Ice Sheet Mass Balance Inter-comparison Exercise

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The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) is an international scientific collaboration attempting to improve estimates of the Antarctic and Greenland ice sheet contribution to sea level rise and to publish data and analyses concerning these subjects. IMBIE was founded in 2011 and is a collaboration between the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) of the United States, and contributes to assessment reports of the Intergovernmental Panel on Climate Change (IPCC). [1] IMBIE has led to improved confidence in the measurement of ice sheet mass balance and the associated global sea-level contribution. [2] [3] [4] The improvements were achieved through combination of ice sheet imbalance estimates developed from the independent satellite techniques of altimetry, gravimetry and the input-output method. Going forwards, IMBIE provides a framework for assessing ice sheet mass balance, and has an explicit aim to widen participation to enable the entire scientific community to become involved.

Contents

Results

IMBIE 2012

The IMBIE project produced its first estimate of ice sheet mass balance in 2012 as a direct contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change. [2] IMBIE 2012 included an international team of 47 scientists based in 26 separate institutions, and was co-led by Andrew Shepherd and Erik Ivins. Over the course of the 19-year survey (1992 – 2011), the average rates of mass balance of the Antarctic and Greenland ice sheets were estimated to be -71 ± 53 and -152 ± 49 Gt yr−1, respectively, and the total ice loss equated to a global rise in sea level of 11.1 ± 3.8 mm. [2] Examining the ice sheet regions individually showed that the Greenland, West Antarctic and Antarctic Peninsula ice sheets all lost mass between 1992 and 2011, whilst the East Antarctic ice sheet had undergone a slight snowfall-driven growth. [2] The Greenland ice sheet the largest mass and accounted for about two-thirds of the combined ice sheet loss over the study period. In Antarctica, the largest mass losses have occurred in the West Antarctic Ice Sheet. However, despite occupying just 4% of the total ice sheet area, the Antarctic Peninsula has accounted for around 25% of the Antarctic mass losses. [2]

IMBIE 2018 (Antarctica)

In 2018 the IMBIE project produced an updated assessment of ice loss in Antarctica, combining 24 satellite surveys produced by 84 scientists from 44 international organisations. [3] In this assessment, the IMBIE project reported that between 1992 and 2017 Antarctica lost 2720 ± 1390 billion tonnes of ice, equivalent to an increase in global sea levels by 7.6 ± 3.9 mm. [3] Prior to 2012, Antarctica lost ice at a steady rate of 76 billion tonnes per year – a 0.2 mm per year contribution to sea level rise. However, since then there has been a sharp, threefold increase - between 2012 and 2017 Antarctica lost 219 billion tonnes of ice per year, a 0.6 mm per year sea level contribution. [3] Almost all of the ice lost from Antarctica has been triggered by warming oceans melting their outlet glaciers, which causes them to speed up. [3] Comparison to sea level rise projections provided in the fifth assessment report of the Intergovernmental Panel on Climate Change [5] revealed that Antarctic ice losses are tracking the worst-case climate warming scenarios, which could result in an extra 10 cm of sea level rise by 2100. [6]

IMBIE 2020 (Greenland)

In 2020 the IMBIE project produced an updated assessment of ice loss in Greenland, combining 26 satellite surveys produced by 96 scientists from 50 international organisations. [4] The findings show that Greenland has lost 3902 ± 342 billion tonnes of ice since 1992 – enough to push global sea levels up by 10.8 ± 0.9 millimetres. [4] The rate of ice loss has risen from 34 billion tonnes per year in the 1990s to 234 billion tonnes per year in the last decade – a seven-fold increase within three decades. [4] The team also used regional climate models to show that half of the ice losses were due to surface melting as air temperatures have risen. The other half has been due to increased glacier flow, triggered by rising ocean temperatures. Ice losses peaked at 345 billion tonnes per year in 2011 – ten times the rate of the 1990s - during a period of intense surface melting.  Although the rate of ice loss dropped to an average 206 billion tonnes per year since then, this remains seven times higher than ice losses in the 1990s and does not include all of 2019, which could set a new high due to widespread summer melting. [7] Comparison to sea level rise projections provided in the fifth assessment report of the Intergovernmental Panel on Climate Change [5] revealed that Greenland ice losses are also tracking the worst-case climate warming scenarios, which could result in an extra 7 cm of sea level rise by 2100. [4]

Combining both ice sheets, the rate of ice loss has risen by a factor six in just three decades, up from 81 billion tonnes per year in the 1990s to 475 billion tonnes per year in the 2010s. [3] [4] This means that the polar ice sheets are now responsible for a third of all sea level rise. [8]

See also

Related Research Articles

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An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are found in Antarctica and the Arctic. The boundary between the floating ice shelf and the anchor ice that feeds it is the grounding line. The thickness of ice shelves can range from about 100 m (330 ft) to 1,000 m (3,300 ft). The world's largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica. When a large piece of an ice shelf breaks off, this can lead to the formation of an iceberg. This process is also called ice calving.

<span class="mw-page-title-main">Ice sheet</span> Large mass of glacial ice

In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.

<span class="mw-page-title-main">Amundsen Sea</span> Arm of the Southern Ocean

The Amundsen Sea is an arm of the Southern Ocean off Marie Byrd Land in western Antarctica. It lies between Cape Flying Fish to the east and Cape Dart on Siple Island to the west. Cape Flying Fish marks the boundary between the Amundsen Sea and the Bellingshausen Sea. West of Cape Dart there is no named marginal sea of the Southern Ocean between the Amundsen and Ross Seas. The Norwegian expedition of 1928–1929 under Captain Nils Larsen named the body of water for the Norwegian polar explorer Roald Amundsen while exploring this area in February 1929.

<span class="mw-page-title-main">West Antarctic Ice Sheet</span> Segment of the continental ice sheet that covers West (or Lesser) Antarctica

The Western Antarctic Ice Sheet (WAIS) is the segment of the continental ice sheet that covers West Antarctica, the portion of Antarctica on the side of the Transantarctic Mountains that lies in the Western Hemisphere. It is classified as a marine-based ice sheet, meaning that its bed lies well below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.

<span class="mw-page-title-main">Antarctic ice sheet</span> Earths southern polar ice cap

The Antarctic ice sheet is one of two ice sheets on Earth and covers about 98% of the Antarctic continent. It is the largest single mass of ice on Earth, with an average thickness of over 2 kilometres (1.2 mi). It is distinct from the Antarctic sea ice. The Antarctic ice sheet covers an area of almost 14 million square kilometres and contains 26.5 million cubic kilometres of ice. The other ice sheet on Earth is the Greenland ice sheet.

<span class="mw-page-title-main">Greenland ice sheet</span> Vast body of ice in Greenland, Northern Hemisphere

The Greenland ice sheet is an ice sheet about 1.67 km (1.0 mi) thick on average, and almost 3.5 km (2.2 mi) at its thickest point. It is almost 2,900 kilometres (1,800 mi) long in a north–south direction, with the greatest width of 1,100 kilometres (680 mi) at a latitude of 77°N, near its northern margin. It covers 1,710,000 square kilometres (660,000 sq mi), around 80% of the surface of Greenland, and is the second largest body of ice in the world, after the East Antarctic ice sheet. It is sometimes referred to as an ice cap, or inland ice or its Danish equivalent, indlandsis. The acronyms GIS or GrIS are also frequently used in the scientific literature.

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Thwaites Glacier is an unusually broad and vast Antarctic glacier located east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. It was initially sighted by polar researchers in 1940, mapped in 1959–1966 and officially named in 1967, after the late American glaciologist Fredrik T. Thwaites. The glacier flows into Pine Island Bay, part of the Amundsen Sea, at surface speeds which exceed 2 kilometres (1.2 mi) per year near its grounding line. Its fastest-flowing grounded ice is centered between 50 and 100 kilometres east of Mount Murphy. Like many other parts of the cryosphere, it has been adversely affected by climate change, and provides one of the more notable examples of the retreat of glaciers since 1850.

<span class="mw-page-title-main">Ice stream</span> A region of fast-moving ice within an ice sheet

An ice stream is a region of fast-moving ice within an ice sheet. It is a type of glacier, a body of ice that moves under its own weight. They can move upwards of 1,000 metres (3,300 ft) a year, and can be up to 50 kilometres (31 mi) in width, and hundreds of kilometers in length. They tend to be about 2 km (1.2 mi) deep at the thickest, and constitute the majority of the ice that leaves the sheet. In Antarctica, the ice streams account for approximately 90% of the sheet's mass loss per year, and approximately 50% of the mass loss in Greenland.

<span class="mw-page-title-main">Retreat of glaciers since 1850</span> Shortening of glaciers by melting

The retreat of glaciers since 1850 is well documented and is one of the effects of climate change. The retreat of mountain glaciers, notably in western North America, Asia, the Alps and tropical and subtropical regions of South America, Africa and Indonesia, provide evidence for the rise in global temperatures since the late 19th century. The acceleration of the rate of retreat since 1995 of key outlet glaciers of the Greenland and West Antarctic ice sheets may foreshadow a rise in sea level, which would affect coastal regions. Excluding peripheral glaciers of ice sheets, the total cumulated global glacial losses over the 26-year period from 1993 to 2018 were likely 5500 gigatons, or 210 gigatons per yr.

<span class="mw-page-title-main">Criticism of the IPCC Fourth Assessment Report</span>

The IPCC Fourth Assessment Report (AR4) is a report on climate change created with the help of a large number of contributors, both scientists and governmental representatives. There has been considerable political controversy over a small number of errors found in the report, and there have been calls for review of the process used to formulate the report. The overwhelming majority view of scientists with expertise in climate change is that errors, when found, are corrected, and the issues as identified do not undermine the conclusions of the report that the climate system is warming in response to increased levels of greenhouse gases, largely due to human activities.

<span class="mw-page-title-main">East Antarctic Ice Sheet</span> Segment of the continental ice sheet that covers East Antarctica

The East Antarctic Ice Sheet (EAIS) is one of two large ice sheets in Antarctica, and the largest on the entire planet. The EAIS lies between 45° west and 168° east longitudinally.

<span class="mw-page-title-main">Ice-sheet dynamics</span> Technical explanation of ice motion within large bodies of ice

Ice sheet dynamics describe the motion within large bodies of ice such as those currently on Greenland and Antarctica. Ice motion is dominated by the movement of glaciers, whose gravity-driven activity is controlled by two main variable factors: the temperature and the strength of their bases. A number of processes alter these two factors, resulting in cyclic surges of activity interspersed with longer periods of inactivity, on both hourly and centennial time scales. Ice-sheet dynamics are of interest in modelling future sea level rise.

The Centre for Polar Observation & Modelling (CPOM) is a Natural Environment Research Council (NERC) Centre of Excellence that studies processes in the Earth's polar environments. CPOM conducts research on sea ice, land ice, and ice sheets using satellite observations and numerical models.

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Between 1901 and 2018, the average global sea level rose by 15–25 cm (6–10 in), or an average of 1–2 mm per year. This rate accelerated to 4.62 mm/yr for the decade 2013–2022. Climate change due to human activities is the main cause. Between 1993 and 2018, thermal expansion of water accounted for 42% of sea level rise. Melting temperate glaciers accounted for 21%, with Greenland accounting for 15% and Antarctica 8%. Sea level rise lags changes in the Earth's temperature. So sea level rise will continue to accelerate between now and 2050 in response to warming that is already happening. What happens after that will depend on what happens with human greenhouse gas emissions. Sea level rise may slow down between 2050 and 2100 if there are deep cuts in emissions. It could then reach a little over 30 cm (1 ft) from now by 2100. With high emissions it may accelerate. It could rise by 1 m or even 2 m by then. In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming amounts to 1.5 °C (2.7 °F). It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F).

<span class="mw-page-title-main">Eric Rignot</span> American scientist

Eric J. Rignot is the Donald Bren, Distinguished and Chancellor Professor of Earth system science at the University of California, Irvine, and a Senior Research Scientist for the Radar Science and Engineering Section at NASA's Jet Propulsion Laboratory. He studies the interaction of the polar ice sheets in Greenland and Antarctica with global climate using a combination of satellite remote sensing, airborne remote sensing, understanding of physical processes controlling glacier flow and ice melt in the ocean, field methods, and climate modeling. He was elected at the National_Academy_of_Sciences in 2018.

<span class="mw-page-title-main">Ice2sea</span>

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<span class="mw-page-title-main">Climate change in Antarctica</span> Impacts of climate change on Antarctica

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<span class="mw-page-title-main">Past sea level</span> Sea level variations over geological time scales

Global or eustatic sea level has fluctuated significantly over Earth's history. The main factors affecting sea level are the amount and volume of available water and the shape and volume of the ocean basins. The primary influences on water volume are the temperature of the seawater, which affects density, and the amounts of water retained in other reservoirs like rivers, aquifers, lakes, glaciers, polar ice caps and sea ice. Over geological timescales, changes in the shape of the oceanic basins and in land/sea distribution affect sea level. In addition to eustatic changes, local changes in sea level are caused by tectonic uplift and subsidence.

Isabella Velicogna is a geoscientist known for her work using gravity measurements from space to study changes in the polar ice sheets and water storage on Earth.

References

  1. ↑ "imbie.org" . Retrieved March 17, 2020.
  2. 1 2 3 4 5 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. (November 30, 2012). "A Reconciled Estimate of Ice-Sheet Mass Balance". Science. 338 (6111): 1183–1189. Bibcode:2012Sci...338.1183S. doi:10.1126/science.1228102. hdl: 2060/20140006608 . ISSN   0036-8075. PMID   23197528. S2CID   32653236.
  3. 1 2 3 4 5 6 Shepherd, Andrew; Ivins, Erik; Rignot, Eric; Smith, Ben; van den Broeke, Michiel; Velicogna, Isabella; Whitehouse, Pippa; Briggs, Kate; Joughin, Ian; Krinner, Gerhard; Nowicki, Sophie (June 2018). "Mass balance of the Antarctic Ice Sheet from 1992 to 2017". Nature. 558 (7709): 219–222. Bibcode:2018Natur.558..219I. doi:10.1038/s41586-018-0179-y. hdl:2268/225208. ISSN   1476-4687. PMID   29899482. S2CID   49188002. Archived from the original on July 8, 2018. Alt URL
  4. 1 2 3 4 5 6 Shepherd, Andrew; Ivins, Erik; Rignot, Eric; Smith, Ben; van den Broeke, Michiel; Velicogna, Isabella; Whitehouse, Pippa; Briggs, Kate; Joughin, Ian; Krinner, Gerhard; Nowicki, Sophie (March 2020). "Mass balance of the Greenland Ice Sheet from 1992 to 2018". Nature. 579 (7798): 233–239. doi:10.1038/s41586-019-1855-2. hdl: 11585/771651 . ISSN   1476-4687. PMID   31822019. S2CID   209316760. Archived from the original on March 27, 2020. Alt URL
  5. 1 2 Intergovernmental Panel on Climate Change, ed. (2014), "Sea Level Change", Climate Change 2013 - The Physical Science Basis, Cambridge University Press, pp. 1137–1216, doi:10.1017/cbo9781107415324.026, ISBN   978-1-107-41532-4 , retrieved March 17, 2020
  6. ↑ Slater, Thomas; Shepherd, Andrew (December 2018). "Antarctic ice losses tracking high". Nature Climate Change. 8 (12): 1025–1026. Bibcode:2018NatCC...8.1025S. doi:10.1038/s41558-018-0284-9. ISSN   1758-6798. S2CID   91480834.
  7. ↑ "Guest post: How the Greenland ice sheet fared in 2019". Carbon Brief. September 6, 2019. Retrieved March 17, 2020.
  8. ↑ Change, NASA Global Climate. "Sea Level | NASA Global Climate Change". Climate Change: Vital Signs of the Planet. Retrieved March 17, 2020.

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