A CPOM-led study, which shows that 28 trillion tonnes of ice have disappeared from the surface of the Earth since 1994 due to greenhouse gas emissions, has captured media and public attention.
CPOM researchers Professor Andy Shepherd, Dr Tom Slater (first author on the paper, and Dr Isobel Lawrence are quoted in a number of articles, including The Guardian:
“To put the losses we’ve already experienced into context, 28 trillion tonnes of ice would cover the entire surface of the UK with a sheet of frozen water that is 100 metres thick,” added group member Tom Slater from Leeds University. “It’s just mind-blowing.“
The research has been translated in to at least 9 different languages, and high-profile attention includes Greta Thunberg, Caroline Lucas and the World Economic Forum.
High temperatures in the Arctic during the last interglacial “the warm period around 127,000 years ago“ have puzzled scientists for decades. Now the UK Met Office’s Hadley Centre climate model has enabled an international team of researchers to compare Arctic sea ice conditions during the last interglacial with present day. Their findings are important for improving predictions of future sea ice change.
During spring and early summer, shallow pools of water form on the surface of Arctic sea-ice. These “melt ponds” are important for how much sunlight is absorbed by the ice and how much is reflected back into space. The new Hadley Centre model is the UK’s most advanced physical representation of the Earth’s climate and a critical tool for climate research and incorporates sea-ice and melt ponds.
Using the model to look at Arctic sea ice during the last interglacial, the team concludes that the impact of intense springtime sunshine created many melt ponds, which played a crucial role in sea-ice melt. A simulation of the future using the same model indicates that the Arctic may become sea ice-free by 2035.
Dr David Schroeder, CPOM staff researcher at the University of Reading, who developed and co-led the implementation of the melt pond scheme in the climate model, said: “This shows just how important sea-ice processes like melt ponds are in the Arctic, and why it is crucial that they are incorporated into climate models.”
Professor Danny Feltham, CPOM Sea Ice Lead, and Professor Julienne Stroeve, CPOM Associate Investigator, were also co-authors of the study.
CPOM researchers Victoria Lee and Tony Payne have co-authored, alongside Robin S. Smith (NCAS), an article on Atmospheric Blocking and Greenland Melt for the UK Earth system modelling project (UKESM) July newsletter.
Atmospheric blocking occurs when near-stationary high-pressure systems divert westerly flow for a week or more. It can cause extreme regional weather such as heatwaves in summer and cold spells in winter. This article explores the connection between blocking over Greenland and enhanced surface melting of the ice sheet in UKESM1.ice N96 ORCA1 present-day run.
Mean summer geopotential height at 500 hPa in metres with white contours every 25 m for years 1985, 1991, 2004 and 2011. GBI is calculated inside the region marked by magenta lines. Black contours mark the edge of land:
A comprehensive annual climate overview, on which CPOM researchers were co-authors, has been released by the Copernicus Climate Change Service (C3S) containing invaluable insight intothe state of our climate in 2019 to help build up a long-term picture of how it is changing.
Key findings included:
2019 was the warmest year on record for Europe
11 of the 12 warmest years occurred since 2000 in Europe
Long-term view shows clear warming trend across the last four decades
European Arctic relatively colder than in recent years but summer heatwave causes record surface ice melting in Greenland.
The Greenland Ice Sheet section of the report provides further information: The European State of the Climate 2019, compiled by C3S from a range of data sources with contributions from key players in the field of climate science, offers a complete overview of annual and seasonal conditions across the whole of Europe and the European Arctic which are compared with the long-term average. This gives a clear picture for policymakers, planners, industry sectors, businesses and individuals to help put in place mitigation and adaptation measures against the effect of climate change.
KEY MESSAGES:
In Summer 2019, the Greenland ice sheet experienced record melting.
Model estimates indicate that as a result, the surface mass balance anomaly was the lowest on record, at 320 gigatonnes (Gt) below the 1981-2010 average.
During summer 2019, warm air reached the Greenland ice sheet and persistent anticyclonic conditions trapped it there for an extended period. The result was widespread surface melting across the entire ice sheet, with satellite observations showing that 95.8% of the ice sheet surface experienced melting at least once during the summer months. The figure below shows the daily extent of the melt for all of Greenland, with a large peak in late July and early August.
Percentage of the total area of the Greenland ice sheet experiencing melting on a daily basis. The blue line shows melt extent during 2019. The dark grey line shows the mean value for the 1981-2010 reference period. The light grey area shows the range over the 1981-2010 reference period, with the lowest and highest values for each day omitted. Data source: Polar portal Greenland daily surface melt estimate. Credit: DMI Polar Portal.
The Greenland ice sheet gains mass through snowfall during winter and loses mass through surface melting during late spring and summer (usually from May through to the end of August). The difference between the accumulation and melting of snow and ice is called the surface mass balance. Surface mass balance is calculated annually for 1 September to 31 August, based on models that simulate the different surface processes. It does not take into account ice losses from icebergs calving or glacier ice melting at the margins of the ice sheet due to warm ocean temperatures. Generally, the surface mass balance is positive.
The 2019 surface mass balance was the lowest since the start of the record in 1949, with a negative anomaly of 320 gigatonnes (Gt) per year compared to the 1981-2010 average. Below-average snowfall and an early start to the melting season (mid-April) resulted in the early exposure of bare ice. This further enhanced melting, as bare ice reflects less solar energy than fresh snow, in what is termed melt-albedo feedback.
Between 1992 and 2018, surface mass balance accounted for just over half of the total ice loss (50.3%) in Greenland. However, surface mass balance is highly variable from year to year. While 2019 saw a record low surface mass balance year, the two previous years were above the 1981-2010 average by 80 and 150 Gt, respectively. The remaining ice losses are due to discharge and are measured using satellites; discharge losses have progressively increased from -52 ± 44 Gt/yr for 19921997 to -75 ± 21 Gt/yr for 2012-2017. As the discharge data are not yet available for 2019, it is not possible at this stage to make the full ice loss assessment for 2019.
Carlo Buontempo, Director of the Copernicus Climate change Service (C3S), comments: “It is now more vital than ever before that everyone has access to this information to help us understand the longer-term implications of climate change and what organisations and individuals can do to reduce its effects. One exceptional warm year does not constitute a warming trend, but to have detailed information from our operational service, that covers many different aspects of our climate, we are able to connect the dots to learn more about how it is changing.”
Greenland and Antarctica are losing ice faster than in the 1990s and are both tracking the Intergovernmental Panel on Climate Change’s worst-case climate warming scenario.
As a result, this will lead to an extra 17 centimetres of sea level rise by 2100.
A team of 89 polar scientists from 50 international organisations have produced the most complete picture of polar ice sheet loss to date.
Altogether, data from 11 different satellite missions were used, including measurements of the ice sheets’ changing volume, flow and gravity.
The findings, published in two companion articles in Nature, show that Greenland and Antarctica lost 6.4 trillion tonnes of ice between 1992 and 2017 pushing global sea levels up by 17.8 millimetres. Of the total sea level rise, 10.6 millimetres (60%) was due to Greenland ice losses and 7.2 millimetres (40%) was due to Antarctica.
“If Antarctica and Greenland continue to track the worst-case climate warming scenario, they will cause an extra 17 centimetres of sea level rise by the end of the century.“
PROFESSOR ANDREW SHEPHERD, IMBIE CO-LEADER
The combined 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. This means that the polar ice sheets are now responsible for a third of all sea level rise.
The assessment, led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory in California, was supported by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA).
In their Fifth Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will rise 53 centimetres by 2100, and it is estimated that this would put 360 million people at risk of annual coastal flooding.
But the IMBIE Team’s studies shows that ice losses from both Antarctica and Greenland are rising faster than expected, tracking the IPCC’s worst-case (high-end) climate warming scenario.
Professor Shepherd said: “Every centimetre of sea level rise leads to coastal flooding and coastal erosion, disrupting people’s lives around the planet.
“If Antarctica and Greenland continue to track the worst-case climate warming scenario, they will cause an extra 17 centimetres of sea level rise by the end of the century.
“This would mean 400 million people are at risk of annual coastal flooding by 2100.
“These are not unlikely events with small impacts; they are already underway and will be devastating for coastal communities.”
Almost all of the ice lost from Antarctica and half of that lost from Greenland has been triggered by oceans melting their outlet glaciers, which causes them to speed up. The remainder of Greenland’s ice losses are due rising air temperature, which has melted the ice sheet at its surface.
Combined losses from both ice sheets peaked at 552 billion tonnes per year in 2010 and averaged 475 billion tonnes per year for the remainder of the decade. The peak loss coincided with several years of intense surface melting in Greenland, and last summer’s Arctic heatwave means that 2019 should set a new record for polar ice sheet loss. Antarctica and Greenland are now losing ice five and seven times faster than they were in the 1990s, respectively.
“The findings reported by IMBIE demonstrate the fundamental importance of using satellites to monitor the evolution of ice sheets“
JOSEF ASCHBACHER, ESA’S DIRECTOR OF EARTH OBSERVATION PROGRAMMES
Dr Ivins said: “Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise.
“While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence.
“Our project is a great example of the importance of international collaboration to tackle problems that are global in scale.
Guofinna Aoalgeirsdottir, Professor of Glaciology at the University of Iceland and lead author of the Intergovernmental Panel on Climate Change’s sixth assessment report, who was not involved in the study, said:
“The IMBIE Team’s reconciled estimate of Greenland and Antarctic ice loss is timely for the IPCC. Their satellite observations show that both melting and ice discharge from Greenland have increased since observations started.
“The ice caps in Iceland had similar reduction in ice loss in the last two years of their record, but summer 2019 was very warm in this region which resulted in higher mass loss. I would expect a similar increase in Greenland mass loss for 2019.
“It is very important to keep monitoring the big ice sheets to know how much they raise sea level every year.”
ESA’s Director of Earth Observation Programmes, Josef Aschbacher, comments: “The findings reported by IMBIE demonstrate the fundamental importance of using satellites to monitor the evolution of ice sheets, and for evaluating models used to predict the effects of climate change.”
Further information
Image credits: Hamish Pritchard and Professor Andrew Shepherd
Greenland is losing ice faster than in the 1990s and is tracking the Intergovernmental Panel on Climate Change’s high-end climate scenario.
As a result, 40 million more people will be exposed to coastal flooding by 2100.
A team of 89 polar scientists from 50 international organisations have produced the most complete picture of Greenland ice loss to date.
The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Team combined 26 separate surveys to compute changes in the mass of Greenland’s ice sheet between 1992 and 2018. Altogether, data from 11 different satellite missions were used, including measurements of the ice sheet’s changing volume, flow and gravity.
The findings, published today in Nature, show that Greenland has lost 3.8 trillion tonnes of ice since 1992 – enough to push global sea levels up by 10.6 millimetres.
The rate of ice loss has risen from 33 billion tonnes per year in the 1990s to 254 billion tonnes per year in the last decade – a seven-fold increase within three decades.
“On current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century.”
PROFESSOR ANDREW SHEPHERD, CPOM DIRECTOR
The assessment, led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory in California, was supported by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA).
In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels would rise 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding.
But this new study shows that Greenland’s ice losses are rising faster than expected and are instead tracking the IPCC’s high-end climate warming scenario, which predicts 7 centimetres more.
Professor Shepherd said: “As a rule of thumb, for every centimetre rise in global sea level another six million people are exposed to coastal flooding around the planet.
“On current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century, so 400 million in total due to all sea level rise.
“These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities.”
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 were due to increased glacier flow, triggered by rising ocean temperatures.
Ice losses peaked at 335 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 238 billion tonnes per year since then, this remains seven times higher and does not include all of 2019, which could set a new high due to widespread summer melting.
Dr Ivins said: “Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise.
“While computer simulation allows us to make projections from climate change scenarios, the satellite measurements provide prima facie, rather irrefutable, evidence.
“Our project is a great example of the importance of international collaboration to tackle problems that are global in scale.”
“IMBIE’s reconciled estimate of Greenland ice loss is timely for the IPCC. Their satellite observations show that both melting and ice discharge from Greenland have increased.”
GUOFINNA AOALGEIRSDOTTIR, UNIVERSITY OF ICELAND
Guofinna Aoalgeirsdottir, Professor of Glaciology at the University of Iceland and lead author of the Intergovernmental Panel on Climate Change’s sixth assessment report, who was not involved in the study, said:
“The IMBIE Team’s reconciled estimate of Greenland ice loss is timely for the IPCC. Their satellite observations show that both melting and ice discharge from Greenland have increased since observations started.
“The ice caps in Iceland had similar reduction in ice loss in the last two years of their record, but this last summer was very warm here and resulted in higher loss. I would expect a similar increase in Greenland mass loss for 2019.
“It is very important to keep monitoring the big ice sheets to know how much they raise sea level every year.”
Further information
Image credits: Ian Joughin
The paper “Mass balance of the Greenland Ice Sheet from 1992-2018” by the IMBIE Team, is published in Natureon 10 December 2019.
Seven areas of fast-flowing ice on the Antarctic Peninsula have been formally named after Earth observation satellites, following a request by CPOM scientist Anna Hogg.
Dramatic changes in the shape of the Antarctic ice sheet have become emblematic of the climate crisis. Reports of iceberg calving, changes in ice-sheet speed, thickness and mass have informed the climate change debate, and are largely thanks to routine monitoring by an international fleet of Earth observation satellites.
Recognising the importance of observations from space, the UK Antarctic Place-names Committee has approved seven new names for international use.
Reports of iceberg calving, changes in ice-sheet speed, thickness and mass have informed the climate change debate, and are largely thanks to routine monitoring by an international fleet of Earth observation satellites. And, in respect for the critical role that satellites play in measuring and monitoring glaciology, the UK Antarctic Place-names Committee has approved seven new names for areas of fast-flowing ice on the Antarctic Peninsula
The decision follows a request by Dr Hogg, who identified that the major glaciers flowing westwards from the Dyer Plateau on the Antarctic Peninsula are thinning and flowing at rates of more than 1.5 metres a day.
Dr Hogg is an expert in Earth observation of the Polar Regions and uses satellite data to study the remote Antarctic and Greenland Ice Sheets. Her research published in 2017 that identified the thinning of the Dyer Plateau and linked increase ice flow in Western Palmer Land to ocean melting would not have been possible without satellite observations.
In deference to the critical role that satellites play in measuring and monitoring Antarctic glaciology, Dr Hogg requested that seven glaciers monitored in her study be named after the satellites. The names will be added to the British Antarctic Territory Gazetteer and will be available for use on all maps, charts and in all future publications.
Dr Hogg said: “Naming the glaciers after the Earth observation satellites we use to measure them is a great way to celebrate the international collaboration in space, and on big science questions.
“Satellite observations provide scientists with information on some of the most inaccessible regions on Earth. Without this data we would have a very unclear picture of how our rapidly changing environment is affecting glaciers around the world.
“The European Space Agency satellite missions allow us not only to understand the changes that are taking place in the fastest warming region on the planet but give us the means to predict what could happen to this region in the future.
“It’s fantastic news that the Government of the British Antarctic Territory have formally approved these new place names, which will be on the record forever more.”
Seven newly named ice streams
The Ers Ice Stream that flows west between Jensen Nunataks and Gunn Peaks was named after the two ESA satellites ERS-1 and ERS-2 that operated between 1991 and 2011. They provided the first high-resolution, wide-swath and day-and-night images that were used to calculate the speed and direction of the flow of glacier ice.
The Envisat Ice Stream, lies further to the west and commemorates ESA’s largest Earth observation satellite, which was launched in 2002 and operated until 2012. It carried 10 instruments that extended the datasets generated by ERS-1 and ERS-2.
The Cryosat Ice Stream flows further west and is named after the ESA Earth Explorer satellite launched in 2010. CryoSat was designed specifically to detect changes in the height of polar ice using a sophisticated instrument that provides high-accuracy elevation measurements over the rugged ice-sheet margins and for sea ice in polar waters. CPOM Director Professor Andy Shepherd is the principal scientific advisor to ESA for this mission.
Still further west lies the Grace Ice Stream, which commemorates the joint Gravity Recovery and Climate Change Experiment (GRACE) mission run by NASA and the German Aerospace Center. Between 2002 and 2017, the mission mapped, for the first time, Earth’s time-varying gravitational field, detecting Antarctic ice-sheet mass changes with unprecedented accuracy.
The Sentinel Ice Stream is named after the more recent series of satellites that ESA develops for the EU’s Copernicus programme to the environment and climate change. This programme provides open access to images, allowing the public to easily view and witness ongoing, year-round changes in Antarctica and the rest of the world.
The ALOS Ice Rumples are named after a Japan Aerospace Exploration Agency mission. Its optical and radar image data acquired between 2006 and 2011 have been used to map ice in the polar regions, with dedicated imaging campaigns to capture Antarctic ice-sheet surface changes during the International Polar Year campaign that ran between 2007 and 2009.
Finally, the Landsat ice stream is the most westerly of the newly named glaciers. It is named after the joint NASA/US Geological Survey series of Landsat Earth observation satellites that have been operating since 1972. Landsat has been one of the primary satellite systems used in Antarctic studies, providing over 40 years of uninterrupted mapping of the continent for climate and environment studies.
Bolstering climate research
Fifteen space agencies currently collaborate on coordinating Antarctic data collection from a wide range of satellites, and on the planning of data acquisition and products to address the needs of the scientific community, under the banner of the World Meteorological Organization’s Polar Space Task Group.
Mark Drinkwater, ESA chair of the task group, said: “Interagency planning is paying dividends for polar science, with more comprehensive multi-satellite, multi-instrument datasets and better coverage than previously possible, which enables the science community to address today’s key climate research challenges.
“This gesture of naming Antarctic glaciers after these ground-breaking satellites is a mark of recognition of the importance of Earth observation data in addressing the climate crisis.”
In only 25 years, ocean melting has caused ice thinning to spread across West Antarctica so rapidly that 24% of its glacier ice is now affected, according to a new study.
By combining 25 years of European Space Agency satellite altimeter measurements and a model of the regional climate, CPOM have tracked changes in snow and ice cover across the continent.
Led by CPOM Director Professor Andy Shepherd, the team found that Antarctica’s ice sheet has thinned by up to 122 metres in places, with the most rapid changes occurring in West Antarctica where ocean melting has triggered glacier imbalance.
This means that the affected glaciers are unstable as they are losing more mass through melting and iceberg calving than they are gaining through snowfall.
They also found that the pattern of glacier thinning has not been static.
Since 1992, the thinning has spread across 24% of West Antarctica and over the majority of its largest ice streams, the Pine Island and Thwaites Glaciers, which are now losing ice five times faster than they were at the start of the survey.
Professor Andrew Shepherd said: “We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica’s most vulnerable glaciers, and their losses are driving up sea levels around the planet.”
The study, published today in Geophysical Research Letters, used over 800 million measurements of the Antarctic ice sheet height recorded by the ERS-1, ERS-2, Envisat, and CryoSat-2 satellite altimeter missions between 1992 and 2017 and simulations of snowfall over the same period produced by the RACMO regional climate model.
Together, these measurements allow changes in the ice sheet height to be separated into those due to weather patterns, such as less snowfall, and those due to longer term changes in climate, such as increasing ocean temperatures that eat away ice.
Professor Shepherd explained: “In parts of Antarctica the ice sheet has thinned by extraordinary amounts, and so we set out to show how much was due to changes in climate and how much was due to weather.”
To do this, the team compared the measured surface height change to the simulated changes in snowfall, and where the discrepancy was greater they attributed its origin to glacier imbalance.
They found that fluctuations in snowfall tend to drive small changes in height over large areas for a few years at a time, but the most pronounced changes in ice thickness are signals of glacier imbalance that have persisted for decades.
Time sequence of Antarctic glacier ice thickness change (left) and associated contribution to sea level rise (right) between 1992 and 2017.
Professor Shepherd added: “Knowing how much snow has fallen has really helped us to detect the underlying change in glacier ice within the satellite record.
“We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica’s most vulnerable glaciers, and their losses are driving up sea levels around the planet.
“Altogether, ice losses from East and West Antarctica have contributed 4.6 mm to global sea level rise since 1992.”
Dr Marcus Engdahl of the European Space Agency, a co-author of the study, added: “This is an important demonstration of how satellite missions can help us to understand how our planet is changing.
“The polar regions are hostile environments and are extremely difficult to access from the ground. Because of this, the view from space is an essential tool for tracking the effects of climate change.”
The ERS-1, ERS-2, ENVISAT and CryoSat-2 satellite radar altimetry time-series produced in this study was funded by the European Space Agency Climate Change Initiative and the data is freely available online.
The RACMO regional climate model data used in this study were provided by Michiel van den Broeke and Stefan Ligtenberg of the University of Utrecht
Tom Slater, a final year PhD student at CPOM Leeds, is being presented with the Piers Sellers prize for exceptional PhD research.
The prize, awarded annually by the Priestley International Centre for Climate, will be presented as part of an event to mark the Centre’s new home in the Priestley Building at the University of Leeds.
Tom’s work involves using satellites to measure the height of the Antarctic and Greenland ice sheets and how they change over time, as well as their respective contributions to global sea level rise. He was nominated for the award by his supervisor, CPOM Director Professor Andy Shepherd, who commended him on developing new methods for processing satellite altimeter observations of the polar ice sheets.
“Tom’s PhD has led to significant methodological advances, extending the value of satellite altimeter data for polar science.”
“In addition to his ground-breaking technical work, Tom has also applied his knowledge to address important scientific problems. He has published 3 first author articles during the first two years of his PhD, including one in Nature Climate Change, and he has also co-authored two others including one in Nature and one in Nature Geosciences. He also has two further first author articles and one co-author article in preparation. This is an outstanding body of technical and applied work.”
Professor Shepherd also praised his student for his work tracking Antarctic ice losses: “Tom showed they were tracking the upper range of sea level projections [from the IPCC’s Fifth Assessment] If Antarctic ice losses continue to follow this trend, the ice sheet will be responsible for an additional 10 cm of sea level rise by 2100. This is a major revision and has significant implications for coastal communities and climate policy.”
A recently-launched satellite mission is now proving a valuable addition to Antarctic monitoring efforts, according to work published this week in The Cryosphere.
The study, carried out by CPOM researchers alongside European Space Agency (ESA) and industry partners, shows the potential of Sentinel-3 – one of the EU Copernicus satellite missions – to contribute towards long-term ice sheet monitoring programmes.
From its orbit 815 km above the Earth, Sentinel-3 is able to detect the height of the ice surface at the remote Lake Vostok test site in East Antarctica to within tens of centimetres.
The scientists also found that Sentinel-3 could detect where the ice surface was rapidly lowering, establishing the satellite’s credentials as a new platform which can help to monitor Antarctica’s contribution to sea level rise.
Copernicus Sentinel-3 satellite maps Antarctic Ice Sheet elevation change: Antarctic Ice Sheet elevation change mapped by Copernicus Sentinel-3A between 2016 and 2018. Contains modified Copernicus Sentinel data (2018)/processed by CPOM/McMillan
Determining how well Sentinel-3 functions over ice sheets is particularly important given that CryoSat-2, ESA’s dedicated polar mission, is already operating well beyond its planned lifetime.
CryoSat-2 is designed to fly in a unique orbit, maximising coverage of coastal areas of the ice sheet, and mapping the regions close to the North and South Poles that were beyond the reach of previous satellites.
Although Sentinel-3 “which has to balance many tasks“ cannot match this coverage, it still holds potential as a valuable long-term monitoring platform for decades to come.
Lead author Dr Mal McMillan, CPOM scientist at Lancaster University, said: “Although the Sentinel-3 altimeter was primarily designed to monitor the oceans, we wanted to test how well it works over ice, and to see whether it is able to detect signs of ice sheet change. Through the support offered by ESA’s Scientific Exploitation of Operational Missions element, we have been able to study the performance of the Sentinel-3 mission for several years now, and we are pleased to be able to publish these results”
He added: “From what we can see here, with just two years’ worth of data, Sentinel-3 is going to be a very useful tool for surveying the Antarctic ice sheet.”
Sentinel-3. Credit: ESA
Sentinel-3 uses a radar technique called Delay-Doppler altimetry to make high resolution measurements of the height of the ice sheet.
Where the ice is relatively flat, Sentinel-3 could map its height to within 10 cm of measurements taken by aircraft, as part of NASA’s Operation Icebridge campaign.
Dr McMillan explained: “This level of accuracy means that we can also use Sentinel-3 to track important features on the ice surface, like the fingerprint of active subglacial lakes draining and refilling beneath several kilometres of ice.”
Using radar satellites like Sentinel-3 over ice nonetheless has its challenges. For example, measurements over Antarctica’s steeper, craggy coastal areas were less accurate because of how the rough landscape affects the radar signal.
Future research into Sentinel-3’s performance, as well as further improvements to data processing, will help take these effects into account. In the meantime, Sentinel-3 has already shown its value as a new tool for detecting ice sheet change.
Co-author Jerome Benveniste of the European Space Agency summarised: “We are delighted with the early promise shown by Sentinel-3 for ice sheet monitoring, and are increasingly confident that it will be a long-term asset to climate science.”
Notes
The full paper is: McMillan, M. et al. (2019) Sentinel-3 Delay-Doppler altimetry over Antarctica, The Cryosphere 13, 1-14 doi:10.5194/tc-13-1-2019
The Sentinel-3A satellite, part of the European Union’s Copernicus Programme was launched on 16 February 2016, followed by Sentinel-3B on 25 April 2018. Each satellite provides coverage up to a latitude of 81.35áµ’, yielding regular, monthly observations of much of Earth’s polar ice sheets. Sentinel-3 is unique in being the first mission to operate in high-resolution Delay-Doppler (or Synthetic Aperture Radar—SAR) mode across the entire ice sheet.
