Download New Zealand glacier response to climate change of the past 2

Global and Planetary Change 22 Ž1999. 155–168
www.elsevier.comrlocatergloplacha
New Zealand glacier response to climate change of the past 2
decades
T.J. Chinn
)
Alpine and Polar Processes Consultancy, C r -NIWA, P.O. Box 6414, Dunedin, New Zealand
Received 22 September 1997; accepted 19 February 1999
Abstract
Oblique aerial photography of 111 glaciers during the past 2 decades has recorded a reversal of the past century
glacier-recession trend. Cirque glaciers show little response to the recent mass balance increase; mountain glaciers show
visible advances. Some valley glaciers have advanced, some have thickened in the upper trunk, and the larger ones and those
with proglacial lakes continue to recede. The shift to advance is driven by an average lowering of snowlines of 67 m,
equivalent to a cooling of 0.478C if other factors are held constant. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: glaciers; fluctuations; New Zealand
1. Introduction
From a programme begun in 1977, which records
end-of-summer snowlines on selected glaciers
throughout the Southern Alps, data are available on
glacier length and mass balance changes. This paper
takes the opportunity of a recent trend towards positive glacier balances to examine the change in length
of New Zealand glaciers in response to the climate
of the last 2 decades, in an attempt to isolate the
timing of the climate change responsible for the
)
Corresponding author. Tel.: q64-3-477-8615; fax: q64-3479-0134.
E-mail address: [email protected] ŽT.J. Chinn.
glacier changes. Responses are discussed in terms of
different types of glaciers.
2. Glacier observations in New Zealand
The Southern Alps of New Zealand lie athwart
the prevailing westerly weather systems, and generate a strong west–east orographic precipitation gradient with an associated steep eastward rise of glacier
equilibrium line altitudes. Extreme maritime glaciers
occur west of the Main Divide, with ‘dry’ balance
glaciers and rock glaciers lying to the east. New
Zealand glaciers are mainly high activity maritime
types with precipitation at or well above 3 mra.
A total of 3149 glaciers has been inventoried for
New Zealand ŽFig. 1. ŽChinn, 1991., but few glacier
termini have been systematically monitored. The
most comprehensive set of fluctuations are recorded
0921-8181r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 8 1 8 1 Ž 9 9 . 0 0 0 3 3 - 8
156
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
Fig. 1. Distribution of the glaciers of the Southern Alps, South Island, New Zealand.
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
157
Table 1
Summary of glacier size changes of the past century Žfrom Chinn, 1996..
DL Žkm., average change in glacier length.
DL Ž%., average change in length as a proportion of original length.
Rate Žmra., average rate of recession.
DElev Žm., average rise of glacier mean elevations.
D Area Ž%., average change in area of a limited number of glaciers
DL Žkm.
DL Ž%.
Rate Žmra.
DElev Žm.
D Area Ž%.
Cirque glaciers
Alpine glaciers
Valley glaciers
Glaciers with lakes
y0.78
y48
y7.8
y84
–
y1.17
y44
y11.7
y137
y32
y1.77
y29
y17.7
y68
y25
y1.8
y24
y18
y16
y23
for Franz Josef Glacier Žeg, Suggate, 1950; Sara,
1968. and Stocking Glacier ŽSalinger et al., 1983..
The two glaciers show a high degree of conformity
in terminus behaviour. Sporadic terminus measurements are also available for the Fox Glacier ŽSara,
1968., Ivory Glacier ŽAnderton and Chinn, 1978.,
Dart Glacier ŽBishop and Forsyth, 1988. and Whakapapanui Glacier ŽKrenek, 1959; Heine, 1962.. Observations of the large valley glaciers; Tasman, Hooker,
Mueller and Godley Glaciers of Mount Cook National Park, have been summarised by Gellatly
Ž1985a.. Many intermittent and opportunistic obser-
Fig. 2. Fluctuations of the terminus position of Franz Josef Glacier. Amplitude of the changes are the greatest of all glacier fluctuations
measured in the New Zealand Southern Alps.
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T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
vations of other glaciers are available from various
sources.
2.1. Glacier length–climate correlations
Correlations of glacier terminus fluctuations with
temperature and precipitation have been attempted
only for the Franz Josef Glacier ŽSuggate, 1950;
Hessell, 1983; Gellatly and Norton, 1984. and Stocking Glaciers ŽSalinger et al., 1983., but results are
ambiguous. Hessell Ž1980. argued that an implied
warming was artificial and that the terminus changes
could be explained by precipitation changes; whereas
Salinger Ž1982. showed that the termius changes
were related to a 0.58C warming. A more refined
result was obtained by Woo and Fitzharris Ž1992.,
who modelled the mass balance of the Franz Josef
Glacier and related the results to variations of the
terminus position. Glacier length variations have been
compared with variations in atmospheric circulation
patterns reconstructed back to 1911 ŽFitzharris et al.,
1992., where a strong linkage was found.
The frequent and intensive measurements required
for mass balance studies have been carried out at
Fig. 3. Example of cumulative length changes of three characteristic glacier types from the Swiss Alps. Small cirque glaciers such as the
Pizol, have low basal shear stresses and respond directly to annual mass balance and snowline variability through depositionrmelting of
snowrfirn at the glacier margin. Medium-size mountain glaciers, such as the Trient, flow under high basal shear stresses and react
dynamically to decadal mass–balance variations in a delayed and strongly smoothed manner. The Franz Josef Glacier is of this type. Large
valley glaciers, such as the Aletsch, damp decadal mass–balance variations but exhibit strong signals of secular trends. The Tasman Glacier
is an example of this type Žfrom Haeberli, 1995..
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
only a few New Zealand glaciers, with the longest
and most complete record of 7 balance years from
the Ivory Glacier ŽAnderton and Chinn, 1978..
2.2. Termination of the little ice age in New Zealand
The glaciers of New Zealand have retreated dramatically during the past century ŽTable 1.. Between
about A.D. 1750 and 1890, persistent retreat appears
to have begun at different times on different glaciers,
and to have proceeded at different rates. Recession
has been spectacular at some glaciers, but others
have shown very little change in length. Dates from
moraines indicate that for many glaciers, the maximum was reached around 1600 ŽWardle, 1973; Gellatly et al., 1988. followed only by minor retreat
before the rapid wasting during the 20th century
ŽGellaty, 1985b.. The most rapid collapse of all
glaciers occurred in the mid 20th century ŽFig. 2...
Within the general recession, some glaciers made
minor resurgences while others have steadily diminished, with variations similar to the Swiss examples
of Fig. 3. Literature on the Franz Josef and Fox
Glaciers deals mainly with retreat since the 1890s,
but moraines indicate that these glaciers attained a
maximum in 1750 ŽLawrence and Lawrence, 1965..
3. Glaciers and climate
Glacier fluctuations are among the clearest signals
of climate change because glaciers are effectively
highly sensitive, large-scale climate instruments.
However, they do not measure simple temperature or
snowfall changes, rather they indicate a complex
combination of mass and energy exchange at the
Earth’s surface. Air temperature and precipitation,
the two elements most commonly correlated with
glacier fluctuations, are only two elements of the
complex chain of processes linking climate and
glacier fluctuations ŽHaeberli, 1995..
3.1. Response time
Direct, undelayed changes to a glacier result from
annual cycles of mass–balance change at the glacier
surface which are subsequently transmitted downglacier to produce the indirect, delayed reaction to
climate forcing of the glacier front. Following a
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change in mass balance, there is a lag before the
length of a glacier starts to change, and it will
continue to change until a new equilibrium length is
reached. This time taken for a glacier to fully adjust
to a change in its mass balance is the ‘filling time’ or
‘ volume response time’ ŽPaterson, 1994, p. 319;
Ruddell, 1995.. Volume response time has been
found to be related to an index of glacier thickness
and ablation loss at the terminus ŽJohannesson et al.,
1989.. Response times for most valley glaciers are in
the order of 10–50 years ŽOerlemans, 1994.. The lag
between a change in mass balance and the first
significant response at the terminus Žnot including
the immediate effects of terminus ablation changes.
is the ‘lag time’ or ‘terminus response time’ ŽPaterson, 1994, p. 319. which occurs many years before
the volume response time. These varying terminus
response times for the onset of observed glacier
readvances, which constitute an expression of differing glacier responses to the same climate change, is
the subject of this study.
3.2. Glacier length changes
Different types of glaciers have different response
times, making it inappropriate to compare or combine terminus behaviour of different types of glaciers,
or indeed, to use length changes of a single glacier as
being representative of climate change. Differing
responses to climate forcing of different types of
glaciers is demonstrated in Fig. 3, which gives length
changes for three Swiss glaciers Žcomparative measurements of this nature are not available for New
Zealand glaciers.. These differing responses indicate
that glaciers should be separated into different categories, and that it is normally inappropriate to compare the terminus behaviours of Franz Josef Glacier
with the Tasman Glacier. However it may be appropriate to compare them over periods longer than their
response times, say over 100 years.
4. Method
4.1. Data from annual snowline programme flights
Annual oblique aerial photography flights have
been made at the end of summer over the Southern
Alps since 1977, originally to record glacier occurrence for the New Zealand glacier inventory, ŽChinn
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T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
and Whitehouse, 1980. and latterly to record endof-summer snowlines as an indicator of net mass
balance change. After completion of the inventory,
49 selected ‘index’ glaciers, arranged in transects
across the Southern Alps, were selected for continuing annual end-of-summer snowline surveys. This
monitoring programme is ongoing and uses the position of the end-of-summer snowline or equilibrium
line elevation ŽELA. as defined by Meier and Post
Ž1962. as a surrogate for mass balance ŽChinn, 1995..
During the 20-year period of monitoring, the trend of
glacier recession has reversed, with positive balances
occurring in most years since 1980, and more recently all glaciers have shown positive balances ŽFig.
4.. Some of the values given in this figure differ by
small amounts from Chinn Ž1995. as the position of
the estimated long term, or steady state ELA, has
been revised for a number of glaciers to improve
consistency with regional trends. For a few glaciers
the range of measured ELAs has also been compressed to conform with the Southern Alps measured
average. There were no snowline survey flights in
1979, 1990 and 1991.
Photographs on these flights were both of the
‘index’ glaciers and the termini of the larger glaciers,
the majority of which were re-photographed in 1995.
One hundred and eleven glaciers selected from those
photographed over the past 20 years on the snowline
monitoring flights are used in this study. All available photographs for each glacier were examined in
chronological order and the terminus changes noted
in Tables 2–4 as advance ŽA., stationary ŽS., or
recession ŽR.. Because of the photograph quality or
angle of view, changes at some glaciers could not be
defined and are tabulated as undefined ŽU..
Medium-altitude oblique photographs, taken from
about 3000 m, have limited resolution, making it
impractical to measure the changes as absolute distances. Although some spectacular changes have occurred, the majority of changes were only minor and
difficult to detect on the photographs; it was impossible to detect changes of the small cirque glaciers.
From simple mass balance processes, however, it
follows that, where snow cover remains over the
glacier terminus after the end of summer, there has
been no ice loss and the glacier must have advanced
by an amount equal to ice flow. The ‘advance’ of
these cirque glaciers is immediate and was initiated
in the year of observation, consequently they are not
included in the estimates of response times.
Fig. 4. The percentage of all index glaciers measured each year indicating positive proxy mass balances. Numbers indicate total number of
glaciers observed each year.
Table 2
Fluctuations of mountain glaciers, 1977 to 1997, with terminus response times to a 1976"1 positive balance
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
161
162
Table 3
Fluctuations of valley glaciers, 1977 to 1997, with terminus response times to a 1976"1 positive balance. Vs valley glaciers; Dsdebris mantled glaciers
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
Table 4
Fluctuations of glaciers with lakes, 1977 to 1997, with terminus response times to a 1976"1 positive balance. C s cirque; Vs valley; M s mountain; Dsdebris mantled;
L s proglacial lake
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
163
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T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
The dataset has been subdivided into the three
sizertype classifications of Haeberli Ž1995 and Fig.
3. in order to compare glaciers of similar response
times. The subdivision is basically by glacier size,
but also takes some account of shape and slope.
Ž1. Small, low-shear–stress cirque glaciers ŽC.
reflect changes in climate and mass balance almost
without delay.
Ž2. Large, high-shear–stress mountain glaciers
ŽM. react to decadal variations in climate and mass
balance forcing with an enhanced amplitude after a
delay of several years.
Ž3. Valley glaciers ŽV. with low-gradient tongues
and frequently debris mantled give strong and efficiently-smoothed signals of secular trends with a
delay of several decades.
Glaciers entering proglacial lakes ŽL. are frequetly decoupled from climate response ŽKirkbride,
1993. and these have been placed into a separate
category.
Debris covered glaciers ŽD. have been identified
but not separated from the valley glaciers. Debris
cover is proportionally highest on large valley
glaciers, with an average of more than 25% of their
surfaces mantled, whereas alpine glaciers average
- 10% cover ŽChinn, 1996..
5. Results
The 2-decade record of terminus behaviour of 78
glaciers interpreted from oblique photographs is presented for 38 mountain glaciers ŽTable 2.; 26 valley
glaciers ŽTable 3. and 14 glaciers having proglacial
lakes ŽTable 4..
5.1. Response times
Tables 2–4 identify the first occurrences of the
reversal of terminus recession within the limits of the
Fig. 5. Tasman Glacier equilibrium line elevations from 1959 to 1997.
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
intervals of the surveys. Assuming that the majority
of these readvances are in response to the same
climate variation, then the table indicates comparative terminus response times. Using the long, detailed record of the Franz Josef glacier, which has
strongly enhanced responses to climate ŽFig. 2., the
time of the general change from negative to positive
balances may be isolated. Terminus response times
for this glacier have been variously estimated to be 5
years ŽSuggate, 1952.; 4 to 8 years ŽSoons, 1971.; 5
to 7 years ŽHessell, 1983.; 5 to 7 years ŽHooker,
1995.; and 4 to 5 years ŽTyson et al., in press.. At
the nearby Stocking Glacier Salinger et al. Ž1983.
also found a 5 to 7 year terminus response.
The Franz Josef Glacier had a well documented
vigorous advance commencing in the 1983–1984
ablation season. From the above response times, the
positive mass balances responsible for this advance
would have occurred during the 1976–1978 period.
A long record of ELA values for the nearby Tasman
165
Glacier is available since 1959 ŽChinn, 1995..This
record ŽFig. 5. clearly shows a series of low ELAs
from 1974 to 1977. This is slightly earlier by 1 or 2
years than the positive balance period predictable
from the response times found for the Franz Josef
Glacier. Positive balances dominated in 1977, the
year that snowline surveys commenced. This information suggests that the positive mass balances responsible for glacial readvances occurred towards
the end of the 1974 to 1977 period. 1976 " 1 year
has been selected for use in this study as the time of
commencement of the wave of positive mass balance
that has reversed the general recession. Terminus
response times of the glaciers to a 1976 pulse are
listed in Tables 2–4.
5.2. Cirque glaciers (C)
From aerial observations of form and changes, all
cirque glaciers appear to have regained equilibrium
Fig. 6. Percentage of 38 mountain glaciers advancing.
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T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
since the end of the LIA by the time this study
commenced. Therefore, their response to climate
change since the end of the LIA has taken less than
100 years. However, despite 2 decades of dominantly positive balances, the slow advance of these
glaciers remains undectable at the resolution of the
photographs.
balances prior to the 1974–1977 event. The dominant resurgence took place in 1983, followed by a
decline in the number of glaciers advancing. A second advance pulse is evident from 1989 to 1995
ŽFig. 6.. Response times range from 5 years to more
than 20 years as a few glaciers have yet to commence the general readvance.
5.3. Mountain glaciers (M)
5.4. Valley glaciers (V)
Thirty eight mountain glaciers ŽTable 2. includes
the steep responsive glaciers which are expected to
have attained equilibrium with climate change since
the end of last century. The data for the changes to
these glaciers are from direct observations of changes
at the termini, although many of the changes are
small and barely detectable. The advances recorded
in 1978–1979 and 1981 may indicate exceptionally
short response times Žas in the case of the steep
Crow Glacier., or may be a response from positive
Twenty six valley glaciers ŽTable 3. exhibit a
characteristic slow, dampened response of low-gradient glaciers of Fig. 2. The 1983 initial pulse evident
in mountain glaciers has been dampened into a more
general resurgence culminating in 1986, some 2 to 4
years later than that for the mountain glaciers ŽFig.
7.. Again, there appears to be a second pulse of
advances peaking in 1994.
This group includes the debris covered glaciers
which may go through a long period of loss by
Fig. 7. Percentage of 26 valley glaciers advancing.
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
lowering before entering a phase of catastrophic
retreat by glacierkarst decay. Many have detached
stagnant debris-covered ice plus avalanche ice obscuring ill-defined trunk positions. However, the
wave of positive balances has travelled the full length
of many of these glaciers. Table 3 indentifies the
glaciers yet to show a readvance. Response times for
this group range from 9 to well over 20 years.
5.5. Glaciers haÕing proglacial lakes (L)
The 13 mainly large valley glaciers entering lakes
ŽTable 4. show that these glaciers had yet to attain
equilibrium with the climate before the recent increase in balances occurred. A thickening pulse travelling down the trunk, may be observed on many of
them, but this has served only to retard the expansion
of the proglacial lakes. Although only one of these is
advancing, the cliffed termini on a few of them have
ceased retreating and are now stationary. Response
times for this group are more than 20 years and may
be as much as hundreds of years.
6. Discussion
Despite the nearly continuous period of positive
mass balances during the past 20 years, with end-ofsummer snow commonly remaining over the entire
lower glacier surfaces, the advance of cirque glaciers
remains undetectable on the aerial photographs. On a
few of these glaciers, small proglacial lakes which
had developed by the beginning of the period have
persisted.
In contrast, larger, more active mountain glaciers
have responded with visible advances. Valley
glaciers, both clean and debris-mantled, have also
shown either a re-advance or visible thickening in
the upper trunk areas. Conversely, larger debriscovered glaciers have demonstrated continued recession that many have yet to fully respond to the
climate warming of the past century while others
display a continuing thinning of the lower trunk,
with glacierkarst formation suggesting that proglacial
lakes may be about to develop. Those with proglacial
lakes are continuing to recede as their lakes expand.
Response times are a result of a complex interaction between the climate signal and the geometry of
167
the glacier. Correlations of the observed response
times with glacier lengths and surface gradients are
very poor; For response time ; length, r 2 s 0.125;
; gradient, r 2 s 0.205 and for response time ;
lengthrgradient, r 2 s 0.123.
If precipitation has remained constant, then a
temperature change responsible for the observed
lowering of the ELAs may be estimated from the
atmospheric lapse rate. From the 49 snowline ‘index’
glaciers, 672 ELA readings are available for the
period 1977 to 1997 where the average difference
between the estimated steady state ELAs and the
observed annual ELAs, gives a snowline depression
of 67 m. Using a standard lapse rate of 0.78C per 100
m, the downward shift represents a general cooling
of 0.478C since the late 1970s. A mean trend fitted
through the ELA record for the Tasman Glacier ŽFig.
5. suggests a fall of 160 m in the ELA since 1960.
In a study of a century of glacier recession to the
late 1970s, Chinn Ž1996. found an upward ELA shift
of circa 84 m for cirque glaciers. This is equivalent
to a warming of circa 0.68C. This comparison indicates that the present ‘cool climate’, if continued,
will not bring the glaciers to near their LIA size.
This is demonstrated by the fluctuations of the Franz
Josef Glacier, which although its active advance has
slowed as it presumably approaches equilibrium with
the recent climate, has only regained its 1960 extent.
In a study of past and present glaciers of the
Waimakariri basin, Chinn Ž1975. found an ELA rise
of 200 m, equivalent to 1.48C warming since the end
of the LIA. Salinger Ž1979. suggests that measured
temperatures over the past century show a warming
of circa 1.08C, with most of the rise occurring since
the 1950s.
This study demonstrates the complexity of glacier
response to climate forcing. To derive climate inferences from glacier-length changes, sophisticated
methods must be used to accomodate differences in
response times due to differences in glacier geometry.
Acknowledgements
This work was carried out under contract No.
CO5624 of the New Zealand Foundation for Research, Science and Technology. I am grateful for
168
T.J. Chinnr Global and Planetary Change 22 (1999) 155–168
the helpful comments by Dr C. Raymond and an
anonymous journal reviewer.
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