Glaciers

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From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change

Model studies indicate that CO2-induced global warming will result in significant melting of earth’s glaciers, contributing to a rise in global sea level. Global data on glaciers do not support claims made by the IPCC that most claciers are retreating or melting.

Contents

Global Trends

The full story must begin with a recognition of just how few glacier data exist. Of the 160,000 glaciers presently known to exist, only 67,000 (42 percent) have been inventoried to any degree (Kieffer et al., 2000). Mass balance data (which would be positive for growth, negative for shrinkage) exist for more than a single year for only slightly more than 200 (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 10 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 we really know very little about the true state of most of the world’s glaciers.

During the fifteenth through nineteenth centuries, widespread and major glacier advances occurred during a period of colder global temperature known as the Little Ice Age (Broecker, 2001; Grove, 2001). 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. In many instances the rate of glacier retreat has not increased over the past 70 years, during a time when the atmosphere experienced the bulk of the increase in its CO2 content.

In an analysis of Arctic glacier mass balance, Dowdeswell et al. (1997) found that of the 18 glaciers with the longest mass balance histories, just over 80 percent 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.” 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, which is hardly what one would expect in the face of what some 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).

Despite reports that Himalayan glaciers are threatened with severe losses due to climate change, Hewitt (2011) suggests that, in reality, late and post-Little Ice Age glaciers have been recently expanding. The Canadian researcher reports that Karakoram glaciers have only declined by 5% or so since the early 20th century, "mainly between the 1920s and 1960s." Losses slowed thereafter, but "since the late 1990s we have reports of glaciers stabilizing and, in the high Karakoram, advancing (Hewitt, 2005; Immerzeel et al., 2009)." Total snow cover has also been increasing. It seems that glacial extent and sustained high elevations of the main Karakoram, together with all-year accumulation, help to buffer glaciers against warming. Additionally, Hewitt notes that "with high-altitude precipitation occurring as snowfall in summer and winter, [glaciers] may benefit from increased moisture transportation from warmer oceans.”

Jan Mayen is a volcanic island located in the North Atlantic Ocean, between Iceland and Svalbard. Noting that a reduction in glacial ice volume in Iceland and Svalbard has been observed since the mid-1990s, authors Rolstad Denby and Hulth (2011) say that "it is of interest to determine whether the same is true for Jan Mayen glaciers, where very few glaciological data are available." Working with geodetic data derived from optical images of the island obtained in 1949, 1975 and 2008, the authors were able to provide initial information on ice-volume changes there over the past six decades.

From 1975-2008, the ice volume in the southern part of Jan Mayen Island clearly increased, and the data suggest that there was also an increase in ice volume from 1949-2008, although the latter result was not statistically significant. Since the 1980s, however, “sea-ice has now retreated in response to the sizable regional warming,” but with greater evaporation and a concomitant winter precipitation increase of 7%, "the increase in ice volume in the southern parts may be explained by orographic effects on precipitation.” It appears that in coastal regions where warming causes winter sea-ice to no longer form, the extra moisture made available to the local atmosphere by nearby evaporation can sometimes enhance the delivery of snowfall to the land, leading to a buildup of glacial mass, even in a warming environment, as demonstrated by the Jan Mayen experience.


References

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Related Links

Glaciers in Antarctica

Glaciers in Africa

Glaciers in the Arctic

Glaciers in Europe

Glaciers in North America

Glaciers in South America

External Links

CO2Science.org

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