Ž .Global and Planetary Change 22 1999 155–168www.elsevier.comrlocatergloplacha

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

T.J. Chinn )

Alpine and Polar Processes Consultancy, Cr -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 centuryglacier-recession trend. Cirque glaciers show little response to the recent mass balance increase; mountain glaciers showvisible advances. Some valley glaciers have advanced, some have thickened in the upper trunk, and the larger ones and thosewith 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 recordsend-of-summer snowlines on selected glaciersthroughout the Southern Alps, data are available onglacier length and mass balance changes. This papertakes the opportunity of a recent trend towards posi-tive glacier balances to examine the change in lengthof New Zealand glaciers in response to the climateof the last 2 decades, in an attempt to isolate thetiming of the climate change responsible for the

) Corresponding author. Tel.: q64-3-477-8615; fax: q64-3-479-0134.

Ž .E-mail address: t.chinn@niwa.cri.nz T.J. Chinn

glacier changes. Responses are discussed in terms ofdifferent types of glaciers.

2. Glacier observations in New Zealand

The Southern Alps of New Zealand lie athwartthe prevailing westerly weather systems, and gener-ate a strong west–east orographic precipitation gradi-ent with an associated steep eastward rise of glacierequilibrium line altitudes. Extreme maritime glaciersoccur west of the Main Divide, with ‘dry’ balanceglaciers and rock glaciers lying to the east. NewZealand glaciers are mainly high activity maritimetypes with precipitation at or well above 3 mra.

A total of 3149 glaciers has been inventoried forŽ . Ž .New Zealand Fig. 1 Chinn, 1991 , but few glacier

termini have been systematically monitored. Themost comprehensive set of fluctuations are recorded

0921-8181r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0921-8181 99 00033-8

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168156

Fig. 1. Distribution of the glaciers of the Southern Alps, South Island, New Zealand.

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Table 1Ž .Summary of glacier size changes of the past century from Chinn, 1996 .

Ž .DL km , average change in glacier length.Ž .DL % , average change in length as a proportion of original length.Ž .Rate mra , average rate of recession.Ž .DElev m , average rise of glacier mean elevations.Ž .DArea % , average change in area of a limited number of glaciers

Cirque glaciers Alpine glaciers Valley glaciers Glaciers with lakes

Ž .DL km y0.78 y1.17 y1.77 y1.8Ž .DL % y48 y44 y29 y24Ž .Rate mra y7.8 y11.7 y17.7 y18Ž .DElev m y84 y137 y68 y16Ž .DArea % – y32 y25 y23

Žfor Franz Josef Glacier eg, Suggate, 1950; Sara,. Ž .1968 and Stocking Glacier Salinger et al., 1983 .

The two glaciers show a high degree of conformityin terminus behaviour. Sporadic terminus measure-

Žments are also available for the Fox Glacier Sara,. Ž .1968 , Ivory Glacier Anderton and Chinn, 1978 ,

Ž .Dart Glacier Bishop and Forsyth, 1988 and Whaka-Ž .papanui Glacier Krenek, 1959; Heine, 1962 . Obser-

vations of the large valley glaciers; Tasman, Hooker,Mueller and Godley Glaciers of Mount Cook Na-tional Park, have been summarised by GellatlyŽ .1985a . 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 fluctuationsmeasured in the New Zealand Southern Alps.

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168158

vations of other glaciers are available from varioussources.

2.1. Glacier length–climate correlations

Correlations of glacier terminus fluctuations withtemperature and precipitation have been attempted

Žonly for the Franz Josef Glacier Suggate, 1950;.Hessell, 1983; Gellatly and Norton, 1984 and Stock-

Ž .ing Glaciers Salinger et al., 1983 , but results areŽ .ambiguous. Hessell 1980 argued that an implied

warming was artificial and that the terminus changes

could be explained by precipitation changes; whereasŽ .Salinger 1982 showed that the termius changes

were related to a 0.58C warming. A more refinedŽ .result was obtained by Woo and Fitzharris 1992 ,

who modelled the mass balance of the Franz JosefGlacier and related the results to variations of theterminus position. Glacier length variations have beencompared with variations in atmospheric circulation

Žpatterns reconstructed back to 1911 Fitzharris et al.,.1992 , where a strong linkage was found.

The frequent and intensive measurements requiredfor 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 thePizol, have low basal shear stresses and respond directly to annual mass balance and snowline variability through depositionrmelting ofsnowrfirn at the glacier margin. Medium-size mountain glaciers, such as the Trient, flow under high basal shear stresses and reactdynamically to decadal mass–balance variations in a delayed and strongly smoothed manner. The Franz Josef Glacier is of this type. Largevalley glaciers, such as the Aletsch, damp decadal mass–balance variations but exhibit strong signals of secular trends. The Tasman Glacier

Ž .is an example of this type from Haeberli, 1995 .

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168 159

only a few New Zealand glaciers, with the longestand most complete record of 7 balance years from

Ž .the Ivory Glacier Anderton and Chinn, 1978 .

2.2. Termination of the little ice age in New Zealand

The glaciers of New Zealand have retreated dra-Ž .matically during the past century Table 1 . Between

about A.D. 1750 and 1890, persistent retreat appearsto have begun at different times on different glaciers,and to have proceeded at different rates. Recessionhas been spectacular at some glaciers, but othershave shown very little change in length. Dates frommoraines indicate that for many glaciers, the maxi-

Žmum was reached around 1600 Wardle, 1973; Gel-.latly et al., 1988 followed only by minor retreat

before the rapid wasting during the 20th centuryŽ .Gellaty, 1985b . The most rapid collapse of all

Ž .glaciers occurred in the mid 20th century Fig. 2. .Within the general recession, some glaciers mademinor resurgences while others have steadily dimin-ished, with variations similar to the Swiss examplesof Fig. 3. Literature on the Franz Josef and FoxGlaciers deals mainly with retreat since the 1890s,but moraines indicate that these glaciers attained a

Ž .maximum in 1750 Lawrence and Lawrence, 1965 .

3. Glaciers and climate

Glacier fluctuations are among the clearest signalsof climate change because glaciers are effectivelyhighly sensitive, large-scale climate instruments.However, they do not measure simple temperature orsnowfall changes, rather they indicate a complexcombination of mass and energy exchange at theEarth’s surface. Air temperature and precipitation,the two elements most commonly correlated withglacier fluctuations, are only two elements of thecomplex chain of processes linking climate and

Ž .glacier fluctuations Haeberli, 1995 .

3.1. Response time

Direct, undelayed changes to a glacier result fromannual cycles of mass–balance change at the glaciersurface which are subsequently transmitted down-glacier to produce the indirect, delayed reaction toclimate forcing of the glacier front. Following a

change in mass balance, there is a lag before thelength of a glacier starts to change, and it willcontinue to change until a new equilibrium length isreached. This time taken for a glacier to fully adjustto a change in its mass balance is the ‘filling time’ or

Ž‘volume response time’ Paterson, 1994, p. 319;.Ruddell, 1995 . Volume response time has been

found to be related to an index of glacier thicknessŽand ablation loss at the terminus Johannesson et al.,

.1989 . Response times for most valley glaciers are inŽ .the order of 10–50 years Oerlemans, 1994 . The lag

between a change in mass balance and the firstŽsignificant response at the terminus not including

.the immediate effects of terminus ablation changesŽis the ‘lag time’ or ‘terminus response time’ Pater-

.son, 1994, p. 319 which occurs many years beforethe volume response time. These varying terminusresponse times for the onset of observed glacierreadvances, which constitute an expression of differ-ing glacier responses to the same climate change, isthe subject of this study.

3.2. Glacier length changes

Different types of glaciers have different responsetimes, making it inappropriate to compare or com-bine terminus behaviour of different types of glaciers,or indeed, to use length changes of a single glacier asbeing representative of climate change. Differingresponses to climate forcing of different types ofglaciers is demonstrated in Fig. 3, which gives length

Žchanges for three Swiss glaciers comparative mea-surements of this nature are not available for New

.Zealand glaciers . These differing responses indicatethat glaciers should be separated into different cate-gories, and that it is normally inappropriate to com-pare the terminus behaviours of Franz Josef Glacierwith the Tasman Glacier. However it may be appro-priate to compare them over periods longer than theirresponse times, say over 100 years.

4. Method

4.1. Data from annual snowline programme flights

Annual oblique aerial photography flights havebeen made at the end of summer over the SouthernAlps since 1977, originally to record glacier occur-

Žrence for the New Zealand glacier inventory, Chinn

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168160

.and Whitehouse, 1980 and latterly to record end-of-summer snowlines as an indicator of net massbalance change. After completion of the inventory,49 selected ‘index’ glaciers, arranged in transectsacross the Southern Alps, were selected for continu-ing annual end-of-summer snowline surveys. Thismonitoring programme is ongoing and uses the posi-tion of the end-of-summer snowline or equilibrium

Ž .line elevation ELA as defined by Meier and PostŽ . Ž .1962 as a surrogate for mass balance Chinn, 1995 .During the 20-year period of monitoring, the trend ofglacier recession has reversed, with positive balancesoccurring in most years since 1980, and more re-

Žcently all glaciers have shown positive balances Fig..4 . Some of the values given in this figure differ by

Ž .small amounts from Chinn 1995 as the position ofthe estimated long term, or steady state ELA, hasbeen revised for a number of glaciers to improveconsistency with regional trends. For a few glaciersthe range of measured ELAs has also been com-pressed to conform with the Southern Alps measuredaverage. There were no snowline survey flights in1979, 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 thosephotographed over the past 20 years on the snowlinemonitoring flights are used in this study. All avail-able photographs for each glacier were examined inchronological order and the terminus changes noted

Ž . Ž .in Tables 2–4 as advance A , stationary S , orŽ .recession R . Because of the photograph quality or

angle of view, changes at some glaciers could not beŽ .defined and are tabulated as undefined U .

Medium-altitude oblique photographs, taken fromabout 3000 m, have limited resolution, making itimpractical to measure the changes as absolute dis-tances. Although some spectacular changes have oc-curred, the majority of changes were only minor anddifficult to detect on the photographs; it was impos-sible to detect changes of the small cirque glaciers.From simple mass balance processes, however, itfollows that, where snow cover remains over theglacier terminus after the end of summer, there hasbeen no ice loss and the glacier must have advancedby an amount equal to ice flow. The ‘advance’ ofthese cirque glaciers is immediate and was initiatedin the year of observation, consequently they are notincluded 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 ofglaciers observed each year.

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168 161

Tab

le2

Flu

ctua

tion

sof

mou

ntai

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acie

rs,

1977

to19

97,

wit

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usre

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toa

1976

"1

posi

tive

bala

nce

()

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Globaland

Planetary

Change

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168162

Table 3Fluctuations of valley glaciers, 1977 to 1997, with terminus response times to a 1976"1 positive balance. Vs valley glaciers; Dsdebris mantled glaciers

()

T.J.C

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Globaland

Planetary

Change

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168163

Table 4Fluctuations of glaciers with lakes, 1977 to 1997, with terminus response times to a 1976"1 positive balance. Cscirque; Vs valley; Msmountain; Dsdebris mantled;L sproglacial lake

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168164

The dataset has been subdivided into the threeŽsizertype classifications of Haeberli 1995 and Fig.

.3 in order to compare glaciers of similar responsetimes. The subdivision is basically by glacier size,but also takes some account of shape and slope.

Ž . Ž .1 Small, low-shear–stress cirque glaciers Creflect changes in climate and mass balance almostwithout delay.

Ž .2 Large, high-shear–stress mountain glaciersŽ .M react to decadal variations in climate and massbalance forcing with an enhanced amplitude after adelay of several years.

Ž . Ž .3 Valley glaciers V with low-gradient tonguesand frequently debris mantled give strong and effi-ciently-smoothed signals of secular trends with adelay of several decades.

Ž .Glaciers entering proglacial lakes L are fre-Žquetly decoupled from climate response Kirkbride,

.1993 and these have been placed into a separatecategory.

Ž .Debris covered glaciers D have been identifiedbut not separated from the valley glaciers. Debriscover is proportionally highest on large valleyglaciers, with an average of more than 25% of theirsurfaces mantled, whereas alpine glaciers average

Ž .-10% cover Chinn, 1996 .

5. Results

The 2-decade record of terminus behaviour of 78glaciers interpreted from oblique photographs is pre-

Ž .sented for 38 mountain glaciers Table 2 ; 26 valleyŽ .glaciers Table 3 and 14 glaciers having proglacial

Ž .lakes Table 4 .

5.1. Response times

Tables 2–4 identify the first occurrences of thereversal of terminus recession within the limits of the

Fig. 5. Tasman Glacier equilibrium line elevations from 1959 to 1997.

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168 165

intervals of the surveys. Assuming that the majorityof these readvances are in response to the sameclimate variation, then the table indicates compara-tive terminus response times. Using the long, de-tailed record of the Franz Josef glacier, which has

Ž .strongly enhanced responses to climate Fig. 2 , thetime of the general change from negative to positivebalances may be isolated. Terminus response timesfor this glacier have been variously estimated to be 5

Ž . Ž .years Suggate, 1952 ; 4 to 8 years Soons, 1971 ; 5Ž . Žto 7 years Hessell, 1983 ; 5 to 7 years Hooker,

. Ž .1995 ; and 4 to 5 years Tyson et al., in press . AtŽ .the nearby Stocking Glacier Salinger et al. 1983

also found a 5 to 7 year terminus response.The Franz Josef Glacier had a well documented

vigorous advance commencing in the 1983–1984ablation season. From the above response times, thepositive mass balances responsible for this advancewould have occurred during the 1976–1978 period.A long record of ELA values for the nearby Tasman

Ž .Glacier is available since 1959 Chinn, 1995 .ThisŽ .record Fig. 5 clearly shows a series of low ELAs

from 1974 to 1977. This is slightly earlier by 1 or 2years than the positive balance period predictablefrom the response times found for the Franz JosefGlacier. Positive balances dominated in 1977, theyear that snowline surveys commenced. This infor-mation suggests that the positive mass balances re-sponsible for glacial readvances occurred towardsthe end of the 1974 to 1977 period. 1976"1 yearhas been selected for use in this study as the time ofcommencement of the wave of positive mass balancethat has reversed the general recession. Terminusresponse times of the glaciers to a 1976 pulse arelisted in Tables 2–4.

( )5.2. Cirque glaciers C

From aerial observations of form and changes, allcirque glaciers appear to have regained equilibrium

Fig. 6. Percentage of 38 mountain glaciers advancing.

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168166

since the end of the LIA by the time this studycommenced. Therefore, their response to climatechange since the end of the LIA has taken less than100 years. However, despite 2 decades of domi-nantly positive balances, the slow advance of theseglaciers remains undectable at the resolution of thephotographs.

( )5.3. Mountain glaciers M

Ž .Thirty eight mountain glaciers Table 2 includesthe steep responsive glaciers which are expected tohave attained equilibrium with climate change sincethe end of last century. The data for the changes tothese glaciers are from direct observations of changesat the termini, although many of the changes aresmall and barely detectable. The advances recordedin 1978–1979 and 1981 may indicate exceptionally

Žshort response times as in the case of the steep.Crow Glacier , or may be a response from positive

balances prior to the 1974–1977 event. The domi-nant resurgence took place in 1983, followed by adecline in the number of glaciers advancing. A sec-ond advance pulse is evident from 1989 to 1995Ž .Fig. 6 . Response times range from 5 years to morethan 20 years as a few glaciers have yet to com-mence the general readvance.

( )5.4. Valley glaciers V

Ž .Twenty six valley glaciers Table 3 exhibit acharacteristic slow, dampened response of low-gradi-ent glaciers of Fig. 2. The 1983 initial pulse evidentin mountain glaciers has been dampened into a moregeneral resurgence culminating in 1986, some 2 to 4

Žyears later than that for the mountain glaciers Fig..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.

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lowering before entering a phase of catastrophicretreat by glacierkarst decay. Many have detachedstagnant debris-covered ice plus avalanche ice ob-scuring ill-defined trunk positions. However, thewave of positive balances has travelled the full lengthof many of these glaciers. Table 3 indentifies theglaciers yet to show a readvance. Response times forthis group range from 9 to well over 20 years.

( )5.5. Glaciers haÕing proglacial lakes L

The 13 mainly large valley glaciers entering lakesŽ .Table 4 show that these glaciers had yet to attainequilibrium with the climate before the recent in-crease in balances occurred. A thickening pulse trav-elling down the trunk, may be observed on many ofthem, but this has served only to retard the expansionof the proglacial lakes. Although only one of these isadvancing, the cliffed termini on a few of them haveceased retreating and are now stationary. Responsetimes for this group are more than 20 years and maybe as much as hundreds of years.

6. Discussion

Despite the nearly continuous period of positivemass balances during the past 20 years, with end-of-summer snow commonly remaining over the entirelower glacier surfaces, the advance of cirque glaciersremains undetectable on the aerial photographs. On afew of these glaciers, small proglacial lakes whichhad developed by the beginning of the period havepersisted.

In contrast, larger, more active mountain glaciershave responded with visible advances. Valleyglaciers, both clean and debris-mantled, have alsoshown either a re-advance or visible thickening inthe upper trunk areas. Conversely, larger debris-covered glaciers have demonstrated continued reces-sion that many have yet to fully respond to theclimate warming of the past century while othersdisplay a continuing thinning of the lower trunk,with glacierkarst formation suggesting that proglaciallakes may be about to develop. Those with proglaciallakes are continuing to recede as their lakes expand.

Response times are a result of a complex interac-tion between the climate signal and the geometry of

the glacier. Correlations of the observed responsetimes with glacier lengths and surface gradients arevery poor; For response time ; length, r 2 s0.125;; gradient, r 2 s0.205 and for response time ;

lengthrgradient, r 2 s0.123.If precipitation has remained constant, then a

temperature change responsible for the observedlowering of the ELAs may be estimated from theatmospheric lapse rate. From the 49 snowline ‘index’glaciers, 672 ELA readings are available for theperiod 1977 to 1997 where the average differencebetween the estimated steady state ELAs and theobserved annual ELAs, gives a snowline depressionof 67 m. Using a standard lapse rate of 0.78C per 100m, the downward shift represents a general coolingof 0.478C since the late 1970s. A mean trend fitted

Žthrough the ELA record for the Tasman Glacier Fig..5 suggests a fall of 160 m in the ELA since 1960.

In a study of a century of glacier recession to theŽ .late 1970s, Chinn 1996 found an upward ELA shift

of circa 84 m for cirque glaciers. This is equivalentto a warming of circa 0.68C. This comparison indi-cates 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 FranzJosef Glacier, which although its active advance hasslowed as it presumably approaches equilibrium withthe recent climate, has only regained its 1960 extent.In a study of past and present glaciers of the

Ž .Waimakariri basin, Chinn 1975 found an ELA riseof 200 m, equivalent to 1.48C warming since the end

Ž .of the LIA. Salinger 1979 suggests that measuredtemperatures over the past century show a warmingof circa 1.08C, with most of the rise occurring sincethe 1950s.

This study demonstrates the complexity of glacierresponse to climate forcing. To derive climate infer-ences from glacier-length changes, sophisticatedmethods must be used to accomodate differences inresponse times due to differences in glacier geome-try.

Acknowledgements

This work was carried out under contract No.CO5624 of the New Zealand Foundation for Re-search, Science and Technology. I am grateful for

( )T.J. ChinnrGlobal and Planetary Change 22 1999 155–168168

the helpful comments by Dr C. Raymond and ananonymous journal reviewer.

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