CALM Program Description 

The active layer is the layer of earth materials between the ground surface and permafrost that freezes and thaws on an annual basis. The active layer is extremely important in many of Earth’s cold regions because the permafrost immediately below it can form an impermeable layer that restricts the majority of geomorphic, hydrologic, and biogeochemical processes to this relatively thin layer.


Climate models indicate that sustained warming will be more pronounced in the high latitudes than in other regions. Given the temperature dependence of ice and its mechanical properties, warming or thawing of ice-rich permafrost can result in very substantial impacts on natural and human systems in cold environments. Considerable evidence exists that warming is well underway in the high-latitude regions (e.g., Hinzman et al. 2005). The roles of permafrost in climate-change science are discussed in a report by the U.S. Arctic Research Commission’s Permafrost Task Force (2003).


In regions underlain by ice-rich permafrost, sustained climatic warming could lead to a widespread increase in the thickness of the active layer. This, in turn, can result in differential settlement of the ground surface and cause damage to roads, structures, and utility lines. Thaw subsidence can also alter local hydrological patterns and lead to profound ecological changes (e.g., Jorgenson et al. 2006, Shur and Jorgenson 2007). Another important consequence of increased active-layer thickness is that carbon sequestered in the uppermost permafrost reservoir can be released to the atmosphere in the form of greenhouse gases. A net increase in the efflux of CO2 and CH­4 to the atmosphere provides a positive feedback effect on climatic warming (Shuur et al. 2008).


In light of these challenges, it is necessary to monitor and model interannual, decadal, and secular variations in the active layer at a variety of geographic scales, ranging from local to global. To achieve these goals, the CALM (Circumpolar Active Layer Monitoring) program was established in the early 1990s. CALM’s goals include monitoring the thickness of the active layer (e.g., Hinkel and Nelson 2003; Streletskiy et al. 2012), the temperature in the near-surface layers of the permafrost regions (e.g., Hinkel et al. 2001; Nyland et al. 2012), and surface movements attributable to frost heave and thaw  settlement (Shiklomanov et al. 2013). Observations are made in both built and natural environments (e.g., Klene et al. 2013; other references). CALM is among the international permafrost community’s first large-scale efforts to construct a coordinated monitoring program capable of producing data sets suitable for evaluating the effects of climate change. Together with its sister program, the IPA’s Thermal State of Permafrost (Romanovsky et al. 2010, Vieira et al. 2010), CALM comprises GTN-P, the Global Terrestrial Network for Permafrost, itself a component of the Global Terrestrial Observation System and the Global Climate Observation System (GTOS/GCOS). The CALM network’s history,  organizational structure, site descriptions, and initial analytical  results were reported in Brown et al. (2000), Burgess et al. (2000), and Nelson et al. (2008, 2011), and can be found elsewhere on this site.


CALM investigators measure the seasonal depth of thaw at plots of various dimensions using standardized protocols (Nelson and Hinkel 2005). Soil and air temperature, soil moisture content, and vertical movement are also measured at many sites.  These measurements, combined with site-specific information about soils, landscape, and vegetation, can be used to “scale up” assessments of the stability and projected changes to regional and circumpolar scales  (e.g., Nelson et al. 1997; Shiklomanov and Nelson 2002). They also perform an important role in model validation (e.g., Shiklomanov et al., 2007, other references).


CALM currently consists of more than 240 field installations operated by researchers from Canada, China, Denmark/Greenland, Italy, Kazakhstan, Mongolia, New Zealand, Norway, Poland/Svalbard, Portugal, Russia, Spain, Sweden, Norway,  Switzerland, and the United States. The CALM program began as a voluntary effort in 1991, initially as part of ITEX, the International Tundra Experiment. CALM was formalized in late 1997 with a five-year grant from   the U.S. National Science Foundation’s Arctic System Science program to the University of Cincinnati (K.M. Hinkel, Project  Director). After a bridging year supported by the University of Delaware’s  Center for International Studies, a second five-year block of support was awarded by the NSF Arctic Logistics and Research Support program, with the University of Delaware acting as lead institution (F.E.  Nelson and N.I. Shiklomanov, co-PIs). Known as CALM II, this project expanded CALM’s mission to include measurements of movement at the ground surface, anthropogenic-impacts studies, and more extensive thermal monitoring. Two further five-year blocks of support from NSF’s Arctic Observing Program (CALM III (2009-2014) and CALM IV (2014-2019)) are administered through The George Washington University (N.I.  Shiklomanov and D.A Streletskiy, co-PIs), with subcontracts to the University of Montana (A.E. Klene) and Northern Michigan University (F.E. Nelson).


CALM is currently administered through The George Washington University’s Department of Geography. Program participants collect temperature and thaw depth measurements and provide them to the CALM office at GWU. Data are subsequently incorporated into several databases. Analysis, archiving, and distribution of CALM’s long-term observations are integral components of the project. Data analysis is performed in the first instance by the field investigators, and further processing and standardization occur at the grant-holding universities. CALM data are freely available to interested parties on the GTOS Terrestrial Ecosystem Systems (TEMS)  website, on the National Snow and Ice Data Center’s Frozen Ground website, on CD through the International Permafrost Association’s Global Geocryological Data (GGD) system (Parsons et al., 2003), and through the Joint Office for Scientific Support. Scientific results are presented at national and international meetings, and published in international peer-reviewed journals.


CALM’s observing protocols and management practices are developed through consensus. Investigators discuss the program at various scientific meetings, including the IPA’s international and regional conferences, the American Geophysical Union’s Fall Meetings in San Francisco, and the permafrost conferences held periodically in Pushchino, Russia. International workshops concerned exclusively with the CALM program were held in Lewes, Delaware in 2002 and Fairbanks, Alaska in 2008. A third workshop is planned in association with the International Permafrost Conference scheduled for the summer of 2016 in Potsdam, Germany. More information about the CALM workshops and resulting resolutions can be found at CALM WORKSHOPS page.


CALM is a joint effort by the world permafrost community, with abundant help from colleagues engaged in related branches of science. These individuals contribute their time and effort, in most cases without financial compensation. Our results and data are available to all interested parties. The CALM community asks only that our data and resources be used in a scientifically responsible manner, and that users give formal acknowledgment to the program and to individual investigators in any publication, press releases, or web-based activity. 




Literature Cited

Brown, J., Hinkel, K.M., and Nelson, F.E. (2000). The Circumpolar Active Layer Monitoring (CALM) program: historical perspectives and initial results. Polar Geography 24: 165-258.


Hinkel, K.M. and Nelson, F.E. (2003). Spatial and temporal patterns of active layer thickness at CALM sites in northern Alaska, 1995-2000. Journal of Geophysical Research-Atmospheres, 108(D2), 10.129/2001JD000927.


Hinzman, L., Bettez, N., Bolton, W.R., Chapin, F.S., and 31 others (2005). Evidence and implications of recent climate change in northern Alaska and other Arctic regions. Climatic Change, 72: 251-298.


Jorgenson, M.T., Shur, Y., and Pullman, R.R. (2006). Abrupt increase in permafrost degradation in Arctic Alaska. Geophysical Research Letters 33: doi: 10.1029/2005GL024960.


Klene, A.E., Nelson, F.E., and Hinkel, K.M. (2013). Urban - rural contrasts in summer soil-surface temperature and active-layer thickness, Barrow, Alaska, U.S.A. Polar Geography 36(3): 183-201.


Nelson, F.E., and Hinkel, K.M. (2003). Methods for measuring active-layer thickness. In: Humlum, O. and Matsuoka, N. (eds.) A Handbook on Periglacial Field Methods. Longyearbyen, Norway: University of the North in Svalbard, currently online at:< http://www.unis. no/RESEARCH/GEOLOGY/Geo_research/Ole/PeriglacialHandbook/ActiveLayerThicknessMethods.htm>.


Nelson, F.E. and Shiklomanov, N.I. (2011). The Circumpolar Active Layer Monitoring Network—CALM III (2009-2014): Long-term Observations on the Climate-Active Layer-Permafrost System. pp. 9-21 in: Ambientes Periglaciares, Permafrost y Variabilidad Climática: II Congreso Ibérico de la International Permafrost Association. Alcalá, Spain: Universidad de Alcalá Servicio de Publicaciones.


Nelson, F.E., Shiklomanov, N.I., Hinkel, K.M., and Brown, J. (2008). Decadal results from the Circumpolar Active Layer Monitoring (CALM) program. Proceedings of the Ninth International Conference on Permafrost. Fairbanks: University of Alaska Press, pp. 1273-1280.


Nelson, F.E., Shiklomanov, N.I., Mueller, G.R., Hinkel, K.M., Walker, D.A., and Bockheim, J.G. (1997). Estimating active-layer thickness over a large region: Kuparuk River basin, Alaska, U.S.A. Arctic and Alpine Research 29: 367-378.


.Nyland, K.E., Shiklomanov, N.I., Streletskiy, D.A., Klene, A.E., and Nelson, F.E. (2012). Thermal insulating properties of northern Alaskan vegetation and their effects on ground thermal regimes. Proceedings of the Tenth International Conference on Permafrost.  Salekhard, Russia: The Northern Publisher, 295-300.


Romanovsky, V.E., Smith, S.L., and Christiansen, H.H. (2010). Permafrost thermal state in the polar Northern Hemisphere during the International Polar Year 2007-2009: a synthesis. Permafrost and Periglacial Processes. 21: 106-116.


Schuur, E.A.G, J. Bockheim, J.G. Canadell, E. Euskirchen, C.B. Field, S.V Goryachkin, S. Hagemann, P. Kuhry, P.M. Lafleur, H. Lee, G. Mazhitova, F. E. Nelson, A. Rinke, V.E. Romanovsky, N. Shiklomanov, C. Tarnocai, S. Venevsky, J. G. Vogel, and S.A. Zimov (2008). Vulnerability of permafrost carbon to climate change: implications for the global carbon cycle. BioScience 58: 701-714.


Shiklomanov, N.I. and Nelson, F.E. (2002). Active-layer mapping at regional scales: a 13-year spatial time series for the Kuparuk region, north-central Alaska. Permafrost and Periglacial Processes, 13: 219-230.

Shiklomanov, N.I., Anisimov, O.A., Zhang, T., Marchenko, S., Nelson, F.E., and Oelke, C. (2007). Comparison of model-produced active layer fields: Results for northern Alaska. Journal of Geophysical Research—Earth Surface 112(F2); F02S10, doi: 10.1029/2006JF000571.


Shiklomanov, N. I., Nelson, F. E., and Streletskiy, D.A., Hinkel, K. M., and Brown, J. (2008). The Circumpolar Active Layer Monitoring (CALM) program: data collection, management, and dissemination strategies. Proceedings of the Ninth International Conference on Permafrost. Fairbanks: University of Alaska Press, pp. 1647-1652.


Shiklomanov, N.I., Streletskiy, D.A.,  and Nelson, F.E. (2012). Northern Hemisphere component of the global Circumpolar Active Layer Monitoring (CALM) program. Proceedings of the Tenth International Conference on Permafrost. Salekhard, Russia: The Northern Publisher, 377-382.


Shiklomanov, N.I., Streletskiy, D.A., Little, J.D., and Nelson, F.E. (2013). Isotropic thaw subsidence in undisturbed permafrost landscapes. Geophysical Research Letters, 40: 1-6. doi:10.1002/2013GL058295.


Shur, Y., and Jorgenson, M.T. (2007). Patterns of permafrost formation and degradation in relation to climate and ecosystems. Permafrost and Periglacial Processes 18: 7-19.


.Streletskiy, D.A., Shiklomanov, N.I., and Nelson, F.E. (2012). Spatial variability of permafrost active-layer thickness under contemporary and projected climate in northern Alaska. Polar Geography 35(2): 95-116.


U. S. Arctic Research Commission Permafrost Task Force (F.E. Nelson and L.W. Brigham, Lead Authors, 2003). Climate Change, Permafrost, and Impacts on Civil Infrastructure. Washington, D.C.: U.S. Arctic Research Commission, 62 + vi pp.


Vieira, G. Bockheim, J., Guglielmin, M., and 16 others (2010). Thermal state of permafrost and active-layer monitoring in the Antarctic: advances during the International Polar Year 2007-2008. Permafrost and Periglacial Processes, 21: 182-197


The extended list of references available at