R. Franklin
Written Preliminary Exam
Baker
Mountain glaciers are generally in retreat all over the planet. They were commonly at
their last neoglacial advanced positions between about A.D. 1600 and 1900. Which
specific areas of the world are experiencing the most rapid contemporary glacial
retreat, and which areas are experiencing the least retreat (or perhaps even advances)?
Observations from the early twentieth century, qualitative assessments (IPCC 2001)
during the twentieth century and current quantitative studies (Dyurgerov and Meier 2005;
Oerlemans 2005) on the terminal positions and mass balances of mountain glaciers all
show that these ice bodies are retreating at an accelerated rate both in high to mid
latitudes and equatorial positions. Since the last neoglacial advance mountain glaciers
have generally followed a similar pattern of retreat. After reaching their maximum extent
at about A.D. 1550 to 1850 mountain glaciers retreated until about 1940. At this time
recession either declined or reversed as the globe slightly cooled from this time until the
late 1970s. At that time retreat became accelerated and much more widespread and
synchronous. Retreat has further increased since 1995 as the past decade has seen
increasing drought and the highest
Figure 1
temperatures on record (IPCC 2007).
These mountain glaciers and small ice caps
(ice sheets of Greenland and Antarctica
excluded) account for 4% of the land ice
volume yet they contribute 30% of the 20th
century sea-level change due to their
accelerated level of retreat (Dyurgerov
2003).
Data from the World Glacier Monitoring Service in Zurich, Switzerland (UNEP/GRIDArendal) underscores this increased rate of retreat as they
report that, for thirty reference glaciers with continuous mass Fig. 2
balance measurements since 1975 (figure 1, mass balance
subset), average annual mass loss in meters water equivalent
(mwe) for the past decade (0.58 mwe for 1996 – 2005) is
more than double that of the previous decade (0.25 mwe for
1986 – 1995) and more than four times the rate for the period
1976 – 1985 (0.14 mwe).
The glacier lengths represented here in figure 2 from the
2001 IPCC report show the decreasing trend for twenty
glaciers around the world from The Canadian Rockies to
Norway, Svalbard and Switzerland to Kenya, Irian Jaya and
Peru to Chile and New Zealand. All glaciers show a trend of
retreat over the past 400 years with an accelerated loss of
length in the past half century except for glaciers in western
Norway and at New Zealand’s Franz Josef Glacier (New Zealand’s Fox Glacier is also
advancing). At Grindelwald Glacier in Switzerland and Glacier d’Argentiere in France a
readvance occurred during the mid 1900s and this time period encompasses a decreased
rate of retreat elsewhere in Switzerland and Austria.
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R. Franklin
Written Preliminary Exam
Baker
While retreat is occurring at a rapid pace world-wide there are certain regions that are
experiencing above average retreat. Variations in glacier length have been the primary
method of measuring glacial retreat but it has been argued that the measure of mass
balance is a more accurate way of determining the health of a glacier as it is a direct
measure of the exchange of ice mass between the atmosphere land and ocean. Changes
in glacier mass do take longer, however to change the terminus of the glacier, depending
on glacier length and thickness. Dyurgerov and Meier (2005) adopt the mass balance
method of assessing glacier change and while different to the terminus length
measurement method as researchers have found that this method is robust with
measurements made using the other method.
It must be noted that there exists abundant information on the occurrence and retreat of
glaciers world wide (e.g. from GLIMS measurements at the National Snow and Ice Data
Center IN Boulder, Colorado and the World Glacier Monitoring Service in Zurich,
Switzerland) but there have been few comprehensive studies done on standardized
comparisons of global glacial retreat (Oerlemans 2005, Dyurgerov and Meier 2005,
Meier et al 2003, Dyurgerov 2003, Oerlemans 1994).
To account for differences in glacier area and thickness while making a comparison of
retreat rates, Dyurgerov and Meier use a
Figure 3
volume-area scaling method on observational
data (figure 3) and then combines those into
larger climatically homogenous regions (ibid,
Meier et al 2003). They weighted individual
mass balance records by surface area because
of the bias towards observing small glaciers
that has been noted.
Glaciated regions ranked in order of most
glacial retreat to least are determined by
cumulative negative mass balance over the
period 1960 – 1997 are (1)North America,
(2)Alaska, (3)Asia, (4)Southern Hemisphere, the (5)Arctic and (6)Europe, which actually
has a positive cumulative mass balance reported (Meier et al 2003). This differs slightly
from the more recent and widely citied review by Dyurgerov and Meier in 2005 where
the rank of most to least glacial retreat over the past 40 years is: (1)Patagonia (North and
South ice fields), (2)Alaska, (3)northwestern United States/Canada, (4)the
Himalaya/Asia, (5)the Andes, (6)the Arctic and (7)Europe, with a slightly negative
cumulative mass balance reported. This now negative balance may be the result of using
records from more sites in this are and also continued retreat over the period 1997 –
2003.
The areas experiencing the most accelerated glacial retreat are continental mountain
glaciers such as those in the interior of North America (Rocky Mountains and Cascade
and Sierra Nevada ranges), Alaska and the North and South Patagonian Ice Fields and
2
R. Franklin
Written Preliminary Exam
Baker
those occupying steep mountain valleys such as some in New Zealand and the Swiss
Alps. In the central Rockies glaciers are reaching a position last exposed 3000 years ago
(Osborn and Luckman 1988) and the Cascade Range has seen 4 glaciers disappear since
1985 with most remaining glaciers in a state of disequilibrium. Underscoring the
accelerated rate at which these continental glaciers are retreating is while they constitute
25% of the total area of land ice, they contribute 45% of the glacial retreat over the last
forty years (see table 1).
Also experiencing some of the highest retreat rates are the tropical glaciers that were not
included in the main regions addressed by the global studies of Dyurgerov and Meier, the
glaciers of Africa and South America. The Furtwangler Glacier atop Mt Kilamanjaro has
lost 80% of its volume over the past century and Mt Kenya’s glaciers have lost almost
half of their volume (Thompson et al 2002). In the tropical Andes, of note are
Quelccaya, whose outlet glacier, Qori Kalis has retreated to a position that has not been
exposed in 5000 years and Chacaltaya, a glacier in Bolivia that has lost 90% of its
volume since 1940. These glaciers are small and do not count for a large portion of the
global total glacial volume but are important as indicators of high elevation climate
change in the tropics.
Mountain glaciers with less rapid retreat rates are those in Europe and in arctic regions.
This can be noted in the table provided by Dyurgerov (2003) which shows that the Arctic
and Europe have lost a much smaller volume of ice per area of glacier cover. For
example while Europe represents 3.1% of land ice volume its representative meltwater
contribution is only a tenth of that porportion and while the Arctic contributes
approximately 60% of what would be expected for the total ice area of its size.
Table 1. Contributors to Global Water Cycle and Sea Level Rise (Dyurgerov 2002)
Region
% of Total Area
% of Contrbtn to Vol
of mountain land ice
Change 1961-2003
Arctic
52.7
31.5
High Mountain Asia
19.4
23.9
Alaska and Coastal Mountains
15.0
23.0
NW USA and SW Canada
6.5
16.6
Patagonia Ice Fields
3.3
4.7
Europe
3.1
0.3
Advancing glaciers such as those present in the western coastal maritime environments of
New Zealand Europe and North America will be discussed in the next section.
What are the best explanations for these patterns (locations of maximum retreat and
locations of the opposite behavior)? -Discuss your explanations in terms of
climatology, glaciology, local settings, etc.
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R. Franklin
Written Preliminary Exam
Baker
The class of advancing glaciers, while present on the global scene, usually consist of
individual glaciers rather that collectives of glaciers representing an entire region. These
are usually found in coastal regions with a strong maritime climate such as in coastal
Norway, northern coastal North America and the west coast of New Zealand. These
glaciers have positive mass balances as the high rate of snowfall outpaces ablation
occurring at the glacier terminus. This phenomenon is at work on the coast of Norway as
14 out of 25 records of glacier activity showed advance in the 1990s including Engabreen
and Nigaardsbreen Glaciers (Figure 1). This was due to several winters of above average
snowfall in coastal Scandanavia. Interestingly Norway’s continental glaciers for this
same time period showed retreat in concert with the retreat observed for the rest Northern
Europe (Austria, Switzerland etc) (Andreaasen 2005) at the same time as the maritime
glacier advance. Franz Josef and the Fox Glacier in New Zealand have their
accumulation zones in areas of unusually high precipitation. Recent advance at these
glaciers can be attributed to the increased number and intensity of El Nino events, as this
region is sensitive to atmospheric circulation associated with the Pacific Ocean.
Taku Glacier in coastal Alaska comes off from the Juneau Icefield and is a tidewater
glacier ending in the Tuku inlet. This glacier has been advancing since 1860 and its
positive mass balance has allowed it to overcome the recent warming of the 20 th century.
Since 1986 this glacier has had a slight negative mass balance but because of its size this
has had a negligible effect. All of the locations of glaciers showing contemporary
advance (coastal Scandanavia, coastal southern Alaska, New Zealand) are regions that
are effected by the current positive mode of the Atlantic Multidecadal Oscillation
(AMO). This index represents annual ocean temperature anomalies across the northern
Pacific and positive phases (as we are currently in) positively affects rainfall over the
Pacific Northwest, southern Alaska and northern Europe.
Glaciers in continental Europe (Switzerland, Austria) are subject to the effects of the
same climate indices as their coastal neighbors but with less of a maritime influence the
effects are not as pronounced. The regions of northern Europe and the Arctic, which are
experiencing relatively slow retreat rates compared to other areas with mountain glaciers
are strongly influenced by the Atlantic Multidecadal Oscillation. This plays a large part in
mitigating the effect of rising temperatures on glacial mass balance.
Another climate index that controls precipitation over North America is the Pacific
Decadal Oscillation (PDO). This is an index of temperature anomalies over the northern
Pacific Ocean with warm (cool) or positive (negative) phases of the PDO indicating
warmer (cooler) sea surface temperatures (SST) along the coast of Northern America and
cooler (warmer) temperatures in the central North Pacific. A cool phase of the PDO
brings warm and dry winters to the Pacific Northwest and has been correlated with
glacier retreat (Pederson et al 2004). In Glacier National Park, Montana, the 1850’s
glacial maximum was likely produced in part by 70 years of wet cool summers (cool
PDO). The subsequent period of retreat (1917 – 1941) coincides with the warm PDO
phase from 1925 – 1946 and current retreat, accelerating from the mid-1970s onward
corresponds to the current warm phase of the PDO. This retreat pattern, common to
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R. Franklin
Written Preliminary Exam
Baker
glaciers along the North American cordillera, likely is produced in part by the strong
influence of the Pacific Decadal Oscillation in this region.
Climate patterns initiated by ocean pressure and sea surface anomalies such as the PDO,
AMO and the El Nino/Southern Oscillation are responsible for a large portion of glacial
fluctuations but there are other important influences in contemporary glacial retreat.
These factors are volcanic activity and the unusual recent warm temperatures over the
past century and a half.
Porter (1986), looking at Greenland ice sheet acidity levels (a proxy for volcanic
activity), over the last 250 years found that alpine glacial advances correlated to the
spikes in acidity level associated with volcanic eruptions (see figure 4). This response
has a lag time and is also seen in lowered global temperatures in association with
volcanic eruptions throughout the Holocene (Dyurgerov and Meier 2005; Lamarche and
Hirschboeck 1984).
Figure 4. Porter 1986
Temperature trends over the past two
centuries are also closely linked with glacial
activity. Natural temperature variations are
forced by solar activity and volcanic
eruptions and temperature in the post
industrial era has additionally been forced
by anthropogenic aerosol emissions and
greenhouse gas levels (Ammann et al 2007).
Ammann found that using solar, volcanic,
greenhouse gas and tropospheric sulfate
forcings in their NCAR CSM 1.4 general
circulation model robustly simulate the variations and longer term trends in temperature
over the past millennium and specifically the previous two centuries.
Simulations without anthropogenic effects did not produce the full level of warming for
the 20th century. Although natural forcings are responsible for the decadal structure of
temperature patterns, the trend and fluctuations in rising temperatures noted especially
over the past fifty years are not achieved without forcing the model with anthropogenic
sulfates and greenhouse gases. This current trend in warming corresponds to the
accelerated rates in glacier recession that are above what is expected from the range of
natural climate conditions (volcanoes, solar radiation and atmospheric circulation
patterns) (ibid).
What program would you devise to determine where the maximum zones of retreat
should occur over the next several decades?
According to the IPCC climate scenarios we can continue to expect rising temperatures
globally, so areas experiencing current advanced retreat will continue in their dramatic
demise. However changes in temperature for the near future will be greatest at higher
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R. Franklin
Written Preliminary Exam
Baker
latitudes and elevations. This could imply that the relatively slower retreat that the
European and Arctic glaciers are experiencing will accelerate in the future.
A model can be structured based on various factors controlling glacial retreat. From
glacier measurements contained in world databases such as GLIMS or the WGMS,
subsets of glaciers (“glacier hotspot zones”) can be assembled that have combined:






Mean temperatures close to 0 degrees C (will convert additional energy (T)
directly to melting)
ELA near the 0 degree isotherm (most affected by future rise in T)
Locations removed from the zone of influence of maritime climates
Glaciers in permanent disequilibrium
Steep mountain glaciers, e.g. alps of N.Z or Europe (respond rapidly to changes in
T gradients)
Long valley glaciers, e.g. Patagonia, with ablation occurring along the whole
length of their profile (subject to “stepwise” catastrophic failure as they fall into
neg. mass balance)
Overlying this spatial network of glaciers can be another conceptual frame which will
calculate the probability of either continuation or change of current atmospheric modes of
variability. For example, for a change in the PDO there is thought to be a decade or so of
oceanic adjustment time, so glacial activity regimes that are responding in a certain way
to a specific atmospheric circulation can perhaps be projected into the future for a span of
time following a shift in phase of the index of regional interest.
There are two other layers that can be factored into the model. One is a layer
representing both anthropogenic sulfate aerosols and volcanic activity. This layer has the
drawback of not being able to be used for determining retreat very far into the future as
aerosol effects are not as long lasting as other glacial forcing factors and volcanic activity
is not predictable. The other layer is a more monotonic increase in glacial retreat that is
based on rising temperatures under current (and future) greenhouse gas level. Because of
the long residence time in the atmosphere of key GHGs this layer has a little more
“predictive” power than the aerosol layer.
Using these “layers”, researchers can determine which glacial “hotspot” zone’s retreat
will be enhanced or dampened by climate and anthropogenic variables. This will enable
researchers to make an educated guess as to where the maximum zones of glacial retreat
will occur over the next several decades.
References:
Andreassen, L.M., H. Elvehøy, B. Kjøllmoen, R.V. Engeset and N. Haakensen. 2005.
Glacier mass balance and length variation in Norway. Annals of Glaciology, 42.
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Diaz H.F. and Graham N.E. 1996. Recent changes in tropical freezing heights and the
role of sea-surface temperature. Nature 383:152 – 155.
Dyurgerov, M. and M. F. Meier, 2005: Glaciers and changing earth system: A 2004
snapshot. Occasional Note 58, INSTAAR, Boulder, CO, 117 pp.
Dyurgerov M. 2003. Mountain and subpolar glaciers show an increase in sensitivity to
climate warming and intensification of the water cycle Journal of Hydrology
Vol. 282 (1-4) pp 164-176
Intergovernmental Panel on Climate Change: 2001. Report prepared for the IPCC by
Working Group I. Cambridge University Press, Cambridge.
Intergovernmental Panel on Climate Change: 2007. Report prepared for the IPCC by
Working Group I. Cambridge University Press, Cambridge.
LaMarche V.C. and Hirschboeck, K. 1984. Frost rings in trees as records of major
volcanic eruptions. Nature 307 (12) pp. 121 – 126.
Osborn G. Luckman B.H. 1988. Holocene glacier fluctuations in the Canadian Cordillera
(Alberta and British Columbia). Quaternary Science Reviews Vol. 7:2 pp 115 –
128.
Pederson, G. T., D. B. Fagre, S. T. Gray, and L. J. Graumlich, 2004: Decadal-scale
climate drivers for glacial dynamics in Glacier National Park, Montana, USA.
Geophysical Research Letters 31
Porter S.C. 1986. Pattern and forcing of Northern Hemisphere glacier variations during
the last millennium. Quaternary Research 26: 27 – 48.
Thompson LG, Mosley-Thompson E, Davis M, Lin PN, Yao T, Dyurgerov M and Dai J
1993: "Recent warming": ice core evidence from tropical ice cores with emphasis
on Central Asia. Global and Planetary Change, 7, 145-156.
Thompson LG, Mosley-Thompson E, Davis ME, Henderson KA, Brecher HH,
Zagorodnov VS, Mashiotta TA, L in PN, Mikhalenko VN, Hardy DR, Beer J.
2002. Kilimanjaro ice core records: evidence of Holocene climate change in
tropical Africa. Science 298: 589–593.
UNEP/GRID-Arendal, Mass balance reference glaciers in nine mountain ranges,
UNEP/GRID-Arendal
Maps
and
Graphics
Library,
http://maps.grida.no/go/graphic/mass-balance-reference-glaciers-in-ninemountain-ranges (Accessed 27 June 2007).
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