Arctic Sea Ice Update

This is a quick update on the current state of Arctic sea ice. It comes in light of widespread reports, including The Guardian, The Financial Times and The Independent, of significantly anomalous climate patterns for this time of year. Climate blogs, such as Arctic News and Union of Concerned Scientists have offered an immediate analyse of this data, which is summarised below.

November 2016 Arctic Sea Ice Anomaly: Notably, current temperatures across the Arctic are exceedingly high compared to previous years (Figures 1 and 2). Temperatures anomalies in some parts of the Arctic are as great as 20°C (Figure 1). However, the most recent figures (Figure 2) shows that peak warming in the Arctic for November appears to have been passed after a rapid decline. Nevertheless, this means current Arctic temperatures are over 10°C greater than 1958-2002 averages (Figure 2).

Figure 1: Temperature anomalies across the Arctic region for 25 November 2016, relative to 1979-2000. Source: Climate Reanalyzer. Accessed 25 November 2016.

Figure 2: Annual time series of daily Arctic (greater than 80° latitude North) temperature for the year 2016 (red line) and the 1958-2002 mean (green line). Temperature of freezing (i.e. 0°C) is shown for reference (blue line). Source: Danish Meteorological Institute. Accessed 25 November 2016.

The most up to date explanation indicates that these temperatures are caused by perturbed atmospheric patterns. An increased strength jet stream has caused a greater atmospheric transport of warm air to high northern latitudes – creating these large temperature anomalies.

Significantly, increased November Arctic temperatures have triggered a pattern previously unobserved at this time of year – declining Arctic sea ice. As mentioned in a previous post, the observed Arctic sea ice extent annual cycle typically reaches a minimum in September, before growing throughout the Northern Hemisphere autumn and winter. Most recent data (Figure 3) indicate a greatly reduced growth rate, resulting in the lowest ever recorded Arctic sea ice extent for this time of year. Between 16 November 2016 and 20 November 2016, Arctic sea ice extent decreased from 8.674 million km² to 8.625 million km² (Figure 3). Since then, sea ice extent has increased, although it remains significantly below both the 1981-2010 average and 2012, the year with the lowest sea ice minimum extent, for the end of November.

Figure 3: Daily Arctic sea ice extent (area of ocean with at least 15% sea ice) for 2016 (solid blue line) and 1992-2010 mean (solid black line) shown with ±2 Standard Deviations. Sea ice extent for 2012, the year with the lowest minimum sea ice extent is also shown for reference (dashed green line). Source: National Snow and Ice Data Center, updated as of 27 November 2016. Accessed: 28 November 2016.

Academic Context: As these observations are so recent, there is no peer reviewed literature on the extreme warming in November 2016 (although as mentioned earlier this topic has received wide coverage in newspapers and blogs). Hence it is important to put these findings in context of published academic research.

Slow sea ice growth during Northern Hemisphere Autumn is likely to be caused by the culmination of a multidecadal sea ice decline. Climate theory and model experiments indicate that a positive ice-albedo feedback mechanism exacerbates a prolonged period of decline. Hansen et al. (1984) produced the earliest comprehensive analyse of the strength of the sea ice albedo feedback. In this paper, the sea ice feedback is attributed a feedback factor of approximately 1.1 (see Hansen et al. 1984, Equation 4). This essentially means that for a change in mean global temperature, this feedback will contribute a further 10% temperature change in the same direction.  This therefore identifies the sea ice-albedo feedback as one of the most sensitive feedbacks in the climate system.

A renowned paper by Lenton et al.in 2007 highlights the behaviour of sea ice as a threshold response – or ‘tipping point’. The authors define a tipping point as thresholds in the climate system, which when surpassed, trigger a rapid change to a distinct qualitative state. Lenton et al. estimate that Arctic sea ice as part of the climate system which could be subject to a tipping point within 0.5°C to 2.0°C of global warming, and could operate on an approximately 10-year timescale, making it one of the most sensitive parts of the climate system. Recent observed nonlinear behaviour if Arctic sea ice supports this theory and indicates that this particular tipping point may have already been passed.

Finally, sea ice thickness is a factor that has recently received increased attention considering its importance relating to changes in sea ice extent. The 2013 IPCC report includes analysis of sea ice thickness changes, acknowledging that the loss of older, thicker ice contributes to a significantly reduced sea ice minimum extent. This report (pp. 319) indicates a likely average decline in thickness of between 1.3m and 2.3m (between 1980 and 2008). Importance of sea ice thickness is also emphasised in Video 2 of the previous post on this blog. It is important to note that changes in thickness do not directly contribute to the sea ice-albedo feedback, which is dependent on surface area coverage. However, the critical importance of sea ice thickness is being recognised, exemplified by a recent paper by Xieet al. (2016). In the study, sea ice thickness is observed and incorporated into an Arctic sea ice forecasting model for the first time. This is an important advance in sea ice forecasting, as understanding of the processes contributing to sea ice decline improves.

Arctic Sea Ice Visuals

In light of the Arctic sea ice data release discussed in a previous post, several interesting visual tools on the topic have been produced. I have compiled several here, which demonstrate the wide range of ways in which geographical data can be presented:

(1) This first video is taken from the ThinkProgress blog. It shows minimum sea ice volume at an annual resolution (1979 to 2016). The video effectively shows one of them most critical variables associated with the polar regions (it is important to note this shows sea ice volume, not sea ice extent).

(2) This satellite imagery is from the NSIDC and shows monthly averaged sea ice extent for every September (1979 to 2014). Although it is the closest of these visualisations to raw data (showing the images used to calculate the data in Figure 1 of my initial post on the Arctic sea ice minimum) it is limited in the sense that it only shows annual minimum sea ice extent.

(3) A much more detailed approach is this detailed 3D visualization from NASA. This includes the age of sea ice – a factor representative of thickness – as well as a helpful audio explanation. It presents data at a monthly resolution (1984 to 2016) hence showing the seasonal cycle of sea ice. For more detail see the source.

(4) Finally, a much less conventional but none the less informative visualisation is this climate spiral produced by Ed Hawkins at the University of Reading. It captures both the seasonal cycle and the overall (1979 to 2016) decline of Arctic sea ice volume throughout the Anthropocene. 

Research Paper Review: Schannwell et al. 2016

One of the most critical impacts of climate change in the polar regions is Sea Level Rise (SLR) . SLR is one of the most frequently discussed and poorly understood issues in polar science. Loss of sea ice does not contribute to SLR as the melting ice replaces the volume of water it displaced whilst floating. Instead, a significant contribution to SLR from these regions comes from the loss of ice from ice sheets (i.e. Greenland and Antarctica) via discharge from outlet glaciers which carry ice to the ocean. In light of warming polar ocean and air temperatures, the contribution of polar regions to future SLR has become a leading research area. A recent (November 2016) paper by Schannwell et al. has provided an update on the potential contribution of a key region – the Antarctic Peninsula.  Results from this modelling study indicate that the future contribution of this region may have been underestimated – with previously unconsidered processes playing a large role.

Aim and Methodology: The aim of this recent paper is to model ice loss, and subsequent contribution to SLR, from the Antarctic Peninsula. This is a region of the Antarctic which contains a large number of outlet glaciers which terminate either at directly at the ocean, or into ice shelves.  Previous studies have included predictions of SLR from glaciers which terminate at ice shelves, but not those which terminate directly into the Southern Ocean.

Schannwell et al. have sought to address this by including processes from both types of glaciers to model SLR from the Antarctic Peninsula. The British Antarctic Survey Antarctic Peninsula Ice Sheet Model (BAS – APISM) is the primary model which is used. This ice sheet model is forced with climate model output from 13 General Circulation Models (GCMs) from the Climate Model Intercomparison Project Phase 5 (CMIP5) . This results in 300 yearlong transient simulations of climate and corresponding Antarctic Peninsula ice loss from the year 2000 to 2300. These simulations are carried out for two of the IPCC prospective Representative ConcentrationPathways (RCPs) (pp. 1461); RCP4.5 (a ‘stabilization pathway’) and RCP8.5 (a ‘high emissions pathway’).

Results: Model output shows that previously unconsidered glaciers, (i.e. those which terminate directly at the ocean) could contribute to a significant volume of SLR from the Antarctic Peninsula. For RCP4.5 these glaciers alone are responsible for 79% – 89% of total projected SLR by 2300. The magnitude of these contributions can be seen by the pink (maximum value) and blue (minimum value) bars on Figure 1 (the aforementioned percentage is represented in panel ‘a’ by the scale of the pink and blue bars in comparison to the green bar representing SLR from the other processes).  These glaciers contribute to SLR on a similar scale in RCP8.5 (Figure 1, panel b).

In the same Figure, total modelled SLR from both types of glacier is shown, with maximum and minimum projections shown by the solid red and blue lines respectively. This study therefore shows a range of potential total SLR contribution from the Antarctic Peninsula from between 11 ± 2 and 32 ± 16 mm (minimum RCP4.5 value to maximum RCP8.5 value) by the year 2300. Results from the study indicate notable SLR from both types of glaciers in the Antarctic Peninsula, although the relative importance of these newly considered glaciers is greater in the RCP4.5 scenario.

Figure 1, source: Schannwell et al. 2016. Caption as quoted from the paper itself (pp. 167): ‘Combined SLR for RCP4.5 (a) and RCP8.5 (b) scenarios. Solid red upper line and solid blue lower line correspond to combined maximum and combined projection, respectively. Dashed blue lines approximate timing of ice-shelf collapse. Error bars are displayed where available’.

Discussion and Evaluation: Key findings of the study have shown that previously unconsidered processes in the Antarctic Peninsula have led to potentially greatly underestimated projections of SLR from this region. These previously unconsidered factors are particularly relevant in the stabilized RCP4.5 scenario. In context of the future Anthropocene, results from the study indicate a revised annual SLR of between 0.04 ± 0.01 mm a^-1 and 0.11 ± 0.05 mm a^-1 from the Antarctic Peninsula alone. The author notes the significance of these values in terms of recently (2003-2013) observed SLR from the entire Antarctic region of 0.25 ± 0.07 mm a^-1. Although there is a large degree of uncertainty in the new techniques utilised in this research, this paper offers valuable insight into the extent of SLR underestimation, even in a lower scale emissions scenario (RCP4.5). 

2016 Arctic Sea Ice Minimum

The National Snow and Ice Data Center has recently released its data set of Arctic sea ice coverage for the 2016 Northern Hemisphere Summer. These figures show that on 10^th September 2016 Arctic sea ice reached the second lowest annual extent ever recorded. The release of this data is a greatly anticipated metric for the health of the Arctic region for a current year and is one of the most widely published pieces of research on the Arctic. Evidence of a further decline in Arctic sea ice has received global coverage in a variety of formats, including reports in national newspapers, e.g. The Washington Post and The Guardian, and reanalyses in climate blogs.  Climatic impacts relating to Arctic sea ice are varied, including an important albedo feedback mechanism. Hence it is vital this issue is reported and interpreted appropriately.

What the data tells us: The headline statistic is the minimum extent of sea ice in the Arctic Ocean. Sea ice extent is defined as: total area of the Arctic Ocean with at least 15% sea ice coverage – hence it is measured in units of area (km²). The NSIDC, in collaboration with NASA, use microwave measurements from the Defense Meteorological Satellite Program (DMDP). This data is ongoing since November 1978.

It is typically used to compare the minimum daily value recorded each year which is found at the end of the summer melt season. Hence the annual minima are normally reached in September, before sea ice growth recovers over the winter. On 10^th September, Arctic sea ice extent reached a daily value of 4.14 million square kilometres – the lowest value for 2016. As Figure 1 below shows, this is the second lowest annual minima recorded (2016 is represented by the blue line). Only in one other year has there been a lower value of minimum Arctic sea ice extent – in 2012 where it reached 3.39 million square kilometres. This graph indicates the decline of Arctic sea ice extent, as the last five years have all been significantly lower than the 1981 – 2010 average, displaying a decline beyond the scope of natural variability.

Figure 1, source: http://nsidc.org/arcticseaicenews/ on 3/11/2016.

A further trend revealed in the 2016 data is the slow growth of Arctic sea ice during October. As Figure 1 shows, the most recent observations of Arctic sea ice extent are currently at the lowest ever recorded value for this time of year - indeed an extent of less than 2012. This indicates anomalously slow growth of sea ice over October.

Longer term (Anthropocene) trends: It is important to put this data in context of longer term trends of Arctic sea ice extent. In 2013, the IPCC report synthesised research on this subject, with emphasis on the period of satellite observations (i.e. since 1978) to clarify the trend. When analysed on a decadal timescale (Figure 2), the results show an increasing decline in summer sea ice extent over time, although there is a much less pronounced change in winter maximum extent. The 2016 daily minimum falls within the uncertainty values for the most recent three years represented in the figure (2009 – 2012, black line on Figure 2), indicating a continuation of this observed trend throughout the Anthropocene.

Figure 2, source: 2013 IPCC WG1 (pp.235), Figure 4.2. This shows “decadal averages of sea ice extent in the Arctic”.

Analysis of Arctic sea ice extent satellite observations can also be undertaken, at a higher temporal resolution: the annual scale, as shown in Figure 3. This figure is also taken form the 2013 IPCC report (updated from Cosimo and Nishio 2008), and represents changes in sea ice extent as annual anomalies from the November 1978 to December 2012 average. This graph shows that, despite interannual variability, there is a clear decline in annual Arctic sea ice extent.

In the IPCC report this annual data is fitted with red linear regression line (Figure 3). This results in a linear decline in Arctic sea ice extent of 3.8 ± 0.3 % per decade. However, as Figure 1 also shows, observations indicate that Arctic sea ice is not declining at a linear rate on this timescale. In fact, Arctic sea ice extent appears to be declining by a greater amount each decade. Hence a linear analysis may appear inappropriate.

Figure 3, source: 2013 IPCC WG1 pp. 331. This shows “anomalies in Arctic sea ice extent from satellite passive microwave observations”.

Sea Ice Albedo Feedback: Importance of Arctic sea ice extent is frequently referred to in relation to the Sea Ice – Albedo feedback mechanism. Hence I will offer a brief explanation of the mechanisms of this widely established feedback. Theory suggests that changes in the Earth’s surface albedo (i.e. “the fraction of solar radiation reflected by a surface or object” IPCC 2013 pp. 1448) will cause a resultant change in surface temperature. Sea ice has a significantly higher albedo than ocean water, hence a decrease in sea ice extent will theoretically result in an increase of average Arctic surface albedo and a subsequent increase of short wave radiation absorbed in the Arctic region. This will drive an increase in temperature and further loss of sea ice, completing the positive feedback. This positive feedback has been demonstrated in climate model experiments and is widely believed to be a fundamental feedback in the global climate system.

Conclusion: To conclude this post, recent data shows furthering of a well observed pattern of climate change during the Anthropocene – a decline in Arctic sea ice extent. One of the mechanisms driving this loss is a positive albedo feedback. The decline of Arctic sea ice extent appears to be increasingly nonlinear, possibly as a result of this feedback mechanism.

Interesting Links: Here are some links to other blogs which have covered the release of Arctic sea ice data:

•          ThinkProgress 
•          Open Mind 

Introduction

Although the polar regions of the Arctic and Antarctica may feel far removed from the lives of most people, they play a critical role in the global climate system (IPCC 2013). Both these areas are undergoing fascinating changes and subject to ground breaking research, as can be seen by the significant analysis of polar regions in the most recent IPCC report (IPCC 2013). This includes a broad spectrum of research areas including both physical and biological disciplines (Anesio and Laybourn-Parry 2012). Hence the aim of this blog is to discuss and synthesise the scientific research undertaken in some of the most remote parts of the world – the polar regions.

More specifically, this blog will examine issues in the polar regions with relevance to the timescale of the so called ‘Anthropocene’. This is a concept first introduced by Paul Crutzen and Eugene Stoermer in 2000, who specified the need to define the most recent geological epoch as one which is characterized by mankind’s dominant impact on the global climate. Crutzen and Stoermer loosely designate the start of the Anthropocene as “the latter part of the 18^th century” (Crutzen and Stoermer 2000 pp. 17), although a precise commencement date is not necessarily required for these purposes. It is important to consider the Anthropocene an ongoing epoch, as human influence on the climate is by no means in decline. 

Therefore, the focus of this blog is research and issues in the Arctic and Antarctic during the Anthropocene, including their future in this epoch. I hope you enjoy reading, and any comments, thoughts or questions are encouraged.