Water resources

Mountains around the world provide water for downstream communities. Glaciers and snowpacks store the water, and release it in dry seasons as the snow and ice melts. Glaciers are therefore a water resource, but this water resource is threatened by glacier recession.

Water is essential for life on Earth. Human societies use water to irrigate their fields, generate hydropower, for domestic consumption, and for boiodiversity and wildlife.

Perpetual Planet: Water Towers

The World’s Water Towers were ranked and listed by Immerzeel et al. (2020), with the supply and the demand on each mountain water tower being characterised.

For the study, scientists assessed the water towers’ importance, not only by looking at how much water they store and provide, but also how much mountain water is needed downstream and how vulnerable these systems and communities are to a number of likely changes over the next few decades.

By analysing these various factors of the 78 mountain water towers worldwide, scientists have identified the five most relied-upon systems by continent that should be on the top of regional and global political agendas:

  • Asia: Indus, Tarim, Amu Darya, Syr Darya, Ganges-Brahmaputra
  • Europe: Rhône, Po, Rhine, Black Sea North Coast, Caspian Sea Coast
  • North America: Fraser, Columbia and Northwest United States, Pacific and Arctic Coast, Saskatchewan-Nelson, North America-Colorado
  • South America: South Chile, South Argentina, Negro, La Puna region, North Chile

To explore the data in more detail and compare water tower rankings, visit natgeo.com/PerpetualPlanet.

Explore the Water Towers with National Geographic

Water Balance App

The Water Balance App could be useful as a front-of-class tool. It shows soil moisture, snow pack, precipitation, evapotranspiration, runoff and change in storage globally and over time. The Water Balance App presents data on the different inputs, outputs and stores of water around the world over the last 20 years.

Students may be able to work through exploring the app on their own, or in a classroom environment. This is an ArcGIS Online app.

There is a ready-made storymap and guide to maximising success at A-Level here.

Water Balance App https://livingatlas.arcgis.com/waterbalance/

Further reading

The world’s mountain ‘water towers’ are melting, putting 1.9 billion people at risk

Water tower of the Andes. Lynn Johnson/National Geographic

Bethan Davies, Royal Holloway

The year 2019 concludes a decade of exceptional heat, and is on track to be the second or third warmest year on record. While the global average temperature teeters on 1.1°C above the pre-industrial record, the world’s glaciers are in stark retreat.

In high mountain areas, the steady trickle of melting snow in spring has nourished people for generations. Today, 1.9 billion people – or 22% of the world’s population – live downstream of snowpacks and glaciers and depend on them as their main source of drinking water. These icy and snowbound mountain regions could be considered water towers, which provide a regular supply of water for drinking, irrigation and power generation, and provide a life-saving buffer during droughts.

Continue reading

Glaciers as a water resource

Mountains as Water Towers of the World

In many mountainous parts of the world with a seasonal rainfall, glaciers are a reliable water resource in the dry season. Mountains could be called the “Water Towers of the World”1, providing water from glacier melt and orographic rainfall to lowland regions. 

Glacierised drainage basins cover 26% of the global land surface outside of Greenland and Antarctica, and are populated by almost one-third of the World’s population2. Upland areas (above 2000 m above sea level) in southeast Asia supply the five basins of the Indus, Ganges, Yellow, Brahmaputra and Yangtze rivers, providing water to 1.4 billion people (over 20 % of the global population).

The Himalayan river basins and the number of people living in each one.

(Source: Redrawing the map of the world’s international river basins)

High Mountain Asia river basins

(source: https://www.raonline.ch/pages/np/visin/np_rivers1301.html)

Glacier meltwater and runoff

Glacier meltwater and runoff contribute to and module downstream water flow, affecting freshwater availability for irrigation, hydropower, and ecosystems3.

Glacier runoff is typically seasonal, with a minimum in the snow-accumulation season, and a maximum in the melt season. This meltwater can compensate for seasons or years with low streamflow or droughts in downstream regions4.

Mountain glacier and lake in Peru

Global glacier recession

Mountain glaciers around the World are currently shrinking5-7, and this is expected to continue throughout the next century. Globally, glaciers are shrinking by 227 ± 32 gigatonnes per year8, enough to raise global sea levels by 0.63 ± 0.08 mm per year.

The areas shrinking fastest are in north America (-50 gigatonnes per year), northern Arctic Canada (60 gigatonnes per year), the Himalaya region (26 gigatonnes per year), and South America (29 gigatonnes per year)8.

World glaciers and ice sheets mass balance. Glaciers are shown in black. Green circles show glacier area, red circles are how much ice is lost annually.

Glacier “Peak meltwater”

As glaciers shrink, meltwater is released from storage within the glacier. Annual meltwater therefore increases, until a maximum is reached3,9. This maximum has been called ‘Peak Meltwater’.

After Peak Meltwater, runoff decreases as smaller glacier volumes can no longer support rising meltwater volumes. As the glacier retreats and disappears, annual runoff from direct precipitation may return to something like the original value, as water is no longer stored as snow. However melt-season runoff may decline substantially, as the glacier no longer acts as a reservoir. Seasonality of water availability may therefore increase, leading to droughts in dry years or dry seasons.

Essentially, as the glaciers shrink, they provide less and less melt water from long-term storage, which impacts seasonal freshwater availability3.  

Peak Meltwater and glacier recession under a warming climate.

Adapted from Huss and Hock (2018) and Rowan et al. (2018).

The degree to which glacier runoff contributes to downstream meltwater varies according to the basin, with glacier contributions being as much as 25% of the annual water budget. In many of these basins, peak meltwater is expected to have passed (e.g., Ref. 10), or will be passed in the next 20-30 years (e.g. Ref. 11). Ultimately, some projections suggest that up to half of the world’s population could be living in water scarcity by 2100 AD12.

Meltwater stream on Mendenhall Glacier, Alaska. From: Gillfoto, Wikimedia Commons

Global scale peak meltwater?

A recent study by Huss and Hock (2018, Nature Climate Change) computed glacier runoff changes for the Earth’s 56 large-scale (>5000 km2) glacierised drainage basins with at least 30 km2 of ice to 2100 AD, and analysed the effect of glacial recession on streamflow.

In half of the basins, peak meltwater has already been reached. In the remaining basins, the modelled annual glacier runoff continues to rise until the maximum is reached, and then runoff declines. Peak water tends to occur later in basins with larger glaciers and higher ice-cover fractions3.

The researchers used a glacier model and climate model outputs forced by three different emissions scenarios, with peak emissions occurring at 2020 AD (RCP 2.6), 2050 AD (RCP 4.5) and after 2100 AD (RCP 8.5)3.  RCP 2.6 is the closest scenario to the targets of the Paris 2015 climate agreement. Projected temperature increases between 1990-2010 and 2080-2100, range from 1.6 ± 1.1°C (RCP 2.6) to 5.4 ± 2.2°C.

Between 2010 and 2100 AD, glacier volume in the 56 investigated basins was projected to decrease by 43±14% (RCP 2.6), 58±13% (RCP 4.5) and 74±11% (RCP 8.5). For the mid-range RCP 4.5, glacier volume reductions in the individual basins ranged from 37 to 99%1.

Reaching Peak meltwater

Peak meltwater has already been reached in 45% of the basins (year 2017 AD), but annual runoff is expected to continue to rise beyond 2050 AD in 22% of the basins. Basins with larger glaciers and high glacier cover (e.g. Susitna, Jökulsá) tend to reach peak meltwater towards the end of the twenty-first century.

In basins dominated by small glaciers (e.g. western Canada, central Europe, South America), peak meltwater has already passed and meltwater will decline over coming decades.

In most basins fed by High Mountain Asia (Aral Sea, Indus, Tarim, Brahmaputra), annual glacier runoff is projected to rise until the middle of the century, followed by steadily declining glacier meltwater runoff thereafter3.

By the end of the twenty-first century, the seasonal glacier runoff maximum is reduced in 93% of the basins compared with the 1990-2010 average, and runoff is less concentrated during the melt season.

Colours show the modelled year of peak water computed from 11-year moving averages of annual glacier runoff from all the glaciers located in the 56 investigated drainage basins, aggregated in 0.5 × 0.5° grid cells. Peak water is also shown with grey scales for all the macroscale basins, classified in 30-year intervals. The results refer to runoff from the initially glacierized area, and are based on the multimodel mean of 14 GCMs and the RCP4.5 emission scenario. The numbers in brackets below the basin names refer to basin glacierization in per cent. The insets show the modelled annual glacier runoff normalized with the average runoff in 1990–2010 for three selected basins. Triangles depict peak water (± standard deviation), thin lines show results for individual GCMs and G denotes the percentage ice cover. From Huss and Hock, 2018

In 19 of the 56 basins, the glacier runoff change between 2000 and 2090 AD accounts for at least one melt-season month with a reduction in runoff of at least 10% (i.e. glacier runoff reduction exceeds 10% of the basin runoff). This is sufficient to cause water scarcity in these basins.

The most significantly affected basins are in High Mountain Asia (Aral Sea, Indus, Tarim, Balkhash), Peru (Santa), South America (Colorado, Baker, Santa Cruz), and North America (Fraser, Skeena, Taku, Nass)3.


The ratio of glacier runoff change to basin runoff is evaluated for the period July to October (January to April for the southern hemisphere, and throughout the year in the tropics). For basins with substantial glacier runoff decreases in at least one month, the ratio refers to the month (given in brackets below the basin names) with the largest reduction in glacier runoff. Basins with negligible glacier impact (|ΔQ′g/Qbasin|< 5%) are shown in grey, and the remaining basins, which show glacier runoff increases that exceed 5% in at least one month, in dark blue. The results refer to multi-GCM means and RCP4.5. Small dots refer to population density > 100 km−2 on a 0.5 × 0.5° grid as an indicator for potential downstream socio-environmental impacts.

Case study: Glaciers and water resources in the Himalaya

In the Himalaya, Karakorum and Hindu Kush mountains, millions of people rely on the 90,000 glaciers as a water resource9. These glaciers form the headwaters of the Indus, Ganges and Brahmaputra rivers. Glaciers here are highly sensitive to climate change, and are rapidly shrinking7,13. The developing countries in these catchments use this water for agriculture and hydropower, and are vulnerable to changes in their water supply14.

The contribution of glaciers to runoff varies in each basin, ranging from 18.8% in the Dudh Koshi catchment (a major tributary to the Ganges), to 80.6% in the Hunza catchment, which drains into the Indus basin9.

In High Mountain Asia, the glacial ice acts to protect against extreme water shortages on seasonal and longer timescales, because the glacial melt is sustained through droughts while all other stores of water in the basin decline14. Hydrological modelling predicts a decline in glacial meltwater contribution to the overall catchment hydrology by 2065 AD of -8% in the Indus, -18% in the Ganges and -20% in the Brahmaputra1.

In southern China, just north of the border with Nepal, one unnamed Himalayan glacier flows from southwest to northeast, creeping down a valley to terminate in a glacial lake. At the end of the glacier’s deeply crevassed snout sits a glacial lake, coated with ice in this wintertime picture. Just as nearby mountains cast shadows, the crevassed glacier casts small shadows onto the lake’s icy surface. This glacial lake is bound by the glacier snout on one end, and a moraine—a mound formed by the accumulation of sediments and rocks moved by the glacier—on the other. Source: http://earthobservatory.nasa.gov/IOTD/view.php?id=43391&src=eoa-iotd

Glacier water resources in the Indus catchment

In the westerly Indus catchment, meltwater dominates water inputs during drought summers, and predicted glacier loss will add considerably to drought-related water stress14. The Indus and Aral basins are dominated by wet winters, dry summers, and have extensive glaciation14. The summer monsoon in these more westerly basins is also less dominant than that further east.

Map of the Indus River basin with tributaries labeled. Yellow regions are non-contributing parts of the watershed (e.g. the Thar Desert). From Wikimedia Commons (Keenan Pepper, https://commons.wikimedia.org/wiki/File:Indus_River_basin_map.svg)

In these basins, the highest proportion of glacial melt to overall basin hydrology occurs in the upper basins, closer to the glaciers. In the Indus basin, two thirds of the population (>120 million people) lives in the middle altitudes, where glacial meltwater is more significant. The use of water for hydropower and irrigation is concentrated at dams and barrages with average altitudes of 936-1484 m above sea level, in these middle altitudes14. In the Indus, 121 of 143 existing or planned dams are glacier-fed. In the upper Indus, without glaciers, summer monthly water flows would be reduced by 38%, and up to 58% in drought years. Water stress is likely to peak in the relatively dry summers in drought years as the glacier melt declines.

Video on glaciers as a water resource

Here is a video of Bethan Davies talking about glaciers as a water resource in Patagonia and the Himalaya.

Further reading

References

1              Immerzeel WW, van Beek L P H & P, B. M. F. Climate change will affect the Asian water towers. Science 328, 1382–1385 (2010).

2              Beniston, M. Climatic Change in Mountain Regions: A Review of Possible Impacts. Climatic Change 59, 5-31, doi:10.1023/a:1024458411589 (2003).

3              Huss, M. & Hock, R. Global-scale hydrological response to future glacier mass loss. Nature Climate Change 8, 135-140, doi:10.1038/s41558-017-0049-x (2018).

4              Barnett, T. P., Adam, J. C. & Lettenmaier, D. P. Potential impacts of a warming climate on water availability in snow-dominated regions. Nature 438, 303, doi:10.1038/nature04141 (2005).

5              Bamber, J. L., Westaway, R. M., Marzeion, B. & Wouters, B. The land ice contribution to sea level during the satellite era. Environmental Research Letters (2018).

6              Zemp, M. et al. Historically unprecedented global glacier decline in the early 21st century. Journal of Glaciology 61, 745-762, doi:10.3189/2015JoG15J017 (2015).

7              Zemp, M. et al. Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016. Nature, 1 (2019).

8              Gardner, A. S. et al. A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009. Science 340, 852-857, doi:10.1126/science.1234532 (2013).

9              Rowan, A. V. et al. The sustainability of water resources in High Mountain Asia in the context of recent and future glacier change. Geological Society, London, Special Publications 462, 189-204 (2018).

10           Frans, C. et al. Implications of decadal to century scale glacio‐hydrological change for water resources of the Hood River basin, OR, USA. Hydrological processes 30, 4314-4329 (2016).

11           Immerzeel, W., Pellicciotti, F. & Bierkens, M. Rising river flows throughout the twenty-first century in two Himalayan glacierized watersheds. Nature geoscience 6, 742 (2013).

12           Hejazi, M. I. et al. Integrated assessment of global water scarcity over the 21st century under multiple climate change mitigation policies. Hydrology and Earth System Sciences 18, 2859-2883 (2014).

13           Bolch, T. et al. The state and fate of Himalayan Glaciers. Science 336, 310-314 (2012).

14           Pritchard, H. D. Asia’s glaciers are a regionally important buffer against drought. Nature 545, 169-174, doi:10.1038/nature22062 (2017).

What is the global volume of land ice and how is it changing?

How much land ice is there in the World?

Most (99.5%) of the permanent ice volume in the world is locked up in ice sheets and glaciers. The Antarctic Ice Sheet is the largest store of frozen freshwater; it would raise sea levels by 57.9 m (its “sea level equivalent”, or SLE) on full melting (BedMachine). The Antarctic Ice Sheet covers 8.3% of the Earth’s land surface.

The Greenland Ice Sheet has a sea level equivalent ice volume of 7.42 m, and covers 1.2% of the global land surface (BedMachine).

Finally, glaciers and ice caps have a sea level equivalent ice volume of 0.32 m, covering just 0.5% of the global land surface (Figure 1). There is a nice illustration of this here.

Global glaciers (in yellow) and ice sheets (white). From IPCC AR5

Figure 1. Global land ice. Glaciers are highlighted in yellow, ice shelves in green, ice sheets in white.

Other sources of global ice

There are also small amounts of ice stored in the ground in permafrost regions, frozen lakes and rivers, seasonal snow cover, and so on.

Sea ice (frozen sea water) and ice shelves (frozen floating extensions of land ice; green on Figure 1 above) do not have a “sea level equivalent” of ice volume as they are already floating, so would not raise sea levels on full melting.

Measuring changes in global ice volume

Changes in global ice volume are often expressed in gigatonnes per year (yr-1). A gigatonne is 1,000,000,000 tonnes. 1 kmwater = 1 Gt water; 361.8 Gt of ice will raise global sea levels by 1 mm.

Greenland Ice Sheet

Mass balance of the Greenland Ice Sheet

The Greenland Ice Sheet has been losing mass for over 20 years. The most recent estimates suggest that the Greenland Ice Sheet from 2012 to 2016 had a negative mass balance, losing 247 ± 15 Gigatonnes (Gt) per year of ice volume, contributing 0.69 ± 0.04 mm per year to sea level rise[2]. The mass balance of Greenland has been increasingly negative since 1995, and it is now equivalent to the global contribution to sea level rise from glaciers and ice caps (Figure 2).

Figure 2. Cumulative ice mass loss from Greenland ice sheet 1992–2012[1] (from IPCC AR5).

Driven by changes in surface mass balance

These changes have largely been driven by changes in surface mass balance. While in Greenland 60% of mass loss is through ice discharge across the grounding line to the ocean (as icebergs or melting in the ocean), 40% of mass loss is from surface melt. Increases in surface melt (ablation) are largely responsible for the increasing melting of Greenland [3].

On June 15, 2016, the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 satellite acquired a natural-color image of an area just inland from the coast of southwestern Greenland (120 kilometers southeast of Ilulisat and 500 kilometers north-northeast of Nuuk). From Wikimedia Commons

Figure 3. Surface meltwater on the Greenland Ice Sheet.

The estimates of Greenland Ice Sheet mass balance above include the peripheral glaciers surrounding the larger ice sheet. These peripheral glaciers account for around 15-20% of the total mass imbalance of the ice sheet[2, 4].

These increases in surface melt and mass losses from Greenland are due to recent increases in winter and summer air temperatures, with increases in the size of the ice sheet ablation area (the area with net melting over one year). This is associated with changes in the surface albedo, as ice has a lower albedo than white snow, exacerbating melt. Overall, this is leading to a lowering of the Greenland Ice Sheet surface elevation (Figure 4), and a decrease in ice volume.

Acceleration in outlet glaciers

Ice discharge from the major outlet glaciers of the Greenland Ice Sheet has also increased, with glaciers accelerating in western Greenland (e.g. Jakobshavn Isbrae, JI) (Figure 4). This faster ice flow leads to these outlet glaciers discharging more ice volume to the ocean as icebergs than is replaced by snow, so the outlet glaciers are also thinning, as can be seen by the red on the figure below.

Figure 4. Average rates of surface elevation change (dh/dt) through time (2010-2017) for the Greenland and Antarctic Ice Sheets[2].

Antarctic Ice Sheet

Antarctic Ice Sheet ice volume

The best estimates of Antarctic volume come from BEDMAP2 [5]. BEDMAP2 provides us with a detailed map of the base of the ice sheet, derived mostly from radar data. There are three ice sheets in Antarctica, each with their own unique characteristics. They are the larger East Antarctic Ice Sheet (EAIS), with an SLE of 53.3 m, the West Antarctic Ice Sheet (WAIS), with an SLE of 4.3 m, and the Antarctic Peninsula Ice Sheet (APIS) with an SLE of 0.2 m.

Surface elevation of the Greenland and Antarctic ice sheets (IPCC AR5)

Figure 5. BEDMAP2 (Fretwell et al., 2013; IPCC AR5).

Antarctica surface mass balance

It is very cold in Antarctica, with very limited surface melt [6]. There is abundant accumulation in the coastal parts of Antarctica, especially western West Antarctica and on the APIS.  The figure below shows where surface mass balance is highest; reds and yellows indicate far more snowfall than is lost through surface melting. It is cold and dry in the centre of the East Antarctic Ice Sheet, with very little snowfall or surface melt.

The average ice-sheet integrated surface mass balance of Antarctica is +2418 ± 181 Gt yr-1 [6].

Figure 6. Mean (1979–2010) surface mass balance [mm w.e. y−1]. [6]

Changes in Antarctic mass balance

Most mass loss in Antarctica is driven through ocean melting and iceberg calving[7, 8]. This ice discharge to the ocean through the grounding line is increasing as outlet ice streams are accelerating and grounding lines are retreating (see here). Thus increased ice flow in Antarctica accounts for almost all recent increases in mass losses.

The sea level rise contribution from Antarctica was 0.49 – 0.73 mm yr-1 from 2012-2017, mostly from the APIS and WAIS and due to acceleration of outlet glaciers in Amundsen Sea Embayment (e.g. Pine Island Glacier/Thwaites Glacier) (Figure 4; 7)[2].

Ice streams of Antarctica with Pine Island Glacier and Thwaites glacier highlighted.

Figure 7. Location of Pine Island and Thwaites Glacier in Antarctica, with ice velocity from Rignot et al. 2011

Including ice gained and lost through all mechanisms, the current mass balance of Antarctica from 1992 to 2017 was:

  • EAIS: +5 ± 46 Gt yr-1
  • WAIS: –94 ± 27 Gt yr-1
  • APIS: –20 ± 15 Gt yr-1
  • Total Antarctic Ice Sheet: -109 ± 56 Gt yr-1

Antarctic Ice Sheet mass balance changed from 2012 to 2017 to -219 ± 43 Gt yr-1 [8] . Mass losses from West Antarctica are driving most of the total mass losses from Antarctica, with the mass balance of East Antarctica showing negligible changes [8].

Shepherd et al. 2018

Figure 8. Mass changes in Antarctica (Shepherd et al. 2018).

Glaciers and Ice caps

Glacier extent

The amount of ice contained in global glaciers and ice caps is mapped by the Randolph Glacier Inventory[9, 10]. This inventory uses satellite imagery and a formalised methodology to organise researchers working on mapping glaciers and glacier change. The Randolph Glacier inventory estimates that there are 198,000 glaciers worldwide (Figure 9); however, this is an arbitrary number as it depends on:

  • Subdivision of glaciers and mapping of ice divides
  • Accuracy of the digital elevation model used
  • Minimum area threshold; it is hard to map glaciers smaller than 0.2 km2 and so this is usually set as a minimum area threshold. There could be up to 400,000 glaciers if small glacierettes are included (but they only account for 1.4% of glacierised area).

Bamber et al. 2018

Figure 9. Global glaciers (yellow) and their area (pie charts) [2, 10].

The RGI estimates a total glacierised area of: 726,000 km2

  • Subantarctic and Antarctic: 132,900 km2
  • Arctic Canada North: 104,900 km2
  • Asia: 62,606 km2
  • Low latitudes: 2346km2
  • 44 % is in Arctic regions, 18% in Antarctic & Subantarctic.

Global glacier ice volume

An estimate of global ice volume in glaciers and ice caps remains a “grand challenge” in glaciology; there are few glaciers with direct measurement by radar [11]. Bed topography and thus ice thickness is usually then estimated, either by volume-area scaling [12, 13], inversions of ice surface slope and velocity [14, 15], or from numerical modelling of ice flow [16].

Our best current estimate of global glacier ice volume is[16]:

  • 170 x 103 ± 21 x 103 km3 (moutain glaciers & ice caps outside Greenland & Antarctica)
  • = 0.43 ± 0.06 m SLE.

Glacier recession

Glaciers worldwide are receding. The key methods for mapping glacier change include:

  • Satellite images (1970s-present)[17]
  • Topographic maps (~1900 to present)
  • Geomorphological evidence of glacier extent (LIA/sig. advances)
  • Automated and manual mapping from satellite imagery
  • Limit realistically of mapping glaciers min. 0.2 km2

Mass loss can also be quantified from analysis of glacier surface elevation change (dh/dt)[18, 19] using digital elevation model differencing, satellite gravimetry or altimetry, and in-situ surface mass balance measurements [20].

The figure below shows the current best estimates of ice volumes lost from Antarctica and Greenland from 2012-2016 (taken from Bamber et al. 2018) and from glaciers around the world. Bamber et al. 2018 do not provide an individual assessment of ice volume lost from each area, so here I have plotted ice volumes lost from 2003-2009 from Gardner et al. 2013. Each region corresponds to those mapped out in Figure 9 and glacier outlines are from GLIMS and the Randalph Glacier Inventory.

Note that peripheral glaciers around Greenland and Antarctica are included in the assessment for the ice sheets (cf. Bamber et al. 2018). These glaciers are however changing rapidly, and indeed account for a large portion of the overall change.

World glaciers and ice sheets mass balance

Figure 10. Global glacier mass budgets from 2012-2016 by Bamber et al. 2018 (ice sheets) and 2003-2009 (glaciers; Garder et al. 2013).

These data, recently compiled by Bamber et al. 2018, give a global estimate of mass loss from glaciers of -227 ± 31 Gt yr-1 (2012-2016). This does not include losses from peripheral glaciers around Greenland and Antarctica, which are included in the ice sheet mass balance assessments.

IPCC AR5

Figure 11. Global glacier melt (IPCC AR5)[1]

This has led the World Glacier Monitoring Service (WGMS) to state: “rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history” [21].

This global melt is a challenge for society. While the sea level rise from glaciers is ultimately constrained by their small ice volume globally, they remain important as sources of freshwater [22]; their melting poses new hazards to mountain communities[23-25], and they remain important for local economies [26].

Summary

Global changes in land ice volume were recently summarised by Bamber et al. (2018):

Ice mass Total ice volume % Global land surface Volume change 2012-2016 Sea level contribution 2012-2016
EAIS 53.3 m SLE 8.3% -19 ± 20 Gt yr-1 0.05 ± 0.06 mm yr-1
WAIS & APIS 4.5 m SLE -172 ± 27 Gt yr-1 0.48 ± 0.08 mm yr-1
Greenland 7.36 m SLE 1.2% -247 ± 15 Gt yr-1 0.69 ± 0.04 mm yr-1
Global glaciers and ice caps* 0.43 m SLE

(113,915 to 191,879 Gt)

0.5% -227 ± 31 Gt yr-1 0.63 ± 0.08 mm yr-1
Total 12.5% -665 ± 48 Gt yr-1 1.85 ± 0.13 mm yr-1

*excl. glaciers peripheral to ice sheets

Accelerating mass loss from land ice

Mass loss is accelerating (Figure 12), with changes in ocean melt driving recession in Antarctica, increased ice discharge and surface melt driving changes in Greenland, and negative surface mass balances largely driving glacier recession worldwide. Losses from Greenland are now the most significant contributor to global sea level rise (this includes the peripheral glaciers around the ice sheet), recently overtaking glaciers as the largest contributor.

Bamber et al. 2018

Figure 12. Mass losses from glaciers and ice sheets, annually (Bamber et al. 2018)

Below is a nice summary of the key changes and processes from the IPCC AR4:

Figure 13. Summary of global changes in land ice, IPCC AR5 (2013).

Further reading

References

  1. Vaughan, D.G., et al., Observations: Cryosphere, in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, T.F. Stocker, et al., Editors. 2013, Cambridge University Press: Cambridge, UK. p. 317-382.
  2. Bamber, J.L., et al., 2018, Environmental Research Letters.
  3. van den Broeke, M., et al., 2017, Current Climate Change Reports. 3, 345-356.
  4. Bolch T, et al., 2013, Geophys. Res. Lett. . 40, 875-881.
  5. Fretwell, L.O., et al., 2013, The Cryosphere. 7, 375-393.
  6. Lenaerts, J.T.M., et al., 2012, Geophysical Research Letters. 39, L04501.
  7. Pattyn, F., et al., 2018, Nature Climate Change.
  8. Shepherd, A., et al., 2018, Nature. 558, 219-222.
  9. Arendt, A., et al., Randolph Glacier Inventory [v2.0]: A Dataset of Global Glacier Outlines. 2012, Global Land Ice Measurements from Space: Boulder Colorado, USA.
  10. Pfeffer, W.T., et al., 2014, Journal of Glaciology. 60, 537.
  11. Gärtner-Roer, I., et al., 2014, Global and Planetary Change. 122, 330-344.
  12. Bahr, D.B., Estimation of glacier volume and volume change by scaling methods, in Encyclopedia of Snow, Ice and Glaciers. 2014, Springer. p. 278-280.
  13. Bahr, D.B., W.T. Pfeffer, and G. Kaser, 2014, Reviews of Geophysics.
  14. Carrivick, J.L., et al., 2018, Geografiska Annaler: Series A, Physical Geography, 1-23.
  15. Carrivick, J.L., et al., 2016, Global and Planetary Change. 146, 122-132.
  16. Huss, M. and D. Farinotti, 2012, Journal of Geophysical Research: Earth Surface. 117, F04010.
  17. Davies, B.J. and N.F. Glasser, 2012, Journal of Glaciology. 58, 1063-1084.
  18. Willis, M.J., et al., 2011, Remote Sensing of Environment. 117, 184-198.
  19. Willis, M.J., et al., 2012, Geophys. Res. Lett. 39, L17501.
  20. Gardner, A.S., et al., 2013, Science. 340, 852-857.
  21. Zemp, M., et al., 2015, Journal of Glaciology. 61, 745-762.
  22. Immerzeel WW, van Beek L P H, and B.M.F. P, 2010, Science. 328, 1382–85.
  23. Emmer, A., 2017, Quaternary Science Reviews. 177, 220-234.
  24. Emmer, A., Glacier Retreat and Glacial Lake Outburst Floods (GLOFs), in Oxford research Encyclopedias–Natural Hazard Science. 2017, Oxford University Press. p. 1-38.
  25. Harrison, S., et al., 2017.
  26. al, H.M.e., 2017 Earth’s Future 5 418-35.

Antarctic Peninsula has strong sensitivity to surface warming

The Antarctic Peninsula is warming very rapidly, about six times the global average[1-3]. There has been a 95% increase in positive degree day sums since 1948[4]. Glaciers in the region are accelerating, in response to frontal thinning and recession[5]. In addition, ice shelves are collapsing[6], glacier fronts are retreating[7]. The causes for much of these changes has often been attributed to ocean forcing, with warm ocean waters melting these glaciers from below[8-11]. However, while ocean forcing may dominate further south, such as at Pine Island Glacier, a few recent papers have highlighted the importance of surface processes and surface melt induced by warmer surface air temperatures and longer melt seasons, specifically on the Antarctic Peninsula. Continue reading

Glacier recession

Worldwide, glaciers are shrinking and receding. In fact, glacier recession and thermal expansion of the ocean together account for 75% of today’s observed sea level rise. Glaciers are small and have short response times, so they react quickly to changes in air temperature and precipitation. Glaciers around the Antarctic Peninsula are shrinking particularly rapidly, and this is exacerbated by ice shelf collapse.

This section summarises how glaciers are behaving and shrinking around the Antarctic Peninsula, in nearby Patagonia in South America, and more broadly around Antarctica.

Videos

In this video, Prof. Mauri Pelto discusses the glacial recession of Gilkey Glacier on Juneau Icefield, Alaska.

Columbia Glacier, Alaska, is a World Reference Glacier and its recession has been monitored for several decades. You can see the glacier recession in the GIF below. This is a series of Landsat satellite images from 1986 to 2019. See here for more information.

Recession of Columbia Glacier, Alaska

Here is a video from Prof. Mauri Pelto with a timelapse of photographs of this glacier’s recession.

Sea level rise over the next 2000 years

A new paper by Levermann et al. in PNAS uses the record of past rates of sea level rise from palaeo archives and numerical computer models to understand how much sea level rise we can expect per degree of warming in the future. These data suggest that we can expect a global sea level rise of 2.3 m per 1°C of warming within the next 2000 years: well within societal timeframes. A 2°C of warming would result in a global sea level rise of 4.8 m within 2000 years. This would inundate many coastal cities in Europe alone, and cause untold economic and societal damage.

Continue reading

Glacier change in Antarctica

Introduction | Temperatures are rising | Ice shelves are collapsing | Glaciers are shrinking | Glaciers are thinning | Glaciers are accelerating | Sea level is rising | Impact of climate on glaciers | References | Comments |

Introduction

Antarctic Peninsula satellite image. An orthographic projection of NASA's Blue Marble data set (1 km resolution global satellite composite). From Wikimedia Creative Commons by Anna Frodesiak.

Figure 1. The Antarctic Peninsula. An orthographic projection of NASA’s Blue Marble data set (1 km resolution). By Anna Frodesiak.

What is happening around the Antarctic Peninsula? This is a region of very rapid warming, and this has resulted in a whole suite of glaciological changes. What are the implications of this change for us? How do glaciers respond to climate change, how are they related and linked, and what is driving these changes? This article summarises glaciers and climate change around the Antarctic Peninsula.

Temperatures are rising

Figure 2. This image shows the instrumental record of global average w:temperatures as compiled by the w:NASA’s w:Goddard Institute for Space Studies. (2006) “Global temperature change”. Proc. Natl. Acad. Sci. 103: 14288-14293. Following the common practice of the w:IPCC, the zero on this figure is the mean temperature from 1961-1990. This figure was originally prepared by Robert A. Rohde from publicly available data and is incorporated into the Global Warming Art project. Wikimedia Commons.

Climate change is strongly affecting Antarctica. Around the Antarctic Peninsula, temperatures are warming at a rate that is approximately six times the global average. Air temperatures increased by ~2.5°C from 1950-20001. Regional rapid warming here began in the 1930s2. The annual mean air temperature -9°C isotherm has moved southwards, resulting in ice-shelf collapse and glacier recession3. A recent ice core from James Ross Island shows that warming in this region began around 600 years ago and then accelerated over the last century. This rate of warming is unusual, but not unprecedented4. Warming over the Antarctic Peninsula is exacerbated by a strengthening of the Antarctic Oscillation, which is a periodic strengthening and weakening of the tropospheric westerlies that surround Antarctica5. Changing pressure patterns result in flow anomalies, with cooling over East Antarctica and warming over the Antarctic Peninsula.

Figure 3. Antarctic temperature trends, 1981-2007. By Robert Simmon, NASA [Public domain], via Wikimedia Commons

But how unusual is this warmth? Ice core records provide a longer-term perspective on climate over the past four glacial cycles or longer6. The ice-core record indicates that carbon dioxide and temperature co-varied over the last 400 thousand years, which suggests a close link between these ‘greenhouse gases’ and temperature. Ice core records show that methane and carbon dioxide atmospheric concentrations are higher than at any point in the last 650,000 years7. The IPCC states,

“The total radiative forcing of the Earth’s climate due to increases in the concentrations of the LLGHGs CO2, CH4 and N2O, and very likely the rate of increase in the total forcing due to these gases over the period since 1750, are unprecedented in more than 10,000 years”

Figure 4. Ice core record of Antarctic atmospheric gases and temperature change over the past 650,000 years. From the IPCC.

Ice shelves are collapsing

Larsen Ice Shelf in 2004

Larsen Ice Shelf in 2004

What effect is this having on the glaciers of the Antarctic Peninsula? Ice shelves have disintegrated very rapidly over the last few decades8-13, which has destabilised on-shore glaciers, which rapidly thinned and receded following removal of a buttressing ice shelf11,14-21 (quick check – do you understand the difference between ice shelves, sea ice, ice bergs and marine-terminating glaciers?). Higher air temperatures around the Antarctic Peninsula contribute to ice shelf collapse by increasing the amount of meltwater ponding on the surface8,9,22. When combined with ice shelves that are thinning due to melting from below following the incursion of warm ocean currents onto the continental shelf10,23-25, you have a recipe for rapid ice shelf disintegration. With one particularly warm summer, a thinned ice shelf that is close to its threshold is liable to break up very quickly as meltwater ponding on its surface propagates downwards and initiates iceberg calving by hydrofracture. Some of these ice shelves have collapsed for the first time26.

Larsen Ice Shelf

Landsat images showing the collapse of the Larsen Ice Shelf. Note the blue mottled appearance in 2002, resulting from the exposure of deep blue ice.

Landsat images showing the collapse of the Larsen Ice Shelf. Note the blue mottled appearance in 2002, resulting from the exposure of deep blue ice.

The Larsen Ice Shelf collapsed dramatically and very rapidly in 2002, and glaciers that previously fed into the Larsen Ice Shelf have since accelerated, thinned and receded. The ice shelf disintegrated very rapidly, with the main event happening over just one warm summer. The Larsen B Ice Shelf, shown in Figure 5, has been stable throughout the Holocene and this is the first time it has collapsed in the last 10,000 years.

Pine Island Glacier

Antarctic ice shelf thickness changes. Note the rapid thinning of Pine Island Glacier ice shelf in West Antarctica. From Pritchard et al., 2012, Nature. Reprinted by permission from Macmillan Publishers Ltd: Nature (Pritchard et al. 2012), copyright (2012).

Figure 6. Antarctic ice shelf thickness changes. Note the rapid thinning of Pine Island Glacier ice shelf in West Antarctica. From Pritchard et al., 2012, Nature. Reprinted by permission from Macmillan Publishers Ltd: Nature
(Pritchard et al. 2012), copyright (2012).

Ice shelves are warmed from below, and the ice shelves around Pine Island Glacier are thinning and receding. The thinning of these ice shelves may limit their ability to buttress the flow of ice from the interior of the ice sheet. Pritchard et al. (2012) say in their paper in Nature (Figure 6) that melting from the base of ice shelves is the primary driver of Antarctic Ice Sheet ice loss, by reducing the buttressing capability of the ice shelves. The rapid thinning of the Pine Island Glacier ice shelf is caused by warm oceanic water at depth that reaches the underside of ice shelves by travelling along troughs on the continental shelf.

Glaciers are shrinking

Glacier on the Antarctic Peninsula. From Wikimedia Creative Commons.

There is increasing evidence that glaciers around the Antarctic Peninsula are shrinking and receding. Alison Cook found that 87% of the glaciers around the Antarctic Peninsula are receding27,28. Other workers have found evidence of glacier recession and a measureable sea-level contribution29. There is evidence of widespread glacier recession around the northern Antarctic Peninsula21,30. Land-terminating glaciers in this region are shrinking particularly rapidly31, which is significant, as their mass balance is more directly controlled by temperature and precipitation, compared with marine-terminating glaciers, which respond non-linearly to climate forcing.

Glaciers are thinning

A paper published recently in Geophysical Research Letters32 showed that glaciers around the Antarctic Peninsula are thinning. 12 glaciers around the Antarctic Peninsula showed near-frontal surface lowering since the 1960s, with higher rates of thinning for glaciers on the north-western Antarctic Peninsula. Surface lowering ceases at about 400m in altitude across all the glaciers, which may be due to increased high-altitude accumulation32. These marine-terminating glaciers are affected by both oceanic and atmospheric warming. The thinning of these glaciers is bringing them nearer to floatation. Kunz et al (2012) conclude that the majority of the glaciers around the Antarctic Peninsula are likely have been thinning for decades, but that the pattern of surface change is not simple. Lowering is not caused by reduced mass input, as it is not observed at higher elevations (in fact, the amount of lowering has probably been reduced by this higher precipitation).

Glaciers are accelerating

Glaciers are accelerating across the Antarctic Peninsula33. This may be due to the thinning observed at the glacier snouts32,33, and combined with the thinning and recession observed across the Antarctic Peninsula, indicates that there is a climatically-driven rise in sea level from this region. Thinning glaciers are easier to float. Once warm ocean water can access the underside of a glacier, melting from below exacerbates thinning from above, resulting in increased and rapid glacier thinning34. Thinning glaciers accelerate as part of their dynamic response, as changes near the grounding line can impact glacier velocity some distance inland35. Pritchard and Vaughan (2007) argue that thinning as a result of a negative mass balance will reduce the effective stress of a glacier’s bed near the margin, reducing basal resistance and increasing sliding. This leads to further thinning, floatation, rapid calving and increased glacier recession33. The retreat rate will be controlled to a large extent by fjord depth and geometry, and over deepened basins resulting in particularly rapid glacier recession.

Sea level is rising

Recent sea level rise. Credit: Bruce C. Douglas (1997). “Global Sea Rise: A Redetermination”. Surveys in Geophysics 18: 279–292. DOI:10.1023/A:1006544227856. Image from Global Warming art project. Wikimedia Commons

Global sea levels are currently rising at a rate of about 3 mm per year7. The contribution from the Antarctic Peninsula is −41.5 Gt yr−1 36, although a recent study refines this to -34 Gt yr-1 37. King et al. calculate that the Antarctic Ice Sheet as a whole currently contributes about 0.19 mm±0.05 mm per year to global sea level rise, which is largely from the Antarctic Peninsula, the Amundsen Sea sector (including Pine Island Glacier), and which is partly balanced by increased ice accumulation in East Antarctica.

Most modern sea level rise, and sea level rise predicted over the next 100 years, comes from ocean expansion and the melting of small glaciers and ice caps. However, the amount that the sea level will rise in the future depends not only on temperature, glacier recession and ocean warming and expansion, but also the dynamic behaviour of the West Antarctic Ice Sheet. Marine Ice Sheet Instability may result in rapid future sea level rise, contributed to by ice-shelf collapse and the dynamic behaviour of ice streams. How much will Antarctica contribute to sea level rise in the future? You can read more about that in this blog post.

Ice streams of Antarctica with Pine Island Glacier and Thwaites glacier highlighted.

Impact of climate on glaciers

The Antarctic Peninsula is particularly vulnerable to climate change due to its small size and northerly latitude2. It receives high snowfall but high melt, with a large number of days above 0°C in the summer months33. It interrupts the Circumpolar Westerlies and is liable to be affected by small changes in these winds. Increased numbers of positive degree days 32 coincide with increased rates of thinning on Antarctic Peninsula marine-terminating glaciers, and increased meltwater ponding and hydrofracture on ice shelves. Glaciers are thinning and receding in response to warmer temperatures, and thinning glaciers are easier to float. We know that basal melting of ice shelves drives ice sheet loss34, and we can observe the impacts of climate change around the Antarctic Peninsula today.

Further reading

Go to top or jump to Glacier Recession.

References


1. Turner, J., Colwell, S.R., Marshall, G.J., Lachlan-Cope, T.A., Carelton, A.M., Jones, P.D., Lagun, V., Reid, P.A. & Iagovkina, S. Antarctic climate change during the last 50 years. International Journal of Climatology 25, 279-294 (2005).

2. Vaughan, D.G., Marshall, G.J., Connelly, W.M., Parkinson, C., Mulvaney, R., Hodgson, D.A., King, J.C., Pudsey, C.J. & Turner, J. Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change 60, 243-274 (2003).

3. Morris, E.M. & Vaughan, A.P.M. Spatial and temporal variation of surface temperature on the Antarctic Peninsula and the limit of viability of ice shelves. in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, Vol. Volume 79 (eds. Domack, E.W., Leventer, A., Burnett, A., Bindschadler, R., Convey, P. & Kirby, M.) 61-68 (American Geophysical Union, Antarctic Research Series, Volume 79, Washington, D.C., 2003).

4. Mulvaney, R., Abram, N.J., Hindmarsh, R.C.A., Arrowsmith, C., Fleet, L., Triest, J., Sime, L.C., Alemany, O. & Foord, S. Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history. Nature advance online publication(2012).

5. van den Broeke, M.R. & van Lipzig, N.P.M. Changes in Antarctic temperature, wind and precipitation in response to the Antarctic Oscillation. Annals of Glaciology 39, 119-126 (2004).

6. Augustin, L., Barbante, C., Barnes, P.R.F., Barnola, J.M., Bigler, M., Castellano, E., Cattani, O., Chappellaz, J., DahlJensen, D., Delmonte, B., Dreyfus, G., Durand, G., Falourd, S., Fischer, H., Fluckiger, J., Hansson, M.E., Huybrechts, P., Jugie, R., Johnsen, S.J., Jouzel, J., Kaufmann, P., Kipfstuhl, J., Lambert, F., Lipenkov, V.Y., Littot, G.V.C., Longinelli, A., Lorrain, R., Maggi, V., Masson-Delmotte, V., Miller, H., Mulvaney, R., Oerlemans, J., Oerter, H., Orombelli, G., Parrenin, F., Peel, D.A., Petit, J.R., Raynaud, D., Ritz, C., Ruth, U., Schwander, J., Siegenthaler, U., Souchez, R., Stauffer, B., Steffensen, J.P., Stenni, B., Stocker, T.F., Tabacco, I.E., Udisti, R., van de Wal, R.S.W., van den Broeke, M., Weiss, J., Wilhelms, F., Winther, J.G., Wolff, E.W., Zucchelli, M. & Members, E.C. Eight glacial cycles from an Antarctic ice core. Nature 429, 623-628 (2004).

7. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. & Miller, H.L. (eds.). Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, (Cambridge University Press, Cambridge, 2007).

8. Scambos, T., Fricker, H.A., Liu, C.-C., Bohlander, J., Fastook, J., Sargent, A., Massom, R. & Wu, A.-M. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters 280, 51-60 (2009).

9. Glasser, N.F. & Scambos, T.A. A structural glaciological analysis of the 2002 Larsen B ice shelf collapse. Journal of Glaciology 54, 3-16 (2008).

10. Vieli, A., Payne, A.J., Shepherd, A. & Du, Z. Causes of pre-collapse changes of the Larsen B ice shelf: Numerical modelling and assimilation of satellite observations. Earth and Planetary Science Letters 259, 297-306 (2007).

11. Rack, W. & Rott, H. Pattern of retreat and disintegration of the Larsen B ice shelf, Antarctic Peninsula. Annals of Glaciology 39, 505-510 (2004).

12. Scambos, T., Hulbe, C. & Fahnestock, M. Climate-induced ice shelf disintegration in the Antarctic Peninsula. in Antarctic Peninsula climate variability: historical and palaeoenvironmental perspectives, Vol. Volume 79 (eds. Domack, E.W., Leventer, A., Burnett, A., Bindschadler, R., Convey, P. & Kirby, M.) 79-92 (American Geophysical Union, Antarctic Research Series, Volume 79, Washington, D.C., 2003).

13. Cook, A.J. & Vaughan, D.G. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 4, 77-98 (2010).

14. Rott, H., Müller, F. & Floricioiu, D. The Imbalance of glaciers after disintegration of Larsen B ice shelf, Antarctic Peninsula. The Cryosphere 5, 125-134 (2011).

15. Glasser, N.F., Scambos, T.A., Bohlander, J.A., Truffer, M., Pettit, E.C. & Davies, B.J. From ice-shelf tributary to tidewater glacier: continued rapid glacier recession, acceleration and thinning of Röhss Glacier following the 1995 collapse of the Prince Gustav Ice Shelf on the Antarctic Peninsula. Journal of Glaciology 57, 397-406 (2011).

16. Hulbe, C.L., Scambos, T.A., Youngberg, T. & Lamb, A.K. Patterns of glacier response to disintegration of the Larsen B ice shelf, Antarctic Peninsula. Global and Planetary Change 63, 1-8 (2008).

17. Scambos, T.A., Bohlander, J.A., Shuman, C.A. & Skvarca, P. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters 31, L18402 (2004).

18. Rignot, E., Casassa, G., Gogineni, P., Krabill, W., Rivera, A. & Thomas, R. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf. Geophysical Research Letters 31, L18401 (2004).

19. De Angelis, H. & Skvarca, P. Glacier surge after ice shelf collapse. Science 299, 1560-1562 (2003).

20. Rott, H., Rack, W., Skvarca, P. & De Angelis, H. Northern Larsen Ice Shelf, Antarctica: further retreat after collapse. Annals of Glaciology 34, 277-282 (2002).

21. Davies, B.J., Carrivick, J.L., Glasser, N.F., Hambrey, M.J. & Smellie, J.L. Variable glacier response to atmospheric warming, northern Antarctic Peninsula, 1988–2009. The Cryosphere 6, 1031-1048 (2012).

22. Glasser, N.F., Kulessa, B., Luckman, A., Jansen, D., King, E.C., Sammonds, P.R., Scambos, T.A. & Jezek, K.C. Surface structure and stability of the Larsen C Ice Shelf, Antarctic Peninsula. Journal of Glaciology 55, 400-410 (2009).

23. Walker, R.T., Dupont, T.K., Holland, D.M., Parizek, B.R. & Alley, R.B. Initial effects of oceanic warming on a coupled ocean-ice shelf-ice stream system. Earth and Planetary Science Letters 287, 483-487 (2009).

24. Smith, J.A., Bentley, M.J., Hodgson, D.A., Roberts, S.J., Leng, M.J., Lloyd, J.M., Barrett, M.S., Bryant, C.L. & Sugden, D.E. Oceanic and atmospheric forcing of early Holocene ice shelf retreat, George VI Ice Shelf, Antarctic Peninsula. Quaternary Science Reviews 26, 500-516 (2007).

25. Shepherd, A., Wingham, D., Payne, T. & Skvarca, P. Larsen ice shelf has progressively thinned. Science 302, 856-859 (2003).

26. Domack, E., Duran, D., Leventer, A., Ishman, S., Doane, S., McCallum, S., Amblas, D., Ring, J., Gilbert, R. & Prentice, M. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature 436, 681-685 (2005).

27. Ferrigno, J.G., Cook, A.J., Foley, K.M., Williams, R.S., Swithinbank, C., Fox, A.J., Thomson, J.W. & Sievers, J. Coastal-Change and Glaciological Map of the Trinity Peninsula Area and South Shetland Islands, Antarctica: 1843-2001, 32 (USGS, Denver, 2006).

28. Cook, A.J., Fox, A.J., Vaughan, D.G. & Ferrigno, J.G. Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science 308, 541-544 (2005).

29. Hock, R., de Woul, M., Radic, V. & Dyurgerov, M. Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution. Geophysical Research Letters 36, L07501 (2009).

30. Rau, F., Mauz, F., de Angelis, H., Jana, R., Neto, J.A., Skvarca, P., Vogt, S., Saurer, H. & Gossmann, H. Variations of glacier frontal positions on the northern Antarctic Peninsula. Annals of Glaciology 39, 525-530 (2004).

31. Carrivick, J.L., Davies, B.J., Glasser, N.F. & Nývlt, D. Late Holocene changes in character and behaviour of land-terminating glaciers on James Ross Island, Antarctica. Journal of Glaciology 58(2012).

32. Kunz, M., King, M.A., Mills, J.P., Miller, P.E., Fox, A.J., Vaughan, D.G. & Marsh, S.H. Multi-decadal glacier surface lowering in the Antarctic Peninsula. Geophys. Res. Lett. 39, L19502 (2012).

33. Pritchard, H.D. & Vaughan, D.G. Widespread acceleration of tidewater glaciers on the Antarctic Peninsula. Journal of Geophysical Research-Earth Surface 112, F03S29, 1-10 (2007).

34. Pritchard, H.D., Ligtenberg, S.R.M., Fricker, H.A., Vaughan, D.G., van den Broeke, M.R. & Padman, L. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 484, 502-505 (2012).

35. Payne, A.J., Vieli, A., Shepherd, A.P., Wingham, D.J. & Rignot, E. Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans. Geophysical Research Letters 31, L23401 (2004).

36. Ivins, E.R., Watkins, M.M., Yuan, D.-N., Dietrich, R., Casassa, G. & Rülke, A. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009. J. Geophys. Res. 116, B02403 (2011).

37. King, M.A., Bingham, R.J., Moore, P., Whitehouse, P.L., Bentley, M.J. & Milne, G.A. Lower satellite-gravimetry estimates of Antarctic sea-level contribution. Nature advance online publication(2012).

Shrinking Patagonian Glaciers

This webpage is a shortened and simplified version of the Davies and Glasser 2012 paper published in Journal of Glaciology.

Introduction | Results | Glacier Change | Conclusions | References | Comments |

Introduction

The Little Ice Age

Figure 1. Map of the glaciers of the Patagonian Andes. Note the precipitation gradient west and east across the mountain range.

The Little Ice Age (LIA) is widely recognised in places like the Alps in the northern hemisphere, where glaciers expanded and formed prominent moraines around 150 years ago. During this period of cooler temperatures, there were Frost Fairs on the Thames, which regularly froze over. This period of cooler temperatures also resulted in widespread glacier advances across the Andes in Patagonia, with many glaciers forming prominent moraines. Inside the moraines, the ground remains ice-scoured and relatively bare of vegetation. These geomorphological features can be seen by satellite, which means that it is possible to map the extent of the glaciers during the Little Ice Age across Patagonia. In combination with trimlines, which show the vertical extent and thickness of the glaciers during the Little Ice Age, it has been possible to map changes in glacier volume from the LIA to the present day (see Glasser and others, 2011, Nature Geoscience1). The LIA has also been recorded in the Antarctic Peninsula (with large moraines formed on James Ross Island, for example).

Measuring change by satellite

Figure 2. Mapping the glaciers of the Northern Patagonian Icefield.

Satellite measurements of the Patagonian icefields suggest that they are currently rapidly receding and thinning, with a measureable contribution to eustatic sea level rise2. Many workers argue that the glaciers of the Patagonian Andes are now shrinking at an increased rate as a result of recent climate change3-5. However, these assessments of change are restricted by the availability of maps (last 60 years) and satellite images (last 40 years). In this study (from 40° to 56° South), we used geomorphological evidence of glacier extent during the LIA (~AD 1870) and satellite images to map glacier extent across the Andes over the last 140 years, in 1870, 1975, 1986, 2001 and 2011.

Results

Figure 3. Glacier inventory data from the Patagonian inventory from the year 2011.

We mapped 626 glaciers across the Patagonian Andes, of which 386 drained the major icefields (North Patagonian Icefield, South Patagonian Icefield, Gran Campo Nevado, Cordillera Darwin). A few large glaciers made up the majority of the glacierised area. The remainder were smaller icefields and glaciers in the Chilean Lake District and on volcanoes and mountains. 100 of these glaciers ended in lakes or in the sea. 640 glaciers were mapped during the LIA (the remainder having entirely disappeared).

This data is available to download from the GLIMS database. The full inventory and analysis is available in Davies and Glasser 2012 (Journal of Glaciology).

Glacier change

Figure 4. Graphs illustrating glacier change across Patagonia.

Overall, 90.2% of glaciers shrank between the end of the LIA (approx. 1870) and 2011, 0.3% advanced and no change was observed in 9.5^ of the glaciers.  These small advances were generally short term, and limited to tidewater glaciers. All regions have suffered extensive glacier loss. The greatest annual rates of shrinkage were observed in the small (less than 5 km2 in size) land-terminating glaciers.

Annual rates of shrinkage across the Patagonian Andes increased in each time segment analysed (1870-1986, 1986-2001, 2001-2011), with annual rates of shrinkage twice as rapid from 2001-2011 as from 1870-1986 (0.10% a-1 from 1870-1986, 0.14% a-1 from 1986-2001, and 0.22% a-1 from 2001-2011).

Change in the North Patagonian Icefield

The North Patagonian Icefield experienced rapid recession over the time period, with fastest rates of recession from 2001 to 2011.

Recession of the North Patagonian Icefield, AD 1870 (Little Ice Age) to 2011.

Faster rates of change in different places and different times

Figure 5. These scatter plots show how glaciers are behaving differently at different latitudes, and that land-terminating glaciers are shrinking fastest. Circles represent calving glaciers, and squares represent land-terminating glaciers.

In general, rates of change were fastest from 2001-2011 in more northerly glaciers, with the glaciers in the Chilean Lake District and the Northern Patagonian Icefield shrinking particularly rapidly. The more southerly glaciers, in the Cordillera Darwin, Monte Sarmiento, Isla Riesco and Tierra Del Fuego, shrank fastest from  1986-2001.

This data suggests that the Patagonian glaciers are indeed shrinking faster now than they did in the last century. For example, our calculated rates of area loss from the Northern Patagonian Icefield suggest that there was an increase in annual area loss rates from 0.09% a–1 in the 116 years between AD 1870 and 1986, to 0.12% a–1 in the 15 years between 1986 and 2001, to 0.23% a–1 from 2001 to 2011.

Conclusions

Figure 7. Annual overall rates of shrinkage for glaciers across Patagonia.

The figures opposite and above show that latitude, terminal environment (calving or ending on land) and size exert the strongest controls on glacier shrinkage, with the more northerly, land-terminating, smaller (less than 5 km2) glaciers shrinking fastest. Calving glaciers have been observed to be thinning6-8, but their recession is strongly controlled by calving dynamics. Worldwide, small ice caps and glaciers have reacted particularly dynamically to worldwide increases in temperatures9-11, and it has been proposed that the volume loss from mountain glaciers and ice caps like these is the main contributor to recent global sea-level rise12.

On a regional scale, the large icefields and small icecaps and glaciers north of 56°S suffered particularly rapid shrinkage from 2001-2011, presumably as a result of the decreased precipitation and warmer tropospheric  air temperatures observed in this region2,13-16. The glacierised summits lie in this altitudinal zone, so warming is likely to have a significant control on the mass balance of the glaciers.

There is considerable inter-catchment variability in the behaviour of the glaciers across the Andes, with calving dynamics, latitude and size resulting in glaciers shrinking at different rates. However, overall, annual rates of shrinkage were far faster from 2001-2011 than from 1870-1986 or 1986-2001.

Figure 8. Period of fastest recession for Patagonian glaciers.

Go to top or jump to Ice Shelf Collapse.

Citation

Davies, B.J. and Glasser, N.F. 2012. Accelerating shrinkage of Patagonian glaciers from the Little Ice Age (~AD 1870) to the present day. Journal of Glaciology, 58 (212), 1063-1084. Please use this reference if citing.

References


1.            Glasser, N.F., Harrison, S., Jansson, K.N., Anderson, K. & Cowley, A. Global sea-level contribution from the Patagonian Icefields since the Little Ice Age maximum. Nature Geoscience 4, 303-307 (2011).

2.            Bown, F. & Rivera, A.s. Climate changes and recent glacier behaviour in the Chilean Lake District. Global and Planetary Change 59, 79-86 (2007).

3.            Rignot, E., Rivera, A. & Casassa, G. Contribution of the Patagonia Icefields of South America to sea level rise. Science 302, 434-437 (2003).

4.            Chen, J.L., Wilson, C.R., Tapley, B.D., Blankenship, D.D. & Ivins, E.R. Patagonia Icefield melting observed by Gravity Recovery and Climate Experiment (GRACE). Geophys. Res. Lett. 34, L22501 (2007).

5.            Ivins, E.R. et al. On-land ice loss and glacial isostatic adjustment at the Drake Passage: 2003-2009. J. Geophys. Res. 116, B02403 (2011).

6.            Aniya, M. Recent glacier variations of the Hielos Patagonicos, South America, and their contribution to sea-level change. Arctic Antarctic and Alpine Research 31, 165-173 (1999).

7.            Aniya, M., Sato, H., Naruse, R., Skvarca, P. & Casassa, G. Recent glacier variations in the Southern Patagonia Icefield, South America. Arctic and Alpine Research 29, 1-12 (1997).

8.            Willis, M.J., Melkonian, A.K., Pritchard, M.E. & Ramage, J.M. Ice loss rates at the Northern Patagonian Icefield derived using a decade of satellite remote sensing. Remote Sensing of Environment 117, 184-198 (2011).

9.            Oerlemans, J. & Fortuin, J.P.F. Sensitivity of Glaciers and Small Ice Caps to Greenhouse Warming. Science 258, 115-117 (1992).

10.          Hock, R., de Woul, M., Radic, V. & Dyurgerov, M. Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution. Geophysical Research Letters 36, L07501 (2009).

11.          Meier, M.F. et al. Glaciers Dominate Eustatic Sea-Level Rise in the 21st Century. Science 317, 1064-1067 (2007).

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13.          Giese, B.S., Urizar, S.C., Fu & kar, N.S. Southern Hemisphere Origins of the 1976 Climate Shift. Geophys. Res. Lett. 29, 1014 (2002).

14.          Villalba, R. et al. Large-scale temperature changes across the southern Andes: 20th-century variations in the context of the past 400 years. Climatic Change 59, 177-232 (2003).

15.          Rivera, A., Bown, F., Carriòn, D. & Zenteno, P. Glacier responses to recent volcanic activity in Southern Chile. Environmental Research Letters 7, 1-10 (2012).

16.          Aravena, J.C. & Luckman, B.H. Spatio-temporal rainfall patterns in Southern South America. International Journal of Climatology 29, 2106-2120 (2009).

Go to top or jump to Ice Shelf Collapse

Why study Antarctic Glaciers?

A global system | Dynamic ice streams | Rapid changes | The past is the key to the present | Reconstructing ancient ice sheets | A large jigsaw with many pieces | Further Reading | References | Comments |

A global system

Global thermohaline circulation. From: Wikimedia Commons

Global thermohaline circulation. From: Wikimedia Commons

Why should we study Antarctic glaciers? What can we learn from them? Antarctica plays a vital role in the global oceanic and climatic systems. Cold water is formed in Antarctica. Because freshwater ice at the surface freezes onto icebergs, this water is not only cold, it is salty.

This cold, dense, salty water sinks to the sea floor, and drives the global ocean currents, being replaced with warmer surface waters from the equatorial regions. This is the global thermohaline circulation, and these ocean currents keep Britain warm, and drive the earth’s climatic system.

Water from melting glaciers in Antarctica also has the potential to raise global sea levels. How likely this is to happen, and at what rate, is an important research question that scientists are now trying to answer.

Dynamic ice streams

The Antarctic continent is drained by numerous large ice streams. They have considerable variability at short (sub-decadal) timescales, with recent observations of thinning, acceleration, deceleration, lateral migration and stagnation[1].

The mechanisms controlling these variations and advance and recession of grounding lines include a number of potential forcings, such as oceanic temperatures, sea level changes, air temperatures, ocean tides, subglacial bathymetry, geomorphological features, subglacial meltwater, thermodynamics, and the size of the drainage basin[1].

Rapid changes

Simplified cartoon of a tributary glacier feeding into an ice shelf, showing the grounding line (where the glacier begins to float).

Around the Antarctic Peninsula, a number of ice shelves have recently dramatically collapsed[2-4], resulting in glacier acceleration, thinning and grounding line retreat[5-7]. In fact, Antarctic ice shelves appear crucial to the stability of their tributary glaciers[8], and melting ice shelves could have catastrophic consequences for many glaciers.

This is particularly concerning for the West Antarctic Ice Sheet, which is largely grounded below sea level[9], and removal of this could raise sea levels by 3.3 m[10, 11]. Grounding line recession here could be irreversible, leading to rapid glacier thinning and recession, and sea level rise – see Marine Ice Sheet Instability.

The past is the key to the present

Although the Antarctic Peninsula is currently warming rapidly[12-14], the duration of instrumental observations in Antarctica (ca. 100 years) means that it is difficult to differentiate between natural cycles and occurrences, and dynamic behaviour that is beyond the norm. Are ice-shelf collapses a normal part of ice-sheet behaviour, or are they something more sinister?

Glaciers in Antarctica are largely currently receding and shrinking[15] (see Antarctic Peninsula Glacier Change), but is this a reaction to long-term climate change and natural climatic cycles during the Holocene, or is the rate of shrinkage and recession faster than ever before?

In order to answer these questions, we must look at the palaeo record – how the Antarctic ice sheet, ice shelves and ice streams have behaved over the last few thousand years (see Ice Sheet Evolution).

It is vital to determine what thresholds control ice-sheet behaviour, and whether these have been crossed in the past. By gaining a deeper understanding of past processes, rates of change, rates of ice sheet thinning, and previous temperatures and environmental conditions, we will be better placed to understand how the Antarctic continent as a whole will behave in the future.

Reconstructing ancient ice sheets

Geologists taking rock samples on James Ross Island

We have many tools with which to do this. Terrestrial glacial geologists (such as ourselves) can gain information of past glacial behaviour from mapping and dating former ice sheet extents, and determining the rates at which they receded and thinned, [e.g., 16, 17-19].

Marine geologists do much the same thing on the continental shelf,  but use different tools, such as swath bathymetry and marine sediment cores, dated using radiocarbon dating, palaeo-magnetism and other methods, [e.g., 20, 21-24].

Quaternary scientists can use micro-organisms preserved in marine muds and onshore in lakes[25-27] to reconstruct past temperatures, ocean currents, rates of environmental change[28] and previous ice shelf collapses[29-31]. Other researchers look at raised beaches [32] and palaeo lakes to record previous rates of isostatic uplift and rates of sea level rise[33, 34]; this can help constrain previous ice volumes and rates of ice loss.

A large jigsaw with many pieces

Why should we study palaeoglaciology?

Working with the geologists are numerical modellers, who use the data to test, train and tune numerical models and simulations[35-37].

Through these models, we can make better predictions of future ice sheet behaviour and rates of sea level rise, and ultimately provide policy makers with improved estimates of future change. For an example of some recent modelling work on the former British-Irish Ice Sheet, see the BritIce Modelling Project.

Further Reading

References

1.            Livingstone, S.J., C. O Cofaigh, C.R. Stokes, C.-D. Hillenbrand, A. Vieli, and S.S.R. Jamieson, 2012. Antarctic palaeo-ice streams. Earth-Science Reviews, 111(1-2): 90-128.

2.            Scambos, T., H.A. Fricker, C.-C. Liu, J. Bohlander, J. Fastook, A. Sargent, R. Massom, and A.-M. Wu, 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters, 280(1–4): 51-60.

3.            Glasser, N.F. and T.A. Scambos, 2008. A structural glaciological analysis of the 2002 Larsen B ice shelf collapse. Journal of Glaciology, 54(184): 3-16.

4.            Cook, A.J. and D.G. Vaughan, 2010. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere, 4(1): 77-98.

5.            Pritchard, H.D. and D.G. Vaughan, 2007. Widespread acceleration of tidewater glaciers on the Antarctic Peninsula. Journal of Geophysical Research-Earth Surface, 112(F3): F03S29, 1-10.

6.            Scambos, T.A., J.A. Bohlander, C.A. Shuman, and P. Skvarca, 2004. Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica. Geophysical Research Letters, 31: L18402.

7.            Rignot, E., G. Casassa, P. Gogineni, W. Krabill, A. Rivera, and R. Thomas, 2004. Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf. Geophysical Research Letters, 31(18): L18401.

8.            Pritchard, H.D., S.R.M. Ligtenberg, H.A. Fricker, D.G. Vaughan, M.R. van den Broeke, and L. Padman, 2012. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature, 484(7395): 502-505.

9.            Lythe, M.B., D.G. Vaughan, and the BEDMAP Consortium, 2001. BEDMAP: a new ice thickness and subglacial topographical model of Antarctica. Journal of Geophysical Research, 106(B6): 11335-11351.

10.          Bamber, J.L., R.E.M. Riva, B.L.A. Vermeersen, and A.M. Le Brocq, 2009. Reassessment of the potential sea-level rise from a collapse of the West Antarctic Ice Sheet. Science, 324(5929): 901-903.

11.          Mercer, J.H., 1978. West Antarctic Ice Sheet and CO2 Greenhouse effect – threat of disaster. Nature, 271(5643): 321-325.

12.          Vaughan, D.G., G.J. Marshall, W.M. Connelly, C. Parkinson, R. Mulvaney, D.A. Hodgson, J.C. King, C.J. Pudsey, and J. Turner, 2003. Recent rapid regional climate warming on the Antarctic Peninsula. Climatic Change, 60: 243-274.

13.          Vaughan, D.G., G.J. Marshall, W.M. Connelly, J.C. King, and R. Mulvaney, 2001. Devil in the detail. Science, 293(5536): 1777-1779.

14.          Turner, J., S.R. Colwell, G.J. Marshall, T.A. Lachlan-Cope, A.M. Carelton, P.D. Jones, V. Lagun, P.A. Reid, and S. Iagovkina, 2005. Antarctic climate change during the last 50 years. International Journal of Climatology, 25: 279-294.

15.          Cook, A.J., A.J. Fox, D.G. Vaughan, and J.G. Ferrigno, 2005. Retreating glacier fronts on the Antarctic Peninsula over the past half-century. Science, 308(5721): 541-544.

16.          Bentley, M.J., D.J.A. Evans, C.J. Fogwill, J.D. Hansom, D.E. Sugden, and P.W. Kubik, 2007. Glacial geomorphology and chronology of deglaciation, South Georgia, sub-Antarctic. Quaternary Science Reviews, 26(5-6): 644-677.

17.          Bentley, M.J., C.J. Fogwill, P.W. Kubnik, and D.E. Sugden, 2006. Geomorphological evidence and cosmogenic 10Be/26AL exposure ages for the Last Glacial Maximum and deglaciation of the Antarctic Peninsula Ice Sheet. GSA Bulletin, 118(9/10): 1149-1159.

18.          Fogwill, C.J., M.J. Bentley, D.E. Sugden, A.R. Kerr, and P.W. Kubik, 2004. Cosmogenic nuclides 10Be and 26Al imply limited Antarctic Ice Sheet thickening and low erosion in the Shackleton Range for > 1 m.y. Geology, 32(3): 265-268.

19.          Mackintosh, A., D. White, D. Fink, D.B. Gore, J. Pickard, and P.C. Fanning, 2007. Exposure ages from mountain dipsticks in Mac. Robertson Land, East Antarctica, indicate little change in ice-sheet thickness since the Last Glacial Maximum. Geology, 35(6): 551-554.

20.          Hillenbrand, C.-D., R.D. Larter, J.A. Dowdeswell, W. Ehrmann, C. Ó Cofaigh, S. Benetti, A.G.C. Graham, and H. Grobe, 2010. The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary. Quaternary Science Reviews, 29(19-20): 2741-2763.

21.          Graham, A.G.C., R.D. Larter, K. Gohl, J.A. Dowdeswell, C.-D. Hillenbrand, J.A. Smith, J. Evans, G. Kuhn, and T. Deen, 2010. Flow and retreat of the Late Quaternary Pine Island-Thwaites palaeo-ice stream, West Antarctica. Journal of Geophysical Research-Earth Surface, 115: F03025.

22.          Graham, A.G.C., R.D. Larter, K. Gohl, C.-D. Hillenbrand, J.A. Smith, and G. Kuhn, 2009. Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control. Quaternary Science Reviews, 28(25-26): 2774-2793.

23.          Ó Cofaigh, C., R.D. Larter, J.A. Dowdeswel, C.-D. Hillenbrand, C.J. Pudsey, J. Evans, and P. Morris, 2005. Flow of the West Antarctic Ice Sheet on the continental margin of the Bellingshausen Sea at the Last Glacial Maximum. Journal of Geophysical Research, 110: B11103.

24.          Hillenbrand, C.-D. and W. Ehrmann, 2005. Late Neogene to Quaternary environmental changes in the Antarctic Peninsula region: evidence from drift sediments. Global and Planetary Change, 45(1-3): 165-191.

25.          Björck, S., S. Olsson, C. Ellis-Evans, H. Håkansson, O. Humlum, and J.M. de Lirio, 1996. Late Holocene palaeoclimatic records from lake sediments on James Ross Island, Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology, 121(3-4): 195-220.

26.          Hodgson, D.A., S.J. Roberts, M.J. Bentley, E.L. Carmichael, J.A. Smith, E. Verleyen, W. Vyverman, P. Geissler, M.J. Leng, and D.C.W. Sanderson, 2009. Exploring former subglacial Hodgson Lake, Antarctica. Paper II: palaeolimnology. Quaternary Science Reviews, 28(23-24): 2310-2325.

27.          Smith, J.A., D.A. Hodgson, M.J. Bentley, E. Verleyen, M.J. Leng, and S.J. Roberts, 2006. Limnology of two Antarctic epishelf lakes and their potential to record periods of ice shelf loss. Journal of Palaeolimnology, 35: 373-394.

28.          Domack, E., A. Leventer, S. Root, J. Ring, E. Williams, D. Carlson, E. Hirshorn, W. Wright, R. Gilbert, and G. Burr, Marine sedimentary record of natural environmental variability and recent warming in the Antarctic Peninsula, in Antarctic Peninsula Climate Variability: Historical and Paleoenvironmental Perspectives, E. Domack, et al., Editors. 2003, American Geophysical Union: Washington. 205-222.

29.          Domack, E., D. Duran, A. Leventer, S. Ishman, S. Doane, S. McCallum, D. Amblas, J. Ring, R. Gilbert, and M. Prentice, 2005. Stability of the Larsen B ice shelf on the Antarctic Peninsula during the Holocene epoch. Nature, 436(4): 681-685.

30.          Smith, J.A., M.J. Bentley, D.A. Hodgson, S.J. Roberts, M.J. Leng, J.M. Lloyd, M.S. Barrett, C.L. Bryant, and D.E. Sugden, 2007. Oceanic and atmospheric forcing of early Holocene ice shelf retreat, George VI Ice Shelf, Antarctic Peninsula. Quaternary Science Reviews, 26: 500-516.

31.          Gilbert, R. and E.W. Domack, 2003. Sedimentary record of disintegrating ice shelves in a warming climate, Antarctic Peninsula. Geochemistry Geophysics Geosystems, 4.

32.          Fretwell, P.T., D.A. Hodgson, E.P. Watcham, M.J. Bentley, and S.J. Roberts, 2010. Holocene isostatic uplift of the South Shetland Islands, Antarctic Peninsula, modelled from raised beaches. Quaternary Science Reviews, 29(15-16): 1880-1893.

33.          Roberts, S.J., D.A. Hodgson, M. Sterken, P.L. Whitehouse, E. Verleyen, W. Vyverman, K. Sabbe, A. Balbo, M.J. Bentley, and S.G. Moreton, 2011. Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel, Antarctic Peninsula. Quaternary Science Reviews, in press(0).

34.          Watcham, E.P., M.J. Bentley, D.A. Hodgson, S.J. Roberts, P.T. Fretwell, J.M. Lloyd, R.D. Larter, P.L. Whitehouse, M.J. Leng, P. Monien, and S.G. Moreton, 2011. A new Holocene relative sea level curve for the South Shetland Islands, Antarctica. Quaternary Science Reviews, 30(21-22): 3152-3170.

35.          Le Brocq, A.M., M.J. Bentley, A. Hubbard, C.J. Fogwill, D.E. Sugden, and P.L. Whitehouse, 2011. Reconstructing the Last Glacial Maximum ice sheet in the Weddell Sea embayment, Antarctica, using numerical modelling constrained by field evidence. Quaternary Science Reviews, 30(19-20): 2422-2432.

36.          Whitehouse, P.L., M.J. Bentley, and A.M. Le Brocq, 2012. A deglacial model for Antarctica: geological constraints and glaciological modelling as a basis for a new model of Antarctic glacial isostatic adjustment. Quaternary Science Reviews, 32(0): 1-24.

37.          Pollard, D. and R.M. DeConto, 2009. Modelling West Antarctic ice sheet growth and collapse through the past five million years. Nature, 458(7236): 329-U89.