Climate change impacts on NATURAL SYSTEMS AND PATTERNS 2.5 GLACIERS |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
| Reconstructions | Alps: The extent of Alpine ice is probably more reduced today than ever before during the past 5000 years. Since 1850, the european alpine glaciers have lost about 30 to 40% in glacierized surface area and around 50% in ice volume. |
Haerberli & Beniston 1998 - A | |
Swiss Alps: The investigated glaciers were smaller-than-today during the phases which are represented by the radiocarbon dates, the subfossil samples having been melted out of glaciers following subglacial and englacial transport. The radiocarbon dates do not indicate a random distribution over the Holocene but form eight clusters indicating phases of glaciers contraction and climatic amelioration with development of vegetation at higher elevations and glaciers smaller than present. These cluster recession phases are: 99109550, 90107980, 72506500, 61705950, 52903870, 36403360, 27402620 and 15301170 cal. yr BP. Considering the start of tree growth after glacier recession of approximately 100 years, a moderate climate may have existed prior to data points and periods of smaller-than-today glaciers should therefore be prolonged by some 100200 years. The comparison with other palaeoarchives shows that several dates on glacier oscillations in the Alps are consistent with the present data set. There is also some agreement between the reconstructed phases of glacier recessions obtained here and glacier behaviour beyond the Alps, and especially in Scandinavia. |
Subfossil wood and peat samples from six glacier forelands in the Central Swiss Alps have been collected, and 65 samples have been radiocarbon dated (11 samples were multi-dated). The glaciers considered here are: Unteraar (Central Swiss Alps), Mont Miné (Valais), Tschierva and Forno (Bernina Massif), Ried (Mischabel group), and Trient (Mont Blanc Massif). The authors conclude that the clasts of fossil wood are primarily evidence for englacial and subglacial transport and that trees were not transported by avalanches or humans to the places of sampling. In order to constrain the time of advance, only the outer 510 tree-rings without bark were dated. All conventional radiocarbon measurements reported here were carried out using low activity copper proportional counters filled with CH4 (Fairhall et al., 1961). |
Hormes & al. 2001 - A | |
Europe/Alps: As regards to the end of the Little Ice Age (LIA), often proposed around 1860, it's better to choose the maximal extension of most large glaciers around 1820. This date also seems to have been the maxi maximorum (Lliboutry, 1965). There was an advance in 1860, but it was rather similar to one of these minor re-advances, as in 1890, 1920, and 1980, within a regular retreat since 1820. So, given the various series of length variations and the historic relationships available for the Alps , a LIA extending between 1600 and 1820 can be proposed. These two centuries were characterized by advance and retreat periods, with a marked retreat around 1760. The LIA ended recently and the current glacier decrease is probably partially due to a return to more average climatic conditions at the Holocene scale, as those before 1600s. |
Bibliographic analysis | Reynaud & Vincent 2002 - A | |
French Alps: The 20th century may be divided into four periods: two steady state periods (1907-1941 and 1954-1981) during which the mass of glaciers remained almost constant, and two deficit periods (1942-1953 and 1982-1999) marked by a sharp reduction in glacier mass. The cumulative mass balances of glaciers 2, 3 and 4 have declined only slightly over the 20th century (by ~ 13 m w.e.) and have been almost 0 since 1950. This overall trend contrasts with large local changes observed on the tongues of these glaciers. But the cumulative mass balance of glacier 1 has strongly declined (by ~ 30 m w.e.). The four glaciers have lost mass mainly over two periods : 1942-1953 and 1982-1999. Reconstructed mean accumulation and ablation on the glacier 1 at 2800 m asl show a very sharp mass balance decline between 1942 and 1953 (both increasing ablation and low precipitation). During this period the ablation was very high (even more than in the last period of regression). Glacier advances observed between 1954 and 1981 are clearly related to low ablation values. For the 1982-1999 period, ablation rise significantly and accumulation increase slightly. There is a very strong correlation between these results and results from a previous study on the Sarennes glacier (located 3 km from the glacier 1). The mean ablation rate rose by 44% (from 1.9 to 2.8 m w.e. yr-1) between 1954-1981 and 1982-1999, which corresponds to an energy difference of 22 W m-2. The air temperature increase of 0.8°C between the two periods is responsible for a large part of the ablation rise. A limited increase in incident solar radiation, probably due to decreased cloudiness, could be responsible for a part too. |
1. St Sorlin 2. Gébroulaz 3. Argentière 4. Mer de glace Total cumulative mass balances have been calculated using old maps with elevation contours and recent geodetic measurements (topographic measurements and aerial photographs). Surface area changes over the century have been taken into account using maps and parameters have been adjusted to match reconstructed mass balance with field measurements. Then the magnitude of various climatic forcings capable of explaining the large ablation variations observed has been calculated. The total summer ablation has been converted into energy (assuming that the ablation is due only to melting and that heat conduction into the ice or snow is negligible, as sublimation). |
Vincent 2002 - A | |
European Alps: For the time since the end of the Little Ice Age around 1850, mass-balance reconstructions provide long-term mass-balance averages of -0.25 to -0.3 m w.e. a-1, i.e. three to four times less than the most recently observed values. Grosser Aletschgletscher: Over the past two millennia, characteristic century to half-century mass-balance averages (mean +/- 0.3 and maximum +/- 0.5 m w.e. a-1) are comparable to the loss rates since the Little Ice Age and they were far below those observed since 1981. In fact, the mass losses observed since the mid-1980s (about 0.75 m w.e. a-1) exceed the maximum, and even double the maximum, characteristic long-term loss rates during the past two millennia. |
A straightforward continuity consideration was applied to longer-term cumulative length changes of Grosser Aletschgletscher, Switzerland, (Haeberli and Holzhauser, 2003) which was reconstructed in detail from historical documents, moraine dating and fossil trees for the past 3500 years (Holzhauser et al., 2005). |
Haeberli & al. 2007 - A | |
World: General warming during the transition from the Late Glacial period (between about 21 000 and 10 000 years ago) to the early Holocene (about 10 000 to 6000 years ago) led to a drastic general glacier retreat with intermittent periods of re-advances. About 11 000 to 10 000 years ago, this pronounced warming reduced the glaciers in most mountain areas to sizes comparable with conditions at the end of the 20th century (Grove, 2004). In northern Europe and western North America, which were still influenced by the remnants of the great ice sheets, this process was delayed until about 6000 to 4000 years ago. Several early-Holocene re-advances, especially those in the North Atlantic and North Pacific as well as possibly in the Alps, cluster around an event about 8000 years ago, and were likely triggered by changes in the ocean thermohaline circulation and subsequent cooling resulting from the outbursts of Lake Agassiz (Solomina et al., 2007). On a timescale of hundreds of years there were periods of synchronous glacier advance around the world peaking in the late Holocene in the Northern Hemisphere. The moraines that were formed during the so-called Little Ice Age (from the early 14th to the mid 19th centuries) mark a Holocene maximum extent of glaciers in many regions of the world, although the time period for this maximum varies among the different regions. Glaciers in the European Alps reached their recent maximum extent around 1850 (Maisch et al., 2000; Gross, 1987; Holzhauser & Zumbühl, 2003). There has been a general retreat of glaciers worldwide since their Holocene maximum extent towards the end of the Little Ice Age, between the 17th and the second half of the 19th century, with intermittent periods of glacier re-advance in certain regions. |
Bibliographic review | UNEP 2007 - R | |
|
Observations |
Alps: The total surface area of all 5050 inventoried surface ice bodies is 2909 km2 (Haeberli et al., 1989). The surface area of the 1763 glaciers larger than 0.2 km2 is 2533 km2 (88%). The total volume of these glaciers is calculated as 126 km3, that of the others as 2.6 km3. Total glacier volume in the Alps is estimated at about 130 km3 for the mid-1970s. The most part of the Alpine glaciers are not strictly temperate but rather polythermal. Most glaciers (88%) have mean annual air temperatures at the equilibrium line between -2°C and -6°C, indicating transitional climatic conditions. The sample of presently existing Alpine glaciers is dominated by small and steep glaciers with average thicknesses of a few tens of metres. They react through (vertical) surface altitude changes rather than pronounced (horizontal) advance/retreat. |
The data for the European Alps, containing a total 5050 perennial surface ice bodies, were compiled for the mid-1970s. Only 1763 of these (35%) are larger than 0.2 km2 with complete information available about surface area, total length and maximum and minimum altitude. |
Haeberli & Hoelzle 1995 - A |
| Alps: The estimated total glacier volume in the European Alps was some 130 km3 for the mid-1970s; strongly negative mass balances have caused an additional loss of about 10 to 20% of this remaining ice volume since 1980. In the ablation area and especially towards the snout of valley glaciers, the lowering of ice surfaces in the course of the past century can easily exceed 100 meters. This vertical loss in valley filling induces a change in the stress field inside the confining mountain walls. |
Cf. Haeberli & Hoelzle 1995, Maisch et al. 1997 |
Haeberli & al. 1997 - A | |
| Alps: Since 1850, the european alpine glaciers have lost about 30 to 40% in glacierized surface area and around 50% in ice volume. During the decade 1980-1990, glacier mass losses further ncreased by more than 50% with espect to the secular average for the 20th century. |
Haerberli & Beniston 1998 - A | ||
Swiss
Alps:
About 100 glaciers are thought to have disappeared from the Swiss Alps since they reached their maximum extent in 1850. The percentage retreat is inversely proportional to the initial area of the glacier. Glacier where the original dimension (area, lenght and volume) were small have lost proportionally more ice in their retreat than larger glaciers. The small one thus appear to be more sensitive to climate change. In connection with the 0.5-0.7°C warming since the middle of the 19th century, the total ice-covered areas in the Swiss Alps have declined from about 1800 km2 to 1300 km2. 27% of the areas existing in 1850 have disappeared. On average, swiss glaciers have lost about 490 m (35%) of their original extent since 1850. Glaciers have also narrowed by an average of 40 m. The total volume of ice diminished by approximately one-third. Between 1850 and 1973, the line of equilibrium rose by approximately 70 m (from 2740 to 2810 m asl). The most impacted zone is the central and northern Graubünden region, and the less impacted zone is the bernese Alps region. |
3 important "time windows" in the history of the glaciers provided a basis for the study: the maximum extend of the glaciers in 1850, the present situation (1973, the reference year for the swiss inventory of the glaciers), and various scenarios of glaciers retreat for the 21th century. 2244 swiss glacier units have been recorded in the CH-INVGLAZ database according to about 50 different quality and quantity parameters typical of each glacier analysed. |
Bader & Kunz 2000d - R: PNR31 | |
Europe:
Most, but not all, valley glaciers and small ice caps have been in general retreat since the end of the Little Ice Age. |
IPCC 2001 - R | ||
French Alps: For the four glaciers (St Sorlin, Gébroulaz, Argentière, and Mer de glace), ablation increases linearly with CPDD (cumulated positive degree-day), concerning summer mass balance measurements since at least 1993. It means that globally, the trend is: the higher the CPDD is and the more important ablation is. The relationship between CPDD and ablation is an empirical one. It is not a causality relationship, since both terms are distinct surface-energy balance results. Summer ablation is best correlated to temperature in the low-elevation regions of the glaciers free of rock debris (less influence of the albedo). For the four glaciers, ablation sensitivity to temperature variations globally decreases strongly with elevation. It seems that dispersion is greater over the region close to the equilibrium line, where the albedo pattern can be very different from one year to another. The general trend is that the winter mass balance increases considerably with the valley winter precipitation. A large difference between valley precipitation and winter accumulation is observed on glaciers especially in high-elevation regions. The ratios between winter mass balance and winter valley precipitation are relatively constant with time for each altitude range (above 2400 m asl) but very different from one site to another depending on the topography of the englacial basin. |
Since 1993, systematic winter and summer mass balance measurements (May and September respectively) have been carried out on the glaciers. In the ablation area, winter mass balances are measured by drilling and measuring the snow thickness above the ice. Annual mass balances are determined from stakes inserted in ice. The summer mass balance is then the difference between these two balance terms. Measured summer mass balances have been compared to the CPDD calculated from valley meteorological data. The CPDD is the cumulated temperature higher than 0°C obtained from valley measurements by applying a fixed lapse rate (temperature gradient with altitude) of 6°C km-1. Data on winter mass balance were plotted against valley winter precipitation observed over the same intervals. Only precipitation at temperatures below freezing (at the observation elevation) is taken into account. The ratio between winter mass balance and winter valley precipitation, expressed as a function of elevation, for each glacier has been calculated. |
Vincent 2002 - A | |
| World:
On average of the worldwide sample, larger glaciers have lost around -0.25 m/year, a value which is identical to the value calculated for the larger Swiss glaciers. The reconstructed rates of secular mass losses strongly differ between humid-maritime-type glaciers such as those of western Scandinavia and dry-continental type glaciers in the Altai area, for instance. The sensitivity with respect to secular trends in global warming of maritime-type glaciers is much higher than the one of continental-type glaciers. Swiss
: Direct measurement of mean mass balance
(vs calculated from glacier length change for time intervals >=
the response time of the glaciers) : Average mass losses of long and flat glaciers have exceeded those of smaller glaciers: typical values center around -0.25 m/year for larger glaciers and around -0.11 m/year for the smaller ones. |
Intercomparison is based on 68 glaciers from the Swiss glacier network and 90 selected glaciers worldwide. Swiss glaciers with their overall
length and mean slope were subdivided into five classes as follows : • Class 1 (long and flat valley glaciers, sample: 4 glaciers): glaciers longer than 10 km with a mean slope of < 15j; • Class 2 (intermediate valley and mountain glaciers, sample: 11 glaciers): glaciers with a length between 5 and 10 km and a mean slope between 10° and 25°; • Class 3 (steep mountain glaciers, sample:19 glaciers): glaciers with a length between 1 and 5 km and a mean slope ranging from 15° to 25°; • Class 4 (flat mountain glaciers, sample:14 glaciers): glaciers with a length between 1 and 10 km and a mean slope < 15°; • Class 5: (extremely small and extremely steep glaciers, sample: 20 glaciers): glaciers shorter than 1 km with a mean slope larger than 15° or with a length between 1 and 5 km and a mean slope larger than 25°. |
Hoelzle & al. 2003 - A | |
Belvedere Glacier (Monte Rosa, Italian Alps): From the mid-1980s until 2001 no unusual situation at Ghiacciaio del Belvedere was encountered. In summer 2001, however, heavy crevassing of the glacier surface, a marked increase in thickness, dirty ponds between the glacier and its lateral moraines, and enhanced ice and rock-fall activity from the glacier margins were observed. The processes were interpreted as indicators for a surge-type glacier movement and the local authorities instructed (Haeberli et al., 2002). In the mid-1980s and during 1995-1999, average surface speeds on the lower part of Ghiacciaio del Belvedere were found in the order of up to 40-45 m a-1, or 35 m a-1, respectively (VAW, 1985; Kääb et al., 2003a; Mazza, 2003). During 1999-2001 average speeds of up to 110 m a-1 and during autumn 2001 of up to 200 m a-1 were observed photogrammetrically. Terrestrial surveying and photogrammetry in summer 2002 yielded speeds of up to 80 m a-1. |
Kääb & al 2004 - P | ||
Swiss Alps: Analysis of glacier change for the Swiss Alps reveals the following major findings: The relative loss of glacier area between 1973 and 1998/99 is 18% +/-3% (about 1/5) with an assumed corresponding volume loss of about 1/4 (scaled for all glaciers). Relative change in area between 1985 and 1992 is similar to the period 1992 to 1998/99 with respect to the 1973 glacier size (about -10% in each period). Small changes of glacier size until 1985 (-1%). The average decadal relative loss of area from 1985 to 1998/99 is about seven times higher than from 1850 to 1973 (the samples are not exactly identical). Glaciers smaller than 1 km2 contribute about 40% to the total loss although they cover only 15% of the area. The relative changes in glacier size are highly individual with a fair dependence on glacier size (increasing scatter towards smaller glaciers) and no correlation to other investigated parameters. Only a large number of glaciers from all size classes will give a representative evaluation of ongoing changes. The primary causes for area changes in valley and mountain glaciers are: separation from formerly connected tributaries, emerging rock outcrops, and melting along the perimeter. Shrinkage of small glaciers (glacieretes) is enhanced by disintegration, with an even faster melting of the smaller parts. On average, glacier elevation range decreased by 97 m from 1973 to 1998. These observations can be interpreted as follows: The -20% reduction of glacier area since 1985 is already in the range of the -30% expected in previous studies for the year 2025 (Haeberli et al., 2002). The change is also much faster than observed in the historical record. In particular the not monitored small glaciers contribute to the area loss. The highly variable glacier retreat characteristics (often associated with arbitrary changes in geometry) makes calculation of future glacier behaviour from numerical modelling fairly questionable, at least for the majority of all glaciers. Although changes in glacier surface elevation cannot be measured with TM, the observed changes in glacier geometry indicate a massive down-wasting since 1985 rather than a dynamic response to a changed climate. Further glacier retreat can be expected in the future, as a probable dynamic glacier reaction to the hot decade of the 1990s is still to come. |
The new Swiss glacier inventory 2000 (SGI 2000) shows the possibilities and limitations of a glacier inventory from satellite data using GIS (Geographic Information System) technology in combination with a digital elevation model (DEM). Landsat 5 TM data from 1998 and 1999 are used for the SGI 2000. The large area covered on a single TM-scene (185 km on each side) combined with the high-spatial resolution (30 by 30 m per pixel), favours this sensor for glacier monitoring. In order to facilitate GIS-based processing, the glacier inventories from 1973 and 1850 are digitized. Outlines from 1973 are also used to define glacier basins for intersection with the TM-derived glacier areas. 3D glacier parameters are obtained by fusion of glacier outlines with a DEM and DEM-derived products (such as slope or aspect). The DEM is essential for all pre-processing tasks (e.g., orthorectification of satellite images, digital terrain modelling) as well as post-processing (obtaining 3D glacier parameters, visualization of glacier changes). The GIS is used as the central tool for data processing and integration of various data formats (vector, raster, image), namely: (1) digitizing of glacier outlines, central flow-lines and glacier basins, (2) raster-vector conversion of TM-derived glacier maps and assignment of glacier basins and IDs, (3) calculation of 3D parameters from the DEM and storage in corresponding attribute tables, (4) 2D and 3D visual representation of glacier changes. |
Paul 2004 - T | |
Swiss, French and Austrian Alps: The cumulative centered mass balance
series show a strikingly common feature between the respective behaviours
of the 1, 3, 4 and 5 glaciers. Mass balance fluctuations of the Aletsch
glacier show some discrepancies, especially between 1957 and 1980. It
could be a consequence of the difference of methods used to obtain the
data. The summer mass balance term represents by far the largest contribution to the annual mass balance. The comparison of the standard deviations of each mass balance term leads to the same conclusion and shows that the winter mass balance contribution to the annual mass balance is greater on the 1 glacier than on the 5. It is consistent with the fact that 1 observations are from the accumulation zone only and the decreasing variability of mass balance with elevation. The summer mass balance explains by far the largest part of the annual mass balance correlation between the 1 and 5 glaciers. The cumulative winter mass balance relative
to the 1954-1981 period show strong differences between the 1 and 5 glaciers.
The winter mass balance for 1 shows no trend whereas that shows a strong
positive trend over the last 20 years for 5 (increase by an average of
30 cm w.e./yr), in total opposition with the annual mass balance trend.
For the 5 glacier, between 1954-1981 and 1982-2002, the calculated energy variations are 20 and 11 W m-2 for the snow and ice ablation periods respectively. The air temperature increase between the same periods explains the largest part of the ablation rise. |
Glaciers
of Claridenfirn 1 Aletsch 2 Hintereisferner 3 St Sorlin 4 Sarennes 5 Mass balance variations have been obtained from stakes inserted in the ice in the ablation area and from drilled cores in the accumulation zone. Total cumulative annual mass balances of the Sarennes and St Sorlin glaciers have been extended to cover the entire 20th century using old maps with elevation contours and recent geodetic measurements. For the Aletsch glacier, data have been obtained since 1923 by an indirect method using hydrological data (water flux measurements and precipitation data). The 1953-1999 average rate of decrease has been removed, i.e., each glacier mass balance has been reduced by subtracting the 1953-1999 average mass balance of each glacier from the annual values (cumulative centered mass balance). For winter and summer separate mass balance observations, measurements at only one stake were selected (at 2900 m a.s.l.) : the highest stake of 1 (accumulation zone) and a stake located in the middle of the 5 glacier and representative of the overall glacier mass balance. Finally, using the latent heat of fusion, the snow and ice ablation rates have been converted into energy assuming that the ablation is due only to melting. |
Vincent & al. 2004 - A | |
Mont Blanc Massif: |
Gerbaux 2005 - T | ||
Alps: Under extreme climatic conditions, glaciers can loose more mass in their accumulation area than in their (shaded) ablation area, inverting a normal mass balance profile. This has to be considered if ablation stake measurements are interpreted, or simple degree-day models are used to calculate glacier melt. |
Paul & al. 2005 - P | ||
Swiss Alps: The rise in altitude of the lower limits of the glaciers above 3500m asl has never before been experienced. Correspondingly an increase of glacial river runoff and the rapid filling of the accumulation basin under the periglacial areas have been observed. The total loss of the Alpine glaciers during the 2003 heat wave has been estimated to be around 5 to 10% of the 2002 glacier volume. The glacier thickness decreased to such a degree that these glaciers can no longer support horizontal ice supply. Rather than a slowly retreating, glacier tongues are subsiding and collapsing more and more frequently. |
|
ProClim 2005 - R | |
Mont Blanc massif / Swiss Alps: In 2006, the Mer de Glace front was around 2.3 km higher than at its maximal extension during the Little Ice Age. Heat waves such as the 2003 event have lead to the melting of more than 5% of the total volume of Swiss glaciers whilst many small glaciers are on the verge of disappearing or have disappeared altogether. French-Italian Alps: Supraglacial and juxtaglacial lakes formation, like the Rochemelon lake (Haute Maurienne) or the Lago Effimero at the Belvedere glacier (Piemonte), with a 3Mm3 volume in 2002. |
Deline 2006 - P | ||
Italian
Alps: The Monte Rosa east face is one of the highest flanks in the Alps (2200-4500m a.s.l.). Large parts of the Monte Rosa east face are covered by steep hanging glaciers and firn fields. Since 1850, the hanging glaciers and firn fields have retreated slightly. During recent decades, the ice cover of the Monte Rosa east face experienced an accelerated and drastic loss in extent and thickness. The reconstruction of the glacier retreat based on the first approach shows the continuous retreat of hanging glaciers and firn fields since the end of the Little Ice Age. Unlike the strong retreat of many valley-type glaciers since about 1850, the changes of the steep glaciers in the Monte Rosa east face were not very distinctive from this time until the 1980s. However, during the last few decades an accelerated loss in extent of the ice cover becomes evident. Some glaciers (or parts of glaciers) disappeared within only a few years and they seem to decay through mass wasting. The results of the second approach reveal a slight but progressive deglaciation in the Monte Rosa east face since 1956 and in some parts of the face a drastic loss of the ice-covered area in the last 10-15 years. The analysis of the orthophotos also reveals an occasional increase in the extent of certain firn fields and some hanging glaciers. Together, the two methods give an overview over the glacier retreat and reveal the areas with the most pronounced changes in glaciation. |
The glacier extents for different years were reconstructed by 2 approaches using different data sets. Both approaches were conducted by digitising glacier contours for different years since the early 20th century. |
Fischer & al. 2006 - A | |
| Alps: During the last 100 years, the Alpine glaciers lost around 50% of their weight because of the changes in temperature and the shifts in the precipitation distribution, with consequences on the water runoff during summer. |
Seiler 2006 - P* | ||
| Swiss Alps/Alps:
The extrapolation
of data from the Swiss Alps to the corresponding entire Alpine glacier
sample from 1975 reveals an overall loss in Alpine glacier area of 35%
from 1850 up until 1975 (-2.8% per decade) and almost 50% by 2000 (-3.3%
per decade). The area reduction between 1975 and 2000 is about 22% (-8.8%
per decade), mainly occurring after 1985 (-14.5% per decade) as glacier
fluctuation measurements and satellite-derived data have clearly shown.
Disintegration and “down-wasting” have been predominant processes
of glacier decline during the most recent past.
Changes in glacier volume are calculated by multiplying representative mass balance values with the average surface area of a given time period. Mean mass balance of 9 Alpine glaciers between 1975 and 2000 was almost -0.5 m water equivalent (w.e.) per year (about twice the loss rate reconstructed from cumulative length change since 1850). The cumulative balance of -12 m w.e. over a mean glacier area of 2590 km2 during the 1975-2000 period indicates a lower limit of the corresponding volume loss of 30 km3. As average slope and ELA have increased, but glacier size (as well as altitudinal extent, mass flux and driving stress) decreased, the percentage of volume loss must be even greater than the calculated area loss of 22%. Based on this assumption, the estimated volume loss (30 km3) corresponds to 25-30% of the total Alpine ice volume in the 1970s. This estimates show that the glaciers in the Alps have lost an average of 1% of their volume per year since 1975. On the same basis, total Alpine ice volumes can be estimated roughly as 105 km3 (± 15) in 1975, and 75 km3 (±10) at the turn of the century. Total glacier volume around 1850, with an extrapolated total glacierized area of 4475 km2, is estimated at some 200 km3 or more, and is now close to 1/3 of this value. The average mass balance of -2.5 m w.e. in the extreme year 2003, therefore, eliminated an estimated 8% of the remaining Alpine ice volume within one single year. The following year 2004 with an average mass balance of -1 m w.e. reduced an additional 3%, leading to about 10% volume loss in only two years. Extremely hot and dry summers such as 2003 thus not only induce strong positive feedbacks, but also eliminate increasing percentages of shrinking total ice volume. |
Information on glacier fluctuations in the European Alps is available from earlier and recent glacier inventories together with data compilations on past glacier fluctuations. The fact that the time basis for the corresponding inventory data is not uniform plays a minor role: the center point of the corresponding time interval is thus defined as 1975. Detailed reconstructions of glacier areas around AD 1850 (the recent maximum extent for most glaciers in the European Alps) are available for the Swiss and Austrian Alps. The latest glacier inventory data based on satellite images is available for most of the Swiss Alps in 1998/99 (hereafter attributed to the year 2000 for the sake of simplicity). The Alpine glacier area in 1850 and 2000 is extrapolated by applying relative area changes for individual glacier size classes from the Swiss Alps to the corresponding entire Alpine glacier sample from 1975. |
Zemp & al 2006 - A | |
Western Italian Alps: In consequence of poor winter accumulation of snow and intense summer ice melting, glacier suffered huge mass lasses everywhere throughout this side of alpine range, for the fourth consecutive year. In 2005-06 season, net mass balance was -2.10 m w.e. at Ciardoney glacier, -1.85 m w.e. at Grand Etret glacier (both in Gran Paradiso range), and -2.20 m w.e. at Basodino glacier (Canton Ticino, Switzerland). The comparison between mass balance data of south-western Alps shows that Ciardoney glacier is the most affected by ice losses, in consequence of its geographical position: cumulated mass balance in 1991-92 / 2005-06 period reached -19.7 m w.e., whilst Basodino glacier reached -6.7 m w.e. in the same period (snow accumulation in Canton Ticino mountains is usually much larger than in Gran Paradiso range). Moreover, its lower altitude and sunnier exposure explains higher mass losses than the ones measured at Grand Etret and Timorion glaciers. |
Cat-Berro & Mercalli 2007 - P | ||
European Alps: For the 9 Alpine glaciers, near-equilibrium conditions until 1981 were followed by very strong and continued if not accelerating mass loss (0.7 m w.e. a-1; trend of increase in mass loss 0.03-0.04 m w.e. a-2). During the first 5 years of the 21st century, mean annual mass losses have been close to 1 m w.e. a-1. The hot, dry summer of 2003 alone caused a record mean loss of 2.45 m w.e., roughly 50% above the previous record loss in 1998. Continued non-zero balances indicate ongoing climate forcing (assuming feedbacks from albedo, elevation change, debris cover or dry/wet calving do not affect mass balance for the considered glaciers), and increasing deviations from zero balances reflect accelerating change. Observed and reconstructed mass losses are therefore also a function of glacier size (Hoelzle et al., 2003), with large glaciers reducing their thickness more rapidly than small ones. Morphological phenomena of downwasting (flat longitudinal and concave transversal surface profiles, abundant debris cover, collapse holes above subglacial drainage channels, lake formation) have now become visible on many glacier tongues. With continued thickness losses of 1 m w.e. a-1 or even more, the glaciers with longterm mass-balance time series may disappear within a few decades from now. |
Bibliographic review Uninterrupted in situ measurements since 1967 of mass balance at nine Alpine glaciers (Saint-Sorlin and Sarennes, France; Gries and Silvretta, Switzerland; Careser, Italy; Hintereis, Kesselwand, Vernagt and Sonnblick, Austria) are available. |
Haeberli & al. 2007 - A | |
World:
Mountains glaciers and snow cover have declined on average in both hemispheres. |
IPCC 2007 - R (SP) | ||
Swiss Valais: Under the effect of mild temperature that occured during the winter in the beggining of 2007, including high altitude sites (up to 10°C at 2800m a.s.l), some water runed off from the Proz glacier, a runoff accelerate because of the precipitations... |
Le Nouvelliste 2007 - W | ||
Alps: The mean evolution of nine alpine glacier mass balance between 1965 and 2005 shows that until 1980, the annual variations approximately balanced each other. But since the mid-1980s, a clear continual loss trend, even accelerating, has been detected. On average, for the total glacier extension, the loss reaches 0.5- 1 m water equivalent/year, and even 2.5 m in 2003. The cumulative loss for the 1980-2005 period is about 20 m w.e. The glacier shrinkage observed in the Alps clearly coincides with the increasing trend of average temperature (Zemp et al., 2007). |
Considered glaciers: Saint Sorlin, Sarennes, Silvretta, Gries, Sonnblickkees, Vernagtferner, Kesselwandferner, Hintereisferner and Careser. |
North & al. 2007 - R: OFEV | |
Alps: Fields observations Specific results of glacier changes in Switzerland from 1973 to 1985 to 2000 as well as an extrapolation to the entire Alps have been reported in Paul (2004) and Paul et al. (2004). In Switzerland, glaciers lost about 18% of their area from 1985 to 1998/99 (from 1973 to 1985 the change is only -1%). This corresponds to an average relative area loss of 14% per decade, which is about seven times higher than the decadal loss rate between 1850 and 1973 (-2.2%). There is an even higher relative loss of area towards smaller glaciers, but the scatter among values increases as well, indicating a very specific behaviour of individual glaciers that are smaller than 1 km2. Such small glaciers account also for a major part (44%) of the total area loss since 1973, although they cover only 18% of the total area in 1973. According to the mass balance data from ten Alpine glaciers (IUGG et al., 2005) the mean cumulative specific mass loss was about 17 m water equivalent (we) between 1981 and 2003, corresponding to about -0.8 m we per year. This is about three times the long-term mean value for the 20th century of -0.27 m we (Haeberli and Hoelzle, 1995; Hoelzle et al., 2003). Apart from 3 years (1984, 1995 and 2001) with small mass gains, all years since 1981 exhibit mass losses. A linear trend line on the data points suggests an increasing speed of glacier mass loss. Observations from satellite imagery The recent analysis of satellite data revealed a strong acceleration of glacier shrinkage in the Alps since 1985, with a mean decadal rate of area reduction seven times higher than during the 1850-1973 period (Paul et al., 2004). The analysis of image time series gives indirect evidence that down-wasting (i.e. stationary thinning) has become a major source of Alpine glacier mass loss during the past 20 years. The major indicators of down-wasting that have been observed on Landsat images are: growing rock outcrops, separation from tributaries, formation of pro-glacial lakes, non-uniform geometry changes, e.g. disintegration and shrinkage along the entire perimeter. Such changes can be observed throughout the entire Alps. However, it should be noted that individual glaciers with little or no change can often be found in the same region or even adjacent to a disintegrating glacier. The reason for this high-variability over short distances has not been determined yet. All three glaciers (Taelli, Cavagnoli and Caresèr glaciers) are placed at about the same geographical latitude (46.5° N) and clearly demonstrate how fast disintegration has proceeded in the last 20 years. While Taelli Glacier has already disintegrated into several small patches of ice remnants, Cavagnoli Glacier will likely follow next and the somewhat larger Caresèr Glacier shows rapidly growing regions with rock outcrops. Somewhat larger regions, located in the Gran Paradiso mountain range in the southwestern part of the Alps (FR/I), the Bernina group in the central-southern part (CH/I) and in the Ötztaler Alps in the central-northern part (A/I), have been studied too. In all three regions several processes resulting from the overall glacier down-wasting or shrinkage are visible: formation or growing of proglacial lakes, new rock outcrops, tongue separation, strong retreat, and disintegration. Again, it is obvious that the observed changes took place on an Alpine-wide scale, but nearly unchanged glaciers can often be found within the same region. |
Fields observations Bibliographic review Observations from satellite imagery Observations made by Landsat Thematic Mapper (TM) and ASTER satellite data throughout the Alps will be presented. The examples discussed cover various climatic regions and include glaciers of different exposition and size. However, for better visibility of the changes, some of the more prominent examples have been selected. In principle, the changes can be observed in every region of the Alps, but not necessarily for all in the same region. In high-mountain topography exact orthorectification of satellite data is required if glacier outlines are combined with other sources of georeferenced information (e.g. other satellite sensors or digitized outlines of former glacier extent). This requires a high-resolution digital elevation model (DEM) of appropriate accuracy as well as accurate topographic maps for collection of GCPs (Paul, 2004). |
Paul & al. 2007 - A | |
World/Alps: Over the past hundred years a trend of dramatic shrinking is apparent over the entire globe, especially at lower elevations and latitudes.Within this general trend, strong glacier retreat is observed in the 1930s and 1940s, followed by static conditions around the 1970s and by increasing rates of glacier wasting after the mid 1980s. There are short-term regional deviations from this general trend and intermittent re-advances of glaciers in various mountain ranges occurred at different times. Thirty reference glaciers with almost continuous mass balance measurements since 1975 show an average annual mass loss of 0.58 m water equivalent for the past decade (1996-2005), which is more than twice the loss rate of the period 1986-1995 (0.25 m), and more than four times the rate of the period 1976-1985 (0.14 m). The results from these 30 continuous mass balance series correspond well to estimates based on a larger sample of more than 300 glaciers, including short and discontinuous series (Kaser et al., 2006). In the European Alps, the overall area loss since 1850 is estimated to be about 35 % until the 1970s, when the glaciers covered a total area of 2 909 km2, and almost 50 % by 2000. Total ice volumes in 1850, the 1970s and 2000 are estimated to be about 200 km3, 100 km3 and 75 km3, respectively (Zemp et al., 2006). Observations show intermittent glacier re-advances in the 1890s, 1920s and 1970-1980s (Pelfini & Smiraglia, 1988; Zemp et al., 2007; Patzelt, 1985). After 1985 an acceleration in glacial retreat has been observed, culminating in an annual ice loss of 5-10 % of the remaining ice volume in the extraordinarily warm year of 2003 (Zemp et al., 2005). The strong warming has made disintegration and downwasting increasingly predominant processes of glacier decline during the most recent past (Paul et al., 2004). |
Bibliographic review | UNEP 2007 - R | |
Mont Blanc and Dôme du Goûter ice fields (French Alps): Long-term mass balance deduced from ice fluxes calculated at Dôme du Goûter According to the first method, the calculation results show that the necessary surface mass balance (SMB) to compensate the output flux from the west section is 2.1 m w.e./yr on the average over the west drainage basin area, which is almost twice the value calculated for the east drainage basin area (1.1 m w.e./yr). An error calculation leads to a total uncertainty of ±0.4 m w.e./yr for the computed mean SMB for each drainage basin area. According to the second method, total submergence is 125,900 m3 w.e./yr on WD and 57,000 m3 w.e./yr on ED resulting in respective mean rates of 2.7 and 1.2 m w.e./yr. These results agree well with previous results obtained from the cross-section ice fluxes. Short-term surface mass balance at Dôme du Goûter Although total accumulation varies from year to year, the patterns of spatial distribution vary little. The average accumulation over the 4 years is in good agreement with the submergence rates. Finally, the mean accumulation over these 4 years is 2.21 m w.e./yr, very close to the average submergence velocity (2.16 m w.e./yr) over the area. The good agreement between the average submergence velocity and the 4-years-averaged observed accumulation does not prove that Dôme du Goûter is in a steady-state, as the average accumulation results from only 4 years of observations. However, this analysis shows that the recent observed snow accumulation pattern is maintained from year to year and is similar to the long-term mass balance pattern. Correlation between surface mass balance and valley precipitation A straightforward relationship between accumulation and valley precipitation reveals a correlation coefficient of 0.73 and 0.76 for a linear regression and a power law regression, respectively. As a first approximation, one can assume that the total accumulation over the whole area of Dôme du Goûter is roughly related to the total precipitation at Chamonix and that the accumulation variability is similar to the annual precipitation variability. Given that (1) the long term accumulation rate, calculated from ice fluxes or submergence velocities, is very close to the average accumulation rate observed, (2) there is a good relationship between the accumulation change and the valley precipitation change, and (3) the 1993-1995 and 1997-1999 mean valley precipitation rate is close to the 20th century mean precipitation rate, we can conclude that the Dôme du Goûter SMB did not change significantly over the whole 20th century. Thickness Variations The small thickness changes observed over the 20th century are striking. For both areas, thickness variations do not exceed ±15 m. The average changes are +2.6 m at Dôme du Goûter and -0.3 m at Mont Blanc. Considering the uncertainty interval, i.e., ±5 m, it can be concluded that no significant thickness change is detectable over most of these areas. This study reveals that the very high-elevation ice fields in the Mont Blanc area have not been affected by the climate warming (+1°C in the Alps during the 20th century). This change did not significantly affect the ice deformation rate since the ice temperature remains far below the melting point and therefore keeping the glacier frozen to its bed. |
Long-term mass balance deduced from ice fluxes calculated at Dôme du Goûter The ice fluxes have been calculated through two sections using thickness and surface ice flow velocity measurements. Using available accumulation, velocity, and glacier bed data, two drainage basin areas have been outlined. The ice flux from a western, WD, and an eastern drainage basin, ED, through respective cross sections has been calculated. The glacier is cold and the sliding velocity is assumed to be zero [Paterson, 1994]. Consequently, the mean horizontal ice velocity through the cross section is derived from the analytical formulation proposed by Lliboutry [1981]. The mean surface mass balance (SMB) can also be determined using the vertical velocity observations. The submergence velocities obtained from repeatedly taken stake observations between 1993 and 2004 have been used. These values have been integrated over the drainage basin areas using krigging interpolation to obtain the total submerging ice flux. Short-term surface mass balance at Dôme du Goûter Snow accumulation measurements are not available at every site for each year. However, accumulation data are available in the western part of Col du Dôme for the years 1993-1994,1994-1995, 1997-1998, and 1998-1999. From mass balance observations, average accumulations within this area have been calculated. Correlation between surface mass balance and valley precipitation The closest meteorological station is Chamonix, at an elevation of 1000 m a.s.l., and 8 km from Dôme du Goûter. To compare high elevation accumulation and valley precipitation, a site with numerous accumulation observations has been selected (130 m north of the Col du Dôme). 22 observations are available for time periods ranging from 33 to 221 days between 1994 and 2004. These observations have been divided by the number of days to obtain mean daily accumulation. The next step consists of investigating the precipitation variability observed at meteorological stations in valley locations. For this purpose, the longest precipitation data series in the French Alps have been used, i.e., those of Besse en Oisans and Bourg Saint Maurice, 30 km and 95 km from Chamonix, respectively. Thickness Variations Thickness variations have been deduced by comparing two digital elevation models computed from recent geodetic measurements and an old map dating back to the beginning of the 20th century. Measurements using differential GPS were carried out in 2005 and are accurate to within a few centimeters. The old map [Vallot et al., 1948] was established in 1905. |
Vincent & al. 2007a - A | |
| Col du Dôme (French Alps): Basal temperature is -11°C for both boreholes and the lower 50 meters of ice do not show any significant change in englacial temperature. On the other hand, a strong warming of firn or ice can be seen in the 90-meter upper part from 1994 to 2005. Moreover, note that the 1994 temperature profile was far from a steady state profile, which would exhibit a sustained cooling from the bottom to the top, apart from the top 15 meters influenced by seasonal variations. |
Two deep ice borehole temperature profiles were measured in 1994 and in 2004-2005 at Col du Dôme (4250 m, Mont Blanc area). These two boreholes were drilled at the same location (9 meters apart). |
Vincent & al. 2007b - A | |
|
Modeling |
Alps: The decade 1980-90, with a mean annual mass balance of -0.65 m w.e. as measured on 8 glaciers in the Alps (Caréser, Gries, Hintereis, Kesselwand, Saint Sorlin, Sarennes, Silvretta, Sonnblick; Haeberli & Müller, 1988; Haeberli & Hoelzle, 1993; Haeberli, 1994), may have brought about a loss in surface ice volume of nearly 20 km3 or about 10-20% of the total volume existing around 1970. Correcting the mass balance forcing for each of the 13 glaciers to fit the measured length change gives an average mass balance of 0.33 +/- 0.09 m a-1 average mass loss. If the 1850-1970 period is treated as one single retreat period without consideration of the 35 years of stationary glaciers (1890-1925), the above calculated value reduces to 0.2-0.3 m w.e. a-1. The energy required for melting this amount of ice is 2-3 W m-2. Such values roughly correspond to the observed long term trend of atmospheric warming. It is assumed that in the 1970s at least 35% of the glacierized surface area existing around 1850 has disappeared. The corresponding volume change is estimated at 45-50%. In such a scenario (-0.9 m a-1 during a time interval of 50 years), 441 small glaciers representing 25% of the glaciers larger than 0.2 km2 existing in the mid-1970s would disappear. In comparison with conditions in the mid-1970s, about 1/3 of the surface area and more than 1/2 the ice volume would be lost. |
The data for the European Alps, containing a total 5050 perennial surface ice bodies, were compiled for the mid-1970s. Only 1763 of these (35%) are larger than 0.2 km2 with complete information available about surface area, total length and maximum and minimum altitude. The parameterization scheme is applied to this part of the sample. A first experiment was run to simulate maximum glacier extent around 1850 AD in order to check the proposed scheme (compared to observations on 13 glaciers) and then to simulate changes that have happened since. The results show that the different sensitivities of long-term glacier length as a response of uniform mass balance forcing can be quite well reproduce and that the chosen mass balance forcing (-0.25 m a-1) appears to underestimate slightly the real evolution. In a second step, calculations were made with a mass balance forcing of -0.9 m a-1 during a time interval of 50 years and starting from the conditions of the mid-1970s. This could more or less correspond to the consequences of the IPCC scenario A till 2025. |
Haeberli & Hoelzle 1995 - A |
Alps:
On slopes protected against direct solar radiation, the lowering of glacier surfaces can enable the penetration of negative temperatures (permafrost) into and the formation of ice within the rock walls originally covered by temperate ice. With continued or even accelerated atmospheric warming, large parts of Alpine glaciers could disappear within decades and extended permafrost slopes could start thawing; first from the permafrost table downwards but later and for extended time periods also from the permafrost base (the interior of mountain slopes) upwards. Such a development would be without historical and perhaps even Holocene precedence. |
This process is illustrated by model calculations of transient heat transfer including latent heat effects for the rock spur carrying the Konkordia Hut at the confluence of the main tributaries of the Great Aletsch glacier. |
Haeberli & al. 1997 - A | |
Europe:
At the global scale, there is a simulation of a general decline in valley glacier mass (and consequent rise in sea level), indicating that the effects of higher temperatures generally are more significant than those of additional winter accumulation. Model studies of individual glaciers have shown general retreat with global warming; with a simulated retreat in Alpine glaciers with higher temperatures and changes in winter accumulation. |
IPCC 2001 - R | ||
| French Alps: |
Gerbaux 2005 - T | ||
Alps: Several field studies (Greuell & al. 1997, Strasser & al. 2004, Oerlemans 2000) have confirmed that direct radiation is the most important energy source for glacier melt in the rough topography of the Alps. This is also due to the long ablation period (sometimes exceeding 90 days) and the comparably low albedo of bare glacier ice (about 0.3). As such, glacier albedo becomes the most sensitive variable for glacier melt. However, glacier albedo exhibits a high temporal (e.g. retreat of the snow line) and spatial (e.g. debris cover) variability, constant or even decreasing albedo with altitude and much lower albedo values in the ablation area than generally applied (0.15 instead of 0.35). The modelled mass balance reveals a distribution pattern that is governed by the potential solar radiation, increasing glacier mass loss with altitude using the 2003 albedo, and a three times higher mass loss for the meteorological conditions of 2002/03 compared to the climatic means. The potential solar radiation governs the mass balance distribution in the case of low glacier albedo and long melt periods. |
In this
study, the authors compare multispectral Landsat Thematic Mapper TM-derived albedo values for several glaciers
and three distinct years (1985, 1998, 2003) and assess the influence
of the albedo on glacier mass balance and melt with a distributed mass
balance model that is forced by the 2002/2003 balance year meteorological
conditions (temperature, precipitation, clouds) as well as climatic
mean values. Glacier melt can be calculated from so-called distributed glacier mass balance models, which utilize a digital elevation model (DEM) to ‘distribute’ measured meteorological input variables (e.g. temperature, precipitation) to the topography by means of elevation-dependent lapse rates and DEM modelling for incoming solar radiation (Arnold & al., 1996, Brock & al., 2000, Klok & Oerlemans, 2002). |
Paul & al. 2005 - P | |
Greater Alpine Region: It has been shown that current rates of glacier wastage by far exceed the historical changes and that deglaciation of entire mountain ranges within the coming decades must be taken into account. |
A suite of models with varying complexity was developed. A strong focus was on the development of simple but robust models, that can be widely applied and make efficient use of the climatic time series compiled within ALP-IMP. |
ALP-IMP 2006 - R | |
Alps:
The sensitivity of the line of equilibrium to temperature is between 60 and 120 m/°C according to different authors (Green et al., 1999; Maish, 2000; Vincent, 2002). Six et al. (2002) proposed that the mass balance of alpine glaciers could be negatively correlated to the oscillations of NAO index, as Beniston et al. (1995) proposed for periods of warm temperature and low precipitations. |
Bravard 2006 - P | ||
Swiss Alps/Alps: The scenario of “accelerated loss” would drastically reduce Alpine glacier areas within this century and the scenario of “extreme loss” would cause most of the presently existing glaciers in the Alps to disappear within decades as large parts of the ice is located below 3000 m a.s.l. This scenario should be seen as an upper limit assumption but may not be unrealistic (cf. the 2003 summer conditions, which could involve strong reinforcing effects like albedo feedback, mass balance / altitude feedback, glacier downwasting and collapse). Atmospheric warming of 3°C in summer accompanied by an increase of 10% in annual precipitation would, for instance, raise the rcELA0 by 340 m and reduce the cAA by 75% compared to the 1971-1990 reference period. Depending on the climate scenario chosen, this could take place toward the middle or the end of this century (IPCC, 2001). Due to the strong warming in the past 2 decades, more than 1/3 of this glacier area reduction has already been taking place. An increase in summer air temperature of 5°C would reduce the glacier cover by more than 90% as compared to the reference period. Precipitation changes of ±20% would modify such estimated percentages of remaining ice by a factor of less than 2. Many individual mountain ranges within the Alps would become ice-free under such conditions and only rather small glacier remnants would persist in a few regions with the highest mountain peaks. |
The first method is a purely empirical one that relates documented changes in glacier hypsography (rates of area change for altitudinal bands) to scenarios of glacier shrinking, ranging from “continued loss” (area reduction for the period 1850-1975), “accelerated loss” (loss from 1975-2000), “strongly accelerated loss” (period 1985-2000) and “extreme loss” (using a doubled 1985-2000 loss rate). These scenarios cover the range of documented glacier shrinking rates and are related to a 20th century warming of about 1°C in the European Alps. The second method is a statistically calibrated and distributed model of equilibrium line altitudes (ELA) that utilizes an empirical relation between 6-month summer air temperature and annual precipitation at the steady-state ELA (ELA0). The relation is obtained from long-term mass balance data from 14 Alpine glaciers in combination with gridded precipitation and temperature (interpolated from 12 high-altitude weather stations) of the period 1971-1990 and a DTM of 100 m cell size. |
Zemp & al 2006 - A | |
Alps: Best estimates for total volumes and volume changes (cf. Haeberli et al., 2004; Paul et al., 2004; Zemp et al., 2006) show that glaciers in the European Alps lost about half their total volume (roughly 0.5% a-1) between 1850 and around 1975, another 25% (1% a-1) of the remaining amount between 1975 and 2000, and an additional 10-15% (2-3% a-1) in the first 5 years of this century. |
The latter estimate is obtained from the mean value of the mass-balance observations at nine Alpine glaciers in combination with the new satellite-derived glacier areas from 1998/99 (Paul, 2004) and a simple model of calculating total glacier volume from mean thickness (Maisch et al., 2000). |
Haeberli & al. 2007 - A | |
Alps: Low-latitude mountain chains like the European Alps or the Southern Alps of New Zealand, where glaciers are typically medium-sized and found in quite steep mountains, will experience rapid glacier changes in adaptation to the modified climate. A modelling study shows that the European Alps would lose about 80 % of their glacier cover should summer air temperatures rise by 3°C, and that a precipitation increase of 25 % for each 1°C would be needed to offset the glacial loss (Zemp et al., 2006). |
Bibliographic review | UNEP 2007 - R | |
Col du Dôme (French Alps): The numerical simulations show that reconstructed temperatures in 2005 cannot match the observed temperatures if the latent heat resulting from surface meltwater refreezing is ignored. A simple latent heat flux formulation has been included using a degree-day factor. This factor has been calibrated with observations to a value of 1 ± 0.3 mm/°C/day. This leads to the conclusion that latent heat flux coming from meltwater plays a significant role. Between the beginning of the 20th century and 1940, englacial temperatures were very close to a steady state profile. During the forties, englacial temperatures increased to reach values in 1950 similar to those obtained at the beginning of the nineties. 1980 shows a very near steady state profile preceding the strong warming of recent decades. This result is consistent with observations at Colle Gnifetti (Monte Rosa) in 1982 [Haeberli and Funk, 1991; Lüthi and Funk, 2001]. Over the 1982-2005 period, the summer mean temperature has increased by 1.1°C compared to the 20th century average. It leads to a temperature profile very far from steady state conditions. The exceptional hot summer in 2003, with summer temperature higher by 4.4°C compared to the 20th century average explains only a small part of this change. For the air temperature warming scenarios, a moderate basal warming of 1°C is predicted for 2050. The englacial temperature increase is between 0 and 5°C below a depth of 30 m. For the warmest scenario, the upper 30 m of ice becomes temperate in 2100. Moreover, with the highest value of latent heat flux from refreezing surface meltwater, the glacier could be entirely temperate, apart from the bottom 20 meters. |
The heat-transfer equation within a cold glacier of Malvern [1969] and Hutter [1983] has been used. Englacial temperatures and their changes are computed at daily intervals using an explicit finite-difference scheme with a one meter horizontal layer thickness. Vertical advection in ice is derived from the analytical formulation used by Ritz [1987], Vincent et al. [1997], including horizontal flow. Boundary surface temperatures have been obtained using valley meteorological data and a fixed vertical lapse-rate (5.6°C/km). Meteorological temperatures come from Lyon (Météo France). Surface accumulation has been inferred from precipitation at Besse using a multiplication factor of 3. Model studies were then carried out back to the beginning of the 20th century. |
Vincent & al. 2007b - A | |
European Alps: The model run for the reference period 19711990 show that over the entire Alps, the cAA covers an area of 3059 km2. As the cAA is simply the terrain above the rcELA0, it does not distinguish between glacier surface and ice-free rock walls. In a first order approach this can be taken into account by applying a slope-dependent glacier fraction to the modelled cAA. The corrected cAA equals 1950 km2 and corresponds to a steady-state Accumulation Area Ratio (AAR0) of 0.67 of the measured total Alpine glacier area in the 1970s, which was 2909 km2 (Zemp et al., in press). The modelled cAA corresponds well overall to the real accumulation areas of Alpine glaciers and there are minor quantities of cAA cells in regions with no glacierisation. A general overestimation of the accumulation areas on SESW slopes and underestimation on NENW slopes can be found. A temperature change of ±1°C leads to an average rcELA0 deviation of +137/-125 m, ranging from +112 m (Aosta) to +190 m (Isar) and from -44 m (Vorderrhein) to -201 m (Var), respectively. A precipitation change of ±25% leads to an average rcELA0 deviation of -114/+157 m, with a range similar to the 1°C temperature deviation. MRT-0.6 results in Alpine an average rcELA0-decrease of 75 m, ranging from 24 m to 131 m, and by 65 m within the outlines of the 1973 Swiss Glacier Inventory. The total cAA of the MRT-0.6 run amounts to 4157 km2. MRT+3/P+10 leads to an average rcELA0 rise of 336 m and the disappearance of glaciers in eight out of 28 basins. The corresponding total cAA over the entire Alps shrinks to 812 km2. When the slope-dependent glacier fraction is applied, the cAA of the MRT-0.6 and the MRT+3/P+10 amounts to 2650 km2 and 504 km2, respectively. This corresponds to a cAA deacrease of 26% between 1850 and 19711990, and a 19711990 cAA decrease of 74%. The sensitivity model runs show that a temperature change of ±1°C would be compensated by a precipitation increase/decrease of 25%. The relative precipitation change corresponds to a mean absolute change over the greater Alpine region of about 300 mm. |
An empirical relationship between 6-month summer temperature and annual precipitation at the steady-state equilibrium line altitude (ELA0) is derived from direct glaciological mass balance measurements from 14 Alpine glaciers over the 19711990 period. Using geographical information systems (GIS) techniques and a digital elevation model (DEM: SRTM3), this relationship is applied for the first time to a distributed modelling of the regional climatic ELA0 (rcELA0) and the climatic accumulation area (cAA) over the entire Alps at a spatial resolution of 3 arc sec (approx. 100 m). In addition to the model run for the reference period 19711990, six more model runs were carried out to study the sensitivity of the ELA0 to changes in temperature and precipitation. Temperature and/or precipitation are altered by a uniform deviation over the entire investigation area. MRT+1 and MRT-1 (temperature +/- 1°C) as well as MRP+25 and MRP-25 (precipitation +/- 25%); MRT-0.6 represents a summer temperature cooling of 0.6°C, as assumed by Maisch et al. (2000) for the year 1850; and MRT+3/P+10 applies a warming of the summer temperature of 3°C and a concurrent rise in precipitation by 10%. Reference and sensitivity model runs are analysed for individual glacier regions, within the hydrological basins, as derived from the HYDRO1k DEM, and within the 1973 outlines of the Swiss Glacier Inventory (Kääb et al., 2002; Paul et al., 2002) for glaciers larger than 1 km2. |
Zemp & al. 2007 - A | |
|
Hypothesis |
Alps: 30-50% of existing mountain glacier mass could disappear by 2100 if global warming scenarios in the range of 2-4°C indeed occur. With an upward shift of 200-300 m in the altitude of the line of equilibrium, the reduction in ice thickness could reach 1-2 m per year. |
Maisch 1992 in Bravard 2006 - P | |
Alps:
The situation of the Alpine ice appear to be evolving at a high and possibly accelerating rate towards or even beyond the "warm" limit of natural variability during the upper Holocene (maximum natural glacier retreat for the last 10 000 years). Under an anticipated warming of 4°C, there would be an upward shift of the equilibrium line by some 200 to 300 m and yearly thickness loss of 1 to 2 m for temperate and alpine glaciers. |
Haerberli & Beniston 1998 - A | ||
Swiss Alps: The + 100 m rise of the glaciers' line of equilibrium correspond to a 0.6-0.7°C warming. With a 100 m rise of the snow line (corresponding to year 2015 for IPCC scenario A or year 2025 for IPCC scenario C), a fifth of the present glaciers and a fourth of the glaciated area of the Swiss Alps will disappear. In a + 200 m scenario, 847 of the 1923 existing glaciers will be left. In a +300 m scenario (timescale 2060-2130), over three-quarter of today's glaciers will already have disappeared. |
3 important "time windows" in the history of the glaciers provided a basis for the study: the maximum extend of the glaciers in 1850, the present situation (1973, the reference year for the swiss inventory of the glaciers), and various scenarios of glaciers retreat for the 21th century. 2244 swiss glacier units have been recorded in the CH-INVGLAZ database according to about 50 different quality and quantity parameters typical of each glacier analysed. |
Bader & Kunz 2000d - R: PNR31 | |
World:
Future changes [mass loss] will affect firstly the maritime ones and then, with a certain delay, the continental ones, which are mostly of polythermal or cold stage. |
Hoelzle & al. 2003 - A | ||
Wold: A common aerosol found in the atmosphere over many regions of the earth is black carbon. This substance absorbs sunlight. It is scrubbed from the atmosphere by precipitation and, because it is ubiquitous, is likely to end up in the snow and ice fields of the planet. There it could decrease the surface albedo, causing the snow/ice to absorb solar energy more readily and thereby melt sooner. Measurements of black carbon amounts and its budgets are only now being made. By whatever means, darkening the surface of a snow/ice field will enhance melt rates. It seems that proper inclusion of aerosols in global climate models will increase early melting of snow packs and, especially, glaciers and sea ice. Properly represented aerosols in climate models will apparently also work together with increasing temperature to reduce snow/ice in regions where heavy air pollution exists (for example, China, the western USA and Europe). |
Barnett & al. 2005 - A | ||
World:
Glacierized mountain areas would be among the most heavily affected parts of the world in the event of accelerated future warming. Empirical methods and energy balance considerations indicate that a large fraction (about one-third to one-half) of the presently existing mountain glacier mass on earth could disappear over the next 100 years with anticipated atmospheric changes. With an associated upward shift of the equilibrium line by some 200 to 300 meters, yearly thickness losses of 1 to 2 meters would have to be expected for temperate glaciers, and many low-latitude mountain ranges would lose major parts of their glacier cover within decades. The consequences would include changes in hazard situations, but also in the water cycle and in landscape evolution. |
Due
to the complex interactions of the different variables of the energy balance
in such areas, potential future changes can only be estimated very roughly |
Kääb & al. 2005 - A | |
Western
Italian Alps: If this negative trend continue in next decades - as foreseen by global and regional climate models - small glacier under 3200-3500 m, like Ciardoney one, may completely disappear before 2020-2030, in consequence of ice thickness losses of about 1-2 m / year. |
Cat-Berro & Mercalli 2007 - P | ||
Alps:. Atmospheric warming will increase the proportion of temperate ice in hanging glaciers and affect the thermal and hydraulic conditions of the rock substrate. |
Gruber & Haeberli 2007 - A | ||
Alps: The increasingly fast mass and vertical thickness loss clearly points to an accelerating trend in climatic forcing. The corresponding additional energy flux calculated as the latent heat of the disappearing ice (around 10 Wm-2 as an average of the past 5 years) is about twice the estimated present-day radiative forcing alone (several Wm-2; Wild et al.2005) and most probably relates to important feedback mechanisms. |
Bibliographic review | Haeberli & al. 2007 - A | |
Alps: In the coming years, the alpine glacier retreat will continue, independently of the temperature evolution: indeed, their current extension does not correspond to the present regional climate, which means that the balance is not reached yet (Zemp et al., 2006). If temperature continues to increase by the end of the 21st century, one can expect a glacier retreat in numerous Alpine regions and even possibly their complete disappearance. |
North & al. 2007 - R: OFEV | ||
Alps: A common characteristic of all three glaciers (Taelli, Cavagnoli and Caresèr glaciers) is that they are comparably flat and not protected much by rock walls from direct solar radiation during summer. As such, their disintegration will most-likely continue in the following years as positive feedbacks can accelerate the down-wasting even further. In total, all the processes observed here act together and in the same direction, leading to a self-acceleration of glacier decline. It can be assumed that it will be very difficult to stop this process for several reasons: (1) Most glaciers have lost all of their firn reserves from the 1970s and would need several years with large amounts of snow in winter (and little ablation in summer) to gain some mass that could then be redistributed by increased flow velocity to the glacier front. Although changes in precipitation are difficult to predict, it seems unlikely that the required increase of more than 50% (e.g. Kuhn, 1989) will take place. (2) There is a general trend of increasing temperatures in the future as predicted by nearly all climate models (e.g. Räisänen et al., 2004). This would further enhance the observed changes and also makes the required snowfall in summer less probable. (3) Even the still flowing and fast-reacting steeper mountain glaciers have response times of several years and their actual shape is not yet in balance with current climatic conditions. As such, they would continue to retreat for several more years even if temperatures are not increasing any further. |
Paul & al. 2007 - A | ||
World: According to climate scenarios for the end of the 21st century, changes in global temperature and precipitation range between +1.1 to +6.4 °C and 30 to +30 %, respectively (IPCC, 2007). Such an increase in mean air temperature will continue the already dramatic glacier changes. Cold continental-type glaciers will react in the first instance with a warming of the ice and firn temperatures, whereas glaciers with ice temperatures at the melting point will have to convert the additional energy directly into melting (Oerlemans, 2001; Kuhn, 1981). |
Bibliographic review | UNEP 2007 - R | |
Mont Blanc and Dôme du Goûter ice fields (French Alps): Over the next 100 years, according to climate warming scenarios, a significant part of precipitation could become rain above 4300 m a.s.l. which could warm up the deep firn and ice. Some studies show that substantial warming of the firn temperature at shallow depths has taken place over the last few decades [Lüthi and Funk, 2001; Suter et al., 2001]. Should this warming reach the bottom ice, the ice dynamics would be greatly modified. |
Vincent & al. 2007a - A | ||
Mont Blanc range: In the Mont Blanc area, temperate firn has been observed between 3500 m and 3800 m depending on exposition and on ice advection from upstream [Suter, 2002; Lliboutry et al., 1976]. Thus, following an atmospheric warming of +4°C and a vertical temperature gradient of 0.0056°C/m, this limit should rise to 4210 m for northern expositions. The lower limit of the dry zone, close to 4200 m during the 20th century [Lliboutry et al., 1976], should climb to 4870 m or more. Between 3500 m and 4200 m, the ice temperature at the bed could reach the melting point, which would greatly modify the ice dynamics. As a result, the glacier could start to slide over its bed. Therefore this warming could strongly affect the stability of hanging glaciers. |
Vincent & al. 2007b - A |
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Legend of bibliographical
references:
- * : study taken into account in WP7.
- A : Article (Peer reviewed publication)
- C : Comment
- E : Scientific study (unpublished)
- P : Proceedings
- R : Report
- Re : Experience Feedback
- T : Thesis
- W : Website