Ruitor Glacier Western Italian Alps Ravazzi, 2004

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1 Il ruolo della geomorfologia nella gestione del territorio III Convegno Nazionale AIGeo in onore del Prof. Mario PANIZZA Modena e Alta Val Badia Settembre 2009 Holocene mountain glacier fluctuations a global overview Giuseppe Orombelli Università di Milano-Bicocca

2 Mountain glaciers, mainly composed by ice at the melting temperature, are particularly sensitive to climate changes, responding with ihvariations i in size and ddynamics. Ruitor Glacier Western Italian Alps Ravazzi, 2004

3 Global Glacier Changes: facts and figures Recession of Morteratsch Glacier, Switzerland, between 1985 and Source: J. Alean, SwissEduc ( / Glaciers online (

4 Val Savaranche (Gran Paradiso) - Downwasting of glaciers: remnants of glaciers nested inside LIA moraines CNR IRPI Torino

5 Climate sensitivity of mountain glaciers shown by their relative annual contribution to the eustatic component of the sea level rise, compared to Greenland and Antarctic ice sheets contributions. (Meier et al. 2007) 9,9 0,6 Antarctica Greenland M.glaciers & I.C. Antartide Groenlandia Altri ghiacciai 89,4 Mountain glaciers & ice caps, with less than 1% of the total ice volume, release 60% of the annual eustatic contribution.

6 Mountain glaciers and climate change FAQ - Are the present glaciers less extended than in the Holocene? - Is the present rate of retreat anomalous? I th t h f t t/ ll i di ti - Is the present phase of retreat/collapse indicative of the human forcing? To answer these questions it is necessary to know how glaciers were in the past and how they changed through time

7 Holocene mountain glacier fluctuations - Recent and ongoing glacier fluctuations - Evidence of past glacier fluctuations - The Alpine record (Austrian and Swiss Alps) - Scandinavia and North America - Early and middle Holocene - The Neoglaciation - The Little Ice age - A global overview - The problem of the causes

8 Systematic measurements of glacier fluctuations started in the Alps in 1894 François Alphonse Forel Front position measurements (Forel, 1895) Commission Internationale des Glaciers (1895) Rapports sur les variations périodiques des glaciers

9 % of advancing, retreating and stationary glaciers in the Swiss Alps (from 1879 to 2002): two clear advance phases took place around 1920 and 1980 Herren & Bauden, 2008

10 Northern hemisphere mean annual temperature anomalies (red line) compared to the % of advancing Swiss glaciers (blue bars) The 1920 and 1980 peak advance phases followed with a lag of a decade two temperature minima around 1910 and 1970 (Orombelli, 2007)

11 Compilation by the World New Guinea Glacier Monitoring i Service of Africa glacier length changes since the second half of the New Zealand XIX century: Scandinavia number of advancing g( (blue) and retreating (red) glaciers Centr. Europe from the tropics to the poles. South America At the decadal d time scale glaciers respond to local Northern Asia forcing, but a phase of advance Antarctica ti between 1965 and 1985 is evident in many records Centr. Asia UNEP / WGMS, 2008 North America Arctic Worldwide

12 Length variations of 20 mountain glaciers in the two emispheres e es IPCC, 2001 Since the 2 nd half of the XIX cent. almost all the glaciers in the world are retreating Average regional glacier variations (IPCC, 2007)

13 1300 Little Ice Age Glacier length variations since 1700 AD in various mountain chains, from Alaska to New Zealand (UNEP, 2007). From the end of LIA (2 nd half of XIX cent.) glacier are retreating, with short readvance phases In the last decade all the glaciers are in a marked retreat.

14 Holocene oce e glacier fluctuations: historic, stratigraphic and geomorphic evidence. Incomplete, discontinuous, poorly dated record of glacier advance phases.

15 A long tradition of glacier variation studies in the Alps retreat advance High frequency glacier fluctuations over the entire Holocene (Maisch, 2000)

16 Scandinavian, Alaskan and worldwide Holocene glacier fluctuations, compared with Δ 14 C astmospheric variations: three phases of advance peaked around 5300, 2800 and 200 years BP (Denton & Karlén, 1973) Δ 14 C worldwide Alaska Scandinavia ka BP LIA LIA LIA cross-hatched: h glacier expansion star/white: glacier contraction

17 Subdivisions of the Holocene For the history of mountain glaciers, the Holocene (at least in the Northern hemisphere) can be broadly subdived in three main periods: - a first period ( to ~ 9000 BP) corresponding to Preboreal-Boreal chronozones - a second period ( ~ BP) corresponding the Atlantic chronozone and sometimes indicated as Hypsithermal - a third period ( the last 5000 years) corresponding to Subboreal-Subatlantic Subatlantic chronozones and often referred to as Neoglaciation or Neoglacial

18 Fluctuations of mountain glaciers during the first period (Early Holocene) are poorly known. Glacier advances have been reported in Scandinavia, Canada, Andes, Patagonia. Possibly part of the Egesen moraines in the Alps are Early Holocene in age (Ivy-Ochs et al.,2007). Climate in the Northern hemisphere was still under the influence of remnants of the great Late Pleistocene ice sheets and of extensive meltwater outflows.

19 The second period ( BP) was characterized by a generally reduced d glacier activity. In many mountain chains glaciers where in a prevailing retreated condition and dl localyy l they entirely disappeared. d In the Italian Alps a representative section is shown by the Ruitor Glacier (Western Alps)

20 Ruitor Glacier Buried peat bog near the glacier front 2510 m * *Peat sequence ka BP max Little Ice Age glacier extent (1820?) N 2003

21 The Ruitor peat section: calibrated 14 C ages extends ~ cal BP 9070 ± ±65 BP ~ cal BP Orombelli, 1998

22 Ruitor Glacier was much more reduced than now between 10 and 5,6 ka to avoid interference between peat deposition and meltwater streams 1991 extent compared with LIA (c. 1820) max extent and with supposed pre-neoglacial min extent LIA 1991: - 27% LIA pre-neogl: - 50%? LIA * 1991??? * Peat sequence 10 56kaBP 5.6 Orombelli, 2004

23 max PEG Av. Smaller than now max PEG Rit. BC AD Pasterze and Gepatschferner glaciers (Austria): length changes with respect to the max LIA (~1850) Nicolussi & Patzelt, 2000 Pasterze Gl. was smaller than now from 10.5 to 8.8 ky BP (and several times in the following millennia)

24 Tree ring series Tschierva Gl. smaller than now BP (Joerin et al., 2008)

25 Ruitor Phases of contraction to a size smaller than the present in Swiss glaciers (Joerin et al., 2006)

26 The third period: the last 5000 years This period is often referred to as Neoglaciation (Porter & Denton 1967) since it was characterized by a general reactivation/reappearance of mountain glaciers. Several phases of advance and retreat t punctuated t this period, culminating around 5000, 3800, 3100, 2500, 1400, 900, 650, 350 and 150 years b2k (Wanner et al. 2008) In the Italian Alps there are indirect evidences of the start of the Neoglaciation at the Ruitor, Miage and Niederjoch glaciers.

27 Mont Blanc and Miage Glacier The ice dammed Miage lake and the Neoglacial morainic amphitheatre

28 BP BP The Lake Combal plain dammed by the right lateral moraine of the Miage Gl. and by the small Neoglacial morainic amphiteatre. The lake was first dammed by an avance culminated around 4800 BP.

29 Niederjoch Gl. / Ötzi (~ 5300 cal BP) Baroni & Orombelli, 1995

30 Retreat and advance phases of Alpine glaciers (Italy, Austria and Switzerland). From 10 to 5 ka BP glaciers were mostly less extended than at present. During the last 5 ka BP glaciers advanced repeatedly, reaching more and more advanced frontal positions, following the decline of the N. hemisphere summer solar radiation (from about 520 to 440 W m -2 ) Orombelli, 2007 Ruitor retreat advance Aletsch Oetzi retreat advance Miage 30 N retreat advance phases phases W m N

31 Great Aletsch Glacier fluctuations over the last 3 thousand years (updated to 2005) Bronze Age Warm Period Iron Age Cold Period Roman Warm Period Early Middle Ages Cold Period Medieval Warm Period Little Ice Age: 3 max: retreat advance BAWP IACP RWP EMACP MWP LIA Holzhauser, Magny & Zumbuhl,

32 The Little Ice Age Three max. advances: Hunters in the snow Pieter Bruegel the Elder 1565 Unterer Grindelwald glacier, XVIII century The Medieval Warm Period ends with le beau XIII e siècle (Le Roy L., 2004). During the first decade of 1300 AD the LIA initiates: adverse climate, poor harvest, increased prizes, great famine , high mortality, migrations, mendicity, black death 1348.

33 Timing of global glacier fluctuations during the Holocene. Blue bars indicate times of glacier advance, green bars times when glaciers in the Swiss Alps were smaller than now. Vertical light blue columns are periods of generalized glacier advance (Koch & Clague, 2006).

34 Regional advance (downward) and retreat (upward) phases of mountain glaciers from the Arctic to New Zealand, compared to the extent at the end XX century (horizontal black lines). IPCC, 2007

35 Mid to Late Holocene glacier fluctuations covering eight glacial regions, mainly in the Northernm hemisphere. Above (below) the horizontal Lines: glaciers smaller (larger) than today. Light brown bars: periods of glaciers smaller than today. Coloured dots: possible simultaneous Neoglacial advance phases culminating around 5000, 3800, 3100, 2500, 1400, 900, 650, 350 and 150 years b2k Wanner et al. (2008)

36 Glacier fluctuations in New Zealand compared to N hemisphere records. N.Z glacier advances peaked at around 6500, 3200, 2300, 2000 to 1650, 1400, 1000, 600, 400, 270 to 110 years b2k, not in phase with North hemisph. h Glaciers, exept for the Dark Ages and LIA advances. The extent of the glacier advances decreased from Mid to Late Holocene Schaefer et al., 2009

37 Patterns of Holocene glacier fluctuations in the Cordilleras of North and South America, considered represantative of the two hemispheres, and summer insolation at 60 N and 60 S. Note the increase, along the Holocene, of the glacier extent in the Northern hemisphere, and the decrease in the Southern hemisphere in response to the declining/increasing insolation (Koch( & Clague, 2006)

38 Deviations of insolation from long term mean W/m 2 as a function of latitude for the past 6000 years (Wanner et al. 2008)

39 The causes Long term trends attributed to summer/annual insolation (opposite in the two hemispheres) Short term (decadal to centennial) variations attributed to: - solar activity - volcanic (explosive) activity - ocean thermoaline circulation - internal variability of the climate system (ENSO, NAO, etc.) Ciclicity??? The LIA: a global event (with regional time & amplituide differences) needs a global forcing

40 The present (last decade) retreat/collapse phase of mountain glaciers: worldwide (with few exceptions) and simultaneous. Mountain glaciers, except the small ones, are not yet in equilibrium with the present climate, because of the responso time (from a few decades to more than a century). The rate of decrease of volume has accelerated and It is considered 10 times faster than the average rate of volume decrease during deglaciation, which lasted 7 ka. In conclusion Holocene glacier fluctuations show a general coherent pattern at the millenial time scale, regional to local variability at the secular/decadal time scale, broad similarity during the last millennium, higher coherence during the last century - especially in the last decade.