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Ice-hot news: The IPCC Special Report on the Oceans and the Cryosphere under Climate Change

Ice-hot news: The IPCC Special Report on the Oceans and the Cryosphere under Climate Change

You have probably heard the name “Intergovernmental Panel on Climate Change (IPCC)” mentioned frequently over the last few years. The IPCC is the United Nations body for assessing science related to climate change and it publishes global assessment reports on this topic every 5 to 10 years. Due to the current urgency of the global climate crisis and the need for more information by decision makers, the IPCC decided to publish several smaller more “special” reports between its fifth (published in 2013/2014) and sixth (planned for 2021/2022) assessment reports. The Special Report on the Oceans and the Cryosphere in a changing Climate (short “SROCC”) was published about a month ago. In this blog post, we will give you an overview of the take-home messages about the fate of the  cryospheric elements of our planet – those parts which are frozen!


Why is there a special report about ocean and cryosphere?

Discussions about global warming are often centered around changes in air temperature and changes in places where people live. The cryosphere and the ocean are, by contrast, remote areas without dense human population. However, climate change has a high impact on the cryosphere and oceans and this, in turn, has an effect on places where people live, one prominent example of this being land loss due to sea-level rise. Less talked about but equally impactful, is thawing permafrost, leading to high carbon release to the atmosphere, and melting Arctic sea-ice cover, enhancing Arctic Amplification, which can influence climate in mid-latitudes and globally.

The Special Report on Oceans and the Cryosphere in a changing Climate (SROCC) has the aim of highlighting the links between oceans, cryosphere and sea-level rise to improve policy makers’ understanding of these key elements and of the interdependencies between them (see Fig. 2). This is particularly critical at present, as the 25th Conference of Parties (COP25), organized by the United Nations Climate Change Convention, will be happening in around one month’s time in Santiago de Chile.

Fig. 2: Summary of the changes discussed in the IPCC Special report on the Oceans (white circles) and the Cryosphere (grey circles) under Climate Change [Credit: Box 1, Figure 1 in SROCC].

The Special Report is based on peer-reviewed literature from natural sciences, social sciences and humanities. It represents the most current scientific view on the oceans and the cryosphere. But what exactly are the conclusions of this report and why is it important? This post will guide you through the key points relevant to the cryosphere: permafrost, snow cover, glaciers and ice sheers, and sea ice!

Info box: What is an RCP scenario?

In IPCC reports, the projections for the future climate evolution are conducted using scenarios for the future greenhouse gas emissions. As we do not know how our economy, agriculture, and greenhouse gas emissions will evolve in the future, scientists have developed so-called Representative Concentration Pathways (RCP). Each RCP represents one of several possible futures in economic and agricultural development, resulting in different evolutions in atmospheric greenhouse gases. The higher the concentration of atmospheric greenhouse gases, the more of the heat radiated to space by the Earth’s surface is trapped, leading to a warming of the atmosphere. RCP2.6 represents a future where we radically cut greenhouse gas emissions after a peak in 2020,  RCP4.5 a scenario, where we cut emissions after a peak in 2040, and RCP8.5 represents a scenario in which greenhouse gas levels continue to rise.

Permafrost

Permafrost – ground, which is soil or rock frozen for more than two years in a row – contains one third of global near-surface carbon stocks, and thawing of parts of the permafrost-affected area can render this carbon more available for microorganisms, thus causing emissions of stored carbon as the greenhouse gases CO2 and CH4. This additional source of greenhouse gases could cause more surface warming, thus more permafrost thaw, thus more warming and so on (Mu et al., 2017; Sun et al., 2018a).

Because ice is solid, but water drains away, permafrost thaw can cause changes in the surface (subsidence) in Northern land areas, thus damaging infrastructure and buildings. Thaw can further cause landslides or increase rockfall rates, thus risking mountain accidents and the safety of local communities (PERMOS, 2016).

The IPCC reports that permafrost temperatures have increased by 0.29°C ± 0.12°C from 2007 to 2016 on average for polar and high mountain areas. Sparse long-term data series in heterogeneous alpine environments is the largest challenge faced when quantifying temperature trends in alpine permafrost, which makes up about 28 % of global permafrost, but estimates show a 0.19°C ± 0.05 °C warming per decade in alpine permafrost on average.

Arctic long time series are sparse, but estimates show that from 2007 to 2016, the coldest permafrost areas have warmed by 0.39 °C ± 0.15 °C, whereas the ‘warmer’ permafrost close to thaw has warmed on average by 0.2 °C ± 0.10 °C – more energy has been used for melting of ice.

Fig. 3: Left: Trend in annual average temperatures in high-mountain regions divided into geographical regions and ground material [Credit: Figure 2.5 in the SROCC. Right: Projections for global permafrost area following emission scenarios RCP 2.6, RCP4.5 and RCP8.5 [Credit: Figure 3.10 in the SROCC].

The Special Report concludes that the frequency and intensity of wildfires has increased, removing the organic topsoil and degrading permafrost faster than historically. Read more about fire in the Arctic in this post.

The amount of projected permafrost thaw by 2100 is directly related to the RCP scenario followed by humanity (see explanatory box on RCPs). Overall, permafrost occurrence is projected to be reduced by 8 to 40% for the low-emission scenario RCP 2.6 and 49 to 89 % for the high-emission scenario RCP8.5. While the Arctic permafrost within the first three meters of the surface is projected to have decreased by 2 to 66 % in RCP2.6 and by 30 to 99 % in RCP8.5, the permafrost area of the Tibetan plateau is projected to decrease by 22 % in 2100 under RCP2.6 by 64 % in RCP8.5. In conclusion, if we follow the high-emission scenario RCP8.5, tens to hundreds of gigatons of carbon will be released to the atmosphere by 2100.

The reason for the large intervals of projections are mainly that “translating” air temperature to a ground temperature, hence permafrost presence or absence, is a difficult task due to the impact of surface properties, such as snow depth and vegetation, and ground properties, such as ground ice and carbon content, on energy propagation into and out of the soil surface. IPCC projections are based on a comparison of many models for a more robust estimate – and they simulate precipitation and vegetation patterns differently, thus impacting the simulated permafrost area.

For communities in permafrost regions, for whom 70 % of local infrastructure will be at risk of damage due to permafrost thaw by 2050, short- and long term adaptation and mitigation measures need to complement each other. Measures need to be developed with the use of scientific and local knowledge from Northern communities, and local ecosystem monitoring can be a key data source for this.

You can find full details about permafrost changes in the SROCC Section 2.2.4 and 3.4.

Snow cover

Snow cover is a critical element of the cryosphere, firstly because it absorbs surface runoff from glacier and ice sheet surfaces, and secondly because it has a high albedo, meaning that it reflects more incoming solar radiation than the darker surfaces they cover, such as ground, trees, and ice. Snow covers the terrestrial Arctic (north of 60 ºN) for up to nine months each year, and influences the surface energy budget (through its reflectivity), freshwater budget (through water storage and release), ground thermal regime (through insulation) and ecosystem interactions.

Since the beginning of the satellite era in 1981, spring snow cover extent has declined by over 13% per decade. Snow cover duration has also declined, both in spring (by up to 3.9 days per decade in certain regions) and autumn (by up to 1.4 days per decade in certain regions). Maximum snow depth has been declining, though trends are uncertain because of sparse observations and large spatial variability. These reductions are very likely driven by surface temperature rise in the Arctic. Warming-induced snow cover reduction creates a self-reinforcing cycle where the surface is darker than when it is snow covered and therefore reflects less incoming solar radiation, leading to a warmer surface and even more melting.

Fig. 4: Observed changes in June snow cover extent anomalies, and projected change in June snow cover under low (RCP2.6, blue), medium (RCP4.5) and high (RCP8.5) greenhouse gas emissions scenarios [Credit: Figure 3.10 in the SROCC]

Arctic snow cover duration is projected to decrease (later autumn onset in and earlier spring melting), as a result of continued Arctic-wide warming. However, trends differ between model scenarios. For example, Arctic snow cover duration stabilizes by the end of the century under RCP4.5, whereas under RCP8.5 it declines to -25% (compared to the period 1986 – 2005). In Greenland, snow cover is projected to retreat to higher, flatter areas of the ice sheet. The rate at which this could occur is currently not well reproduced in climate models, mostly due to uncertainty in the way snow processes are included in these models.

Snow cover reductions are already being felt negatively in the Arctic, especially by communities reliant on snow cover for food sources, drinking water, and livelihoods, such as reindeer herding.

You can find full details of the estimates and predictions for ice sheets in SROCC, section 3.4 and in FAQ 3.1.

Sea ice

Sea ice is frozen sea water and displaces as much water as is produced when it melts. Melting sea ice therefore does not play a role for sea-level rise. It is, however, an important element for climate as it reflects large amounts of incoming sunlight back to space (similar to snow); it provides habitat for bacteria, plants and animals below, in, and above the ice; and it influences weather in mid-latitudes, the region between roughly 30 and 60 degrees of latitude, home to over 50% of the human population.

In the context of climate change, sea ice is also an especially good element of the cryosphere  to illustrate the effects of global warming. The Arctic September sea-ice area is directly linked to cumulative CO2 emissions (see this previous post) and therefore changes in sea ice directly reflect, in a very visible way, the path of climate change.

Fig. 5: Observed and modelled historical changes in the Arctic September sea ice extent since 1950 and projected future changes under low (RCP2.6, blue) and high (RCP8.5, red) greenhouse gas emissions scenarios [Credit: Figure SPM1 in the SROCC].

The sea-ice review in SROCC is similar to the Special Report on 1.5°C published end of 2018 (see this previous post). Arctic sea-ice loss was observed in both area and thickness in the past decades and is projected to continue through mid-century. The rate of the loss depends on the amount of warming. In the Antarctic, there is low confidence in the projected sea-ice evolution.

More details about the sea-ice evolution under climate change can be found in Section 3.2 of SROCC.

Polar ice sheets and glaciers

The two polar ice sheets and the world’s glaciers are a fundamental element of the world’s cryosphere. Glaciers and ice sheets cover about 10% of the Earth’s surface and contain around 70% of the world’s fresh water. They regulate the global climate system by interacting with the ocean and atmosphere and provide valuable fresh water resources to much of our planet.

The overwhelming consensus is that the polar regions are losing ice, and that the rate of ice loss has increased. In Greenland, ice loss is occurring through a combination of enhanced surface melting and runoff, and increasing dynamic thinning (ice loss as a result of accelerated ice flow). Greenland has lost around 247 Gt of ice every year between 2012 and 2016. In Antarctica, incursion of warm ocean waters is driving rapid, accelerating ice loss from the West Antarctic Ice Sheet. The mass loss signal from the West Antarctic Ice Sheet (-122 ± 10 Gt yr -1 from 2003 – 2013) is dominated by the increasing ice loss from outlet glaciers in the Amundsen Sea Embayment. On the Antarctic Peninsula, the majority of marine-terminating outlet glaciers are retreating. The pattern of change on the East Antarctic Ice Sheet is more ambiguous and complex, with regional gains and losses and no clear overall mass trend. Increased surface melt intensity and duration on both ice sheets has led to a self-reinforcing cycle, where, like for snow, the melt of the ice sheets uncovers dark surfaces, which absorb more incoming solar radiation than ice, and therefore heat up and lead to further melt. This reduces the capacity of snow and firn to store runoff.

Fig. 6: Ice sheet from above [Credit: Matt Palmer on Unsplash].

Continued ice loss from Greenland and Antarctica is projected to alter the polar regions. While glaciers have been the dominant contributor to global sea-level rise, this will be replaced by ice sheets as they continue to lose mass into and beyond the 21st century.

However, a number of processes that could potentially lead to rapid ice loss in Antarctica are poorly understood, particularly their timescale and future rate. Therefore, large uncertainty remains in projecting future changes to these polar regions, especially beyond this century. Portions of Antarctica resting on bedrock below sea level could be vulnerable to self-sustaining feedbacks such as the Marine Ice Sheet Instability (MISI, see this previous post). It is uncertain from current observational data whether irreversible retreat is underway.

Ice shelves and their interactions with surface meltwater will play a key role in the response of Antarctica to future warming. Freshwater input to the oceans, from icebergs and ice shelves melting, is freshening global water mass currents and circulation, and this may be accelerating. This could inhibit the formation of important oceanic water masses such as the Atlantic Meridional Overturning Circulation and Antarctic Bottom Water. Surface runoff and basal melting from both ice sheets are enhancing the input of dissolved nutrients into fjords and the ocean such as iron, which has been linked to enhanced primary productivity.

The report stresses that low emissions scenarios will potentially limit the rate and magnitude of future changes to the cryosphere. For example, polar glaciers are projected to lose much less mass between 2015 and 2100 under RCP 2.6 compared with RCP 8.5. Ice loss from polar ice sheets and glaciers presents a growing challenge to polar governance, and requires more coordinated efforts to build long-term resilience. In the Arctic, mitigating the effects of climate change can benefit strongly from community-led adaptation.

You can find full details of the estimates and predictions for ice sheets in SROCC, section 3.3 and in FAQ 3.1.

In summary

As a summary of our summary, and if you are interested in the ocean topics as well, have a look at this useful infographic by John Lang!

Here, you can see the most important points for the cryosphere (click on the link below or the picture to have a larger view):

Fig. 7: Parts of a summarizing infographic about SROCC [Credit: John Lang].

Further reading

Edited by Emma Smith


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 postdoctoral researcher at the Max Planck Institute for Meteorology in Hamburg. She investigates new methods to compare sea-ice as simulated by climate models, sea-ice as observed by satellites, and real sea ice. She tweets as @climate_clara.

 

 

 

Jenny Arthur is a PhD student at Durham University, UK. She investigates supraglacial lakes in Antarctica using remote sensing, and is especially interested in their seasonal evolution and interaction with ice dynamics. She tweets as @AntarcticJenny.

Climate Change & Cryosphere – Summer 2019: The year that the Arctic was sunburned

Wildfires in western Greenland in July 2019 were observed by the Landsat 8 satellite. [Photo credit: NASA/Visible Earth]

June, July and August 2019 saw extensive heat waves across Europe, with air temperatures reaching above 40°C in many countries. In response, record breaking ice melt was observed in Greenland and wildfires in Siberia, Alaska, Arctic Canada and Greenland occurred. A particularly dry and warm summer was responsible for hemisphere-wide changes to the cryosphere. In this week’s post, we will review some of the consequences of this very warm summer of 2019 on our Northern Hemisphere cryosphere.


Wildfires

Whilst wildfires are a natural occurrence in forests all over the globe, they are relatively uncommon in the cool, wet Arctic forests. However, with above average air temperatures over much of the Arctic, the conditions of last summer were perfect for widespread Arctic wildfires. One of the biggest problems associated with wildfires is the high CO2 emissions. Summer 2019 saw the highest CO2 emissions from wildfires inside the Arctic circle since 2003. Other direct effects of wildfires in the Arctic include poor air quality and black carbon particles falling on the ice, decreasing its capacity to reflect the sun’s rays (called albedo, which is normally high for the bright snow surface of the Arctic but can be reduced by dark-coloured dust, ash and algae). This reduced albedo of the ice means it absorbs more sunlight, causing it to warm and melt even more (see this post).

Record-breaking Greenland Melt

The term ‘record breaking’ in relation to melting in Greenland is becoming increasingly common. Summers of 2012, 2016 and 2019 have all seen extremely high melt rates, widespread areas of melt and early melt onset in Greenland. Summer 2019 was record breaking for all three of these metrics. Firstly, the melt extent (area of Greenland ice sheet simultaneously melting) peaked early in summer with approximately 30% of the ice sheet’s surface melting on June 13th. For the next two months, the melt extent was above average. A second peak in the melt extent occurred on August 1st, when almost 60% of the ice sheet was melting and over 11 Gigatons of ice was lost (1 Gigaton of water can fill 400,000 olympic size swimming pools).

The maximum melt extent on August 1st 2019, and a graph showing the melt extent throughout 2019. [Photo credit: Polarportal.dk]

Sea Ice Minimum

At the end of August, sea-ice minimum was below 4.6 million square kilometers, which was the third smallest area since the satellite record began. Earlier in the year, between March and June, the sea ice extent was the lowest ever recorded (see our previous blog post for more information about the reasons of this sea ice retreat). A particularly shocking picture of huskies running through bright blue water over the sea ice in northwest Greenland went viral this summer.

The loss of sea ice has multiple impacts on the climate and cryosphere. When the bright, white sea ice melts, it exposes the darker ocean surface. As the dark ocean surface has a lower albedo (is darker) than sea ice, more sunlight is absorbed, further warming the area. This is called Arctic Amplification (see this post). Sea ice loss can also impact the Greenland ice sheet! A loss of sea ice near the coast of Greenland can cause glaciers to calve (large chunks break away) into the ocean when the pressure of the sea ice is removed. Spalte glacier, a tributary of the larger 79°N glacier in the northeast of Greenland, lost an area the size of Manhattan this summer. The whole northeast region had reduced sea-ice cover throughout summer.

A large part of the Spalte Glacier in northeast Greenland detached after the warm summer of 2019. Figure credit: Prof. Jason Box and Karina Hansen

Melting in the Alps

The two European heat waves experienced in June saw air temperatures above 40°C across Spain, France and Germany. These high, sustained temperatures led to high levels of melting across the European Alps. On the highest mountain in Europe, Mount Blanc, a mountaineer discovered a huge melt lake at 3km above sea level, which developed only a few days after the late June heat wave.

Slushy, wet snow and ice has a blue hue. Large parts of sea ice and land ice have the characteristic blue colour of melting ice this summer. [Photo credit: Robert Bye, Unsplash images]

Was summer 2019 just a blip? Or a sign of things to come? Whilst we don’t know the future, it is becoming increasingly clear that record breaking air temperatures and ice melt are becoming more common, which makes many Arctic communities and cryospheric features vulnerable.

Further reading:

Edited by Violaine Coulon


Jenny Turton is a post-doc at Friedrich-Alexander University (FAU) in Erlangen, Germany. Her research focuses on the atmosphere-cryosphere interactions in Northeast Greenland using observations and atmospheric modelling. Her research forms part of a larger project focusing on the ice-ocean-atmosphere links in the 79° north glacier in Greenland.

 

Climate Change & Cryosphere – Why is the Arctic sea-ice cover retreating?

Climate Change & Cryosphere – Why is the Arctic sea-ice cover retreating?

The Arctic Ocean surface is darkening as its sea-ice cover is shrinking. The exact processes driving the ongoing sea-ice loss are far from being totally understood. In this post, we will investigate the different causes of the recent retreat of the Arctic sea-ice cover, using the most updated literature…


Arctic sea ice is disappearing

Due to its geographical position centered around the North Pole, the Arctic Ocean is relatively cold compared to other world oceans. This means that, each winter, ocean temperatures fall below the freezing point, and sea ice forms on top of the ocean surface.

The Arctic sea-ice extent reaches about 15 million km2 in March, at its maximum (see left panel in Fig. 1 and Fig. 2). In spring, the ice starts to melt and reaches its minimum extent in September, which is about three times smaller than its maximum extent (see right panel in Fig. 1 and Fig. 2).

Figure 1: Maps of mean Arctic sea-ice concentration (percentage of sea ice in a given grid cell) in March (left) and September (right), averaged over 1979-2015, from satellite observations. The red line (right panel) shows the sea-ice edge in September 2012 (record minimum) [Credit: Ocean and Sea Ice Satellite Application Facility (OSI SAF)].

Satellite observations clearly show that the Arctic sea-ice cover has been shrinking since the beginning of the satellite record in 1979 (see this post and this post for more information about sea-ice satellite observations). The sea-ice loss is about 13% per decade in September and 3% per decade in March (see this post, this post and this post for further information on recent Arctic sea-ice changes). A recent study using data from a series of different observations (ship reports, airplane surveys, analyses by national services, etc.) shows that the recent Arctic sea-ice loss, as measured by satellites, is unprecedented as far back as 1850.

Figure 2: Seasonal cycle of Arctic sea-ice extent from satellite observations. The solid blue and dashed red lines show the 2019 (ongoing) and 2012 (record minimum) values. The dark gray curve shows the average over the period 1981-2010 with the corresponding uncertainty range in light gray (+/- 2 standard deviations) [Credit: National Snow and Ice Data Center].

The year 2012 was particularly exceptional in the sense that it featured the record minimum in September since the beginning of satellite measurements (dashed red curve in Fig. 2). 2019 was on a ‘good path’ to break this record, but the sea-ice loss rate started to lower from mid-August (blue curve in Fig. 2, see also here).

 

What are the drivers of the Arctic sea-ice loss?

The recent changes in Arctic sea ice have been caused by three main factors:

  1. External forcing: the variability caused by external factors, which can either be human (e.g. anthropogenic greenhouse gas emissions) or natural (e.g. changes in solar activity, volcanic eruptions).
  2. Internal variability: the variability caused by the chaotic nature of processes at work in the climate system. It is internal variability that prevents us to make accurate weather forecasts beyond a few days.
  3. Positive feedbacks: the processes by which a change in the climate can amplify, e.g. the ice-albedo feedback. These feedbacks are described in more detail in this post.

 

External forcing

Several studies have analyzed the links between the changes in external forcing and the recent changes in Arctic sea ice in both observations and models. It has been found that the anthropogenic global warming, caused by increased greenhouse gas concentration in the atmosphere, is the main driver of the long-term sea-ice loss in the Arctic. In particular, Notz and Stroeve (2016) found that for each ton of CO2 released into the atmosphere, the Arctic loses about 3 m2 of sea ice in September, as shown in Fig. 3 below (see this post).

Figure 3: 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 in sea-ice area loss per ton of CO2 emitted [Credit: D. Notz, based on Notz & Stroeve (2016)].

Other changes in external forcing have had a more limited impact on the recent changes in Arctic sea ice. For example, the volcanic eruptions of El Chichón in 1982 and Mount Pinatubo in 1991 caused a small increase in Arctic sea-ice extent (see this study), but their impact cannot be clearly identified in individual climate models (see here). Similarly, the impact of the solar activity on the recent Arctic sea-ice changes is very small.

 

Internal variability

The sea-ice evolution is also strongly subject to internal variability. A good explanation of the concept of internal variability can be found here and in this study.

Internal variability is often estimated using climate models. Running the same model with exactly the same parameters and external forcing, but with slightly different initial conditions (for example a different sea surface temperature), is a common method to get an idea of the internal variability of the climate system. Figure 4 below shows the evolution of the Arctic sea-ice extent using the Community Earth System Model (CESM) run 40 times with different initial conditions. The spread of the ensemble represents the range of the effect of internal variability.

Figure 4: Evolution of Arctic September sea-ice extent using the Community Earth System Model Large Ensemble (CESM-LE) in the less optimistic scenario (RCP8.5). The blue curves show all the 40 model members. The red curve shows the NSIDC satellite observations [Credit: Fig. 1a of Jahn et al. (2016)].

Variations in heat transport from the Atlantic Ocean due to internal variability have caused strong reductions in sea-ice area in the Barents Sea (see this study and this study), and probably other seas located in the Atlantic sector of the Arctic Ocean (as shown here). Changes in large-scale atmosphere circulation, also associated with internal variability, have contributed to sea-ice reductions as well (see this study).

However, several studies found that internal variability was not the key cause of the recent Arctic sea-ice loss over the past 40 years (e.g. this study). Instead, internal variability acts as an amplifier of the external forcing (see this study), so it only explains a small part of the recent Arctic changes. In the climate models used in the IPCC AR5 report, the impact of internal variability is of maximum 1 million km2 (see this study).

 

Feedbacks

A last cause for the recent changes in Arctic sea ice is the presence of positive feedbacks, which can amplify ongoing changes. One of the main feedbacks acting in the Arctic is the ice-albedo feedback (see this post and this study). Since ice reflects more sunlight than water, if the sea-ice cover decreases, more heat is trapped by the surface of the Arctic Ocean, leading to more ice melting.

However, as we have seen above, there is a clear linear relationship between Arctic sea-ice extent and cumulative CO2 emissions (Fig. 3). If the ice-albedo feedback was important in explaining the recent loss of Arctic sea ice, this linear relationship would break after years of strong or weak ice loss, which is not the case.

In fact, the positive feedbacks (like the ice-albedo feedback) are partly compensated by negative feedbacks that stabilize the climate system (see this previous post for a description of feedbacks in polar regions). Thus, while these feedbacks play a key role in the short term, they cannot explain the bulk part of the sea-ice loss since 1979.

 

The future

In conclusion, the recent loss of Arctic sea ice is strongly linked to anthropogenic global warming, although the changes in atmosphere circulation and ocean heat transport, associated with internal variability, also influence the sea-ice evolution. Research continues on the topic in order to capture the exact contribution of the different causes to the Arctic sea-ice loss.

On the long term, Arctic sea ice will continue disappearing. Based on the current emission rates of greenhouse gas emissions into the atmosphere, it is probable that the Arctic Ocean will be ice free during summer before 2050 (see this post, this study and this study).

Due to its linear relationship with CO2 emissions, the Arctic sea-ice cover is a strong indicator for the pace of current climate change. Its rapid disappearance should be seen as a warning light for other impacts to come…

 

Further reading

Edited by Clara Burgard


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

Did you know? – Storms can make Arctic sea ice disappear even faster

Did you know? – Storms can make Arctic sea ice disappear even faster

The increase in air and water temperature due to climate change drives the retreat in the Arctic sea-ice cover. During summer, when sunlight reaches the Arctic, the absorption of heat by the dark ocean water enhances the sea-ice melt through the ice-albedo feedback. During winter, when sunlight does not reach the Arctic, another feedback is at work, as storms enhance the energy transfer between air, ice and water…


How can storms enhance sea-ice melting?

In summer, when the Arctic sea-ice cover is close to its minimum extent, a large storm can rapidly lead to a further decrease in the ice cover. In the case of a storm, the ice breaks up and is pushed together due to the wind-induced waves that quickly develop in the vast areas of open water. Once the storm is over, the resulting small ice pieces drift apart and melt faster than the larger ice pieces would have melted before the storm.

During winter, there is hardly any open water in the Arctic Ocean. An exception is the Barents Sea, where warm ocean water flows in from the North Atlantic and sinks under the surface when it meets the sea ice. Because this inflowing water got warmer over the past couple of decades, the Barents Sea has become nearly ice free in the winter (Polyakov et al, 2017). The “Whaler’s Bay“, north of Svalbard, is experiencing a similar evolution. In this area of open water, where the banks of the bay are formed not by land, but by sea ice, warm ocean water brought by currents sinks under the ice as well. While the effect of the water warming leads to a clear retreat of the ice in both the Barents Sea and Whaler’s Bay, another phenomenon can lead to an even faster retreat: episodic winter storms (e.g. Boisvert et al, 2016) that bring in warm air and push the sea ice northwards.

Until now, scientists observed both processes mainly using ocean moorings and satellite remote sensing sources as winter in-situ observations in this area are very rare.

Fig. 2: N-ICE2015 was based in an ice camp set around RV Lance. The ship was assisted to approx. 84N by an ice breaker and then left to drift out towards the Whaler’s Bay slowly with the sea ice and ocean surface current. [Credit: Paul Dodd, Norwegian Polar Institute].

Observations from the N-ICE 2015 campaign

In early 2015, the Norwegian Polar Institute led a half-a-year-long international expedition in the sea ice north of the Whaler’s Bay (Norwegian Young Sea Ice Cruise, N-ICE2015). During the winter part of the expedition, when air temperatures were typically below -20ºC, six powerful storms brought strong winds and mild temperatures into the region. The atmosphere-ice-ocean measurements recorded by the expedition revealed complex processes of energy transfer resulting in complex combination of thin and snow-covered sea ice, numerous leads, and pressure ridges (see this previous post about sea-ice dynamics).

The observations from N-ICE2015 show that early winter storms deposited a thick snow cover on the ice. Because snow is an excellent insulator, heat from the ocean cannot escape into the atmosphere and the water right under the ice does not cool enough to form further sea ice. This way, the ice stays relatively thin. So thin, that it yields the weight of the deep snow cover and gets submerged under the sea level. Generally, ice floes can be kilometers-wide and have thick steep edges built of pressure ridges that prevent water seeping into the snow from the sides of the floes.

However, each new storm during the observation period came with strong southerly winds that pushed the ice floes northwards with such force that they cracked in much smaller pieces. After the center of the storm passed over the sea ice, the wind direction reverted to southward and the ice stretched again towards Whaler’s Bay. The cracked floes were then less protected from water seeping into the snow from the cracks. Some large cracks even developed into leads with open water. After the storms, northerly winds brought back cold temperatures and cracks, leads, and flooded snow froze rapidly.

At the same time, the motion of the ice floes led to vertical mixing at the ocean’s surface. If this mixing happened right above the sinking warm water, some of the warm water was brought up to the surface and melted the ice from below.

Figure 3: The Arctic Winter Storm Cycle [Adapted from Graham et al. (2019)].

The shallow warm ocean water currents are unique to the Barents Sea and Whaler’s Bay in the Arctic. Further in the Central Arctic, the cold ocean has much less potential to melt sea ice during winter. Still, many powerful storms can reach beyond the North Pole and cross the whole Arctic Ocean. This means that the abundant snowfall, breaking-up of the ice floes, flooding of snow and opening of the leads can be common in large parts of the Arctic Ocean in the winter (for details see Fig. 3 and Graham et al, 2019). This way, a row of passing storms cannot only build a deep snow cover, but also create a broken-up ‘ice-scape’ that is susceptible to melt faster during summer. Moreover, abundance of areas of thin ice which transforms into leads can let enough light into the ocean to trigger large algae bloom earlier than usual in the season (Assmy et al, 2017). In summary, winter storms can make a large cumulative impact that lasts far beyond the short duration of a single storm.

More observations are needed!

Although it provided a lot of new understanding on the importance of storms for the sea-ice evolution, the N-ICE2015 brought some limitations. For example, it ended in June, before we could observe summer melt processes and it was limited to the area north of the Whaler’s Bay. To confirm and further explore the Arctic atmosphere-ice-ocean-ecosystem processes, the international scientific community is launching an even larger expedition in 2019 and 2020.

The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) will be a huge international effort with hundreds of scientists involved in field work, data analysis and research. Its main goal is to collect the data from the ‘new Arctic’ where the sea ice is much thinner than earlier decades. Such data can help improve the climate model projections that still under-represent the recent decline in sea ice extent and volume. MOSAiC will provide observations spanning over the full annual cycle of sea ice, from freeze-up in fall 2019 to melt in summer 2020. Geographically, the expedition will cover vast distances by drifting with the sea ice from the Central Arctic towards the North Atlantic. MOSAiC observations will build on the results from N-ICE2015 and will measure the effects of storms also in the Central Arctic.

Further reading

Edited by Clara Burgard


Polona Itkin is a researcher at the UiT The Arctic University of Norway, Tromsø. She investigates the sea ice dynamics of the Arctic Ocean and its connection to the sea ice thickness and snow depth. In her work she combines the information from in-situ observations, remote sensing and numerical modeling. Polona was a post-doctoral researcher at the Norwegian Polar Institute and one of many early career scientists involved with N-ICE2015. The expedition was highlighted also in their social media project ‘oceanseaiceNPI’: Instagram.com/OceanSeaIceNPI, Twitter.com/OceanSeaIceNPI, Facebook.com/OceanSeaIceNPI, contact Email: polona.itkin@uit.no.

Image of the Week – 5th Snow Science Winter School

The participants to the 5th Snow Science Winter School [Credit: Anna Kontu]

 

From February 17th to 23rd, 21 graduate students and postdoctorate researchers from around the world made their way to Hailuoto, a small island on the coast of Finland, to spend a week learning about snow on sea-ice for the 5th Snow Science Winter School. The course, jointly organized by the Finnish Meteorological Institute and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, brought together a wide range of scientists interested in snow: climate modellers, large-scale hydrologists, snow microstructure modellers, sea-ice scientists and remote sensing experts studying the Arctic, Antarctica and various mountain ranges. The week was spent between field sessions out on the sea-ice, daily lectures, and data analysis sessions, punctuated by amazing food and Finnish saunas to finish the day!


Field sessions

Our field sessions focused on learning to use both standard snow measurement techniques and advanced state-of-the-art methods. We first practiced sampling the thin, crusty snowpack with traditional methods: digging snow pits and recording grain size, temperature profile and density. We then moved to advanced techniques, learning about micro-tomography – which generates 3D images of the snow without destroying the way the individual ice crystals are arranged, near-infrared imagery and the measurement of specific surface area of the snow crystals by recording how a laser beam is reflected and modified as it passes through the snow sample.  These techniques all give information on how the snow crystals are arranged in the snow pack that are not obtainable with the traditional techniques. They also give important parameters for remote sensing validation and snowpack modelling.

The lecturers had brought with them some of the most advanced instruments, in some cases their own unique prototypes, giving us an amazing opportunity to practice working with these instruments. Amongst them was the SLF SnowMicroPen, which can measure the mechanical resistance of the snowpack, the optical sensors IRIS and SnowCube which use the reflection from a laser beam to calculate the surface area of the snow crystals, and a small radar which relates the conductivity of snow to the amount of liquid water mixed in with the snow and the density. On top of that, we honed our sea-ice drilling and measurement skills.  During our field sessions, we were exposed to all the conditions a field researcher might experience, from cloudy skies, over to high winds threatening to blow away all your equipment to crisp, cold blue skies.

The students braving the winds to collect data [Credit: Guillaume Couture]

Practicing snow crystal identification under blowing snow conditions [Credit: Anika Rohde].

Lectures

Our daily lectures covered a range of topics, leaning on the expertise of the instructors of the course. After a short introduction about sea-ice, a well-needed refresher considering the wide range of backgrounds of the participants, we jumped into snow-science. We learned about snow measurements from a field, remote sensing, and modelling perspective. The lectures sparked multiple discussions, from the continual need for more ground-validation for remote sensing data, over spatial representativeness and accuracy of the field samples to modelling approaches and a consideration of the limitations of the observational datasets.

Final projects

After learning how to use these fancy and expensive instruments and using our newly gained knowledge of snow on sea-ice, we were given a day to plan our own field session, collect data, analyze the results and present our result to the other groups on the final afternoon. Some very ambitious projects were quickly checked by reality in the field and the snow conditions were exceptionally challenging. This meant that our data might not perhaps yield any scientific breakthroughs in the field of snow science, but that we certainly learned how to adapt measurement and analysis designs on the fly and will hopefully all have an all-weather plan for the next expedition out into the snow for our various projects at home.

Calculating specific area with the SnowCube [Credit: Anika Rohde].

More than the science

On our second evening, we braved the elements for the ice breaker held in a tent on the sea ice. Luckily, only the ice between the students and lecturers broke so that everyone appeared again at breakfast the next day. The delicious food kept us warm for the duration of the trip and anyone still feeling cold could enjoy the sauna for a truly Finnish experience. Our knowledge gained over the week was tested on the final evening with a sea-ice themed trivia organized by the instructors.

Being this far north provides a great opportunity to witness some elusive northern lights.  During the entire week, we kept a close eye on the aurora borealis forecast, and we finally had a good chance of seeing them on our last night. Needless to say, we put our field gear back on to head outside and were rewarded by a beautiful display of dancing green and pink lights in the skies. A wonderful way to finish a successful week of learning, meeting fellow researchers and sparking new research questions!

The elusive northern lights appearing on our last night in Hailuoto [Credit: Anika Rohde]

The accommodation treated us to some beautiful sunsets! [Credit: Caroline Aubry-Wake]

To finish on a high not, here is a short video summarizing our incredible week in Hailuto! [Credit: Caroline Aubry-Wake]

Edited by Violaine Coulon


Caroline Aubry-Wake is a mountain hydrology PhD candidate at the University of Saskatchewan, Canada. By combining mountain fieldwork in the Canadian Rockies with advanced computer modelling, she aims to further understand how melting glaciers and a changing landscape will impact water resources in the future.

 

 

 

Maren Richter is a PhD student at the Department of Physics of the University of Otago. A physical oceanographer by training, she has turned her focus on the solid state of water to study ice-ocean interactions in Antarctica. Specifically, the effect of platelet ice formed near ice shelf cavities on landfast sea ice thickness evolution and variability on interannual to decadal timescales.

 

Image of the Week – Will Santa have to move because of Climate Change?

Santa Claus on the move [Credit: Frank Schwichtenberg, CC BY 3.0, Wikimedia Commons]

Because of global warming and polar amplification, temperature rises twice as fast at the North Pole than anywhere else on the planet. Could that be a problem for our beloved Santa Claus, who, according to the legend, lives there? It appears that Santa could very well have to move to one of its second residences before the end of this century. But even if he moves to another place, the smooth running of Christmas could be in jeopardy…


But…. Where does Santa live?

The most famous of Santa’s residence is in Lapland, Finland, at Korvatunturi. But since this area is a little isolated, Finns then moved it near the town of Rovaniemi. For Swedes, it’s in Gesunda, northwest of Stockholm. The Danes, them, are convinced that he lives in Greenland while according to the Americans, he lives in the town of North Pole, Alaska. In Norway, there is even disagreement within the country: some Norwegians believe he lives in Drøback, 50 km south of Oslo while other believe he lives in the Northernmost inhabited town in the world: Longyearbyen, Spitsbergen, where Santa even has its own postbox!
Even in the southern hemisphere, Christmas Island claims to be Santa’s second home.

Santa’s huge postbox in Longyearbyen, Spitsbergen [Credit: Marie Kotovitch] and Rovaniemi, Finland: the self-proclaimed “official hometown of Santa Claus” [Credit: Pixabay]

It seems that Santa Claus has many places to stay.. But according to the legend, Santa’s real permanent residence is in fact the true North Pole. However, as shown by the Arctic Report Card 2018, the Arctic sea-ice cover continues its declining trends, with this year’s summer extent being the sixth lowest in the satellite record (1979-2018). The latest IPCC 1.5°C warming special report states that “ice-free Arctic Ocean summers are very likely at levels of global warming higher than 2°C” relative to pre-industrials levels. Considering that the world is currently on course for between 2.6 to 4.8°C of warming relative to pre-industrial levels by 2100, Santa’s home is projected to sink into the Arctic Ocean before the end of the current century. It appears it would be time for Santa to start thinking about which one of his second residences he will choose to move to…

Will Santa have to find a new home? [Credit: Pixabay]

Rudolf might be in trouble…

Of course, if he moves away from the melting North Pole, Santa still needs snow at Christmas to be able to take off his sled. But, actually, this could become a problem.
This year, there was still no snow in Rovaniemi, Finland, the self-proclaimed “official hometown of Santa Claus”, by the end of November, making the local tourist attractions very worried. Luckily, it has now snowed there since, but how does this look like for the years to come? According to the latest Arctic Report Card, the long-term trends of terrestrial snow cover are negative.

Another problem which might complicate Santa’s work was underlined in a study published in 2016. This study showed that reindeers are getting smaller because of warmer Arctic temperatures. How come? During the long winter, reindeers are usually able to find their food (which consists of grasses, lichens and mosses) by brushing aside the snow that covers it. But because of the warmer temperatures, rain now falls on the existing snow cover and freezes. The animals’ diet is thus locked away under a layer of ice. As a result, reindeers are hungry and lose their babies or give birth to much leaner ones. The Arctic Report Card 2018 states that the population of wild reindeer in the Arctic has decreased by more than half in the last two decades.

All this is not going to get better, as Arctic temperatures for the past five years (2014-18) all exceed previous records. According to the Danish Meteorological Institute, in November 2016, Arctic temperatures were reaching an incredible peak at around -5°C while average temperature at this period usually is around -25°C.

Climate change also affects reindeers [Credit: Photo by Red Hat Factory on Unsplash]

Christmas trees also at risk!

You may say that Santa is Santa and that he will be able to find a solution to all these problems. Let’s hope you’re right! But another problem is looming on the horizon: you might soon not be able to welcome Santa in your own home as it should with a beautiful Christmas tree.

Indeed, this summer’s heat waves have strongly affected Christmas tree crops everywhere in Europe. Moreover, a 2015 study shows that native Scandinavian Christmas trees are also affected by climate change, and more specifically by reduced snowfall. The latter acts like an insulation layer which protects the roots from the cold winter.

We hope that this post has made you realize the urgency of the fight against global warming! However, in the meantime, don’t forget that the most important to spend a nice Christmas is the Christmas spirit! We wish you all a very merry Christmas and a wonderful new year!

As a little Christmas gift..

  • If you want to find out the truth about Santa’s real home, you can always check it by yourself by using the Santa Tracker by Google to follow Santa’s Christmas Eve trip and check where he comes back at the end of the night…
  • The highlights of the Arctic Report Card 2018 are summarized in this video.

Further reading

Edited by Clara Burgard

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 – 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.

Image of the Week – Stuck in the ice: could it have been predicted?

Image of the Week –  Stuck in the ice: could it have been predicted?

Expeditions in the Southern Ocean are invaluable opportunities to learn more about this fascinating but remote region of the world. However, sending vessels to navigate the hostile Antarctic waters is an expensive endeavor, not only financially but also from a human perspective. When vessels are forced to turn back due to hazardous conditions or, even worse, become stuck in the ice (as shown in our Image of the Week), a mission full of expectations can quickly turn into a nightmare. Hence there is an increasing demand for reliable information on the navigability of the Southern Ocean a few weeks to a few months in advance. This information could support the final decision whether to start the journey or not, and would allow minimizing the associated risks.


What’s the problem?

In late February 2018, the British vessel RRS James Clark Ross was heading to the Eastern Antarctic Peninsula to investigate the consequences of the calving of a massive iceberg from the Larsen C ice shelf. Unfortunately the vessel had to turn back before reaching its goal due to the unexpected presence of thick sea ice in the region. This story is not unusual. During Christmas 2013, a Russian ship named the Akademik Shokalskiy also got stuck in several meters of Antarctic sea ice. Ironically, one of the rescuing vessels itself (the Chinese Xuě Lóng) got trapped in the ice as well. To prevent such events from happening again, we need to be able to predict the upcoming sea-ice conditions. Can sea-ice conditions be forecast at seasonal time scales? If so, how?

 

Antarctic sea ice, the Year of Polar Prediction and SIPN South

To prevent accidents and unforeseen problems, one goal of the Year Of Polar Prediction is to enhance environmental forecasting capabilities from operational (hours to days) to tactical (weeks to months) time scales in high latitude regions. Several studies support the notion that Antarctic sea ice may be predictable a few months ahead, at least in certain regions (Holland et al. 2017, Chen and Yuan 2004, Holland et al. 2013, Marchi et al. 2018).

To investigate further the predictability of Antarctic sea ice, the Sea Ice Prediction Network South (SIPN South) was launched in 2017. It is a two-year international project endorsed by the YOPP. SIPN South pursues three strategic objectives:

  • Hosting seasonal outlooks of Antarctic sea ice to better understand the sources of sea-ice predictability and the origins of systematic forecast errors in different types of models.
  • Providing news and information on the current state of Antarctic sea ice, disseminating research to a wider audience and reporting ongoing field campaigns.
  • Coordinating realistic seasonal prediction exercises to investigate the potential use of this information for users and customers, primarily ships navigating in the region.

 

February 2018 seasonal sea-ice forecasts

As a first major milestone, SIPN South provided coordinated forecasts of sea ice for February 2018. February is the month with the smallest sea-ice area in the Antarctic, and therefore most of the shipping traffic in the region happens around that time. Participants were asked to provide an estimation of sea-ice coverage (area, concentration) for each day of February 2018, and were asked to issue their predictions by mid-December 2017. 13 research groups participated in this first forecasting experiment, following different approaches: several groups used fully coupled climate dynamical models, while others applied statistical regression methods to predict future ice conditions.

As we all know, the weather is unpredictable beyond a few days. However, previous research has suggested that the statistics of weather (its mean, its variability) can potentially be predicted from months to decades, due to the coupling of the atmosphere with “slower” components of the climate system like the ocean. To reflect this and to accurately estimate the statistics of weather, groups tend to provide not just one forecast, but several of them. These “ensembles” of forecasts provided by each group therefore represent all possible states of the atmosphere, ocean and ice that may prevail in February 2018 – given the known initial conditions of December.

The results of the coordinated experiment are shown in Figure 2. The February mean sea-ice area is shown for each group (colors), along with two actual observational references (black). Bear in mind that the forecast data were issued two months before the actual target date! Here, the forecasts are expressed as anomalies with respect to a reference climatology. All forecasts tend to overestimate the February sea ice area in the Ross Sea. A reason for this wrong estimation might be a very unusual cyclone, which passed over the Ross Sea around the 20th of January 2018 (i.e., between the time the forecasts were issued and the period for verification). This cyclone brought relatively warm air into the region. Furthermore it fractured the ice, opening more areas of open water and possibly increasing the effect of the ice-albedo feedback. Events like this one are not individually predictable several weeks in advance, but a well-designed forecasting system should at least account for this possibility. Despite running ensembles of forecasts, the sea-ice reduction in the Ross Sea was not captured by most forecasts. This may point towards a common and systematic deficiency in these prediction systems.

Figure 2: February 2018 mean regional sea-ice area anomaly (compared to 1979-2014 observed climatology) by longitude, for the 13 submissions, with observed estimates given in black. Solid lines show the ensemble mean for each contribution, with transparent shading indicating the ensemble range (min-max) [Credit: F. Massonnet].

Communicating climate information

Sea-ice area, as shown in Fig. 2, is a primary parameter used by scientists to quantify ice presence in a given region. It is also a useful number to diagnose model-data mismatch. However, sea-ice area is of little use for those who actually need climate information. For someone operating a vessel, the important information is how likely that vessel is to encounter sea ice in a given region for a given day in February. Information from Fig. 2, while certainly useful to scientists, is meaningless to those willing to extract practical information for navigation.

Alongside the work to understand fundamental drivers of sea-ice predictability in order to eventually improve the predictions, it is necessary to consider how potential users will interact with the forecasts. As explained above, climate forecasts are probabilistic in nature. Communicating probabilistic information to a non-trained audience is always a challenging task: for example, how would you interpret a forecast saying that there is a 50% chance of rain for tomorrow?

To reflect the irreducible uncertainty of climate forecasts (see previous section), sea-ice forecasts are generally expressed in terms of sea-ice probability, i.e. the probability that a given region of the Southern Ocean has sea-ice concentration larger than 15%. This probability is derived for each day and each grid cell from the ensemble forecasts contributed by each group (Fig. 3). If well calibrated, this type of information can be useful to those planning operations weeks in advance. For example, all but one model had forecast a high (>80%) probability of ice presence in the Larsen C area (eastern tip of the Antarctic Peninsula) where the RRS James Clark Ross got stuck five months ago. That is, there was a high risk, according to those forecasts, that ice would be present in that area in February. Of course, this does not mean that navigation would have been impossible (ice breakers can still operate in icy waters, provided the ice is thin), but these forecasts provided a first-order warning that there was a significant risk of encountering hazardous ice conditions there.

Figure 3: Probability of sea-ice presence for 15th February 2018, as forecasted by the five groups that submitted daily sea-ice concentration information. The sea-ice edge as observed by two products is shown in white. The probability of presence for a given day corresponds to the fraction of ensemble members that simulate sea-ice concentration larger than 15% in a given grid cell for that day. A dynamic animation of the figure showing all 28 days of February is available on the SIPN South website. [Credit: F. Massonnet]

Forecasting February 2019

The core phase of the Year of Polar Prediction entails “Special Observing Periods”, that is, intensive efforts to monitor the Arctic and Antarctic regions but also to enhance modeling activities (see this previous post). The (unique) Special Observing Period in the Southern Ocean will take place between mid-November 2018 and mid-February 2019. A new call for contributions will be launched by SIPN South to collect sea-ice forecasts for austral summer 2019, hoping that the first exercise in 2018 will raise the interest of even more research groups. A key question will be to assess whether the systems will be able to forecast better the sea-ice conditions in the challenging Ross Sea area, where most forecasts failed. Better insights will hopefully be gained in tracing the origin of systematic model error and lead to an improvement of Antarctic sea ice predictions within the next decade. As reliable climate information is crucially needed in this remote but important region of the world, future efforts to predict Antarctic sea ice will be very welcome!

 

Further reading

Edited by Adam Bateson and Clara Burgard

 


François Massonnet is a F.R.S.-FNRS Post-Doctoral Researcher at the Université catholique de Louvain and scientific collaborator 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 – Icy expedition in the Far North

Image of the Week – Icy expedition in the Far North

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


Who, When and Where?

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

 

What and How?

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

 

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

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

 

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

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

 

Further reading

Edited by Violaine Coulon