Glacier mass balance study is concerned with changes in glacier mass through time, and especially the changes from year to year (Ahlmann, 1948; Meier, 1962; Anonymous, 1969; 0strem & Stanley, 1969; 0strem & Brugman, 1991; Paterson, 1994; Kaser et al., 2002). Glacier mass balance forms the vital link between the changing atmospheric environment and glacier dynamics and hydrology. The most obvious present-day connection between glacier mass balance and global change is the rise in global sea level that will occur if glacier melting increases in response to global warming. Thorarinsson (1940) is usually credited as the first scientist to study the effect of present-day glacier changes on sea level. He stated the problem in terms of the following (slightly paraphrased) questions:

1 Are present-day glaciers in equilibrium?

2 Are glacier changes synchronous, or are the effects of the growth of some offset by the shrinkage of others?

3 Is there a measurable variation in the volume of the oceans due to variations in glacier volume?

These questions are still relevant today but are still difficult to answer. Thorarinsson (1940) established our modern convention of discussing separate sea-level contributions from 'glaciers' (mountain glaciers and ice caps) and 'ice sheets' (Greenland and Antarctica). After a systematic survey of the literature for the major glacial regions, Thorarinsson (1940) concluded that there were widespread and similar amounts of glacier thinning in different regions. He estimated the then-current glacier contribution (late 19th and early 20th Century) to global sea-level rise to be about 0.5 mm yr-1. Thorarinsson (1940) also noted that his estimates of glacier thinning would be improved by '. . . extending to an increased number of districts quantitative investigations into glacier regimes of the kind undertaken by Ahlmann and his assistants round the Norwegian Sea'. He is obviously referring here to the pioneering studies of glacier mass balance, summarized by

Ahlmann (1948). Ahlmann's concepts have since been extended to several hundred glaciers in almost every part of the world (Dyurgerov & Meier, 1997; Cogley & Adams, 1998; Haeberli et al., 1998a; Dyurgerov & Meier, 2000; Braithwaite, 2002; Dyurgerov, 2002, 2003; Dowdeswell & Hagen, 2004; Dyurgerov & Meier, 2004; Haeberli, 2004; Hagen & Reeh, 2004).

Interest in glaciers and sea level was revived in the 1980s by a seminal paper (Meier, 1984) and the results of an international workshop on the topic (Polar Research Board of the National Research Council, 1985). Not surprisingly, The Intergovernmental Panel on Climate Change (IPCC) considered sea-level changes in each of its scientific assessments of climate change (Warrick & Oerlemans, 1991; Warrick et al., 1996; Church et al., 2001). These conclude that the major source of sea level rise to 2100 under expected global warming ('business as usual') will be thermal expansion of sea water with significant extra contributions from increased melting of mountain glaciers and ice caps, excluding Greenland and Antarctica. We can surely all agree that glacier mass balance should be seen within the context of global climate change but very few glacier studies were started with this connection in mind.

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