West Antarctic Ice Sheet

These pages cover information on the West Antarctic Ice Sheet. This is the part of Antarctica west of the Transantarctic Mountains. It is characterised by a bed that is largely below sea level. The two largest ice streams draining the West Antarctic Ice Sheet are Pine Island Glacier and Thwaites Glacier.

Other relevant articles:

Landsat Image Mosaic of the West Antarctic Ice Sheet

Thwaites Glacier

Thwaites Glacier, Antarctica, is of particular concern to scientists. Here, warm water is pushed up onto the continental shelf, where it flows along the bottom until it reaches the floating ice shelf in front of Thwaites Glacier.

Thwaites Glacier today is rapidly losing mass in response to changing atmospheric and oceanic conditions.

Thwaites Glacier
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What is the ice volume of Thwaites Glacier?

Thwaites Glacier in West Antarctica is currently the focus of a major scientific campaign. Why is Thwaites Glacier of so much interest, however? How much ice is there, and how much would sea levels rise if it all melted?

Thwaites Glacier is roughly the size of UK (176 x103 km2). The glacier terminus is nearly 120 km wide, and the bed of the glacier reaches to >1000 m below sea level. Pine Island Glacier and Thwaites Glacier together account for 3% of grounded ice-sheet area, but they receive 7% of Antarctica’s snowfall1.

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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.

Choosing the future of Antarctica

In a new article in the journal Nature, Stephen Rintoul and colleagues present two very different visions of Antarctica’s future, from the perspective of an observer looking back from 2070. In one vision, humanity continues to exploit Earth’s natural resources (such as fossils fuels) and does little to protect the environment, and in the other, there is a global movement towards conservation. The article shows how Antarctica will change over the next 50 years, should either of these two situations occur.

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Mass balance of the Antarctic ice sheet from 1992 to 2017

A new paper with a whole host of authors has just been published in Nature (IMBIE Team, 2018). It provides a new estimate of mass balance of the entire Antarctic Ice Sheet over the last 25 years, the longest and most thorough estimate of this to date.

This article argues that the Antarctic Peninsula, the smallest ice sheet in Antarctica, has lost an average of 20 Gigatonnes (Gt) of ice per year over the 25 year study. This increased during the study and especially since the year 2000.  The West Antarctic Ice Sheet lost 53±29 Gt yr-1 from 1992-1997, but this accelerated to 159±26 Gt yr-1 from 2012-2017. The East Antarctic Ice Sheet is more stable, with small gains (with large errors) over the study period. Continue reading

Is the West Antarctic Ice Sheet collapsing?

Marine ice sheet instability

The West Antarctic Ice Sheet (WAIS) is the world’s most vulnerable ice sheet. This is because it is grounded below sea level, and marine ice sheets such as these are susceptible to rapid melting at their base. Fast-flowing ice streams draining the WAIS (Pine Island Glacier and Thwaites Glacier in particular) into the Amundsen Sea have a grounding line on a reverse bed slope, becoming deeper inland. Recession of the grounding line means that the ice stream is grounded in deeper water, with a greater ice thickness. Stable grounding lines cannot be established on these reverse bed slopes1, because ice thickness is a key factor in controlling ice flux across the grounding line. Thicker ice in deeper water drives increased calving, increased ice discharge, and further grounding-line recession in a positive feedback loop2, 3.  This process is called Marine Ice Sheet Instability4.

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Antarctic Ice Sheet mass balance

How does mass balance vary over Antarctica? | Surface mass balance in the past | Surface mass balance in the future | References | Comments |

How does mass balance vary over Antarctica?

Is Antarctica currently losing or gaining mass? Will this massive ice sheet grow or shrink in the future? And what effect will increased snowfall have over coming centuries? In order to answer these questions, we must analyse the surface mass balance of the Antarctic Ice Sheet.

First, let’s introduce some definitions.

  • Mass balance is the sum of all processes of accumulation and ablation, including those at the ice surface and at the bed, but does not include mass changes due to ice flow1. See this page (Introduction to Glacier Mass Balance) for more information.
  • Surface mass balance is the net balance between the processes of accumulation and ablation on a glacier’s surface (it does not include dynamic mass loss and basal melting)1.
  • Climatic mass balance includes surface mass balance and internal accumulation1.
  • Ice dynamical changes may include changes to ice discharge and acceleration or deceleration of flow, which can lead to dynamic thinning or thickening, ice-shelf collapse, marine ice sheet instability, and other factors resulting in changes in the glacier beyond surface mass balance.

Surface mass balance

Surface mass balance varies extensively over Antarctica. The Antarctic Peninsula has the highest accumulation rates (up to 1500 mm per year), followed by coastal West Antarctica, which has around 1000 mm accumulation per year2. Compare this with the interior of the Antarctic Ice Sheet, where it is dry and cold; here accumulation can be less than 25 mm per year.

Surface mass balance of the Antarctic and Greenland ice sheets. From Van den Broeke et al., 2011.

Surface mass balance of the Antarctic and Greenland ice sheets. From Van den Broeke et al., 2011.

Surface mass balance estimates are constantly improving as scientists gain better understandings of glacio-isostatic adjustment, improve glacier modelling techniques and gain access to higher resolution satellite datasets over longer timescales3. Surface mass balance estimates therefore tend to improve over time, but are subject to large uncertainties4. For this reason, there tends to be differences between the results of different techniques used to measure surface mass balance. Surface mass balance of the grounded Antarctic Ice Sheet is currently estimated at ~2000 gigatonnes per year2, 5, 6, and it is subject to large variability across the ice sheet and through time.

Total mass balance

The figure below shows some recent estimates for total mass balance (including basal processes) over Antarctica7. Each box is bounded by the time interval studied and the uncertainties identified.

Summary of estimates of rates of ice mass change for Antarctica and Greenland. Reprinted by permission from Macmillan Publishers Ltd: [Nature] (Hanna et al., 2013) copyright (2013)

Summary of estimates of rates of ice mass change for Antarctica and Greenland. Reprinted by permission from Macmillan Publishers Ltd: [Nature] (Hanna et al., 2013) copyright (2013)

Overall, a recent estimate puts Antarctic net mass balance at -71 ± 53 gigatonnes per year8, so just negative over the 19 year survey. Mass losses are increasing in West Antarctica and the Antarctic Peninsula. The mass balance of West Antarctica is dominated by dynamic losses from the Amundsen Sea sector, and dynamic gains from the Kamb Ice Stream8. From the period 2005-2010, Shepherd et al. (2012) estimate the mass balance of the entire Antarctic Ice Sheet to be -81 ± 37 gigatonnes per year8.

An unweighted average of recent estimates suggests that Antarctica moved from a weakly negative mass balance in the 1990s to a faster rate of mass loss at a rate of between -45 and -120 gigatonnes per year7. Larger dynamic losses in West Antarctica are being partially offset by increases in accumulation over East Antarctica.

The total mass balance of Antarctica was recently updated here.

Accelerating total mass losses from Antarctica

The GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission shows that total mass loss in Antarctica is accelerating over time. They found that total mass loss increased by 26 ± 14 gigatonnes per year from 2002 to 20099. Rignot et al. (2011) found a smaller acceleration of 14.5±2 gigatonnes per year from 1993-20115, but this change is still three times larger than that found for mountain glaciers and ice caps.

Surface mass balance of Antarctica in the past

How has the surface mass balance of Antarctica changed in the past? Firn and ice-core records can hold the key to providing a longer perspective on surface mass balance than is currently available from satellite records. Frezzotti et al. used 67  of these cores to reconstruct surface mass balance over the last 800 years. They found that current surface mass balance is not exceptionally high compared with the last 800 years10. Periods of high accumulation occurred in the past, in the 1370s and 1610s AD, but there has been an increase of 10% in snow accumulation in some coastal regions since 1850 – a fact that agrees with independent work on the Antarctic Peninsula11.

Surface mass balance of Antarctica in the future

Climate models predict that, for a generally warmer climate, snowfall will increase over Antarctica7. Surface melt will increase around the more northerly Antarctic Peninsula, and dynamic changes such as increased ice discharge12, ice-shelf collapse and grounding line recession13, and marine ice-sheet instability are likely to offset any increases in precipitation7. However, if no dynamical ice response is assumed, then increases in snowfall over the entire continent of 6-16% to 2100 AD and 8-25% to 2200 AD are likely to result in a drop in sea level of 20-43 mm in 2100 and 73-163 in 2200, compared with today14. However, it is more likely that the Greenland and Antarctic ice sheets will lose mass over the next century, with rapid coastal changes, increases in ice flow and ice-shelf collapse all likely4. As a result of these complex expected changes, there are a number of uncertainties in past, present and future ice sheet mass balance.

Further reading

References


1.            Cogley, J.G., Hock, R., Rasmussen, B., Arendt, A., Bauder, A., Braithwaite, R.J., Jansson, P., Kaser, G., Moller, M., Nicholson, L., & Zemp, M. Glossary of Glacier Mass Balance and related terms. Paris: IHP-VII Technical Documents in Hydrology No. 86, IACS Contribution No. 2, UNESCO-IHP. 124 (2011).

2.            Lenaerts, J.T.M., van den Broeke, M.R., van de Berg, W.J., van Meijgaard, E., & Kuipers Munneke, P. A new, high-resolution surface mass balance map of Antarctica (1979–2010) based on regional atmospheric climate modeling. Geophysical Research Letters. 39, L04501 (2012).

3.            Van den Broeke, M., Bamber, J., Lenaerts, J., & Rignot, E. Ice Sheets and Sea Level: Thinking Outside the Box. Surveys in Geophysics. 32, 495-505 (2011).

4.            Alley, R.B., Spencer, M.K., & Anandakrishnan, S. Ice-sheet mass balance: assessment, attribution and prognosis. Annals of Glaciology. 46, 1-7 (2007).

5.            Rignot, E., Velicogna, I., Van den Broeke, M., Monaghan, A., & Lenaerts, J. Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise. Geophysical Research Letters. 38, (2011).

6.    Agosta, C., Favier, V., Krinner, G., Gallée, H., Fettweis, X., & Genthon, C. High-resolution modelling of the Antarctic surface mass balance, application for the twentieth, twenty first and twenty second centuries. Climate Dynamics. 41, 3247-3260 (2013).

7.            Hanna, E., Navarro, F.J., Pattyn, F., Domingues, C.M., Fettweis, X., Ivins, E.R., Nicholls, R.J., Ritz, C., Smith, B., Tulaczyk, S., Whitehouse, P.L., & Zwally, H.J. Ice-sheet mass balance and climate change. Nature. 498, 51-59 (2013).

8.            Shepherd, A., Ivins, E.R., A, G., Barletta, V.R., Bentley, M.J., Bettadpur, S., Briggs, K.H., Bromwich, D.H., Forsberg, R., Galin, N., Horwath, M., Jacobs, S., Joughin, I., King, M.A., Lenaerts, J.T.M., Li, J., Ligtenberg, S.R.M., Luckman, A., Luthcke, S.B., McMillan, M., Meister, R., Milne, G., Mouginot, J., Muir, A., Nicolas, J.P., Paden, J., Payne, A.J., Pritchard, H., Rignot, E., Rott, H., Sørensen, L.S., Scambos, T.A., Scheuchl, B., Schrama, E.J.O., Smith, B., Sundal, A.V., van Angelen, J.H., van de Berg, W.J., van den Broeke, M.R., Vaughan, D.G., Velicogna, I., Wahr, J., Whitehouse, P.L., Wingham, D.J., Yi, D., Young, D., & Zwally, H.J. A Reconciled Estimate of Ice-Sheet Mass Balance. Science. 338, 1183-1189 (2012).

9.            Velicogna, I. Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophysical Research Letters. 36, (2009).

10.            Frezzotti, M., Scarchilli, C., Becagli, S., Proposito, M., & Urbini, S. A synthesis of the Antarctic surface mass balance during the last 800 yr. The Cryosphere. 7, 303-319 (2013).

11.            Thomas, E.R., Marshall, G.J., & McConnell, J.R. A doubling in snow accumulation in the western Antarctic Peninsula since 1850. Geophysical Research Letters. 35, L01706 (2008).

12.          Winkelmann, R., Levermann, A., Martin, M.A., & Frieler, K. Increased future ice discharge from Antarctica owing to higher snowfall. Nature. 492, 239-243 (2012).

13.          Barrand, N.E., Hindmarsh, R.C.A., Arthern, R., Williams, C.R., Mouginot, J., Scheuchl, B., Rignot, E., Ligtenberg, S.R.M., van den Broeke, M.R., Edwards, T.L., Cook, A.J., & Simonsen, S.B. Computing the volume response of the Antarctic Peninsula Ice Sheet to warming scenarios to 2200. Journal of Glaciology. 59, 397-409 (2013).

14.          Ligtenberg, S.R.M., Berg, W.J., Broeke, M.R., Rae, J.G.L., & Meijgaard, E. Future surface mass balance of the Antarctic ice sheet and its influence on sea level change, simulated by a regional atmospheric climate model. Climate Dynamics. 41, 867-884 (2013).

Dealing with uncertainty: predicting future sea level rise

How much sea level rise? | Climate change and rising sea levels | The West Antarctic Ice Sheet | How much sea level rise from Antarctica? | Comments |

How much sea level rise?

A 5 m sea level rise would inundate many coastal cities in Europe. Source: CReSIS

A 5 m sea level rise would inundate many coastal cities in Europe. Source: CReSIS

How much will global sea levels rise in our lifetime, or in the lifetime of our children? We need to know the answer to this question if we are to mitigate effectively against sea level rise, particularly when it’s associated with storm surges, hurricanes and extreme weather events, which test our already strained flood defence schemes. However, uncertainty in the response of polar ice sheets to climate change limits our ability to project sea level rise into the future.

Climate change and rising sea levels

Figure 5. Climate change over the last 11,500 years from multiple proxies. From Marcott et al., 2013

Figure 5. Climate change over the last 11,500 years from multiple proxies. From Marcott et al., 2013. Used with permission from the author.

During the Twentieth Century, the Earth warmed by 0.6 ± 0.2°C. Since 1900 AD, a long-term cooling trend that began around 5000 years ago and culminated in the Little Ice Age in the 1750s (with its ice fairs on the frozen River Thames) has been reversed. Global sea level is now rising at a rate of 3.1 mm per year, which will lead to a total rise of 18-59 cm by 2100 AD. Most of this rise is caused by thermal expansion of the ocean and the melting of small ice caps and glaciers. However, the large polar ice sheets have the potential to contribute to sea level rise above and beyond this modest rate. The West Antarctic Ice Sheet alone could raise global sea levels by 3.3 m if it all melted. But how likely is this to happen, and how quickly?

The West Antarctic Ice Sheet

An unstable marine ice sheet

BEDMAP 2, showing that the bedrock on which the West Antarctic Ice Sheet rests is well below sea level.

BEDMAP 2, showing that the bedrock on which the West Antarctic Ice Sheet rests is well below sea level.

The West Antarctic Ice Sheet is currently warming particularly rapidly, and this warming is associated with increased ocean temperatures and changes to atmospheric circulation, which drives increased upwelling of deep, relatively warm oceanic water onto the continental shelf.

The West Antarctic Ice Sheet is drained by fast-flowing, marine-terminating ice streams and it is surrounded by floating ice shelves. Much of the rock on which the ice sheet rests is below current sea level, and the bedrock slopes downwards towards the centre of the ice sheet. Because of this, the ice sheet is unstable, because as water gets deeper, more icebergs are calved, increasing ice discharge.

Ice streams in West Antarctica are also melted rapidly at their base by those warming ocean waters, leading to melting, recession into deeper water and more melting again. The West Antarctic Ice Sheet may therefore be inherently susceptible to ever faster glacier recession, and could pass tipping points that mean rapid sea level rise irrevocably occurs. Pine Island Glacier, one of the fastest ice streams in the world, is already thinning and receding, making it susceptible to rapid recession in ever deeper water.

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

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

Thinning and retreating ice shelves

Warm ocean waters are melting a cavity beneath Pine Island Glacier

Warm ocean waters are melting a cavity beneath Pine Island Glacier

Ice shelves around the West Antarctic Ice Sheet are thinning as they are melted from below by upwelling warm ocean currents. Ice shelves have been known to disintegrate rapidly over the course of just one summer.

Ice shelves ‘buttress’ or hold back glaciers on the interior of the continent. Rapid removal of bounding ice shelves, such as those around Pine Island Glacier, could therefore result in increased thinning and recession of grounded glaciers, initiating a positive-feedback loop that could be catastrophic.

Increased snowfall

It doesn’t end there. Although there may be more snow over the Antarctic Ice Sheet under a warmer climate, this too could lead to changes in glacier dynamics. Increased snow will steepen surface gradients near the edge of the Antarctic Ice Sheet. Glaciers will flow faster, discharging more icebergs into the ocean, negating any impact the increased snowfall would have in mitigating sea level rise.

Increased meltwater from melting ice shelves also produces a layer of cold, fresh water on the ocean’s surface, which easily freezes, increasing winter sea ice extent. Sea surface temperatures are directly related to snowfall, so cooler sea surface temperatures and more sea ice may actually decrease snowfall over Antarctica.

How much sea level rise from Antarctica?

Sea level rise to 2100. Modified from the IPCC sea level rise estimates (from Wikimedia Commons) and using estimates from Bamber and Aspinall 2013, assuming a uniform rate of sea level rise.

Sea level rise to 2100. Modified from the IPCC sea level rise estimates (from Wikimedia Commons) and using estimates from Bamber and Aspinall 2013, assuming a uniform rate of sea level rise.

Because of these factors, the West Antarctic Ice Sheet could rapidly and catastrophically melt, resulting in as much as 3.3 m of sea level rise within 500 years.

Rates such as these are common in the geological record, but these dynamic behaviours are too difficult for even our most complex computer models to solve.

A new paper in the journal Nature Climate Change by Bamber and Aspinall has attempted to untangle this thorny problem. They pooled different assessments by numerous experts in order to reach a consensus on likely sea level rise by AD 2100.

Bamber and Aspinall used a mid-range carbon emissions scenario, with an increase of 3.5°C above pre-industrial temperatures. They found that the average rate of sea level rise from just the Greenland and Antarctic ice sheets agreed upon by these experts was 5.4 mm per year by 2100 AD.

Combined with melting glaciers and ice caps and thermal expansion of the ocean, Bamber and Aspinall gave a range of 33-132 cm, with 62 cm the average estimate, for sea level rise by 2100. It’s still uncertain, but it’s the best estimate we have for now.

Antarctic datasets

The following is a list of publically available Antarctic datasets. These datasets are often freely accessible, usually providing that you cite the source and often a relevant paper. Do not use data without correct attribution. Many of these datasets have been used in the creation of figures on this website, and I thank all the authors that have contributed their data. There are many more datasets around, but these ones concentrate on Antarctic Glaciers. I hope this list is useful.

Much of this data is aimed at academics rather than as outreach, and assumes users are familiar working with ASCII data or various other GIS formats such as GEOTIFFs. However, many of the Antarctic datasets listed may be interesting to teachers and educators as well as researchers.

Browse the datasets:

BEDMAP2

BEDMAP 2 preview

BEDMAP 2 preview. From BAS.

BEDMAP2 is a compilation of bedrock topography data from around the Antarctic continent. The dataset includes bed topography, ice surface elevation, a rock mask, ice shelf mask, ice thickness and more. Data are available as ASCII files, suitable for loading into a GIS.

Download the PDF from The Cryosphere.

Download BEDMAP2 data.

Citation: Fretwell, L.O., H. D. Pritchard, D. G. Vaughan, J. L. Bamber, N. E. Barrand, R. Bell, C. Bianchi, R. G. Bingham, D. D. Blankenship, G. Casassa, G. Catania, D. Callens, H. Conway, A. J. Cook, H. F. J. Corr, D. Damaske, V. Damm, F. Ferraccioli, R. Forsberg, S. Fujita, P. Gogineni, J. A. Griggs, R. C. A. Hindmarsh, P. Holmlund, J. W. Holt, R. W. Jacobel, A. Jenkins, W. Jokat, T. Jordan, E. C. King, J. Kohler, W. Krabill, M. Riger-Kusk, K. A. Langley, G. Leitchenkov, C. Leuschen, B. P. Luyendyk, K. Matsuoka, Y. Nogi, O. A. Nost, S. V. Popov, E. Rignot, D. M. Rippin, A. Riviera, J. Roberts, N. Ross, M. J. Siegert, A. M. Smith, D. Steinhage, M. Studinger, B. Sun, B. K. Tinto, B. C. Welch, D. A. Young, C. Xiangbin & Zirizzotti, A., 2013. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7, 375-393.

BedMachine

BedMachine is a self-consistent dataset of the bed topography of Antarctica (also for Greenland). It is freely available at the NSIDC.

BedMachine provides a NetCDF on a 450m resolution grid, and has a nominal date of 2012. It gives surface elevation, ice thickness and bed topography, and is an update of BedMap2.

There are some great visualisations of the data set here.

This is an image of the bed topography under the Denman Glacier in Antarctica colored by the elevation. Areas below sea level are colored in shades of blue while areas above sea level are colored in green, yellow and brown. From the NASA Science Visualisation Studio.

Citation:

Morlighem, M., Rignot, E., Binder, T. et al. Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet. Nature Geoscience 13, 132–137 (2020)

Ice velocity

Ice streams of Antarctica. From Rignot et al. (2011).

Ice streams of Antarctica. From Rignot et al. (2011).

The Rignot et al 2011 dataset allows users to download ice velocity across the Antarctic continent. The digital ice motion map is available as a MEaSUREs Earth Science Data Record (ESDR) at the National Snow and Ice Data Centre, Boulder, CO.

Citation: Rignot, E., Mouginot, J. & Scheuchl, B., 2011. Ice Flow of the Antarctic Ice Sheet. Science 333, 1427-1430.

Download the data.

Grounding line data

Rignot et al. 2011 also have a Grounding Line dataset available for download. Download the Grounding Line Data.

Citation: Rignot, E., Mouginot, J. & Scheuchl, B., 2011. Antarctic grounding line mapping from differential satellite radar interferometry. Geophys. Res. Lett. 38, L10504.

Landsat Image Mosaic Antarctica (LIMA)

Landsat Image Mosaic of Antarctica (LIMA) showing location of key ice shelves.

Landsat Image Mosaic of Antarctica (LIMA) showing location of key ice shelves.

Download a beautiful Landsat image mosaic of Antarctica. This dataset was created in support of the International Polar Year (IPY 2007-2008) with a virtually cloudless, seamless, high resolution satellite view of Antarctica. It was created by the USGS, the British Antarctic Survey and NASA.

MOA (MODIS Mosaic of Antarctica) image map

The NSIDC and the University of New Hampshire have assembled a digital image map of Antarctica and surrounding islands. The MODIS Mosaic of Antarctica is 260 swaths of Terra and Aqua MODIS (Moderate Resolution Imaging Spectroradiometer) images acquired between 20th November 2003 and 29th February 2004.

To download the data, users will need to register.

Citation: Haran, T., J. Bohlander, T. Scambos, T. Painter, and M. Fahnestock compilers. 2005, updated 2006. MODIS mosaic of Antarctica (MOA) image map. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Scambos, T., T. Haran, M. Fahnestock, T. Painter, and J. Bohlander. 2007. MODIS-based Mosaic of Antarctica (MOA) data sets: continent-wide surface morphology and snow grain size. Remote Sensing of Environment 111(2): 242-257. 10.1016/j.rse.2006.12.020.

Antarctic Digital Database (ADD)

Research stations and summer camps in Antarctica, using data from the ADD.

Research stations and summer camps in Antarctica, using data from the ADD.

A whole host of resources are available through the ADD. The SCAR Antarctic Digital Database is managed by the British Antarctic Survey and the Scientific Committee for Antarctic Research. Users can use a map viewer to download multiple features across Antarctica in various formats. There is a combination of point (vector) and raster data.

Data includes: hillshade and bathymetry, LIMA mosaic, sea mask, BEDMAP2, coastlines, ice shelf margins, coastal change, contours, elevations, moraines, place names, lakes, streams, subglacial lakes, stations, and bases.

Go to the Map Viewer to access data. Users will need to register to access data.

IBCSO (International Bathymetric Chart of the Southern Ocean)

IBCSO bathymetric charts

IBCSO bathymetric charts

The IBCSO website provides information on sea floor topography. Users can download a PDF chart or Geotiff data of the entire ocean floor.

Access the data.

When using any data from the IBCSO project please cite:

Arndt, J.E., H. W. Schenke, M. Jakobsson, F. Nitsche, G. Buys, B. Goleby, M. Rebesco, F. Bohoyo, J.K. Hong, J. Black, R. Greku, G. Udintsev, F. Barrios, W. Reynoso-Peralta, T. Morishita, R. Wigley, “The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 – A new bathymetric compilation covering circum-Antarctic waters”, Geophysical Research Letters, doi: 10.1002/grl.50413

ASTER GDEM of the Antarctic Peninsula

Antarctic Peninsula 100 m DEM. Cook et al., 2012.

Antarctic Peninsula 100 m DEM. Cook et al., 2012.

This dataset, created by Alison Cook, provides a 100 m resolution surface topography DEM of the Antarctic Peninsula. Data are available via FT in GeoTIFF and ASCII formats.

Download the Data. Users must register to download the data.

Citation: Cook, A. J., T. Murray, A. Luckman, D. G. Vaughan, and N. E. Barrand. 2012. Antarctic Peninsula 100 m Digital Elevation Model Derived from ASTER GDEM. [indicate subset used]. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N58K7711.

Global Land-Ice Measurements from Space (GLIMS)

The GLIMS dataset provides platform-independent GIS shapefiles of glaciers worldwide, including some from the Antarctic Peninsula. Users can browse glacier outlines using the GLIMS viewer, and download relevant glacier shapefiles. Users should cite the author of the shapefile as well as the GLIMS database.

Marine Geoscience Data System (MGDS)

The MGDS provides access to data portals for the NSF. These portals provide free public access to a wide variety of marine geoscience data collected during expeditions across the World’s oceans. Users can explore data using the GeoMapApp. Data available through the Antarctic and Southern Ocean Data Portal include seafloor bathymetry, subbottom profiling, trackline gravity and magnetics, meterological and water column data.

DIVA-GIS

The DIVA-GIS website provides free GIS data for any country in the world, including country boundaries, inland water, roads, railways, population and more.

IPCC data

The IPCC Data Distribution Centre (DDC) for the International Panel on Climate Change (IPCC) provides climatic, socio-economic and environmental data, from the past and also for projections into the future.

Further resources

The NSIDC has a list here of available Antarctica datasets, including:

  • Antarctic 5 km DEM
  • GEOSAT Radar Altimeter DEM Atlas of Antarctica
  • ICESat 500m Laser Altimetry DEM of Antarctica
  • Ice Thickness and Surface Elevation, Southeastern Ross Embayment
  • MODIS MOA image map
  • Radarsat Antarctic Mapping Project DEM V2.

The NSIDC has a great list of easy to use resources that are suitable for K-12 teachers and students, the press, the general public and non-cryospheric researchers. Datasets include:

  • MASIE measurements of daily sea ice extent
  • Sea ice index
  • Frozen ground maps
  • Glacier photographs
  • Atlas of the Cryosphere

Google Earth has fabulous satellite images of Antarctica, and it lets you explore the continent from the comfort of your sofa.

If you know of any more datasets, please add a comment in the box below!

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