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.