Status report on the key climate variables technical supplement to the

Issues and priorities

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  Many of the noted problems arise because (i) snow cover data are collected by numerous agencies with differing goals: runoff assessment and prediction, avalanche hazard; input for weather and climate prediction models; (ii) for the same reason, funding support for snow research is fragmentary and not well co-ordinated in many countries or internationally; (iii) the cost of maintaining surface networks is leading to their contraction and/or switch to automated measurement using different instrumentation (Barry, 1995; Vorosmarty et al. 2001).
  
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  In particular the contraction of in situ observations should be halted. Maintenance of adequate, representative surface networks of snow observations must begin with documentation and analysis of required network densities in different environments.
  

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  Development of optimal procedures to blend surface observations with visible and microwave satellite data and airborne gamma radiation measurements of SWE is urgently needed. This is only just beginning to receive attention through the ongoing Cold Land Processes Experiment (CLP) in the United States (see http://nsidc.org/data/nsidc-0112.html).
  

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  Internationally, snow cover (and other cryospheric variables) are beginning to receive co-ordinated attention through the WCRP Climate and Cryosphere (CliC) project (Allison et al., 2001). Development of snow products that blend multiple data sources and are globally applicable needs urgent focused attention, CliC and GCOS could help lead such an effort.
  

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  Better co-ordination is also needed in other scientific fora including: the International Council on Science (ICSU) and the International Union of Geophysics and Geodetics (IUGG), where the International Commission on Snow and Ice (ICSI) is currently under the International Association of Hydrologic Sciences, and within national agencies.
  

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  The provision of necessary resources to improve and make available existing archives of snow data will require national efforts. These can build on strong international endorsement of the importance of snow cover information for scientific reasons as well as for practical socio-economic reasons in areas with seasonal snow cover, especially in mountains and adjacent lowlands.
  

References

Allison, I., Barry, R.G. and Goodison, B.E. (eds.; 2001): Climate and Cryosphere Project Science and Co-ordination Plan Version 1. WCRP-114, WMO/TD No. 1053, Geneva: 45, 53-54).

Armstrong, R.L. and Brodzik, M.J. (2001): Recent Northern Hemisphere snow extent: a comparison of data derived from visible and microwave sensors. Geophysical Research Letters 28 (19):3673-3676.

Barry, R.G. (1995): Observing systems and data sets related to the cryosphere in Canada: a contribution to planning for the Global Climate Observing System. Atmosphere - Ocean 33 (4): 771-807.

Easterling, D.R., Karl, T.R., Lawrimore, J.H. and Del Greco, S.A. (1999): United States Historical Climatology Network Daily Temperature, Precipitation, and Snow Data for 1871-1997. ORNL/CDIAC-118, NDP-070. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 84 pp.

Goodison, D.E., Brown, R.D. and Crane, R.G. (lead authors; 1999): Cryospheric systems. Eos Science Plan, NASA pp. 261-307. http://eospso.gsfc.nasa.gov/ftp_docs/Ch6.pdf

Serreze, M.C., Clark, M.P., Armstrong, R.L., McGinnis, D.A. and Pulwarty, R.S. (1999): Characteristics of the western United States snowpack from snowpack telemetry (SNOTEL) data. Water Resources Research 7: 2145-2160.

Vorosmarty, C. J and 15 others (The Ad Hoc Group on Global Water Data). (2001) Global water data: An endangered species. EOS 82(3), 54,56,58.

Variable: Glaciers and ice caps
Main climate applications

Fluctuations of glaciers and ice caps in cold mountain areas have been systematically observed for more than a century in various parts of the world. The corresponding changes are considered to be indications of highest reliability concerning world-wide warming trends. Mountain glaciers and ice caps are, therefore, key variables for early-detection strategies in global climate-related observations (Fig. 2.39a in IPCC 2001).

Advanced monitoring strategies integrate detailed observations of mass and energy balance at selected reference glaciers with more widely distributed determinations of changes in area, volume and length; compilation of glacier inventories enables global representativity to be reached (Haeberli et al. 1998).
Long-term mass balance measurements provide direct (undelayed) signals of climate change and constitute the basis for developing coupled energy-balance/flow models for sensitivity studies in view of the complex feed-back effects (albedo, surface altitude, dynamic response) and for use in AOGCMS (model validation, hydrological impacts at regional and global scales, etc.). They combine the geodetic/photogrammetric with the direct glaciological method in order to determine changes in volume/mass of entire glaciers (repeated mapping) with high spatio-temporal resolution (annual measurements at stakes and pits). Laser altimetry and kinematic GPS are applied for monitoring thickness and volume changes of very large glaciers which are the main meltwater contributors to ongoing sea-level rise.
Change in glacier length is a strongly enhanced and easily measured but indirect, filtered and delayed signal of climate change. It represents an intuitively understood and most easily observed phenomenon to illustrate the reality and impacts of climate change. Work on glacier recession has considerable potential to support or qualify the instrumental record of temperature change and to cast further light on regional or world-wide temperature changes before the instrumental era – particularly useful for studies of Holocene climate variability. Glacier length records complement the instrumental meteorological record because some extend further back in time; some records are from more remote areas where there are few if any meteorological observations; and on average, glaciers exist at significantly higher altitude than meteorological stations, which may be very useful in increasing understanding of the differences in temperature change at different levels of the atmosphere.
Glacier inventories are compiled by using a combination of remote sensing and GIS technologies. Repetition takes place at time intervals of a few decades – the characteristic dynamic response time of medium-sized mountain glaciers. Length and area change can be measured for a great number of ice bodies. Area changes mainly enter calculations of sea-level contributions and of regional hydrological impacts, whereas cumulative length change not only influences landscape evolution and natural hazards (especially from ice- and moraine-dammed lakes) but can also be converted to average mass balance over decadal time intervals and, thus, helps establishing the representativity of the few direct mass balance observations.
Beyond aspects of climate change indication, glaciers and ice caps are observed in connection with climate and earth system modelling, water resources management, sea-level modelling (large glaciers are expected to contribute substantially to sea level rise over the next century), natural hazard assessments and community planning with respect to tourism and recreation.

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