The advance/buildup or retreat/melting of glacial ice is often interpreted as a sign of climate change; and teams of glaciologists have been working for years to provide an assessment of the state of the world's many glaciers as one of several approaches to deciphering global climate trends. Although this effort has only scratched the surface of what must ultimately be done, climate alarmists have already rendered their verdict: there has been a massive and widespread retreat of glaciers over the past century, which they predict will only intensify under continued CO2-induced global warming. This assessment, however, may be a bit premature.
The full story must begin with a clear recognition of just how few glacier data exist. Of the 160,000 glaciers presently in existence, only 67,000 (42%) have been inventoried to any degree (Kieffer et al., 2000); and there are only a tad over 200 glaciers for which mass balance data exist for but a single year (Braithwaite and Zhang, 2000). When the length of record increases to five years, this number drops to 115; and if both winter and summer mass balances are required, the number drops to 79. Furthermore, if ten years of record is used as a cutoff, only 42 glaciers qualify. This lack of glacial data, in the words of Braithwaite and Zhang, highlights "one of the most important problems for mass-balance glaciology" and demonstrates the "sad fact that many glacierized regions of the world remain unsampled, or only poorly sampled," suggesting that we really know very little about the true state of most of the world's glaciers.
Recognizing the need for "more comprehensive, more homogeneous in detail and quality" glacier data (Kieffer et al., 2000), we shift our attention to the few glaciers for which such data exist. During the 15th through 19th centuries, widespread and major glacier advances occurred during a period of colder global temperature known as the Little Ice Age (Broecker, 2001; Grove, 2001). Following the peak of Little Ice Age coldness, it should come as no surprise that many records indicate widespread glacial retreat, as temperatures began to rise in the mid- to late-1800s and many glaciers returned to positions characteristic of pre-Little Ice Age times. What people may find surprising, however, is that in many instances the rate of glacier retreat has not increased over the past 70 years; and in some cases glacier mass balance has actually increased, all during a time when the atmosphere experienced the bulk of the increase in its CO2 content.
In an analysis of Arctic glacier mass balance, for example, Dowdeswell et al. (1997) found that of the 18 glaciers with the longest mass balance histories, just over 80% displayed negative mass balances over their periods of record. Yet they additionally report that "almost 80% of the mass balance time series also have a positive trend, toward a less negative mass balance [our italics]." Hence, although these Arctic glaciers continue to lose mass, as they have probably done since the end of the Little Ice Age, they are losing smaller amounts each year, in the mean, which is hardly what one would expect in the face of what climate alarmists incorrectly call the "unprecedented" warming of the latter part of the twentieth century.
Similar results have been reported by Braithwaite (2002), who reviewed and analyzed mass balance measurements of 246 glaciers from around the world that were made between 1946 and 1995. According to Braithwaite, "there are several regions with highly negative mass balances in agreement with a public perception of 'the glaciers are melting,' but there are also regions with positive balances." Within Europe, for example, he notes that "Alpine glaciers are generally shrinking, Scandinavian glaciers are growing, and glaciers in the Caucasus are close to equilibrium for 1980-95." And when results for the whole world are combined for this most recent period of time, Braithwaite notes that "there is no obvious common or global trend of increasing glacier melt in recent years."
As for the glacier with the longest mass balance record of all, the Storglaciaren in northern Sweden, for the first 15 years of its 50-year record it exhibited a negative mass balance of little trend. Thereafter, however, its mass balance began to trend upward, actually becoming positive over about the last decade (Braithwaite and Zhang, 2000).
So, the story glaciers have to tell us about past climate change is both far from clear and far from being adequately resolved. Stay tuned.
References
Braithwaite, R.J. 2002. Glacier mass balance: the first 50 years of international monitoring. Progress in Physical Geography 26: 76-95.
Braithwaite, R.J. and Zhang, Y. 2000. Relationships between interannual variability of glacier mass balance and climate. Journal of Glaciology 45: 456-462.
Broecker, W.S. 2001. Glaciers That Speak in Tongues and other tales of global warming. Natural History 110 (8): 60-69.
Dowdeswell, J.A., Hagen, J.O., Bjornsson, H., Glazovsky, A.F., Harrison, W.D., Holmlund, P. Jania, J., Koerner, R.M., Lefauconnier, B., Ommanney, C.S.L. and Thomas, R.H. 1997. The mass balance of circum-Arctic glaciers and recent climate change. Quaternary Research 48: 1-14.
Grove, J.M. 2001. The initiation of the "Little Ice Age" in regions round the North Atlantic. Climatic Change 48: 53-82.
Kieffer, H., Kargel, J.S., Barry, R., Bindschadler, R., Bishop, M., MacKinnon, D., Ohmura, A., Raup, B., Antoninetti, M., Bamber, J., Braun, M., Brown, I., Cohen, D., Copland, L., DueHagen, J., Engeset, R.V., Fitzharris, B., Fujita, K., Haeberli, W., Hagen, J.O., Hall, D., Hoelzle, M., Johansson, M., Kaab, A., Koenig, M., Konovalov, V., Maisch, M., Paul, F., Rau, F., Reeh, N., Rignot, E., Rivera, A., Ruyter de Wildt, M., Scambos, T., Schaper, J., Scharfen, G., Shroder, J., Solomina, O., Thompson, D., Van der Veen, K., Wohlleben, T. and Young, N. 2000. New eyes in the sky measure glaciers and ice sheets. EOS, Transactions, American Geophysical Union 81: 265, 270-271.