CR
Cryospheric Sciences

Greenland

Image of the Week – The GReenland OCEan-ice interaction project (GROCE): teamwork to predict a glacier’s future

Figure 1: The GROCE project, with 11 working groups and more than 30 scientists from across Germany, aims to understand what the present-day state of the 79°N glacier in Greenland is. On a windy day in May 2019, the GROCE teams met up at the annual update meeting to present findings and discuss the next steps to understand this complex system. Photo credit: Mario Hoppman, AWI


The GROCE project, funded by the German Ministry for Education and Research (BMBF), takes an Earth-System approach to understand what processes are at play for the 79°N glacier (also known as Nioghalvfjerdsfjorden), in northeast Greenland. 79°N is a marine-terminating glacier, meaning it has a floating ice tongue (like an ice shelf) and feeds into the ocean. Approximately 8% of all the ice contained in the Greenland Ice Sheet feeds into the 79°N glacier before it reaches the ocean (Seroussi et al., 2011). Therefore, in a worst-case-scenario where it melted entirely, this would lead to 1.1 m of sea level rise (Mayer et al., 2018). In recent years, the glacier’s ice flow to the ocean has increased in speed (Khan et al., 2014) and at the same time, the atmosphere at the surface in the region has warmed by 3°C over the last 40 years (Turton et al., 2019). This means that the 79°N glacier is being affected by both the warming atmosphere and the warming ocean simultaneously and will therefore be highly sensitive to future climate changes. However, without understanding its current state through accurate monitoring, predicting what the future may hold for this glacier is difficult.

Figure 2: The 79°N glacier and its floating tongue respond to warm waters coming from the surrounding ocean, producing melt-water which circulates underneath the floating tongue. In turn, the less saline melt-water affects and changes the large-scale ocean circulation itself. Simultaneously, at the surface, a warming atmosphere leads to more surface melt-water, some of which drains to the base of the glacier. Infographic credit: Mario Hoppman/AWI/Martin Künsting.

We are 11 different working groups, all attempting to understand the 79°N glacier, each group investigating a different, but complementary, aspect of the glacier. Our investigations include: the interactions between the atmosphere and the ice, the ocean circulation around the ice tongue, melting at the surface of the ice, melting near the bedrock beneath the ice, the location of the grounding line (where the ice meets the ocean and starts to float to form the floating ice tongue), tidal processes and many more (see Figure 2 for some of these processes). The 11 working groups, which includes 34 scientists and PhD students from 8 universities and research institutes, are spread all over Germany: from FAU University of Erlangen-Nürnberg (most southerly) to IOW (Leibniz Institute for Baltic Sea Research Warnemünde) (see Figure 3 for a map of the locations of all the research groups). The project is about to enter its third and final year, which means a lot of exciting new results are emerging from the project and there will be many more to come…

Figure 3: The locations of the 8 main partner universities and research institutions involved in the GROCE project. Figure made with google my maps.

If you’re interested in learning more about the GROCE project, its members or research outcomes, you can find a lot of information on our website: www.groce.de.

Figure 4: Jenny Turton reports on the progress made in regional atmospheric modelling efforts within the last year during the progress meeting in May 2019. Photo credit: Mario Hoppman, AWI

Edited by Marie Cavitte


Jenny Turton is a post-doc researcher in the climate system research group at Friedrich-Alexander University (FAU) in Erlangen. She currently investigates the interaction between the atmosphere and the cryosphere. More specifically, her current research focuses on the link between atmospheric processes and the glacier surface of 79°N glacier in northeast Greenland.

 

Image of the Week – What’s Hot in the Cryosphere? A 2018 review

Image of the Week – What’s Hot in the Cryosphere? A 2018 review

Every year, humanity understands more and more about a remote and unforgiving component of the Earth system – the cryosphere. 2018 has been no exception, and in this blog post we’ll take a look at some of the biggest scientific findings of cryospheric science in 2018. We will then look forward to 2019 and beyond, to see what the future holds for these rapidly changing climate components.


The Cryosphere at 1.5°C warming

In 2018, the IPCC (Intergovernmental Panel on Climate Change) released their report that looked at the impact of 1.5 and 2.0°C of global warming by 2100 on the Earth system. In the Arctic, warming is already in excess of 2.0˚C, driving a very strong decreasing trend in the summer sea-ice extent. The IPCC suggest that sea-ice-free summers will occur once per century at 1.5°C, but this increases to once per decade at 2.0°C. Limiting warming to 1.5˚C will also save 1.5-2.5 million km2 of permafrost thaw (preventing the release of ancient carbon into the atmosphere), 10 cm of sea-level rise contribution from ice sheets and glaciers, and reduce the risk of the irreversible collapse of the ice sheets. Read more about the cryosphere under 1.5°C warming in this previous post.

 

Mass Balance of the Antarctic Ice Sheet

Compiling 24 independent estimates of mass balance, from a number of different remote sensing and modelling techniques, the IMBIE team produced the best estimate of how Antarctica is responding to continued climate warming. The mass balance refers to the net change in ice mass, accounting for all of the inputs and outputs to the ice. They quantify that ice mass loss from West Antarctica has increased three-fold between 1992 and 2017, largely due to melting from a warmer ocean. On the Antarctic Peninsula, the collapse of ice sheets has led to an increase ice mass loss by a factor of 4. East Antarctica is gaining mass slightly, although this is highly uncertain, by 5 ± 46 billion tonnes per year. Overall, Antarctica has lost 2,720 ± 1,390 billion tonnes of ice in this 25-year time period, and this mass loss is accelerating. Read more about these results in this previous post.

Mass loss from the Antarctic ice sheet is accelerating, largely due to ocean warming impacting West Antarctica. East Antarctica is very slightly gaining mass, but this doesn’t go anywhere near balancing out mass loss across the continent [Credit: NASA Goddard].

A polluted cryosphere

It’s easy to think of the cryosphere as a pristine, beautiful, untouched landscape. However, research from 2018 has shown us that the remoteness of Polar Regions has not protected them from man-made pollution. In one litre of melted Arctic sea-ice, 234 particles of plastic and over 12,000 particles of microplastics were found, which will only go onto adversely impact Arctic wildlife by spreading through the ecosystem. Radioactive material from the Chernobyl accident has also been found to be concentrated in dark sediments found on Swedish glaciers. As these glaciers melt, this concentration of radioactive material may be released in meltwater. In Greenland, lead pollution found in ice cores has provided exciting new insight into wars, plagues and invasions during the Roman Empire.

In 2018, we saw a glimpse of the geological secrets that Greenland hides beneath its ice sheet. However, there is still a hidden world that future field-based campaigns or airborne radar missions will help to unravel [Credit: NASA Goddard].

What secrets is Greenland hiding?

In 2018, we got our best ever look beneath the Greenland ice sheet. Scientists from the British Antarctic Survey and NASA found that the hotspot (a thermal plume in the Earth’s mantle) currently under Iceland was once beneath Greenland, between 80 to 50 million years ago. This hotspot was discovered by studying the magnetism of minerals beneath the ice. Using airplanes, radio waves and sediment that’s washed out from underneath the ice sheet has also revealed a massive 31 kilometre wide meteorite crater underneath Hiawatha glacier. Given it’s beneath three kilometres of ice, the age of this crater is unknown, but given the interest and speculation in connecting this event to an abrupt cooling period 12,000 years ago (the Younger Dryas), we may know very soon.

 

Blast Off!

Satellites remain one of the most popular methods of monitoring the vast, hostile cryosphere. In 2018, a new generation of earth observation missions launched. ESA’s Sentinel-3B continues the Copernicus programme, monitoring the reflectivity of the ice, elevation and sea-ice thickness. NASA’s GRACE FO mission continues the successful first GRACE mission, which used gravimetry to ‘weigh’ different regions of ice. NASA also launched ICESat-2, which will provide global elevation data at unprecedented spatial resolution on a 91-day repeat orbit. Each satellite is being finely tuned to make sure it’s working exactly as intended, and we’ll get the first science from them in 2019. Stay tuned!

Remote sensing data has provided us with answers to some of the biggest questions in the cryosphere. We use it to help quantify mass loss, sea-level rise and glacial retreat. In 2019, new missions will take our knowledge of cryospheric sciences to new heights! [Credit: Liam Taylor]

A look ahead to 2019

On the ground, getting inside the ice will continue to provide fascinating insights into the history of the cryosphere – from reconstructing winds in sub-Antarctic islands using ice cores, to further insights deep inside the world’s highest glacier. As permafrost continues to thaw, we are likely to hear of more discoveries of woolly mammoths, ancient diseases and carbon release. The IPCC will also publish their special report devoted to The Ocean and Cryosphere in a Changing Climate, which will provide the best overall state of the cryosphere to date. And, of course, the infamously named ‘Boaty McBoatface’ will provide us with incredible data from beneath sea-ice and ice shelves when the RRS Sir David Attenborough is launched. 2018 has been a truly exciting year to be a cryospheric scientist, and 2019 looks set to be another hot one!

 

Edited by Adam Bateson


Liam Taylor is a PhD student at the University of Leeds and Centre for Polar Observation and Monitoring. His research looks at identifying novel remote sensing methods to monitor mountain glaciers for water resource and hazard management. He is passionate about climate change and science communication to a global audience, as an educator on free online climate courses and through his personal blog. You can find Liam on Twitter.

Ice-hot news: The cryosphere and the 1.5°C target

Ice-hot news: The cryosphere and the 1.5°C target

Every year again, the Conference of Parties takes place, an event where politicians and activists from all over the world meet for two weeks to discuss further actions concerning climate change. In the context the COP24, which started this Monday in Katowice (Poland), let’s revisit an important decision made three years ago, during the COP21 in Paris, and its consequences for the state of the cryosphere…


1.5°C target – what’s that again?

Last October, the International Panel on Climate Change (IPCC) released a special report (SR15) on the impacts of a 1.5°C global warming above pre-industrial levels. This target of 1.5°C warming was established during the 21st conference of the parties (COP21), in a document known as the Paris Agreement. In this Agreement, most countries in the World acknowledge that limiting global warming to 1.5°C warming rather than 2°C warming would significantly reduce the risks and impacts of climate change.

But wait, even though achieving this target is possible, which is not our subject today, what does it mean for our beloved cryosphere? And how does 1.5°C warming make a difference compared to the 2°C warming initially discussed during the COP21 and previous COPs?

A reason why the cryosphere is so difficult to grasp is the nonlinear behaviour of its components. What does this mean ? A good basic example is the transition between water and ice. At 99.9°C, you have water. Go down to 0.1°C and the water is colder, but this is still water. Then go down to -0.1°C and you end up with ice. The transition is very sharp and the system can be deeply affected even for a small change in temperature.

As a main conclusion, studies conducted in the context of SR15 show that, below 1.5°C of global warming, most components of the cryosphere will be slightly affected, while above that level of warming, there is more chance that the system may respond quickly to small temperature changes. In this Ice Hot News, we review the main conclusions of the SR15 concerning ice sheets, glaciers, sea ice and permafrost, answering among others the question if achieving the 1.5°C target would prevent us to trigger the potential nonlinear effects affecting some of them.

Ice sheets

The two only remaining ice sheets on Earth cover Greenland and Antarctica. If melted, the Greenland ice sheet could make the sea level rise by 7 m, while the Antarctic ice sheet could make it rise by almost 60 m. A recent review paper (Pattyn et al., 2018), not in SR15 because published very recently, shows that keeping the warming at 1.5°C rather than 2°C really makes the differences in terms of sea level rise contribution by the two ice sheets.

Greenland is a cold place, but not that cold. During the Holocene, the surface of the ice sheet always melted in summer but, in the yearly mean, the ice sheet was in equilibrium because summer melt was compensated by winter accumulation. Since the mid-1990s, Greenland’s atmosphere has warmed by about 5°C in winter and 2°C in summer. The ice sheet is thus currently losing mass from above and its surface lowers down. In the future, if the surface lowers too much, this could accelerate the mass loss because the limit altitude between snow and rainfalls may have been crossed, further accelerating the mass loss. The temperature threshold beyond which this process will occur is about 1.8°C, according to the Pattyn et al., 2018 paper.

Antarctica is a very cold continent, much colder than Greenland, but it has been losing mass since the 1990s as well. There, the source of the retreat is the temperature increase of the ocean. The ocean is in contact with the ice shelves, the seaward extensions of the ice sheet in its margins. The warmer ocean has eroded the ice shelves, making them thinner and less resistant to the ice flow coming from the interior. And if you have read the post about the marine ice sheet instability (MISI), you already know that the ice sheet can discharge a lot of ice to the ocean if the bedrock beneath the ice sheet is deeper inland than it is on the margins (called retrograde). MISI is a potential source of nonlinear acceleration of the ice sheet that, along with other nonlinear effects mentioned in the study, could trigger much larger sea level rise contribution from the Antarctic ice sheet above 2 to 2.7°C.

You can find complementary informations to the Pattyn et al., 2018 paper in SR15, sections 3.3.9, 3.5.2.5, 3.6.3.2 and in FAQ 3.1.

Glaciers crossing the transantarctic mountains, one of them ending up to Drygalski ice tongue (left side) in the Ross sea. The ice tongue is an example of those ice shelves that form as grounded ice flows toward the sea from the interior. Ice shelves are weakened by a warmer ocean, which accelerates upstream ice flow [Credit: C. Ritz, PEV/PNRA]

Glaciers

Over the whole globe, the mass of glaciers has decreased since pre-industrial times in 1850, according to Marzeion et al., 2014. At that time, climate change was a mix between human impact and natural variability of climate. Glacier response times to change in climate are typically decades, which means that a change happening, for instance, today, still has consequences on glaciers tens of years after. Today, the retreat of glaciers is thus a mixed response to natural climate variability and current anthropogenic warming. However, since 1850, the anthropogenic warming contribution to the glacier mass loss has increased from a third to more than two third over the last two decades.

Similarly to the Greenland ice sheet, glaciers are prone to undergo an acceleration of ice mass loss wherever the limit altitude where rainfall occurs more often than snowfall is higher and at the same time the glacier surface lowers. However, as opposed to ice sheets, glaciers can be found all over the world under various latitudes, temperature and snow regimes, which makes it difficult to establish a unique temperature above which all the glaciers in the world will shrink faster in a nonlinear way. There are, however, model-based global estimates of ice mass loss over the next century. The paper from Marzeion et al., 2018, shows that under 1.5-2°C of global warming, the glaciers will lose the two thirds of their current mass, and that for a 1°C warming, our current level of warming since pre-industrial times, the glacier are still committed to lose one third of their current mass. This means the actions that we take now to limit climate change won’t be seen for decades.

You can find complementary informations in SR15, sections 3.3.9, 3.6.3.2 and in FAQ 3.1.

Sea ice

As very prominently covered by media and our blog (see this post and this post), the Arctic sea-ice cover has been melting due to the increase in CO2 emissions in past decades. To understand the future evolution of climate, climate models are forced with the expected CO2 emissions for future scenarios. In summer, the results of these climate model simulations show that keeping the warming at 1.5°C instead of 2°C is essential for the Arctic sea-ice cover. While at 1.5°C warming, the Arctic Ocean will be ice-covered most of the time, at 2°C warming, there are much higher chances of a sea-ice free Arctic. In winter, however, the ice cover remains similar in both cases.

In the Antarctic, the situation is less clear. On average, there has been a slight expansion of the sea-ice cover (see this post). This is, however, not a clear trend, but is composed of different trends over the different Antarctic basins. For example, a strong decrease was observed near the Antarctic peninsula and an increase in the Amundsen Sea. The future remains even more uncertain because most climate models do not represent the Antarctic sea-ice cover well. Therefore, no robust prediction could be made for the future.

You can find all references were these results are from and more details in Section 3.3.8 of the SR15. Also, you can find the impact of sea-ice changes on society in Section 3.4.4.7.

Caption: Sea ice in the Arctic Ocean [D. Olonscheck]

Permafrost

Permafrost is ground that is frozen consecutively for two years or more. It covers large areas of the Arctic and the Antarctic and is formed or degraded in response to surface temperatures. Every summer, above-zero temperatures thaw a thin layer at the surface, and below this, we find the boundary to the permafrost. The depth to the permafrost is in semi-equilibrium with the current climate.

The global area underlain by permafrost globally will decrease with warming, and the depth to the permafrost will increase. In a 1.5°C warmer world, permafrost extent is estimated to decrease by 21-37 % compared to today. This would, however, preserve 2 millions km2 more permafrost than in a 2°C warmer world, where 35-47 % of the current permafrost would be lost.

Permafrost stores twice as much carbon (C) as the atmosphere, and permafrost thaw with subsequent release of CO2 and CH4 thus represents a positive feedback mechanism to warming and a potential tipping point. However, according to estimates cited in the special report, the release at 1.5°C warming (0.08-0.16 Gt C per year) and at 2°C warming (0.12-0.25 Gt C per year) does not bring the system at risk of passing this tipping point before 2100. This is partly due to the energy it takes to thaw large amounts of ice and the soil as a medium for heat exchange, which results in a time lag of carbon release.
The response rates of carbon release is, however, a topic for continuous discussion, and the carbon loss to the atmosphere is irreversible, as permafrost carbon storage is a slow process, which has occurred over millennia.

Changes in albedo from increased tree growth in the tundra, which will affect the energy balance at the surface and thus ground temperature, is estimated to be gradual and not be linked to permafrost collapse as long as global warming is held under 2°C.

The above-mentioned estimates and predictions are from the IPCC special report Section 3.5.5.2, 3.5.5.3 and 3.6.3.3.

Slope failure of permafrost soil [Credit: NASA, Wikimedia Commons].

So, in summary…

In summary, what can we say? Although the 1.5°C and 2°C limits were chosen as a consensus between historical claims based on physics and a number that is easy to communicate (see this article), it seems that there are some thresholds for parts of the cryosphere exactly between the two limits. This can have consequences on longer term, e.g. sea-level rise or permanent permafrost loss. Additionally, as the cryosphere experts and lovers that we are here in the blog team, we would mourn the loss of these exceptional landscapes. We therefore strongly hope that the COP24 will bring more solution and cooperation for the future against strengthening of climate change!

Further reading

Edited by Clara Burgard and Violaine Coulon


Lionel Favier is a glaciologist and ice-sheet modeller, currently occupying a post-doctoral position at IGE in Grenoble, France. He’s also on twitter.

 

 

 

Laura Helene Rasmussen is a Danish permafrost scientist working at the Center for Permafrost, University of Copenhagen. She has spent many seasons in Greenland, working with the Greenland Ecosystem Monitoring Programme and is interested in Arctic soils as an ecosystem component, their climate sensitivity, functioning and simply understanding what goes on below.

 

 

Clara Burgard is a PhD student at the Max Planck Institute for Meteorology in Hamburg. She investigates the evolution of sea ice in general circulation models (GCMs). There are still biases in the sea-ice representation in GCMs as they tend to underestimate the observed sea-ice retreat. She tries to understand the reasons for these biases. She tweets as @climate_clara.

 

Image of the Week – Greenland’s fjords: critical zones for mixing

Image of the Week – Greenland’s fjords: critical zones for mixing

One of the most challenging research questions to address in the Arctic is how freshwater discharge from Greenland’s largest glaciers affects the biogeochemistry of the ocean. Just getting close to the calving fronts of these large marine-terminating glaciers is difficult. Fjords, hundreds of kilometers long and full of icebergs which shift with the wind and roll as they melt, make the commute a little difficult. Navigating these fjords to within a few kilometers of Greenland’s largest glaciers requires a combination of luck, skillful handling of small boats and a ‘fortune favors the brave’ attitude to sampling which would probably upset even the most relaxed of University Health and Safety Officers. The limited field data we have from Greenland’s fjords must therefore be combined with other data sources in order to understand what happens between glaciers and the ocean.


The Challenge

The amount of freshwater discharged from the Greenland ice sheet into the ocean increases in response to climate change. This may affect both the fisheries which support the island’s economy and the carbon sink associated with fjord systems – the largest per unit surface area in the ocean. As a consequence, we need to assess how exactly this cold freshwater will affect the ocean. To do so requires collaboration of scientists with different backgrounds:

  • glaciologists, to understand the different components of freshwater released (ice melt, surface runoff, subglacial discharge),

  • physicists, to understand the fate of freshwater within a dynamic water column,

  • chemists, to understand how the availability of resources shifts in response to increasing freshwater

  • biologists, to understand the net effects of multiple physio-chemical changes to the environment on living organisms.

In the context of climate change it is also always worth remembering that the increase in Greenland ice sheet discharge occurs alongside other changes in the Arctic, such as the disappearance of sea ice and warming of the atmosphere and ocean. Thus, we really must unleash 4-dimensional thinking in order to understand the processes that are currently at work in the whole Arctic.

Recent work around Greenland has shown that one particularly important factor in determining how a glacier affects downstream marine ecosystems is whether it terminates on land or in the ocean. When a glacier sits in the ocean and releases meltwater at depth, this cold freshwater rapidly mixes with deep nutrient-rich seawater. This buoyant mix, known as an upwelling plume, rises upwards in the water column. These buoyant plumes act as a ‘nutrient pump’ bringing macronutrients from deep seawater to the surface and thus driving quite pronounced summertime phytoplankton blooms. Around Greenland, these blooms are quite remarkable. Summertime productivity in the open Atlantic is generally quite limited, while the main time of year when phytoplankton bloom is spring. In several of Greenland’s fjords, however, phytoplankton bloom over the meltwater season (around May-September). Understanding how these upwelling-driven blooms operate, and more importantly how they will change in the future, is a formidable challenge. There is an almost complete lack of either physical or biogeochemical data within a few kilometers of most large marine-terminating glaciers and thus our ability to quantify the relationship between discharge and downstream productivity is limited.

Contrasting effects of meltwater around Greenland depending on where the glacier terminates with respect to sea-level. [Credit: Fig 3 from Hopwood et al., (2018)].

Modelling what we cannot measure

Fortunately however, the field of subglacial discharge modelling is relatively well advanced. Since the 1950s, plume models have been used to describe reasonably well the subglacial discharge downstream of glaciers. Whilst all of Greenland’s glacier fjords are unique, we can at least model the processes that underpin the ‘nutrient pump’ leading to such unusual summertime productivity around Greenland.

One thing is particularly clear from the use of these models. The depth at which a glacier sits in the water column is a major factor for the magnitude of the upwelling effect. If a glacier retreats inland, this is generally bad news for downstream marine productivity. As marine-terminating glaciers retreat, the nutrient pump rapidly collapses if the glacier moves into shallower water – irrespective of what happens to the volume of discharged meltwater. For a majority of Greenland’s glaciers for which the topography under the glacier has been characterised, this will be indeed the case under climate change: as the glaciers retreat inland, their grounding lines will get shallower and shallower. The ‘nutrient pump’ associated with each one will therefore also diminish.

Outlook

There are still many things we don’t know about environmental change around Greenland, as our almost complete lack of data outside the meltwater season and very close to marine-terminating glacier termini still hinders our understanding of some critical processes. Only by adopting more inter-disciplinary methods of working and deploying new technology will these data-deficiencies be addressed.

Further reading

 

Edited by Sophie Berger and Clara Burgard


Mark Hopwood is a postdoc at GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany. He investigates how environmental changes, such as increasing freshwater discharge in the Arctic or declining oxygen in the tropics, affect the availability of nutrients to biota in the marine environment. By using a combination of fieldwork and targeted process studies the main goal is to identify and quantify biogeochemical feedbacks that act to amplify or dampen the response of marine biota to perturbations. He tweets as @Markinthelab. Contact Email: m.hopwood@geomar.de

Image of the Week – Oh Sheet!

Image of the Week – Oh Sheet!

The Antarctic and Greenland ice sheets are major players in future sea level rise. Still, there is a lot about these ice sheets we do not understand. Under the umbrella of the World Climate Research Programme, the international scientific community is coming together to improve ice sheet modelling efforts to better grasp the implications of climate change for ice sheet evolution, and consequently, sea level rise…


What are ice sheets?

An ice sheet is a massive chunk of glacier ice that sits on land – covering an area greater than 50,000 square kilometres (or 1.6 times the size of Belgium) by the official definition. Currently, the only two ice sheets on Earth are in Antarctica and Greenland. Ice in ice sheets flows from inland toward the coast under gravity. Due to the geothermal heat flux, ice sheets are usually warmer at the base than on the surface. When basal melting occurs, the melted water lubricates the ice sheet and accelerates the ice flow, forming fast-flowing ice streams. When ice flows down a coastline into the ocean, it may float due to buoyancy. The floating slab of ice is called an ice shelf (see these previous posts for more on ice shelves). The boundary that separates the grounded ice and floating ice is called the grounding line.

 

Why do we care about ice sheets?

The most uncertain potential source of future sea level rise is the contribution from ice sheets. According to observations, the Greenland and Antarctic ice sheets have contributed approximately 7.5 and 4 mm of sea level rise respectively over the 1992-2011 period, and the contribution is accelerating. Knowing how the ice sheets will behave under future emission scenarios is crucial for risk assessment and policy-making (see this previous post for more on Antarctic ice sheets).

In addition to the direct impact on sea level rise, ice sheets interact with other components of the climate system. For example, ice discharge affects ocean circulation and marine biogeochemistry; changes in orography influence the atmosphere condition and circulation. In turn, the ice sheets gain mass primarily from snow fall, and lose mass through surface melting, surface sublimation, basal melting and ice discharge to the ocean, which are influenced by atmospheric and oceanographic processes. In Antarctica, the mass loss due to basal melting and iceberg calving is larger than snowfall accumulation. The Greenland Ice Sheet is also losing mass through iceberg calving and surface water runoff.

 

What’s CMIP?

Global coupled climate models are developed by different groups of scientists around the world to improve our understanding of the climate system. These models are highly complex, representing interactions between the ocean, atmosphere, land surface and cryosphere on global grids. The Coupled Model Intercomparison Project (CMIP) is a collaborative framework which provides a standard experimental protocol for the different models. The protocol includes a range of greenhouse gas emissions scenarios for future climate projections. Model output is made publicly available and forms the basis for assessments such as the Intergovernmental Panel on Climate Change (IPCC) reports. The latest phase (CMIP6) is underway now.

 

What’s ISMIP6?

Ice sheets were considered as passive elements of the climate system previously and were not explicitly included in the CMIP process. However, observations of the rapid mass loss associated with dynamic change in ice sheets highlight the need to couple ice sheets to climate models. New developments in ice sheet modelling allow previously-omitted key processes which affect ice sheet dynamics on decadal timescales, such as grounding-line migration and basal lubrication, to be simulated with higher confidence.

ISMIP6 is an international effort designed to ensure that projections from ice sheet models are compatible with the CMIP6 process, bringing together scientists from over twenty institutions (Fig. 2). It aims to improve sea level projections, exploring sea level contribution from the Greenland and Antarctic ice sheets in a changing climate and investigating interactions between ice sheets and the climate system.

 

ISMIP6 Experiments

As shown in Figure 1, the objectives of ISMIP6 rely on three distinct modeling efforts:

  1. CMIP atmosphere-ocean general circulation models (AOGCM) without an ice sheet component
  2. standalone dynamic ice sheet models (ISMs) that are driven by forcing provided by CMIP
  3. fully coupled atmosphere-ocean-ice sheet models (AOGCM-ISMs).

 

In the first phase, ISMIP6 will compare output from different ice sheet models run in ‘standalone’ or ‘offline coupled’ mode. This means that they receive forcings from the climate model components like the ocean and atmosphere without feeding back. These experiments will be used to explore the uncertainty associated with ice sheets physics, dynamics and numerical implementation. In particular, ISMIP6 is currently focused on gaining insight into the uncertainty in ice sheet evolution resulting from the choice of initialization methods (the initMIP efforts for the Greenland and Antarctic ice sheets) and understanding the response of the Antarctic ice sheet to a total loss of the ice shelves (ABUMIP).

The model output of the initMIP simulations for Greenland is now publicly available.

Fig. 2: Participants of ISMIP6 standalone ice sheet modeling.

 

ISMIP6 workshop

Regular meetings are organised to update and facilitate communication between the participants. The most recent workshop was hosted in the Netherlands during 11 – 13 September 2018. The topic of the workshop was “Developing process-based projections of the ice sheets’ contribution to future sea level.” Participants aimed to evaluate the output of the CMIP6 climate models and obtain forcing for standalone ice sheet model experiments. During the workshop, scientists made progress on establishing the experimental protocols for the ice sheet model simulations that will be discussed in the IPCC sixth assessment report.

Fig.3: Participants in the ISMIP6 workshop in Leiden, Netherlands [Credit: Heiko Goelzer]

Further reading

Edited by Lettie Roach and Clara Burgard


Sainan Sun does her postdoctoral research with Frank Pattyn at Université Libre de Bruxelles (ULB). She achieved her doctoral degree in 2014, majoring in ice sheet modeling at Beijing Normal University, Beijing, China. In her PhD study, she applied the BISICLES ice sheet model to Pine island glacier, Aurora drainage basin and Lambert-Amery drainage basin to describe the dynamical response of the Antarctic ice sheet to perturbations in boundary conditions. For the project at ULB, she aims to investigate the ice shelf features based on data acquired in Roi Baudouin ice shelf, Antarctica, and to estimate the potential instability of the Antarctic ice sheet using the f.ETISh ice sheet model. Contact Email: sainsun@ulb.ac.be

Image of the Week – Icy expedition in the Far North

Image of the Week – Icy expedition in the Far North

Many polar scientists who have traveled to Svalbard have heard several times how most of the stuff there is the “northernmost” stuff, e.g. the northernmost university, the northernmost brewery, etc. Despite hosting the four northernmost cities and towns, Svalbard is however accessible easily by “usual-sized” planes at least once per day from Oslo and Tromsø. This is not the case for the fifth northernmost town: Qaanaaq (previously called Thule) in Northwest Greenland. Only one small plane per week reaches the very isolated town, and this only if the weather permits it. And, coming from Europe, you have to change plane at least twice within Greenland! It is near Qaanaaq, during a measurement campaign, that our Image of the Week was taken…


Who, When and Where?

In January 2017, a few German and Danish sea-ice scientists traveled to Qaanaaq to set up different measurement instruments on, in and below the sea ice covering the fjord near Qaanaaq. While in town, they stayed in the station ran by the Danish Meteorological Institute. After a few weeks installation they traveled back to Europe, leaving the instruments to measure the sea-ice evolution during end of winter and spring.

 

What and How?

The goal of the measurement campaign was to measure in a novel way the evolution of the vertical salinity and the temperature profiles inside the sea ice, and the evolution of the snow covering the ice. These variables are not measured often in a combined way but are important to understand better how the internal properties of the sea ice evolve and how it affects or is affected by its direct neighbors, the atmosphere and the ocean. The team had to find a place remote enough from human influence, and with good ice conditions. As there are only few paved roads in Qaanaaq, cars are not the best mode of transport. The team therefore traveled a couple of hours on dog sleds (in the dark and at around -30°C!), with the help of local guides and their well-trained dogs (see Fig. 2 and 3).

 

Fig. 2: While the humans were working, the dogs could take a well-deserved break [Credit: Measurement campaign team].

Once on the spot, the sea-ice measurement device was introduced into the ice by digging a hole of 1m x 1m in the ice, placing the measurement device in it, and waiting until the ice refroze around it. Additionally, a meteorological mast and a few moorings were installed nearby (see Image of the Week and Fig. 3) to provide measurements of the atmospheric and oceanic conditions during the measurements. Further, a small mast was installed to enable the data to be transferred through the IRIDIUM satellite network.

 

Fig. 3: Small meteorological mast with dog sleds in the background [Credit: Measurement campaign team].

Finally, the small instrument family was left alone to measure the atmosphere-ice-ocean evolution for around four months. After this monitoring period, in May, the team had to do this trip all over again to get all the measurement devices back. Studying Greenlandic sea ice is quite an adventure!

 

Further reading

Edited by Violaine Coulon

Image of the Week — Climate change and disappearing ice

The first week of the Climate Change summit in Bonn (COP 23  for those in the know) has been marked by Syria’s decision to sign the Paris Accord, the international agreement that aims at tackling climate change. This decision means that the United States would become the only country outside the agreement if it were to complete the withdrawal process vowed by President Trump.

In this context, it has become a tradition for this blog to use the  United Nations climate talks as an excuse to remind us all of some basic facts about climate change and its effect on the part we are most interested in here: the cryosphere! This year we have decided to showcase a few compelling animations, as we say “a picture is sometimes worth a thousand words”…


Arctic sea ice volume

Daily Arctic sea ice volume is estimated by the PIOMAS reconstruction from 1979-present [Credit: Ed Hawkins]

The volume of Arctic sea ice has declined over the last 4 decades and reached a record low in September 2012. Shrinking sea ice has major consequences on the climate system: by decreasing the albedo of the Arctic surface, by affecting the global ocean circulation, etc.

More information about Arctic sea ice:

Land ice losses in Antarctica and Greenland

Change in land ice mass since 2002 (Right: Greenland, Left: Antarctica). Data is measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites. [Credit: Zack Labe]

Both the Antarctic and Greenland ice sheets have been losing ice since 2002, contributing to global sea-level rise (see previous post about sea level) .  An ice loss of 100 Gt raises the  sea level by ~0.28 mm (see explanations  here).

More information about ice loss from the ice sheets:

 

The cause: CO2 emissions and global warming

Finally we could not close this post without showing  how the concentration of carbon dioxide have evolved  over the same period and how this has led to global warming.

CO₂ concentration and global mean temperature 1958 – present. [Credit:Kevin Pluck]

More information about CO2 and temperature change

  • Global Temperature | NASA: Climate Change and Global Warming
  • Carbon dioxide | NASA: Climate Change and Global Warming

More visualisation resources

Visualisation resources | Climate lab

 

Edited by Clara Burgard

Image of the Week – The true size of Greenland

Fig. 1: Greenland is slightly bigger than  Austria, Belgium, Denmark, France, Germany, Ireland, Italy, Poland, Portugal, the Netherlands and the United Kingdom together [Credit: The True Size].

Greenland is a critical part of the world, which is regularly covered on this blog, because it hosts the second largest ice body on Earth – the Greenland Ice Sheet. This ice sheet, along with its small peripheral ice caps, contributes by 43% to current sea-level rise.

However, despite being the world’s largest island Greenland, appears disproportionately large on the most common world maps (Fig. 2). Our new image of the week takes a look at the true size of Greenland…


Fig. 2: World (Mercator) map used by many online mapping applications. [Credit: D. Strebe/Wikimedia commons]

How big is Greenland?

We could simply tell you that Greenland stretches over ~2 million km². For most people, this figure would however not speak for itself.   Luckily, The True Size is a web application that comes to our rescue by enabling us to compare the true size of all the countries in the world.

As we can see in Fig. 1, Greenland is in fact only slightly bigger than Austria, Belgium, Denmark, France, Germany, Ireland, Italy, Poland, Portugal, the Netherlands and the United Kingdom together.

Similarly, Greenland is also (Fig. 3):

  • roughly the size of the Democratic Republic of Congo

  • could fit 1.4 times in India

  • 4.2 times smaller than than the United States

  • could fit 3.5 times in Australia

Fig. 3: Greenland vs Democratic Republic of Congo, Australia, the United States and India. [Credit: The True Size]

 Greenland is therefore big but not as big as what is suggested by the most common maps (Fig. 2). As a result, one can therefore wonder why the most popular world maps distort the size of the countries.

All maps are wrong but some are useful

To map the world, cartographers must project a curved surface on a flat piece of paper. There are different approaches to do so but all distort the earth surface in some ways. For instance, conformal projections preserve angles and shapes but change the size of the countries, whereas equal-area projections conserve the sizes but distort the shapes. As a result, a map projection that suits all purposes does not exist. Instead, the choice of the projection will depend on the use of the map.

Fig. 4: Mercator cylindrical projection [Credit: National Atlas of the United States]

The most popular projection, the Mercator projection (Fig. 2),  is used by many online mapping applications (e.g. google maps, OpenStreetMap, etc.). In Mercator maps, the Earth’s surface is projected on a cylinder that surrounds the globe (Fig. 4). The cylinder is then unrolled to produce a flat map that preserves the shapes of landmasses but tends to stretch countries towards the poles. This is why the size of Greenland is exaggerated in many world maps.

Why does google map use the Mercator projection then?

If Google Maps and other web mapping services rely on the Mercator projection, it is not to make countries at high latitudes appear bigger, but, because those tools are mainly intended to be used at local scales. The fact that the Mercator projection preserves angles and shapes therefore ensures minimal distortions at the city-level: two perpendicular streets will always appear perpendicular in Google Maps. This is not necessarily the case at high latitudes with projections that preserves areas (as can be seen here).

Interested in this topic? Then, you might enjoy this video !

Image of the Week: Petermann Glacier

Figure 1: Satellite images showing the front of Petermann glacier from spring to autumn 2016 [Credit: LandSAT 8 (NASA) and L. Dyke]

Our image of the week shows the area around the calving front of Petermann Glacier through the spring, summer, and autumn of 2016. Petermann Glacier, in northern Greenland, is one of the largest glaciers of the Greenland Ice Sheet. It terminates in the huge Petermann Fjord, more than 10 km wide, surrounded by 1000 m cliffs and plunging to more than 1100 m below sea level at its deepest point. In 2010 and 2012, the glacier caught the world’s attention with two large events, which caused the glacier to retreat to a historically unprecedented position.


In Fig. 1 we see the changes happening through the season on Petermann glacier – and they are huge. The animated map highlights many different processes. As areas emerge from the Polar night at the start of spring, the shadows quickly shorten and the light levels become noticeably higher.  This is followed by the melting of the snow, first on south-facing slopes, and eventually to on the high-elevation areas in the mountains. As the sun returns, meltwater starts forming on the surface of the glacier, this is visible as vast turquoise lakes. Finally, the sea ice in the fjord succumbs to the seasonal warming of the ocean and atmosphere, it thins, and then completely disintegrates at around day 205.

The change in the glacier is perhaps the most interesting phenomenon. It is possible to observe the glacier flowing and advancing into the fjord. In addition, several large rifts near the front open through the course of the year. These will eventually spread across the front of the glacier and a new, huge iceberg will be born. These rifts are being closely monitored, and it is likely that when the iceberg calves it will bring cause Petermann Glacier to retreat to a new historical minimum.

The image above is an example of a new type of map, it takes cartography into the 4th dimension—time. Technological advances have only recently made it possible to create a map like this; with the launch of Landsat 8 and Sentinel-2 it is now possible to receive regular, high-resolution, and free satellite images of high latitude areas. These data have been projected onto a new, high quality digital elevation model (Howat et al., 2013) to create this map.

 

Further Reading

Howat, I. M., Negrete, A., and Smith, B. E. (2014). The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasetsThe Cryosphere8 (1): 1509–1518

Edited by Nanna B. Karlsson


Laurence Dyke is a postdoctoral researcher at The Geological Survey of Denmark and Greenland (GEUS) in Copenhagen (DK). His work is primarily focussed on understanding the history of the Greenland Ice Sheet, from both marine and terrestrial perspectives. He works with marine sediment cores and surface exposure dating to investigate what triggered changes in glacier behaviour over the last 12 thousand years. Understanding the past is key to predicting the future! He tweets as @LaurenceDyke

Image of the Week – A new way to compute ice dynamic changes

Fig. 1: Map of ice velocity from the NASA MEaSUREs Program showing the region of Enderby Land in East Antarctica [Credit: Fig. 1 from Kallenberg et al. (2017) ].

Up to now, ice sheet mass changes due to ice dynamics have been computed from satellite observations that suffer from sparse coverage in time and space. A new method allows us to compute these changes on much wider temporal and spatial scales. But how does this method work? Let us discover the different steps by having a look at Enderby Land in East Antarctica, for which ice velocities are shown in our Image of the Week…


Mass balance of ice sheets

The mass balance of an ice sheet is the difference between the mass gain of ice, primarily through snowfall, and the mass loss of ice, primarily via meltwater runoff and ice dynamic processes (e.g. iceberg calving, melting below ice shelves). When the mass gain is equal to the mass loss, the ice sheet is in balance. However, if one exceeds the other, the ice sheet either gains or loses mass.

Measuring mass balance changes of ice sheets is crucial due to their potential contribution to sea level rise (see previous post). You can have a look at this nice review for further details about the recent changes in the mass balance of the two biggest ice sheets on Earth, i.e. Antarctica and Greenland.

Ice mass changes from snowfall and meltwater runoff (what we call ‘surface mass balance’ changes) are reasonably well simulated by regional climate models, which give good agreement with observations (see this study for Antarctica and this one for Greenland). Mass changes from ice dynamics are more complex to obtain. They are commonly estimated by combining ice velocity and ice thickness. Ice velocity is measured via satellite radar interferometry, while ice thickness is obtained thanks to airborne radar. Unfortunately, these measurements have sparse temporal and spatial coverage, especially in Antarctica, which makes the computation of mass changes from ice dynamics challenging.

A new method to estimate ice dynamic changes

Kallenberg et al. (2017) conducted a study focussing on Enderby Land in East Antarctica (see our Image of the Week) in which they use a novel approach to estimate ice dynamic changes. This region of Antarctica has experienced a slightly positive mass balance in past years, meaning that the ice sheet has slightly thickened in this region.

Kallenberg et al. (2017) first used satellite observations to compute the total changes in ice sheet mass. They took advantage of two high-technology datasets. The first one, “Gravity Recovery And Climate Experiment” (GRACE), measures changes in the Earth’s gravity field, from which ice mass changes can be derived. A summary explaining how GRACE works can be found in this previous post. The second satellite dataset, “Ice, Cloud, and land Elevation Satellite” (ICESat), measures changes in ice surface elevation, from which changes in ice mass can be computed by using ice density.

However, Kallenberg et al. (2017) were not interested in the total ice mass changes, as obtained from GRACE and ICESat satellites, but rather in ice dynamic changes. They subtracted two quantities from the total mass changes in order to obtain the remaining dynamic changes:

  1. Surface mass balance changes: changes from processes happening at the surface of the ice sheet (e.g. snow accumulation, meltwater runoff). These changes were obtained from model simulations using the Regional Atmospheric Climate Model (RACMO2), for which details can be found in this previous post.
  2. Glacial Isostatic Adjustment: changes in land topography due to ice loading and unloading. These changes were computed from Glacial Isostatic Adjustment models.

What does this study tell us?

The results of this study show that it is possible to compute changes in ice mass resulting from ice dynamics with higher spatial and temporal coverage than before, using a combination of satellite observations and models.

Also, the use of two different satellite datasets (GRACE and ICESat) shows that they agree quite well with each other in the region of Enderby Land (see Fig. 2). This means that using one or the other dataset does not make a big difference.

Finally, this new method also shows that differences between GRACE and ICESat reduce when using the newer version of RACMO2 for computing surface mass balance changes. This tells us that comparing results of ice dynamics from both satellites with different models is a good way to identify which models correctly simulate surface processes and which models do not.

Fig. 2: Ice dynamic changes (dH/dt, where H is ice thickness and t is time) computed from (a) GRACE and (b) ICESat and expressed in meters per year [Credit: Fig. 5 from Kallenberg et al. (2017) ].

Further reading

Edited by Clara Burgard and Emma Smith


David Docquier is a post-doctoral researcher at the Earth and Life Institute of Université catholique de Louvain (UCL) in Belgium. He works on the development of processed-based sea-ice metrics in order to improve the evaluation of global climate models (GCMs). His study is embedded within the EU Horizon 2020 PRIMAVERA project, which aims at developing a new generation of high-resolution GCMs to better represent the climate.