CR
Cryospheric Sciences

Arctic

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 – Sea-ice dynamics for beginners

Image of the Week – Sea-ice dynamics for beginners

When I ask school children or people who only know about sea ice from remote references in the newspapers: ‘How thick do you think is the Arctic sea ice?’, I often get surprising answers: ’10 meters? No, it must be thicker – 100 meters!’. It seems like sea ice, often depicted as a uniform white cover around the North Pole and as a key element in accelerated warming of the Polar Regions, imposes a majestic image. Unfortunately, sea ice is much more fragile.


Growing in the current

Actually, sea ice is on average just about 2 m thick. It used to be thicker, up to 3 m, but such ice needs several winters to grow and is quite rare in the modern-day Arctic as winters are warmer than they used to be (see this previous post). Currently, more than half of the Arctic sea-ice area melts away completely during summer and grows back during the next winter. Such a thin layer of frozen water floating on the ocean is not strong enough to resist the forces of the wind, which pushes it around in ocean surface currents. In order for the ice to move, it has to deform and breaks into ice floes (read more in this previous post). Some ice floes move apart (divergence) in leads and polynyas (see this previous post), while others are pressed together (convergence) in pressure ridges, where blocks of ice pile up against and on top of each other (see our Image of the Week).

Ice grows from the ocean surface layer by water freezing. This is called thermodynamical growth. Thermodynamical growth produces most of the ice forming in the time from freeze-up in fall until the ice becomes about 1 to 2 m thick in mid-winter. At that point, sea ice approaches equilibrium thickness, i.e. the sea ice is thick enough to insulate the cold atmosphere from the relatively warm ocean. But because sea ice deforms, it can continue growing during the rest of the winter too. Pressure ridges sails can stick several meters out of the icy landscape, while their much larger and bulkier keels are hidden below the surface. Ridges can store large volume of sea ice – about a third (Hansen et al, 2013)! At the same time, new ice can grow in leads where open water is exposed to the atmosphere.

The following video is a collection of movies showing consequences and acts of sea-ice deformation. The first part is taken from R/V Lance – the ice-strengthened research ship of Norwegian Polar Institute, while she is navigating along a lead in late winter. Observe how much space is taken by pressure ridges! The second part of the movie shows a pressure ridge growing. Listen to the sound of deforming ice!

Another positive feedback

In winter, temperatures are so low that all the fractures, leads and pressure ridges freeze back – they heal. In summer, however, these damages are the first to appear again. Dark water with low albedo (read more about the albedo feedback in this post) is exposed and the ice melts faster in such regions. Because the Arctic sea ice became relatively thin over the recent decades, it also became less resistant to the forces of the wind. Such thin ice breaks more easily (e.g. Itkin et al, 2017). This means that, as more of such damaged ice is present in summer, the ice cover melts faster. So, here is an additional positive feedback for the Arctic ice under climate change: thinner ice melts faster also because it has become weaker and therefore breaks up easier.

Further reading

Edited by Clara Burgard


Polona Itkin is a Post-doctoral Researcher at the Norwegian Polar Institute, Tromsø. She investigates the sea ice dynamics of the Arctic Ocean and its connection to the sea ice thickness. In her work she combines the information from in-site observations, remote sensing and numerical modeling. Polona is part of the social media project ‘oceanseaiceNPI’ – a group of scientists that communicates their knowledge through social media channels:

Instagram.com/OceanSeaIceNPI, Twitter.com/OceanSeaIceNPI, Facebook.com/OceanSeaIceNPI, contact Email: polona.itkin@npolar.no

Image of the Week – Summer is fieldwork season at EastGRIP!

Image of the Week – Summer is fieldwork season at EastGRIP!

As the days get very long, summer is a popular season for conducting fieldwork at high latitudes. At the North East Greenland Ice Stream (NEGIS), the East Greenland Ice-core Project (EastGRIP) is ongoing. Several scientists are busy drilling an ice core through the ice sheet to the very bottom, in continuation to previous years (see here and here). This year, amongst others, several members from the European Research Council (ERC) supported synergy project ice2ice are taking part in the work at EastGRIP. Besides sleeping in the barracks that can be seen in our Image of the Week, the scientists enjoy the international and interdisciplinary setting and, of course, the work in a deep ice core drilling camp…


Life at the EastGRIP camp

In total, 22 people live in the camp (see Fig.2): 1 field leader, 5 ice core drillers, 4 ice core loggers, 3 people working with the physical properties of the ice, 2 are doing continuous water isotope analysis, 2 surface science scientists, 2 field assistants, and 1 mechanic, 1 electrical engineer and most important an excellent cook. We cover a variety of nationalities: British, Czech, Danish, French, German, Japanese, Korean, Norwegian, Russian and more. The crew changes every four weeks and the EastGRIP project aims to get as many young scientists (Master and PhD students) into camp as possible, so that it also works as a learning environment for new generations. In total, the number of people that have and will spent time at EastGRIP this season is almost 100, making it a buzzing science hub. This environment leads to extensive science discussions over the dinner table and therefore facilitates the interdisciplinary connections so vital in ice core science.

Fig.2: The current crew at EastGRIP dressed up for the Saturday party (tie and dress obligatory!) [Credit: EastGRIP diaries].

Science at the EastGRIP camp

The main aim of the EastGRIP project is to retrieve an ice core by drilling through the North East Greenland Ice Stream (NEGIS) up to a depth of 2550 m (!). Ice streams are responsible for draining a significant fraction of the ice from the Greenland Ice Sheet (see Fig. 3). We hope to gain new and fundamental information on ice stream dynamics from the project, thereby improving the understanding of how ice streams will contribute to future sea-level change. The EastGRIP project has many international partners and is managed by the Centre for Ice and Climate, Denmark with air support carried out by US ski-equipped Hercules aircraft managed through the US Office of Polar Programs, National Science Foundation.

Fig. 3: Ice velocities from RADARSAT synthetic aperture radar data are shown in color and illustrate the wedge of fast-flowing ice that begins right at the central ice divide and cuts through the ice sheet to feed into the ocean through three large ice streams (Nioghalvfjerds isstrømmen, Zachariae isbræ, and Storstrømmen). [Credit: EastGRIP, data from Joughin et al., 2010]

Currently, four Norwegian and Danish scientists from the ice2ice project have joined the EastGRIP project to conduct field work at the ice core drilling site. The ice2ice project focuses on how land ice and sea ice influence each other in past, present, and future. Thus, being at the EastGRIP site is a great opport

unity for us in ice2ice to learn more about how the fast-flowing ice stream in North East Greenland may influence the stability of the Greenland ice cap and to enjoy the collaborative spirit at an ice core drilling site.

 

This year’s fieldwork at EastGRIP started in May and will continue until August. We aim to make it through the brittle zone of the ice. This is a zone where the gas bubbles get enclosed in the ice crystals and thus the ice is, as the name indicates, more brittle than at other depths. Unfortunately for us, the brittle zone makes it very hard to retrieve the ice in a great quality. This is because of the pressure difference between the original depth of the ice and the surface, that causes the ice to fracture when it arrives at the surface. We are doing our very best to stabilize the core and several optimizations in terms of both drilling and processing of the ice core are being applied.

Fig. 4: Cross-section view of an ice core [Credit: Helle Astrid Kjær].

Still, a large part of the core can already be investigated (see Fig. 4) for water isotopes to get information about past climate. Also, ice crystals directions are being investigated through thin slices of the ice core to help better understanding the flow of the NEGIS. On top of the deep ice core, which is to be drilled to bedrock over the coming years, we are doing an extensive surface program to look at accumulation changes.

In the large white plains…

Despite all the fun science and people, when you are at EastGRIP for more than 4 weeks, you have a very similar landscape everyday and can miss seeing something else than just the great white. About a week ago, a falcon came by to remind us of the rest of the world (see Fig. 5). It flew off after a couple of days. We will follow its path to the greener parts of Greenland when we will soon fly down to Kangerlussuaq. Someone else will then take over our job at EastGRIP and enjoy the wonders of white…

Fig.5: Visit of a falcon [Credit: Helle Astrid Kjær].

Further reading

Edited by Clara Burgard


Helle Astrid Kjær is a postdoc at the Centre for Ice and Climate at the Niels Bohr Institute at University of Copenhagen. When she is not busy in the field drilling and logging ice cores, she spends most of her time in the lab retrieving the climate signal from ice cores. These include volcanic events, sea salts, dust with more by means of Continuous Flow Analaysis (CFA). Further she is hired to manage the ice2ice project.

Image of the Week — High altitudes slow down Antarctica’s warming

Elevations in Antarctica. The average altitude is about 2,500m. [Credit: subset of Fig 5 from Helm et al (2014)]

When it comes to climate change, the Arctic and the Antarctic are poles apart. At the north of the planet, temperatures are increasing twice as fast as in the rest of the globe, while warming in Antarctica has been milder. A recent study published in Earth System Dynamics shows that the high elevation of Antarctica might help explain why the two poles are warming at different speeds.


The Arctic vs the Antarctic

At and around the North Pole, in the Arctic, the ice is mostly frozen ocean water, also known as sea ice, which is only a few meters thick. In the Antarctic, however, the situation is very different: the ice forms not just over sea, but over a continental land mass with rugged terrain and high mountains. The average height in Antarctica is about 2,500 metres, with some mountains rising as high as 4,900 metres.

A flat Antarctica would warm faster

Mount Jackson in the Antarctic Peninsula reaches an altitude of 3,184 m  [Credit: euphro via Flickr]

Marc Salzmann, a scientist working at the University of Leipzig in Germany, decided to use a computer model to find out what would happen if the elevation in Antarctica was more like in the Arctic. He discovered that, if Antarctica were flat, there would be more warm air flowing from the equator to the poles, which would make the Antarctic warm faster.

As Antarctica warms and ice melts, it is actually getting flatter as time goes by, even if very slowly. As such, over the next few centuries or thousands of years, we could expect warming in the region to speed up.

Reference/further reading

planet_pressThis is modified version of a “planet press” article written by Bárbara Ferreira and originally published on 18 May 2017 on the EGU website
(a Serbian version is also available, why not considering adding a new language to the list? 🙂 )

Image of the Week – Heat waves during Polar Night!

Fig. 1: (Left) Evolution of 2-m air temperatures from a reanalysis over December 2016. (Right) Time series of temperature at the location of the black cross (Svalbard). Also shown is the 1979-2000 average and one standard deviation (blue). [Credit: François Massonnet ; Data : ERA-Interim]

The winter 2016-2017 has been one of the hottest on record in the Arctic. In our Image of the Week, you can see that air temperatures were positive in the middle of the winter! Let’s talk about the reasons and implications of this warm Arctic winter. But first, let’s take a tour in Svalbard, the gateway to the Arctic…

A breach in the one of the world’s largest seed vaults

The Global Seed Vault on Svalbard (located at the black cross in our Image of the Week) is one of the world’s largest seed banks. Should mankind face a cataclysm, 800,000 copies of about 4,000 species of crops can safely be recovered from the vault. Buried under 120 m of sandstone, located 130 m above sea level, and embedded inside a thick layer of permafrost, the vault can withstand virtually all types of catastrophe – natural or man-made. This means, for example, that it is high enough to stay above sea level in case of a large sea-level rise, or that it is far enough from regions that might be affected by nuclear warfare. But is it really that safe? Last winter, vault managers reported water flooding at the entrance of the cave, after an unexpected event of permafrost melt in the middle of polar night. Not enough to put the seeds at risk (they are safely guarded in individual chambers deeper in the mountainside), but worrying enough to raise concern about how, and why such an event happened…

Fig. 2: Entrance of the Svalbard Global Seed Vault. [Credit: Dag Terje Filip Endresen, Wikimedia Commons ].

Soaring temperatures in the Arctic

The Arctic region is often dubbed the “canary in the coal mine” for climate change: near-surface temperatures there have risen at twice the pace of the world’s average, mainly due to the process of “Arctic Amplification whereby positive feedbacks enhance greatly an initial temperature perturbation. Increases in lower-troposphere Arctic air temperatures have occurred in conjunction with a dramatic retreat and thinning of the sea-ice cover in all seasons, a decrease of continental spring snow cover extent, and significant mass loss from glaciers and ice sheets (IPCC, 2013)

Winter temperatures above freezing point

The last two winters (2015-2016 and 2016-2017) have been particularly exceptional. As displayed in our Image of the Week for winter 2016-2017 and here for 2015-2016 (see also two news articles here and here for an accessible description of the event), temporary intrusions of relatively warm air pushed air temperatures above freezing point in several parts of the Arctic, even causing sea ice to “pause” its expansion at a period of the year where it usually grows at its fastest rate (see Fig. 3).

Fig.3 : Mean Arctic sea ice extent for 1981 to 2010 (grey), and the annual cycles of 1990 (blue), and 2016-2017 (red and cyan, respectively). [Credit: National Snow and Ice Data Center. Interactive plotting is available here ]

Cullather et al. (2016) and Overland and Wang (2016) conducted a retrospective analysis of the 2015-2016 extreme winter and underlined that the mid-latitude atmospheric circulation played a significant role in shaping the observed temperature anomaly for that winter (see also this previous post). Scientists are still working to analyse the most recent winter temperature anomaly (2016 – 2017).

Unusual?

How unusual are such high temperatures in the middle of the boreal winter? It is important to keep in mind that the type of event featured in our Image of the Week results from the superposition of weather and climate variability at various time scales, which must be properly distinguished. At the synoptic scale (i.e., that of weather systems, several days), the event is not exceptional. For example, a similar event was already reported back in 1975! It is not surprising to see low-pressure systems penetrate high up to the Arctic.

At longer time scales (several months), the observed temperature anomaly in the recent two winters is more puzzling. The winter 2015-2016 configuration appears to be connected with changes in the large-scale atmospheric circulation (Overland and Wang, 2016). To understand the large-scale atmospheric circulation, scientists like to map the so-called “geopotential heightfield for a given isobar, that is, the height above sea level of all points with a given atmospheric pressure. The geopotential height is a handy diagnostic because, in a first approximation, it is in close relationship with the wind: the higher the gradient in geopotential height between two regions, the higher the wind speed at the front between these two regions. The map of geopotential height anomalies (i.e., deviations from the mean) for the 700 hPa level in December (Fig. 4) is suggestive of the important role played by the large-scale atmospheric circulation on local conditions. The link between recent Arctic warming and mid-latitude atmospheric circulation changes is a topic of intense research.

Fig.4: Anomaly in 700 hPa geopotential height, December 2016 (with regard to the reference period 1979-2000) [Credit: François Massonnet; Data: ERA-Interim]

Finally, at climate time scales (several years to several decades), this event is not so surprising: the Arctic environment has changed dramatically in the last few decades, in great part due to anthropogenic greenhouse gas emissions. With a warmer background state, there is higher probability of winter air temperatures surpassing 0°C if synoptic and large-scale variability positively interact with each other, as seems to have been the case during the last two winters.

What does this mean for future winters?

The rapid transformation of the Arctic is already having profound implications on ecosystems (Descamps et al., 2016) and indigenous populations (e.g., SWIPA report). To a larger extent, it can potentially affect our own weather: we polar scientists like to say that “what happens in the Arctic, does not stay in the Arctic”. The unusual summers and winters that large parts of Europe, the U.S. and Asia have experienced in recent years might be related to the rapid Arctic changes, according to several scientists – but there is no consensus yet on that matter. One thing is known for sure: the last two winters have been the warmest on record, but this might just be the beginning of a long chain of more extreme events…

Further reading

Edited by Scott Watson and Clara Burgard


François Massonnet is a F.R.S.-FNRS Post-Doctoral Researcher at the Université catholique de Louvain and affiliated at the Barcelona Supercomputing Center (Spain). He is assessing climate models as tools to understand (retrospectively and prospectively) polar climate variability and beyond. He tweets as @FMassonnet. Contact Email: francois.massonnet@uclouvain.be

Image of the Week – Ice Ice Bergy

Image of the Week – Ice Ice Bergy

They come in all shapes, sizes and textures. They can be white, deep blue or brownish. Sometimes they even have penguins on them. It is time to (briefly) introduce this element of the cryosphere that has not been given much attention in this blog yet: icebergs!


What is an iceberg?

Let’s start with the basics. An iceberg, which literally translates as “ice mountain”, is a bit of fresh ice that broke off a glacier, an ice shelf, or a larger iceberg, and that is now freely drifting in the ocean. As an approximation, you can consider that since an iceberg is already in the water (about 90% under water even), its melting does not contribute to sea-level rise. However, if you remember our Sea Level “For Dummies” post, you know that the melting of fresh ice reduces the ocean’s density and makes it expand. Icebergs are found at both poles, although they tend to be larger in the Southern Ocean. The largest iceberg ever spotted there was 335 by 97 km, which represents an area larger than Belgium !

Modelled trajectories of icebergs around Antarctica. The different colours represent different size classes, ranging from 0-1 km² (class 1) to 100-1000 km² (class 5). [Credit: subset of Fig 2 from Rackow et al (2017)]

Icebergs can drift over thousands of kilometres (Rackow et al., 2017), during several years. A more thorough account of the life of an iceberg will be given in a future post, but be aware that among other things, as it drifts:

  • The iceberg is eroded by the waves and melted by the relatively warm ocean;
  • It can split in several pieces because of this melting and mechanical stress;
  • Sea ice can freeze around it, trapping it in the pack ice.

This means that the iceberg changes shape a lot, and can be tricky to monitor (Mazur et al, 2017).

Why do we want to monitor icebergs?

You may have heard of the Titanic, and hence are aware that icebergs pose a risk for navigation not only in the polar regions but even in the North Atlantic. Icebergs also are large reservoirs of freshwater, and depending on how and where they melt, this inflow of melted freshwater can really affect the ocean; it even dominates the freshwater budget in some Greenland fjords (Enderlin et al., 2016).

Icebergs have traditionally been rather understudied, so we are only now discovering how important they are and how they interact with the rest of the climate system: increasing sea ice production (A. Mazur, PhD thesis, 2017), biological activity (Vernet et al., 2012), and even carbon storage (Smith et al., 2011). And sometimes, they have penguins on them!

All eyes in the CryoTeam are now turned to the Antarctic Peninsula, where a giant iceberg may detach from the Larsen C ice shelf soon. To learn how we know that, check this video made by ESA. And of course, continue reading us – we’ll be reporting about the birth of this monster berg!

An iceberg by Antarctica [Credit: C. Heuzé]

Edited by Sophie Berger

Further reading

  • Enderlin et al. (2012), Iceberg meltwater fluxes dominate the freshwater budget in Greenland’s iceberg-congested glacial fjords, Geophysical Research Letters, doi:10.1002/2016GL070718

  • Mazur et al. (2017), An object-based SAR image iceberg detection algorithm applied to the Amundsen Sea, Remote Sensing of Environment, doi:10.1016/j.rse.2016.11.013

  • Rackow et al. (2017), A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates, Journal of Geophysical Research: Oceans, doi: 10.1002/2016JC012513
  • Smith et al. (2011), Carbon export associated with free-drifting icebergs in the Southern Ocean, Deep Sea Research, doi: 10.1016/j.dsr2.2010.11.027
  • Vernet et al. (2012), Islands of Ice: Influence of Free-Drifting Antarctic Icebergs on Pelagic Marine Ecosystems, Oceanography, doi:10.5670/oceanog.2012.72

Image of the Week – The ups and downs of sea ice!

Image of the Week – The ups and downs of sea ice!

The reduction in Arctic sea-ice cover has been in the news a lot recently (e.g. here) – as record lows have been observed again and again within the last decade. However, it is also a topic which causes a lot of confusion as so many factors come into play. With this Image of the Week we will give you a brief overview of the ups and downs of sea ice!


In general, Arctic sea ice is at its minimum extent at the end of the summer (September), and its maximum extent at the end of the winter (March). Our Image of the Week (Fig. 1) shows the summer and winter sea ice cover over the last year. In September 2016, the Arctic sea-ice minimum covered the second smallest extent since the beginning of satellite observations (38 years). Only 4.14 million square kilometres of the Northern Hemisphere were covered by sea ice on the day of minimum extent (September 10th). The maximum sea-ice extent was observed on March 7th 2017, only 14.42 million square kilometres of sea ice were observed: the lowest maximum since the beginning of satellite observations.

How long do we have until Arctic summer sea-ice cover is completely gone?

The Arctic Ocean is defined as ice-free, when the sea-ice area does not exceed 1 million km². Due to the close relationship between CO2 emissions and the sea-ice area (see one of our previous posts), it is likely that the summer Arctic sea-ice cover will fall below this threshold during the 21st century. Under the highest emission scenario (RCP 8.5 – IPCC, 2015), an almost ice-free Arctic in September is likely to occur before the middle of the century. It is, however, not easy to predict the exact year of an ice-free Arctic summer as the extent of the ice cover depends on many parameters influencing the freezing and melting of the ice.

On one hand, some parameters and their effect on the sea-ice cover are well understood and their future evolution can be projected quite well through climate models. For example, changes in the sea surface temperature tend to affect the starting date of the freezing period while changes in air temperature tend to affect the starting date of the melting period. As both air temperature and sea surface temperature are projected to increase in the long term, due to climate change, the period where ice can be present will be reduced more and more.

On the other hand, some parameters lead to several concurring effects, which are difficult to separate clearly and not always fully understood. Therefore, their future evolution and influence on sea ice is not totally clear. For example, the sea-ice loss leads to more open ocean areas, which absorb solar radiation, causing warming and therefore leading to faster sea-ice melting – a mechanism called “sea-ice albedo feedback”. At the same time, more open ocean areas also lead to more evaporation and therefore more clouds, which shield the ice from solar radiation and therefore lead to less warming of the ice and ocean surfaces.

Still, even if we knew the effect and long-term evolution of all these parameters, the exact date of ice-free Arctic could not be defined easily in advance. Why? The chaotic nature of the atmosphere leads to very short-term effects that influence the ice cover as well…

Be careful! A record minimum does not always mean a record maximum (and vice versa)!

On shorter time scales, sudden changes in the atmospheric circulation can have a large impact on sea-ice extent. Therefore, it is not guaranteed that a year with a record low maximum will have a record low minimum and vice versa. For example, heat waves and warm air outbreaks or high winds due to the transport of low pressure systems into the Arctic can lead to a more rapid decline of the sea-ice cover. The other way round, if the atmosphere from lower latitudes does not disturb the Arctic region, the sea-ice cover can stabilise again.

What about this year (2016/2017 season)?

Sometimes, it is not clear why sea-ice retreats rapidly. For example, the low 2016 minimum came as a surprise as the cover started with a very low minimum but then did not melt as fast as in previous years, due to average or below average temperatures. Only shortly before the minimum extent, stormy conditions came into play and led to the low extent that was observed (see Fig. 2).

Figure 2: Comparison of Arctic sea-ice extent between different years for summer (left) and winter (right). [Credit: Image courtesy of the National Snow and Ice Data Center]

The reasons for the record low 2017 maximum are better understood. The Arctic Ocean was not covered by much ice to begin. Then, the autumn and winter in the Arctic were very warm with air temperatures from October 2016 to February 2017 being from 2.5 to up to 5 degrees in some regions higher than on average.

From the Arctic to the Antarctic

In the last decades, although it recovered in some years between the record lows, the Arctic sea-ice cover has overall been declining. This is not the case on the other side of the planet, in Antarctica. Note that Antarctica is a complete different setting than the Arctic Ocean. The former being a continent surrounded by ocean and sea ice, the latter being an ocean with sea ice surrounded by continents.

Figure 3: Comparison of Antarctic sea-ice extent between different years for summer (left) and winter (right). [Credit: Image courtesy of the National Snow and Ice Data Center]

In recent decades, Antarctic sea-ice has been increasing very slowly (see Fig.3). Scientists were puzzled as such an evolution was not expected in a global warming framework. Explanations for this behaviour are that this is likely due to changing wind and surface pressure patterns around Antarctica. Contrary to this trend, this year (2016/2017) was a record low maximum and minimum in Antarctic sea-ice cover. This change is puzzling scientists even more. It remains unclear up to now if this is a permanent shift in the tendency of Antarctic sea ice or if this a single event. Be sure that the next months will be full of papers trying to explain this change in behaviour, it is going to be exciting!

Further reading

Edited by Emma Smith

Image of the Week — The ice blue eye of the Arctic

Image of the Week — The ice blue eye of the Arctic

Positive feedback” is a term that regularly pops up when talking about climate change. It does not mean good news, but rather that climate change causes a phenomenon which it turns exacerbates climate change. The image of this week shows a beautiful melt pond in the Arctic sea ice, which is an example of such positive feedback.


What is a melt pond?

The Arctic sea ice is typically non-smooth, and covered in snow. When, after the long polar night, the sun shines again on the sea ice, a series of events happen (e.g. Fetterer and Untersteiner, 1998):

  • the snow layer melts;

  • the melted snow collects in depressions at the surface of the sea ice to form ponds;

  • these ponds of melted water are darker than the surrounding ice, i.e. they have a lower albedo. As a result they absorb more heat from the Sun, which melts more ice and deepens the pond. Melt ponds are typically 5 to 10 m wide and 15 to 50 cm deep (Perovich et al., 2009);

  • eventually, the water from the ponds ends up in the ocean: either by percolation through the whole sea-ice column or because the bottom of the pond reaches the ocean. Sometimes, it can also simply refreeze, as the air temperatures drop again (Polashenski et al., 2012).

Melt ponds cover 50-60% of the Arctic sea ice each summer (Eicken et al., 2004), and up to 90% of the first year ice (Perovich al., 2011). How do we know these percentages? Mostly, thanks to satellites.

Monitoring melt ponds by satellites

Like most phenomena that we discuss on this blog, continuous in-situ measurements are not feasible at the scale of the whole Arctic, so scientists rely on satellites instead. For melt ponds, spectro-radiometer data are used (Rösel et al., 2012). These measure the surface reflectance of the Earth i.e. the proportion of energy reflected by the surface for wavelengths in the visible and infrared (0.4 to 14.4 μm). The idea is that different types of surfaces reflect the sunlight differently, and we can use these data to then map the types of surfaces over a region.

In particular for the Arctic, sea ice, open ocean and any stage in-between all reflect the sunlight differently (i.e. have different albedos). The way that the albedo changes with the wavelength is also different for each surface, which is why radiometer measurements are taken for a range of wavelengths. With these measurements, not only can we locate the melt ponds in the Arctic, but even assess how mature the pond is (i.e. how long ago it formed) and how deep it extends. These values are key for climate change predictions.

Fig. 2: Melt pond seen by a camera below the sea ice. (The pond is the lighter area) [Credit: NOAA’s climate.gov]

Melt ponds and the climate

Let’s come back to the positive feedback mentioned in the introduction. Solar radiation and warm air temperature create melt ponds. The darker melt ponds have a higher albedo than the white sea ice, so they absorb more heat, and further warm our climate. This extra heat is also transferred to the ocean, so melt pond-covered sea ice melts three times more from below than bare ice (Flocco et al., 2012). This vicious circle heat – less sea ice – more heat absorbed – even less sea ice…, is called the ice-albedo feedback. It is one of the processes responsible for the polar amplification of global warming, i.e. the fact that poles warm way faster than the rest of the world (see also this post for more explanation).

The ice-albedo feedback is one of the processes responsible for the polar amplification of global warming

But it’s not all doom and gloom. For one thing, melt ponds are associated with algae bloom. The sun light can penetrate deeper through the ocean under a melt pond than under bare ice (see Fig. 2), which means that life can develop more easily. And now that we understand better how melt ponds form, and how much area they cover in the Arctic, efforts are being made to include more realistic sea-ice properties and pond parametrisation in climate models (e.g. Holland et al., 2012). That way, we can study more precisely their impact on future climate, and the demise of the Arctic sea ice.

Edited by Sophie Berger

Further reading

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Image of the Week – For each tonne of CO2 emitted, Arctic sea ice shrinks by 3m² in summer

Declining sea ice in the Arctic is definitely one of the most iconic consequences of climate change. In a study recently published in Science, Dirk Notz and Julienne Stroeve find a linear relationship between carbon dioxide (CO2) emissions and loss of Arctic sea-ice area in summer. Our image of this week is based on these results and shows the area of September Arctic sea ice lost per inhabitant due to CO2 emissions in 2013.


What did we know about the Arctic sea ice before this study?

Since the late 1970s, sea ice has been dramatically shrinking in the Arctic, losing 3.8% of its area per decade. Sea-ice area is at its minimum in September, at the end of the melting season.

The main cause of this loss is the increase in surface temperature over the recent years (Mahlstein and Knutti, 2012), which has been more pronounced in the Arctic compared to other regions on Earth (Cohen et al., 2014). The use of statistical methods involving both observations and climate models shows that the recent warming in the Arctic can be attributed to human activity, i.e. mainly greenhouse gas emissions (Gillett et al., 2008). This suggests a direct link between human activity and Arctic sea-ice loss, which is confirmed in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

How exactly is sea-ice loss related to CO2 emissions ?

Notz and Stroeve (2016) relate the Arctic sea-ice decline to cumulative CO2 emissions since 1850 (i.e. the total amount of CO2 that has been emitted since 1850) for both observations and climate models. Cumulative CO2 emissions constitute a robust indicator of the recent man-made global warming (IPCC, 2014).

The two quantities are clearly linearly related (see Figure 2). From 1953 to 2015, about 3.5 million km² of Arctic sea ice have been lost in September while 1200 gigatonnes (1 Gt = 10e9 tonnes) of CO2 have been emitted to the atmosphere. This means that for each tonne of CO2 released into the atmosphere, the Arctic loses 3 m² of sea ice.

Fig 2: Monthly mean September Arctic sea-ice area against cumulative CO2 emissions since 1850 for the period 1953-2015. Grey circles and diamonds show the results from in-situ (1953-1978) and satellite (1979-2015) observations, respectively. The thick red line shows the 30-year running mean and the dotted red line represents the trend of 3 m² sea-ice area loss per tonne of CO2 emitted. [Credit: D. Notz, National Snow and Ice Data Center ]

Starting from the relationship between cumulative CO2 emissions and sea-ice area, it is then easy to attribute to each country in the world their own contribution to sea-ice loss based on their CO2 emissions per capita. The countries that stand out in the map are thus the countries emitting the most in relation to their population.

Could the Arctic be ice-free in the future?

If this relationship holds in the future (in other words, if we extend the red dotted line to zero sea-ice area in Figure 2), adding 1000 Gt of CO2 in the atmosphere would free the Arctic of sea ice in September. Since we are currently emitting about 35 Gt CO2 per year, it would take less than 30 years to have the Arctic free of sea ice in the summer (which confirms previous model studies (e.g. Massonnet et al., 2012)).

Edited by Clara Burgard and Sophie Berger

Further reading

DavidDavid 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.

Polar Exploration: Perseverance and Pea Sausages

Polar Exploration: Perseverance and Pea Sausages

Born on this Day

Portrait of Ludvig Mylius-Erichsen by Achton Friis. [Credit: Danish Arctic Institute].

On this day in 1872 – 145 years ago –Ludvig Mylius-Erichsen, Danish author and polar explorer, was born. He led two expeditions to Greenland and successfully mapped the then unknown northeastern part of the country. The second expedition was his last. The expedition was surprised by an early onset of spring and could no longer use their dog sledges. The two Danes, Mylius-Erichsen and Høeg Hagen died in November 1907 of cold and hunger. Their bodies have never been found. The last remaining expedition member, the Greenlander Brønlund, continued the journey alone but perished a few weeks later. His body and the expedition diary was found in 1908.

Thousands of Pea Sausages

The tin on the image above contains “pea sausage” and was essentially the world’s first ready meal: A mixture of ground peas, beef fat, bacon, spices and salt. Pea sausage was invented in 1867 in Germany and was a common part of military and expedition rations up until the beginning of the 20th century.

Mylius-Erichsen’s expedition brought along 1756 tins of this kind. Each tin contained 6 tablets of pea sausage, that mixed with ¼ water would make a nourishing soup. And the taste? On his first expedition, Mylius-Erichsen wrote:

“The evening meals in the three boxes consisted mainly of different kinds of sturdy soups, black pudding, meat pie, beef, pea sausage and sizeable portions of vegetable such as cabbage, beans and carrots. We only used one third of the evening meal rations on the way out. We did not like the taste of the meat but black pudding, peas and the different kinds of soup were heavenly”.

And later:

“Jørgen and I had dinner at Amarfik’s, and dinner consisted both days of little auks boiled in our last portion of pea sausage – a wonderful dish…”

Members of Mylius-Erichsen’s first expedition: Brønlund, Bertelsen, Mylius-Erichsen, Rasmussen and Moltke. [Credit: Danish Arctic Institute].

Photos and descriptions are from the Danish Arctic Institute (@arktiskinstitut) where you can also see a full 360 degrees photo of the tin.

Check out more historical footage from Greenland in a previous Image of the Week showing aerial photos from the 1930s.

Edited by: Sophie Berger