are preserved at greater depths (see Figure 3).

Figure 2: Four selected temperature series over 26 months from various depths in a borehole in the permafrost in Janssonhaugen, Svalbard. Note how the temperature signal from the surface becomes weaker with depth. Seasonal variations are evened out at a depth of 15–20 m. Monitoring the temperatures at these depths indicates changes in the ground surface energy balance with a time resolution of about 5–10 years. Long-term temperature changes at the surface are preserved at greater depths (see Figure 3).

<b>Figure 3A:</b> Annual temperature gradients in the permafrost for the year 2000 from Janssonhaugen (3A) and Juvvasshøe (3B below). The depth of the temperature sensors is indicated. The figures show that the year 2000 was particularly warm at both sites. Long-term changes in the annual temperature of the ground surface shape the temperature gradient. The dashed line is an extrapolation of the temperature gradient from the deepest 30 meters of the boreholes. The gradients show a clear bend toward the surface from about 60–70 meters depth, as can be seen in the shaded area. The bend is a result of a warming of the permafrost. The ground surface temperature has increased 1.0–2.0°C over the last 60–80 years at Janssonhaugen, and 0.5–1.0°C over the last 20–40 years at Juvvasshøe.

Figure 3A: Annual temperature gradients in the permafrost for the year 2000 from Janssonhaugen (3A) and Juvvasshøe (3B below). The depth of the temperature sensors is indicated. The figures show that the year 2000 was particularly warm at both sites. Long-term changes in the annual temperature of the ground surface shape the temperature gradient. The dashed line is an extrapolation of the temperature gradient from the deepest 30 meters of the boreholes. The gradients show a clear bend toward the surface from about 60–70 meters depth, as can be seen in the shaded area. The bend is a result of a warming of the permafrost. The ground surface temperature has increased 1.0–2.0°C over the last 60–80 years at Janssonhaugen, and 0.5–1.0°C over the last 20–40 years at Juvvasshøe.

Figure 3B

Additional contacts and information:

Ketil Isaksen is a senior scientist at the Norwegian Meteorological Institute, Climatology Division, Oslo
(ketil.isaksen@met.no)
Johan Ludvig Sollid is a professor at the Department ofPhysical Geography, University of Oslo
(j.l.sollid@geografi.uio.no)
Permafrost and Climate in Europe - PACE (http://www.cf.ac.uk/earth/pace/) EU-Project which was co-ordinated by Professor Charles Harris, Department of Earth Sciences, Cardiff University (harrisc@cardiff.ac.uk)