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Glacier Network (GTN-G)
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Focal points: Wilfried Haeberli and Roger Barry

San Rafael: Glaciar San Rafael (Northern Patagoniana Icefield) as seen from the ASTER satellite sensor on 20 May 2000. The glacier now terminates in a pro-glacial lake which might accelerate its future retreat. The large moraine surrounding the lake is from the historical maximum extent of the glacier.

Mountain glaciers have been systematically observed for more than a century in various parts of the world. Glaciers and ice caps are, therefore, prime indicators in early-detection strategies in global climate-related observations. Although forming only about 0.7 percent of the global ice volume, they are of great importance regionally as water resources, and glacial melt contributes to the observed sea level rise.

Monitoring of glaciers

Advanced monitoring strategies developed by the World Glacier Monitoring Service (WGMS) for GTN-G within GTOS integrate detailed observations of mass balance and flow at selected reference glaciers for process understanding and numerical modelling, with more widely distributed determinations of changes in length, area and volume; repeated compilation of glacier inventories enables global coverage to be reached. In all, glaciers and ice caps are estimated to be about 160 000, covering an area of about 785 000 km2. Basic information for about 44% (approx. 71 000) of these glaciers is currently stored in the World Glacier Inventory (WGI) and is available in digital form from a Web site at the National Snow and Ice Data Center (NSIDC), University of Colorado at Boulder (link below). Quantitative information was mainly obtained from aerial photographs or topographic maps from the 1970s and 1980s, of varying quality. Many areas are still missing, although preliminary overview data (mainly total area) has been compiled for these. For assessment of glacier changes over decades and globally, WGI provides the most comprehensive data set. In close cooperation with NSIDC and WGMS, the Global Land Ice Measurement from Space (GLIMS) project is compiling modern (circa 2000) data sets in a standardized format by analysis of multispectral Landsat TM/ETM+ and ASTER satellite scenes. Outlines for 51 000 glaciers are now available online.

History of data collection

Worldwide collection of information about ongoing glacier change was initiated for about 50 Alpine glaciers in 1894, with the founding of the International Glacier Commission. In 1986, WGMS was established to maintain and continue data collection when two former services – the Permanent Service on Fluctuations of Glaciers (PSFG) and the Temporary Technical Secretariat for the World Glacier Inventory (TTS/WGI) – were combined. WGMS is based in Zurich, Switzerland, and collects standardized observations on changes in mass, length, area and volume of glaciers with time (glacier fluctuations). Close collaboration with the GLIMS project forms a basis for systematic integration of remote sensing data for future worldwide glacier observation.

History of data collection

WGMS has managed the Global Terrestrial Network for Glaciers (GTN-G) since its creation in 1998. The GCOS Essential Climate Variables for glaciers and ice caps are mass balance and length/area. GTN-G prepares reports on annual mass balance for some 60 glaciers (most records beginning in the 1950s–1960s), and length changes for some 550 glaciers worldwide. Satellite-based glacier inventories are compiled within the GLIMS-project.

Rapid glacier loss

The Fluctuations of Glaciers report for 1995–2000 and the Glacier Mass Balance Bulletin for 2002–2003 (85 sites) are available and illustrate the acceleration of glacier melt in the last two decades. The implication is that many low-latitude mountain ranges may become deglaciated within a few decades, especially glaciers in tropical mountains, but also glaciers with a long series of mass-balance observations that now constitute the core of the observational network. Since 2000, ice loss in the European Alps has been around 15% (3% per year) of the total remaining volume.

Recent activities

1. Publication of a new glacier inventory for the Indian Himalaya, which is being digitized for incorporation in the WGMS database.

2. Development of mass balance measurement projects in New Zealand and Patagonia.

3. The presentation of photographic pairs for 14 Alaskan glaciers with century-long records (see link).

For further information, refer to the following sites:

Alaskan glaciers records

World Data Centre for Glaciology site

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© FAO   ::   Global Terrestrial Observing System - GTOS   ::   15 January 2007