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Cryospheric Sciences

Cryospheric Sciences

Image of the Week – Permafrost features disappearing from subarctic peatlands

Image of the Week – Permafrost features disappearing from subarctic peatlands

Some of the most remarkable, marginal features of permafrost – palsas – are degrading and disappearing metre by metre from North European peatlands, and are driven close to extinction by the climate change.


What are these permafrost features?

A palsa is a peat mound with an icy core, which stays frozen throughout summer due to the insulating property of dry peat. These mounds can rise up to 10 metres above the surface of surrounding mire (wet terrain dominated by peat-forming vegetation), and they may occur as just a single palsa, group of palsas or as an extensive, but not very high (ca. 1 to 2 m) peat “platform”. The occurrence of palsas is limited by such factors as: low mean annual air temperature (< 0 °C), low annual precipitation (< 500 mm) and at least 40–50 cm thickness of peat layer, which is needed to sufficiently insulate the core during summer (Seppälä, 2011).

The established theory on palsas formation (Seppälä, 2011) is the following:

  1. The formation of a palsa begins when a part of mire freezes deeper in a windblown area with thinner snow cover, which normally protects the ground below from freezing temperatures.

  2. If the frozen peat doesn’t melt completely during summer, an ice lens forms inside the peat layer resulting in uplifting of the mire surface in this area.

  3. In the following winters, the snow is even more likely to be windblown from the mound, which again fosters deeper penetration of frost and formation of new ice lenses.

  4. As soon as a part of mire rises above the water level, the vegetation starts to change and the peat dries out, which contributes to the survival of the ice core during summers.

 

Breaking of the surface and erosion is a natural “step” for mature palsas, when the permafrost has reached the mineral ground below the peat. The melting of a palsa is a form of thermokarst, i.e. thawing of ice-rich permafrost (see this post for more details about thermokarst).

Block-erosion of peat on ridge-type palsa in Nierivuoma mire in Enontekiö, Finland [Credit: Mariana Verdonen].

Palsa, peat hummock or permafrost plateau?

The terminology used when speaking about these permafrost mounds varies, usually according to the continent the research was conducted on or the background of the authors. The term “palsa” comes from Lapland, and was used by Sami and northern Finns to refer to “hummock rising out of a bog with a core of ice” (Seppälä, 1972). In Fennoscandia, this term is used commonly for all main types: ridges, mounds and plateau palsas, whereas in North America the more common terms are either ‘peat or permafrost plateau’ or ‘wooded palsa’ depending on the shape and vegetation cover of the feature (Luoto et al, 2004).

Degrading permafrost of Fennoscandia

More often than not, one may encounter a desolate sight in North European palsa mires: most of the permafrost mounds are degrading by block erosion and/or melting away as a result of thawing of their frozen core. The vegetation that once was growing on hummocks above the wet mire surface, is now dead black in shallow thermokarst ponds surrounding palsas here and there. Although, in some places the conditions may still be favorable for new palsas to form, the general picture is devastating. Palsas are disappearing in most of their area of existence, and it is happening fast.

Thawing palsas of Nierivuoma captured from drone in July 2018. This peatland sprawls across ~7 km2 and is the largest palsa mire in Finland [Credit: Timo Kumpula].

Why should we care?

As climatic change is likely to increase winter and summer precipitation, and is already notable in rising mean annual air temperatures, palsas are predicted to disappear in Fennoscandia almost completely by the end of the 21st century (Fronzek et al, 2010).

It is noteworthy, that the palsa mire is the only mire and bog habitat that is listed as “critically endangered” in the 2016 European Red List of Habitats. While some other cold climate ecosystems may shift to higher latitudes and altitudes, palsa mires seem to be restricted from developing in higher areas, especially because of the required peat layer thickness (Luoto et al, 2004).

If just the loss of this diverse ecosystem type is not alarming by itself, there are couple of issues that I want to highlight:

  • Thawing of the perennially frozen peat changes the carbon fluxes of palsa mires as carbon previously trapped by permafrost becomes available for decay. As the area of dry peat surface decreases, more carbon is released into the atmosphere in the form of more effective greenhouse gas methane (CH4) instead of carbon dioxide (CO2). Recently, also the effects of permafrost thaw on the emissions of nitrous oxide (N2O), which is a strong greenhouse gas, have gained more attention (Marushchak et al, 2011).

  • The heterogeneity formed by variety of mire surfaces, thermokartst ponds and dry palsa mounds creates favorable conditions for species richness in these subarctic environments. In particular, the number and density of bird species seems to be high in the zone of palsa mires compared to more southern mire zones in Fennoscandia, even though no species have been reported to be exclusive to palsa mires (Luoto et al, 2004). This relationship, as well as overall significance of palsa mires for biodiversity is still poorly understood, however.

References

 

Edited by Clara Burgard


Mariana Verdonen is an Early Stage Researcher at the University of Eastern Finland. She focuses on optical, multi-temporal and multiscale remote sensing of environmental changes in Arctic and Subarctic areas. Mariana’s scientific interests are generally in geomorphology, permafrost-landscape dynamics and remote sensing of the Cryosphere. She tweets as @MarianaVerdonen. Contact Email: mariana.verdonen@uef.fi

Image of the Week – Ice-Spy: the launch of ICESat-2

The second generation Ice Cloud and land Elevation Satellite (ICESat-2) from NASA fires 10,000 pulses every second to take elevation measurements up to every 70 cm on-the-ground. This data will offer lots of opportunities for scientists to understand the changing cryosphere in more detail than ever before [Credit: NASA’s Goddard Space Flight Center].

On September 15th, 2018, at 18:02 local time, NASA launched its newest satellite – the second generation Ice, Cloud and land Elevation Satellite (ICESat-2). ICESat-2 only contains one instrument – a space laser that fires 10,000 pulses per second to Earth to measure elevation. Its primary purpose is for monitoring the ever changing cryosphere, so naturally there are plenty of ice enthusiasts that are excited for the data it will provide!


Blast off! ICESat-2 launches successfully from California, on the Delta II Rocket [Credit: NASA / Bill Ingalls].

Space laser?

The space laser is referred to more formally as an ‘altimeter’ (specifically, the Advanced Topographic Laser Altimeter System; ATLAS). Each of the 10,000 pulses per second contain around 20 trillion photons (the elementary unit that makes up light). The instrument works by measuring the time it takes for the photons to travel to Earth, reflect off the surface, and bounce their way back to the receiver. When the land is higher in elevation, there is less distance for the photons to travel, so they arrive back quicker and vice versa. The detector only lets in light at 532 nanometres in the visible spectrum. This means only the target photons are detected and sunlight is filtered out. An on-board clock measures time to a billionth of a second for maximum precision. The 10,000 pulses per second compares to just 40 per second in the original ICESat mission, giving us measurements every 70 cm on-the-ground. ICESat-2 repeats its orbit every 91 days, so we get elevation measurements for everywhere on Earth every 3 months.

What happened to the original ICESat?

ICESat launched in 2003 and lasted 7 years before its mission came to an end when its primary instrument stopped functioning. Its final task was to propel itself into Earth’s atmosphere and burn up on re-entry. In its lifetime, ICESat helped us to quantify decreasing Arctic sea-ice thickness, estimate global above ground biomass using forest canopy height and even find lakes beneath Antarctica. It was such a success that, since 2010, NASA have flown planes (Operation IceBridge) over the cryosphere with the same instruments to bridge the gap in the data loss between the two ICESat missions.

Operation IceBridge flies over ice sheets, ice shelves, glaciers and sea-ice to ensure there is no gap in data between the ICESat missions. You can see more of the stunning imagery collected from Operation IceBridge here! [Credit: NASA’s Goddard Space Flight Center]

What new science will we get from ICESat-2?

The primary purposes of the mission are to measure elevation change of ice sheets, glaciers, sea-ice and the subsequent impacts of sea-level rise. Whereas the original ICESat mission had a single laser beam with 40 pulses per second, ICESat-2 has 6 laser beams with 10,000 pulses per second, which gives an unprecedented level of detail. On the original mission, the orbit may have only provided a single track across a mountain glacier, but the new mission will have significantly more measurements. The higher spatial resolution of ICESat-2 means that the satellite can be used to identify and track icebergs that cross shipping lanes, provide extra measurements of sea-ice thickness for subsistence hunters and detect small topographic changes in potentially active volcanoes. There are many other potential applications of ICESat-2, including for non-cryospheric research, but there will also be many unforeseen applications of the new data that will come about with time.

I’m so excited! When will the first results start coming out?

Whenever satellites are launched with the purpose of earth observation, there is a long period of time when the instruments need to be checked to ensure they are working as intended. NASA will be calibrating ICESat-2 for a few months after launch to ensure the outputs are of the highest possible quality, so don’t expect any publicly available data until early 2019. It’s worth getting it right early in the mission because ICESat-2 has enough fuel on board to last 7 years, so mistakes early on can lead to delays or reduce the overall quality of data collected over the mission. If you can’t wait, however, you can see the first height measurements from Antarctica here!

The first data from NASA’s newest satellite – the second generation Ice Cloud and land Elevation Satellite (ICESat-2). ICESat-2 fires 10,000 pulses every second to take elevation measurements up to every 70 cm on-the-ground. This elevation data shows the first track across the Antarctic ice sheet. Who knows what new science we will discover during its mission! [Credit: NASA’s Goddard Space Flight] Center.

Find out more

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 – (Un)boxing the melting under the ice shelves

Image of the Week – (Un)boxing the melting under the ice shelves

The Antarctic ice sheet stores a large amount of water that could potentially add to sea level rise in a warming world (see this post and this post). It is currently losing ice, and the ice loss has been accelerating in the past decades. All this is linked to the melting of ice – not at the surface but at the base, underneath the so-called ice shelves which form the continuation of the Antarctic ice sheet over the ocean. These floating ice shelves (represented in color in our Image of the Week) are melted by ocean water from underneath. How can this process called ‘sub-shelf melting’ be included in ice-sheet models? One simple way is to divide the ice-shelf cavity into a number of ocean boxes. Let’s briefly see how it works.


How to model sub-shelf melting in ice-sheet models?

There are three main ways to do so – which way is most suitable depends on the application:

  1. The most elaborated approach is to use ocean models that resolve ocean dynamics underneath the ice shelves. However, they need a lot of computational power.

  2. As an alternative, simple parameterizations in which melting is a function of the depth of the ice-shelf base can be used. However, such parameterizations are for many applications too simple…

  3. Recently, intermediate approaches that include the basic ocean dynamics have been developed (e.g. Lazeroms et al., 2018; Pelle et al., in review). One such approach is the ocean box model (Olbers and Hellmer, 2010) that we extended for the use in an ice-sheet model. Our extension is called Potsdam Ice-shelf Cavity mOdel (PICO, Reese et al., 2018).

In the following, we take a closer look into the approach of PICO…

“Boxing” the cavity circulation

In Antarctic ice-shelf cavities (i.e. the water below the ice shelves), in general, an overturning circulation transports ocean water from the sea floor along the ice-shelf base towards the calving front (see Figure 2). It is driven by the “ice-pump” (Lewis and Perkin, 1986): ice melting near the grounding line (separation between the grounded ice sheet and the floating ice shelf) reduces the density of the ambient water. It becomes buoyant and rises along the shelf base towards the ocean. Through this process, new water from outside of the ice-shelf cavity is “pumped” along the continental shelf towards the grounding line. This leads to the typical pattern of highest melting near the deep grounding lines and lower melting towards the calving front.

 

Figure 2: Schematic showing the ocean boxes following the ice-shelf base, with the first box B1 near the grounding line, and the last box Bn at the calving front. The arrows indicate the overturning circulation. The ocean water enters the cavity from box B0 which is at depth of the continental shelf, in front of the ice shelf. [Credit: Fig. 1 of Reese et al. (2018)]

 

By dividing the ice-shelf cavity into 2 to 5 ocean boxes, the transport of the overturning circulation is simplified while the sub-shelf melt pattern is captured. The open ocean conditions are simply represented by the ocean reservoir box B0 (Figure 2). And the circulation is driven by the differences in water density between the ocean reservoir (B0 in Figure 2) and the first box near the grounding line (B1 in Figure 2). The model computes sub-shelf melting successively over the ocean boxes, starting near the grounding line.

Sub-shelf melting with PICO

Sub-shelf melting can vary a lot in-between ice shelves (Figure 1). Antarctic ice-shelf cavities can roughly be sorted into two types (Joughin et al., 2012). The first category are the cold cavities in which the ocean water is close to the freezing point and in which sub-shelf melting is generally low, about 0.1 meter per year. The second category are warm cavities which have a temperature of about 1 degree – that does not sound like much, but for an ice shelf, this feels like being in a sauna – and sub-shelf melting can easily exceed 10 meters per year. Small changes in ocean temperatures can hence have large effects on sub-shelf melting. An increase in sub-shelf melting thins the ice shelf, as for example observed in the Amundsen Sea region in West Antarctica (see this post). The ice shelves there are examples for warm cavities, and a cold cavity is, for instance, underneath the Filchner-Ronne Ice Shelf (see Figure 1 for the specific locations).

In reality, of course, things are much more complicated than simulated by our PICO model. For example, the Coriolis effect can influence ocean circulation in the cavities, sills in the bed can block access of warm water to the grounding line and so on…

Applications of PICO

To summarize, PICO is a simple and efficient modeling tool that can capture the general pattern of sub-shelf melting observed in Antarctica today. Being implemented in the Parallel Ice Sheet Model, it is openly available, so if you got excited about what it can do and want to use it yourself, you’re welcome to download it!

Further reading

Edited by David Docquier


Ronja Reese is a postdoctoral researcher at the Potsdam Institute for Climate Impact Research, Germany, in the group of Prof. Dr. Ricarda Winkelmann. She investigates ice dynamics in Antarctic with a focus on ice-ocean interactions and ice-shelf buttressing. She developed and implemented PICO together with Ricarda Winkelmann, Torsten Albrecht, Matthias Mengel and Xylar Asay-Davis. Contact Email: ronja.reese@pik-potsdam.de

Image of the Week – Breaking the ice: river ice as a marker of climate change

Figure 1. Dates of ice breakup on Alaskan river reaches wider than 150 m calculated using Moderate Resolution Imaging Spectroradiometer (MODIS) data. [Credit: Wayana Dolan].

Common images associated with climate change include sad baby polar bears, a small Arctic sea ice extent, retreating glaciers, and increasing severe weather. Though slightly less well-known, river ice is a hydrological system which is directly influenced by air temperature and the amount and type of precipitation, both of which are changing under a warming climate. Ice impacts approximately 60 % of rivers in the Northern Hemisphere and therefore will be a clear indicator of climate change over the coming century.


River ice terminology

First, I think it is important to get some quick vocabulary out of the way. There are three primary variables used to study large-scale trends in river ice:

  • Ice freeze-up: The process of ice accumulation on a river reach (a segment of a river), usually during the autumn or winter.
  • Ice breakup: The process of ice loss from a river segment. Breakup style is often related to a pulse of increased runoff from snow melt, known as the spring flood wave. Thermal breakup occurs when river ice melts prior to the arrival of the spring flood wave. It is a slow and relatively calm process. Alternatively, mechanical breakup occurs when ice on a river has not melted prior to the arrival of the spring flood wave. Mechanical breakups often cause severe ice jam floods, whereas thermal breakups are rarely associated with flooding events. You can observe an example of mechanical ice breakup and associated ice jam flooding in 2018 on the North Saskatchewan River at Petrofka Orchard on the video below [Credit: Planet Labs, Inc.].
  • Ice cover duration: The length of time a river segment is ice-covered between freeze-up and breakup.

Now that we know these key phrases, let’s get to the good stuff!

Why should you care about river ice?

Shifts in river ice cover duration can be used as an indicator for Arctic climate change due to its relationship with air temperature and precipitation (Prowse et al. 2002). Hotter air temperatures generally relate to earlier ice breakup, later ice freeze-up, and shorter ice cover duration. These trends in breakup and freeze-up have been observed over the past 150 years on multiple rivers in the Northern Hemisphere by Magnuson et al. 2000. Many arctic communities rely on ice roads, which often travel across frozen rivers, lakes, and wetlands. These roads are important for transporting food, fuel, and mining equipment, to predominately first nations people. They are also commonly used by people who live subsistence-based lifestyles for hunting and trapping during the winter months. If ice cover duration shortens, these roads will be stable for a shorter period each winter. Alternatively, longer ice-free seasons would allow for decreased shipping costs in many boreal and Arctic regions, which currently use ice breaking to clear shipping pathways (Prowse et al. 2011). Another trend observed in several large Arctic rivers is a shift from mechanical breakup to thermal breakup (Cooley & Pavelsky, 2016). While this change could lead to a decrease in ice jam flood damage to hydropower and other infrastructure, it could also cause a dramatic decrease in sediment and nutrient transport to near-river Arctic ecosystems such as floodplains and deltas.

Recent research has shown ice cover trends to be geographically complex and dependent upon variables such as air temperature, basin size, and precipitation (Bennett & Prowse, 2010; Prowse et al. 2002; Rokaya et al. 2018). However, many of these trends are poorly understood on a pan-Arctic scale.

How do we measure changes in river ice?

From the early-1980s through the mid-2000s, satellites missions such as Landsat and the Moderate Resolution Imaging Spectroradiometer (MODIS) began allowing researchers to study ice on rivers in inaccessible areas. However, computing power limited the size and scale of rivers which could be observed. More recently, data processing through platforms like Google Earth Engine allow river ice to be studied on a much larger scale.

The University of North Carolina at Chapel Hill (UNC) has a working group which makes use of these new programs to study changes in pan-Arctic river and lake ice. My current project seeks to quantify historical river ice breakup and freeze-up using MODIS. We have developed an ice detection algorithm that has successfully been applied to all river reaches in Alaska wider than 150 m, limited by the 250 m spatial resolution of MODIS (Figure 1). Note that our detection algorithm can be applied to rivers which are slightly sub-pixel in width. I am currently working on calculating trends in this dataset and the expansion of the algorithm to pan-Arctic rivers, so that we can better identify which regions in the Arctic are changing the fastest. A quick glance at the dataset reveals that ice breakup is highly variable through time and space, even between upstream and downstream reaches of the same river. Internal variation in breakup dates within a given river may be caused by temperature gradients along the river profile, changes in elevation, as well as variation in the amount and type of precipitation. Additionally, preliminary work by UNC postdoctoral researcher Xiao Yang uses Google Earth Engine, Landsat, and MERRA-2 data to globally model river ice (Figure 2). This model can be applied to future climate change scenarios to see how river ice will change as the temperature warms. Keep an eye out for this paper in the next few months!

Figure 2. Preliminary results from modelling global river ice coverage using Landsat imagery, latitude, longitude, and surface air temperatures from MERRA-2. Colors refer to the percentage of the total river length in each area that is ice-covered each month (aggregated from 1984 to 2018) [Credit: Xiao Yang].

Future outlook

River ice cover duration is expected to shorten as the climate warms. Shifts in ice breakup and freeze-up processes can impact sediment and nutrient delivery, Arctic transportation and hunting, and ice-related hazards. However, our preliminary results show that river ice breakup varies both spatially and temporally throughout Alaska (Figure 1). Ongoing research at UNC will allow researchers to identify areas of the pan-Arctic which are most vulnerable to river ice-related change.

Further resources

Edited by Scott Watson


Wayana Dolan is a current M.S. student and future Ph.D. student at the University of North Carolina at Chapel Hill (USA) working with Dr. Tamlin Pavelsky. Her current research involves using remote sensing to study large-scale changes in river ice. She is passionate about any project that allows her to do Arctic fieldwork. Dolan also works with the WinSPIRE program – a summer research internship for female high school students in North Carolina. You can contact her by email or on twitter as @wayana_dolan.

 

Image of the Week – Karthaus Summer School 2018

Beautiful and cozy Golden Rose hotel on the left; blissful and small Italian village, Karthaus, on the right [Credit: Rohi Muthyala].

Nearly every year since the late 90s, during the summer, the picturesque Karthaus has hosted 10-day glaciology course. This school is a platform for glaciologists to explore, learn and expand their knowledge base. This helps researchers become multi-faceted: to view glaciology from the perspective of those specializing in other backgrounds such as hydrology, geomorphology, oceanography, etc. which complement one another in defining glaciology. Along with the intense course work, one can wholeheartedly cherish the exotic food, cozy resort, spellbinding views and delicious wine!


Time to learn

Day used to start at 8 am with a healthy breakfast and then we head out to Katharinaberg to attend the lectures. Morning session of the course composed of four lectures with coffee breaks in between to keep us alert. These lectures were on a gamut of topics including numerical and analytical modeling, continuum mechanics, glacier hydrology, mass balance of the ice sheets, thermodynamics of ice, geophysical methods, geodynamics, ice core analysis, polar oceanography and geomorphology, etc. Lectures began with basics in every topic and gradually evolved into complex concepts, enabling students understand the subject better, irrespective of their specialization. After four hours of lectures, we, surrounded by lustrous green hills, enjoyed a delicious three-course lunch.

Afternoon session was all about application of the concepts learned in the morning into numerical exercises and group projects. We were divided into 12 groups to work as a team for a group project. Each group was assigned a topic and a teacher to work with. Results from the group projects presented on the last day of the course, astonished me by the level of research we could accomplish in 10 days, showing the amount of knowledge gained through the program.

Outdoor afternoon session in Kartharinaberg [Credit: F. Pattyn]

After school

School ended at 5 pm, leaving us with ample time to relax before dinner. While some students enjoyed it hiking, trail running and chilling in the sauna, I spent this time exploring Karthaus with a bunch of friends I made at the school and tried to capture the beauty of nature with my camera. Then was the best part of the evenings – a five-course dinner with lots of wine and stories from our fellow glaciologists. I have never had such an exotic five-course meal, which was so tasty that I couldn’t help but overeat. To top the delicious food, we had musical performances by Frank Pattyn and Johannes Oerlemans. I was amazed to know that most of the teachers have their own specialty with an instrument and that it’s a tradition at Karthaus to enjoy the evenings with their performances. After a two-hour long dinner, we moved to the bar next to the restaurant and continued our entertainment with games, wine and chatting. I wished there were more than 24 hours in a day to spend at Karthaus. This summer school is a complete package of education and entertainment.

Dinners at karthaus, with 5-course meal, wine and music (Frank Pattyn on Piano and Johannes Oerlemans on Bass) [Credit: Rohi Muthyala]

Entertainment after dinner with wine, games, chatting and as you can see, some map reading as well. Apparently, this year students are the most solemn group ever [Credit: Rohi Muthyala].

Adding to the fun, in the middle of the course, we had a day-off that most of us spent by going on an excursion to the Otztal Alps. A bus ride to Kuzras, a cable car to the top of Hochjochferner and hike down into the valley led us to the edge of the glacier where some stepped onto a glacier and/or entered an ice cave for the first time in their life. We stopped by Bellavista (Schonne Aussicht hut) for a hot meal and drinks before hiking higher onto the Italian Alps. Though we had been lucky with perfect clear skies throughout the course, we got a cloudy weather on our day-off to the Alps. Nonetheless, the experience of going well above the clouds in the cable car was the best start for the day.

Hiking on a cloudy day from the top of Hochjochferner gletscher to bellavista [Credit: Rohi Muthyala].

All in all

This summer school would be an intense and beneficial experience for students in all stages of education. Be it a beginner in glaciology or an experienced final year Ph.D. student, I think the course has a lot to offer to every student. Especially to the students with no glaciology background, this could be a place to learn the basics and understand how to look for answers you are trying to find. With three years of experience going to Greenland for research as an Arctic hydrologist, I was still ignorant in some concepts (such as geomorphology, geodynamics, thermodynamics, etc) that are not directly related to my dissertation. This program opened paths for understanding those concepts in a productive way. I highly recommend this summer program to every graduate student studying glaciology and especially to those who are not from Europe, with few opportunities such as this to learn the basics in wide range of topics from glaciology.

Another best outcome of this course was the opportunity to interact with fellow students and build a network for future collaborations. AGU and EGU have been mostly exclusive, and this provided an opportunity for me (from an American university) to get to know my fellow researchers from other parts of the world. I would also like to highlight the women participation in this course (roughly 50%) and appreciate the organizing committee’s effort to encourage more women in this field. Huge thanks to the organizing committee and all the teachers for their effort in making this an incredible experience. Special thanks to the convener, Johannes Oerlemans, for coordinating such a quintessential summer school.

Class photo in Katharinaberg [Credit : W.J. van de Berg]

Edited by Violaine Coulon


Rohi Muthyala is a PhD candidate from Rutgers University (New Jersey, USA), working with Asa Rennermalm. Muthyala comes from a multidisciplinary background of atmospheric, environmental sciences and geography, and currently focuses her research on Arctic hydrology and hydrological modeling. Objective of her dissertation is to model surface hydrological processes influencing the transport of meltwater over the surface of Greenland ice sheet.

Image of the Week – Promoting interdisciplinary science in the Arctic: what is IASC?

Image of the Week –  Promoting interdisciplinary science in the Arctic: what is IASC?

The Arctic is one of the fastest changing regions on the Earth, where climate change impacts are felt both earlier and more strongly than elsewhere in the world. As an integral part of the Earth system, the Arctic is shaped by global processes, and in turn, Arctic processes influence the living conditions of hundreds of millions of people at lower latitudes. No one country or community can understand the Arctic alone. Big Arctic science questions require ambitious Arctic science – but researchers sometimes need a little help bridging both national and disciplinary boundaries. That‘s a lofty mission, but how does the International Arctic Science Committee (IASC) achieve it? Read on!


How does IASC support science?

Each IASC member country appoints up to two members to each of IASC’s 5 scientific Working Groups (Atmosphere, Cryosphere, Marine, Social & Human, and Terrestrial). These groups allocate IASC‘s scientific funds for small meetings, workshops, and projects. Follow the to see the science priorities of each group, find out about upcoming Working Group activities, and explore the expertise of their members!

Understanding the future of the Arctic means we need to invest in the Arctic researchers of today. Therefore, At least 40% of IASC’s working group funds must be co-spent with another working group, to encourage interdisciplinary projects. Check out upcoming events in 2019 like the Year Of Polar Prediction Arctic Science Workshop, High Latitude Dust Workshop, Snow Science Workshop, and Network on Arctic Glaciology meeting – just to name a few!

What else does IASC do?

IASC convenes the annual Arctic Science Summit Week (ASSW), which provides the opportunity for coordination, cooperation and collaboration between the various scientific organizations involved in Arctic research and to economize on travel and time. In addition to IASC meetings, ASSW is a great opportunity to host Arctic science meetings and workshops. ASSW2019 will be in Arkhangelsk, Russia.

IASC influences international Arctic policymakers by being an observer to the Arctic Council and contributing to its work. IASC projects include contributing experts to an assessment on marine plastic pollution in the Arctic, helping coordinate reviews for the first Snow, Water, Ice, and Permafrost Assessment (SWIPA) report, and co-leading the Arctic Data Committee & Sustaining Arctic Observing Networks.

Supporting Early Career Researchers

At least one third of IASC‘s scientific funds must be spent on supporting early career researchers (see the image of the week)! In addition, the IASC Fellowship Program is meant to engage early career researchers in the Working Groups and give them experience in helping lead international and interdisciplinary Arctic science activities. Applications are now open and due by 19 November!

IASC convenes the annual Arctic Science Summit Week (ASSW), which provides the opportunity for coordination, cooperation and collaboration between the various scientific organizations involved in Arctic research and to economize on travel and time. In addition to IASC meetings, ASSW is a great opportunity to host Arctic science meetings and workshops. ASSW2019 will be in Arkhangelsk, Russia.

Get Involved!

Do you have a great idea that you think IASC might want to support? Or want to learn more about IASC? Connect with IASC on Facebook, and sign up to receive our monthly newsletter! You are also encouraged to reach out to the relevant national/disciplinary IASC Working Group experts, IASC Council member, and the IASC Secretariat.

Further reading

Edited by Adam Bateson


Allen Pope is the IASC Executive Secretary. IASC scientific funds are provided from national member contributions. The IASC Secretariat in Akureyri, Iceland is supported by Rannís, the Icelandic Centre for Research. The IASC Secretariat is responsible for the day-to-day operations and administration of IASC. Allen also maintains an affiliation as a Research Scientist at the National Snow and Ice Data Center at the University of Colorado Boulder where he continues research based on remote sensing of glacier mass balance and surface hydrology. You can find out more about Allen and his research at https://about.me/allenpope. He also enjoys sharing and discussing polar science with the public and tweets @PopePolar.

Image of the Week – Alien-iced

Image of the Week – Alien-iced

What do Chile and Jupiter’s moon Europa have in common? If you like astronomy, you may reply “space missions!” – Chile’s dry air and clear skies make it an ideal location for telescopes like the VLT or ALMA, while Europa’s inferred subsurface ocean will be studied by the upcoming mission to Jupiter JUICE, due to launch in 2022. But Chile’s high altitude Atacama desert and Europa’s frozen surface also have another feature in common, as you can see in this Image of the Week: ice spikes!   


Penitentes is the word

The official name of these ice spikes is “Penitentes”, Spanish for penitents. Why? As you might see (with quite some imagination) on the Image of the Week, there is some resemblance with a kneeling and praying procession.

Fields of penitentes ranging from a few centimetres to five metres can be found above 4000 m altitude both in the Andes and Himalayas, the only places on Earth where the right conditions exist for their formation. Because although it looks as if the snow is just blown into penitentes by unidirectional winds, in reality everything is due to thermodynamics…

I promise I will not write the equations this time (see this previous post); instead, I invite you to read them in this paper. In summary, penitentes form where snow is in contact with very dry and very cold air. As the sun shines, the snow absorbs the energy and heats up from inside, so much and so fast that the only way to be rid of that heat is by changing phase, directly from solid to water vapour (this is called sublimation). Since snow is anything but a smooth surface, sun rays will in fact be more concentrated at given locations on the snow, so that sublimation occurs only at specific points. But it is a self-amplifying mechanism: sublimation will leave a little crater behind in the snow, whose shape will concentrate even more the sun rays and lead to further sublimation. And this is how the penitentes get their shape.

 

Penitentes and the Atacama Pathfinder EXperiment (APEX) telescope. Photo: Babak Tafreshi/ ESO

Where is the link with Europa?

Hopefully by now, you are happy because you have just learnt about yet another weird-but-wonderful cryospheric phenomenon on Earth. But, remember how the post was about about Europa in the beginning? This is because researchers have recently analysed data from the past mission to Jupiter Galileo that might suggest that the conditions are right on Europa for penitentes to exist. They had to use the careful phrasing because the data resolution was not good enough to see the actual individual penitentes and had instead to rely on their thermic signature.

As reported in the media storm of these last two weeks (see here, here or here for example), this is an important discovery for the planning of future space missions. Which landing site to use? Play it safe and land far from these ice blades, or go and study them but risk destroying your lander? Either way, we shall continue reporting about the cryosphere, from this world and beyond…

Reference/Further reading

 

Edited by Clara Burgard

Do clouds affect melting over Antarctic ice shelves?

Schematic showing the effects of cloud microphysics on the radiative properties of clouds for shortwave solar radiation (a & b) and longwave terrestrial radiation (c & d) [Credit: Ella Gilbert].

The Antarctic Peninsula is the ‘canary in the coalmine’ of Antarctic climate change. In the last half-century it has warmed faster than most other places on Earth, and considerable change has consequently been observed in the cryosphere, with several ice shelves collapsing in part or in full. Representing this change in models is difficult because we understand comparatively little about the effect of atmospheric processes on melting in Antarctica, especially clouds, which are the main protagonists of this Image of the Week…


The Antarctic Peninsula: a part of the southern continent that is surrounded by ice shelves, but also a place that has seen rapid and dramatic changes in the last decades. Until recently, the Antarctic Peninsula was one of the most rapidly warming regions on Earth, with annual mean surface temperatures rising by as much as 2.5°C between the 1950s and early 2000s in some places (Turner et al., 2005; 2016).

That warming has been linked to the demise of the region’s ice shelves: since 1947, more than half of the peninsula’s ice shelves have thinned, lost area, or collapsed entirely (Cook & Vaughan, 2010). Most recently, that includes Larsen C, whose area was reduced by 12% in July 2017 following a calving event where an iceberg four times the size of London broke away from the ice shelf. As a result, the ice shelf has slipped down the rankings from the 4th largest ice shelf on the continent to the 5th largest.

 

What makes ice shelves melt?

Evidence suggests that ice shelves on the peninsula are being warmed mostly from the top down by the atmosphere. This is contrary to what’s happening on other Antarctic ice shelves, like those in West Antarctica that are being eroded from beneath by the warming ocean. Atmospheric processes are much more important over peninsula ice shelves than those elsewhere on the continent.

To understand the effect of the atmosphere on melting at the top of ice shelves, we need to know how much energy is entering the surface of the ice shelf, how much is leaving, and use what’s left over to determine whether there’s residual energy available to melt the ice. That’s the general principle of the surface energy balance, and it’s called a ‘balance’ because it is usually just that – the amount of energy flowing into and out of the ice shelf averages out over the course of say, a year, to produce a net zero sum of energy left for melting. However, there are times when this balance can become either negative, leading to growth of the ice shelf, or positive, leading to ice loss via melting.

 

What affects the surface energy balance?

Many different processes influence the surface energy balance, such as weather patterns and atmospheric motion. For instance, when warm, dry air blows over an ice surface, which happens during ‘foehn‘ wind events (German readers will know this means ‘hairdryer’: a descriptive name for the phenomenon!), this can produce a surplus of energy available for melting (Grosvenor et al., 2014; King et al., 2017; Kuipers Munneke et al., 2018). If the surface temperature reaches 0°C, melting occurs.

 

What do clouds have to do with it?

Clouds also greatly influence the surface energy balance by affecting the amount of radiation that reaches the surface. The amount of incoming solar (shortwave) radiation that reaches the surface, and the amount of terrestrial (longwave) radiation that escapes is affected by what stands in the way – clouds. Of course, this obstacle is important for the surface energy balance because it affects the balance between the energy flowing into and out of the surface. However, the fine-scale characteristics of clouds (aka ‘microphysics’) produce different, often interacting and sometimes competing, effects on the surface energy balance, some of which are shown in the schematic above. Examples of these properties include:

  • Water phase (how much ice and liquid there is)
  • Number concentration (how many particles)
  • Particle size
  • Ice crystal shape

The amount of ice and liquid in a cloud can affect how much energy it absorbs, reflects and emits – for instance, the more liquid a cloud contains, the more energy it emits towards the surface, because it is thicker and tends to be warmer than a cloud with lots of ice. However, clouds made up of lots of tiny liquid droplets also tend to be brighter than ice clouds containing larger crystals, which means they reflect more incoming solar radiation back into space. This example is a typical one where different microphysical properties cause competing effects, which makes them difficult to separate from each other.

 

Radiative forcing (RF, solid bars) and Effective radiative forcing (ERF, hatched bars) of climate change during the Industrial Era (1750-2011) [Credit: adapted from IPCC Fifth Assessment Report, Figure 8.15: pp. 697].

What do we know about Antarctic clouds?

The short answer is: not that much. Clouds are the largest source of uncertainty in our estimates of global climate change (check out the huge range of error in the estimates of cloud-driven radiative forcing in the figure above, from the IPCC’s most recent report), and the science of Antarctic clouds is even more unclear because we don’t have a great deal of data to base our understanding on. To measure clouds directly, we need to fly through them – a costly and potentially dangerous exercise, especially in Antarctica.

 

Flying through a gap in cloud near Jenny Island on the approach to Rothera research station, on the Antarctic Peninsula, at the end of a data collection flight in November 2017 [Credit: Ella Gilbert].

Filling the gap

In somewhere like Antarctica where we don’t have much observational data, we have to rely on other tools. That’s where computer models can be really useful – so long as we can be confident in the results they produce. Unfortunately, that’s part of the problem. Cloud properties and their effects on the surface energy balance are complex: we know that much. But modelling those properties is even more complex, because we have to simplify things to be able to turn them into computer code.

There is hope though! Recent studies (e.g. Listowski et al., 2017) have shown that models can more realistically represent Antarctic cloud microphysics if they use more sophisticated ‘double moment’ schemes, which are able to simulate more microphysical properties. With more accurate microphysics comes better representation of the surface energy balance, and improved estimates of melt over Antarctic ice shelves.

 

Further reading

  • On the effect of foehn on wintertime melting over Larsen C:

Kuipers Munneke, P., Luckman, A. J., Bevan, S. L., Gilbert, E., Smeets, C. J. P. P., Van Den Broeke, M. R., Wang, W., Zender, C., Hubbard, B., Ashmore, D., Orr, A. King, J. C. (2018). Intense winter surface melt on an Antarctic ice shelf. Geophysical Research Letters 45, 7615–7623. doi:10.1029/2018GL077899

  • On clouds in Antarctica:

Lachlan-Cope, T. (2010). Antarctic clouds. Polar Research 29 (2), 150–158. doi:10.1111/j.1751-8369.2010.00148.x

  • On modelling cloud microphysics over the Antarctic Peninsula:

Listowski, C., & Lachlan-Cope, T. (2017). The Microphysics of Clouds over the Antarctic Peninsula – Part 2: modelling aspects within Polar WRF. Atmospheric Chemistry and Physics 17, 10195-10221. doi:10.5194/acp-17-10195-2017

Edited by Clara Burgard


Ella Gilbert is a PhD student at the British Antarctic Survey, where she uses climate modelling and observational data to understand the drivers of melt on the Larsen C ice shelf. She’s a big fan of clouds, polar science, and science communication. You can find her on Twitter @Dr_Gilbz, on her website www.larsenc.com, or the old fashioned way by email.

Image of the Week – On thin [Arctic sea] ice

Thin, ponded sea ice floes in Nares Strait [Credit: Christopher Horvat and Enduring Ice]

Perhaps the most enduring and important signal of a warming climate has been that the minimum Arctic sea ice extent, occurring each year in September, has declined precipitously. Over the last 40 years, most of the Arctic sea ice has thus been transformed to first-year ice that freezes in the winter and melts in the summer.           
Concern about sea ice extent and area is valid: since sea ice is a highly reflective surface, a reduction of its area has a significant effect on the energy budget of Earth’s climate. Yet it is well-documented that, in the summertime, when sunlight is strongest, the biggest changes to sea ice volume are coming from effects not associated with changes to ice area, but with changes to sea ice thickness, like increased melt ponding. The change from thick, reflective multi-year summer sea ice to thin, ponded, less-reflective first-year ice are seen throughout the Arctic. In places like Nares Strait, the region of the Canadian Arctic that separates Canada from Greenland (seen above), commonly referred to as the “last ice area”, this is true as well.


The “Enduring Ice” Expedition

In the summer of 2016 and 2017, 4 filmmakers and a scientist (that’s me!) set out to examine Nares Strait, the area that separates Ellesmere Island in Canada from Northern Greenland (see map below). The Strait has been designated the “last ice area” by the World Wildlife Fund, a region which is expected to remain fully covered in thick sea ice even as the rest of the Arctic sea ice cover melts.

Nares Strait [Credit: Enduring Ice, LLC]

Yet when we arrived, what we found was anything but the promised land of thick, multi-year ice. Instead, all of the ice we encountered was thin, heavily ponded, and fragmented. In decades past, the presence of multi-year floes would dam Nares Strait, allowing ice-free passage for kayakers. Instead, the fractured ice poured through the strait, making passage impossible. Faced with an impassable strait, we resorted to pulling the kayaks over the land, moving a total of 100 km in 45 days.

The “Enduring Ice” Expedition [Credit: Christopher Horvat and Enduring Ice]

Most projections have the Arctic totally ice-free in September by 2050, meaning there will truly be no multi-year ice left at all. Yet as the Arctic still cools dramatically in winter, during the summer months (from May to July) when solar radiation is highest, the total area of the Arctic covered in sea ice is still high, but now covered by thin first-year ice. At the same time, the ongoing warming has thinned the Arctic sea ice by more than half (Kwok, 2008).

The albedo of first year ice can be half or less that of multi-year thicker ice (Light, 2008). Since the Arctic has thinned substantially over the last 40 years, the consequences of this thinning on the Arctic and Earth climate system are dramatic.

More and more solar radiation is absorbed by thinner ice. Excess solar absorption leads to ocean and atmospheric warming, and to more sea ice melting, a process known as the ice-albedo feedback. It was previously thought that regions covered by sea ice where inhospitable to photosynthetic life. However, thinning sea ice is likely responsible for the increase in phytoplankton blooms in the Arctic, as more light is transmitted through the thinner ice.

The Arctic sea ice cover is rapidly transitioning from thick, multi-year ice to thin, ponded, first-year sea ice.  As we can see, this thinning is resulting in a totally new Arctic climate system.

Further Reading

Edited by Violaine Coulon and Sophie Berger


Chris Horvat is a NOAA climate and global change postdoctoral fellow at Brown University in Providence, RI.  He tweets as @chhorvat and you can also reach him on his website.