The active layer is a 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 permafrost can form an impermeable layer at depth that restricts the majority of geomorphic, hydrologic, and biogeochemical processes to this relatively thin layer.
Climate models indicate that sustained warming will 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 could 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 (Morrison et al., 2000; Serreze et al., 2000). The roles of permafrost in climate-change science are discussed in a report by the U.S. Arctic Research Commission 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 lead to 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., 2001). An additional consequence of increased active-layer thickness is that carbon sequestered in the uppermost permafrost reservoir can be released 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.
Scientists therefore found it 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, the temperature in the near-surface layers of the permafrost regions, and surface movements attributable to frost heave and thaw settlement. 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 program (Romanovsky et al. 2002), 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). Details are provided in Brown et al. (2000), Burgess et al. (2000), and Nelson et al. (2003a). The CALM network’s history, organizational structure, site descriptions, and initial analytical results were reported in the monograph by Brown et al. (2000), also found elsewhere on this site.
CALM currently consists of more than 125 field installations operated by researchers from Canada, China, Denmark/Greenland, Italy, Kazakhstan, Mongolia, New Zealand, Norway, Poland/Svalbard, Russia, Sweden/Svalbard, 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 (OPP-9732051) 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 NSF Arctic Logistics and Research Support program (GRANT #), with the University of Delaware acting as the lead institution (F.E. Nelson and N.I. Shiklomanov (Co-PIs). Known as CALM II, this project has expanded CALM’s mission to include measurements of movement at the ground surface, anthropogenic-impacts studies, and more extensive thermal monitoring.
CALM investigators measure the seasonal depth of thaw at plots of various dimensions using a standard protocol. 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 (REFERENCES). They also provide perform a critical role in model validation (e.g., Oelke et al., 2004).
CALM is currently administered through the University of Delaware (UDel) Department of Geography. Participants collect the necessary temperature and thaw depth measurements and provide them to the CALM office at UDel, and they 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 occurs at UDel. 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 widely in international scientific journals.
The first CALM Workshop, sponsored by the U.S. National Science Foundation’s Arctic System Science Program, was held in November 2002 at the University of Delaware’s Virden Center in Lewes. The Workshop brought together 33 participants from six countries for intensive work of discussions, presentations, data exchange, and planning. A series of extended abstracts resulting from the workshop appears in a supplementary volume of the Proceedings of the Eighth International Conference on Permafrost (Haeberli and Brandova et al, 2003). Two collections of papers with origins in the workshop have been published (Nelson, 2004a, b).
The workshop in Delaware provided an opportunity to discuss sampling protocols, instrumentation, and analytic methods. Consensus was reached on several important issues. These were communicated as The CALM Workshop Resolution (Nelson et al., 2003b), which contains the following recommendations:
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