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The Global Terrestrial Network for Glaciers (GTN-G)

Official website: GTN-G

Contact: Michael Zemp, World Glacier Monitoring Service

The Global Terrestrial Network for Glaciers (GTN-G) is a monitoring and observing network that provides data and information to the scientific community and to the wider public on the state of glaciers. GTN-G was developed by the GCOS/GTOS Terrestrial Observation Panel for Climate (TOPC) to design a global observing strategy and set in place a Global Terrestrial Network (GTN) for monitoring glaciers and ice caps in the terrestrial domain in support of the United Nations Framework Convention on Climate Change (UNFCCC).


Figure 1: Schematic overview of GTN-G and its interaction with international organizations, the scientific community, national agencies, the media, and the wider public (Source: GTN-G website; blue and green arrows show the flow data compilation, as well as the main source of funding (orange dots) and the formal links to international bodies (red and green dots))


GTN-G is jointly run by three operational bodies: the World Glacier Monitoring Service (WGMS), the US National Snow and Ice Data Centre (NSIDC), and the Global Land Ice Measurements from Space Initiative (GLIMS). A GTN-G Steering Committee was established and set in place in 2009 to support, coordinate and advise the three operational bodies concerning monitoring and data reporting (see GNT-G organigramm). The network tries to implement the global observation strategy of GCOS for the ECV Glaciers and Ice Caps by compiling and disseminating standardized observations, monitoring protocols and methods on glacier distribution and their changes over time. The GTN-G strives to combine in-situ observations with remotely sensed data, the local understanding of glacier processes with global coverage, and traditional measurements with new technologies by using an integrated and multi-level monitoring strategy.

WGMS is operated through a small central service hosted at the Department of Geography at the University of Zurich, Switzerland, and is based on a network of national correspondents and principal investigators active in glacier monitoring. WGMS and NSDIC are services of the World Data System (WDS) of the International Council for Science (ICSU), which is also a sponsor of GCOS. The WGMS provides standardized observations on changes in mass, volume, area and length of glaciers with time (Fluctuations of Glaciers), as well as statistical information on the distribution of perennial surface ice in space (World Glacier Inventory). In addition, information on special events (e.g. surges, calving instabilities, ice avalanches, lake outbursts) is available. All data and information is freely available for scientific and educational purposes. The use requires acknowledgement to the WGMS and/or the original investigators and sponsoring agencies according to the available meta-information.

Past and recent activities of GTN-G

GCOS-ECVs: Glaciers and Ice Caps (mass balance, length/area; indirectly: Ice Sheets, Sea Level, Snow Cover) (please see GTOS-60, and GTOS-61)

GTN-G has been focusing on the collection and publication of standardized data on glacier fluctuations at five-year intervals, prepares a bulletin to report mass balance data of selected reference glaciers and ice caps at two-year level intervals, manages and upgrades the already existing inventory of glaciers and ice caps, encourages international organizations and Member States to use satellite observations to reach a global coverage of glaciers and ice caps, and tries to regularly assess ongoing changes.

Databases have been developed to fulfil the need for a detailed inventory of the world’s glaciers, with the two main operational databases being the World Glacier Inventory (WGI; WGMS and NSIDC 1989, updated 2012) based primarily on aerial photographs and maps of the second half of the 20th century, and the Glacier Land Ice Measurements from Space database (GLIMS 2011), which is the continuation of the WGI task primarily based on satellite data from the 21st century. The WGMS metadata browser/map, created in close collaboration with ESRI, comprises an overview on available glacier fluctuation series and helps data users to search for information of individual glaciers, geographical regions, and measurement types (e.g. front variation, glaciological mass balance, geodetic thickness change, etc.). The corresponding metadata lists then can be provided in Excel and/or Google Earth formats. The metadata browser allows to directly download minimal data series of glacier changes together with corresponding survey and reference years.

GCOS is supporting GTN-G in its efforts to maintain continuous monitoring of glaciers, and tries to facilitate the strengthening and coordination to meet the full users’ range of user needs for glacier development and linked climate-related observations.

Future plans

The role of glaciers within the earth system is very important. As everywhere on earth ice is changing, permafrost is thawing and temperatures are rising, there is a strong need to be able to monitor and observe changes in glacier lengths/areas even closer. Clear overall trends are indicating a global glacier recession, which is likely to accelerate even stronger in the coming years and decades. GTN-G will further help to get a more focused view on what is happening, as there are still gaps that remain in general understanding and the ability to model key processes.

GTN-G will continue to prepare annual mass balance reports, and is especially trying to display the acceleration of glacier melt in the last two decades and the indication that especially small tropical glaciers may be lost in the next twenty years. Recent activities have involved the publication of a new glacier inventory for the Indian Himalaya, the development of a mass balance measurement projects in New Zealand and Patagonia, and the presentation of photographic pairs for 14 Alaskan glaciers with century-long records. For more information, please also see the Report of the 15th Session of the TOPC.