Antarctica and Climate Change

Since the early 20th Century, global air temperatures have shown an increasing trend. This pattern has coincided with the continuous release of greenhouse gasses into the atmosphere. The rising temperatures are already having negative effects on many of our natural environments including, oceans, deserts, and glacial landscapes, including Antarctica.

The warming stripes below show annual global average temperatures from 1850 to 2019. The more red the colour, the more above-average the temperature. You can see that recent years have been far warmer than any time in the last 100 years.

Global temperature stripes from 1850-2019 (Ed Hawkins: Show Your Stripes)

Exploring Antarctica’s climate changes in the past, present and future

Ice core from GISP2 illustrating the annual layers. From the US National Oceanic and Atmospheric Administration, Wikimedia Commons.

Since the beginning of time, before humans were even present, climate has been changing. It has been switching between warmer than present periods, known as interglacials, and colder than present periods, known as glacials. Over the last million years, it has made this switch approximately every 100,000 years.

Archives of past climate change

We know this by using environmental archives, such as ice cores from Antarctica. These ice cores are long poles of ice which contain annual layers of ice from thousands of years ago – some even from 800,000 years ago! Each winter a new layer of snow is formed and over time it is compacted and forms an annual layer of ice.

Ice core locations in Antarctica
Antarctic ice core drill sites with depth and record duration. From the US ITASE project.

Ice cores are often drilled from the centre of an ice sheet where there is the thickest and slowest-moving ice. This means the scientists can get really long records without the layers of ice being deformed.

These ice-core records provide important information about these past changes in the climate system, the ice thickness, and can also tell us about the change in atmospheric gasses over time, as shown in the figure below. This figure is showing the change in temperature and ice thickness from two different ice cores (EPICA and Vostok) from the East Antarctic Ice Sheet.

Antarctica and Present-Day Warming

The effects of increasing temperatures on environments can already be seen in some areas of the globe, including Antarctica. Antarctica is one of the fastest warming places on Earth because of a process known as polar amplification. Alongside air temperature rises, the oceans around Antarctica are also warming.

This rapid warming is causing oceans to warm allowing increased melt on the underside of ice shelves, causing them to eventually collapse. Ice shelves have an important role in holding back the ice on the land. Therefore, when ice shelves collapse, it causes the ice on the land to become unstable and flow faster.

The West Antarctic Ice Sheet

The West Antarctic Ice Sheet is of great concern to scientists as the bedrock beneath the extensive coastline of ice shelves is sloping. This means that the grounding line, which is the point at which the ice begins to float, is beneath areas of much thicker ice, as shown on the figure below. The thicker ice flows much faster, therefore causing a greater amount of ice discharge into the oceans.

Illustration of the sloping bedrock beneath the West Antarctic Ice Sheet

Future Climate Change and Antarctica

Global sea levels since the industrial period (1850) have shown an increasing trend. Sea levels are increasing by more than 3 mm per year and are set to increase as global air temperatures rise. As Antarctica has the largest store of freshwater, it has the greatest potential to affect sea levels around the world.

Antarctica has a total sea level equivalent of almost 60m. This means that, that if the whole of the Antarctic continent were to melt, then there will be almost 60m of sea level rise. This would effect many coastal regions all around the world.

Antarctica has this much sea-level-equivalent because it is just so huge. It is bigger than the United States of America and has an average thickness of ice of 2.4 km, all over the continent. In some places, the ice is more than 4000 m thick!

Ice SheetSea Level Equivalent
The Antarctic Peninsula0.2m
The West Antarctic Ice Sheet4.3m
The East Antarctic Ice Sheet53.3m
Sea level equivalents for Antarctica’s ice shelves

Future sea level rise

Much of the British coastline is currently protected by a sea wall, promenade or another type of coastal defence. These have been built to protect the land from large storm events, however due to the rising sea level, storms surges are getting larger. This means that over time, coastal defences are not able to defend from storm events as the waves are able to topple over the defences causing more flooding inland.

Climate change in Antarctica StoryMap

You can learn more about climate change in Antarctica through this interactive ESRI StoryMap. It is free to use and will open in your browser, no need to download any special software.

StoryMap collection exploring climate change in Antarctica. This StoryMap Collection is targeted for people aged ~13/14 upwards.

Further reading

Changing Antarctica

Antarctica is a vast ice sheet. The continent is larger than the United States of America, and has enough ice to raise global sea levels by ~58 m if it all melted. It is extremely cold, with very little surface melt.

However, it is changing rapidly. Parts of West Antarctica are grounded well below sea level, which can act to destabliise the ice sheet. Warm ocean currents are able to melt ice shelves from below, and cause a retreat of the grounding line of tidewater glaciers. These articles outline how Antarctica is changing.

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
Continue reading

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.

Continue reading

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.

Post by Jacob Bendle. Continue reading

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.

Continue reading

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).

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