Arctic Sea Ice More Resilient Than Thought

Arctic sea ice volumes in the autumn of 2014 are above the average set over the last five years and sharply up on the lows seen in 2011 and 2012, according to the latest satellite data.

Data from the European Space Agency (ESA) CryoSat-2 satellite to be presented to the American Geophysical Union’s Fall Meeting in San Francisco later today (Monday 15 December, 2014) will show Arctic sea ice volumes in October and November 2014 averaging 10,200km3 – slightly down on the 10,900km3 reported in 2013 but sharply up on the lows seen in 2011 and 2012.

This is the second year in a row where a relatively cool Arctic summer has led to less sea ice melting than has been typical during the summers of recent years and this has resulted in thicker and older ice surviving into the autumn and winter during both 2013 and 2014.

The team of researchers from University College London (UCL) who are presenting the CryoSat-2 data to the AGU Fall Meeting state in the abstract of their presentation that their data indicates “the Arctic sea ice pack may be more resilient than has been previously considered”.

The autumn 2014 volume is the second-highest since satellite measurements of Arctic sea ice thickness began in 2010, and the data shows that “the five-year average is relatively stable”, according to ESA.

This news comes as the US National Snow and Ice Data Center (NSIDC) reported that Arctic sea ice extent – the area of ocean covered by sea ice – in November was “fairly average”.

It is a combination of sea ice extent and sea ice thickness which gives rise to sea ice volume. CryoSat was designed to measure sea-ice thickness across the entire Arctic Ocean using radars, and this has allowed scientists to monitor the overall change in Arctic sea ice volume accurately over the last five years.

However, researchers are careful to caution that this apparent stability shown in the satellite data does not mean there has been a recovery in Arctic sea ice. A news release from ESA quotes Professor Andrew Shepherd from UCL and the University of Leeds as saying: “We must to take care when computing long-term trends as this CryoSat assessment is short when compared to other climate records”. Shepherd is one of the authors of the AGU presentation.

Here is a news release from the European Space Agency regarding this research issued on 15 December 2014:

CryoSat has delivered this year’s map of autumn sea-ice thickness in the Arctic, revealing a small decrease in ice volume. In a new phase for ESA’s ice mission, the measurements can now also be used to help vessels navigate through the north coastal waters of Alaska, for example.

Measurements made during October and November show that the volume of Arctic sea ice now stands at about 10 200 cubic km – a small drop compared to last year’s 10 900 cubic km.

The volume is the second-highest since measurements began in 2010, and the five-year average is relatively stable. This, however, does not necessarily indicate a turn in the long-term downward trend.

“We must to take care when computing long-term trends as this CryoSat assessment is short when compared to other climate records,” said Prof. Andrew Shepherd from University College London and the University of Leeds.

“For reliable predictions, we should try other approaches, like considering what is forcing the changes, incorporating the CryoSat data into predictive models based on solid physics, or simply waiting until more measurements have been collected.”

CryoSat was designed to measure sea-ice thickness across the entire Arctic Ocean, enabling scientists to monitor accurately the overall change in volume.

While the amount of ice normally fluctuates depending on the season, longer-term satellite records show a constant downward trend in ice extent during all seasons, in particular in summer, with a minimum occurring in the autumn of 2012.

Establishing whether the ice volume is following a similar trend is one of CryoSat’s key mission objectives.

A team of UK researchers at the Centre for Polar Observation and Modelling are presenting their findings this week at the American Geophysical Union’s autumn meeting in San Francisco, California.

“October is interesting because it is the first month we get data directly following the sea-ice minimum in September, so that’s where we see the largest interannual variability in our volume estimates,” said the Centre’s Rachel Tilling, who is working on the CryoSat measurements as part of her PhD studies.

Launched in 2010, CryoSat has long surpassed its planned three-year life. At the mission’s recent mid-term review, it was further extended until February 2017.

Tommaso Parrinello, ESA’s CryoSat Mission Manager, said, “CryoSat has already achieved outstanding results, both within its original mission objectives and for unexpected applications.

“Looking ahead, we are working hard to prototype new operational capabilities so that the measurements can be used for routine assessments in climate science and for services affected by Arctic sea ice.”

To test this, scientists have produced an assessment of sea-ice thickness north of Alaska and eastern Russia with data acquired over the last month. Products like this could prove useful for maritime services, such as shipping and exploration.

End of ESA news release.

Despite a well-documented ~40% decline in summer Arctic sea ice extent since the late 1970’s, it has been difficult to estimate trends in sea ice volume because thickness observations have been spatially incomplete and temporally sporadic. While numerical models suggest that the decline in extent has been accompanied by a reduction in volume, there is considerable disagreement over the rate at which this has occurred. We present the first complete assessment of trends in northern hemisphere sea ice thickness and volume using 4 years of measurements from CryoSat-2.

Between autumn 2010 and spring 2013, there was a 14% and 5% reduction in autumn and spring Arctic sea ice volume, respectively, in keeping with the long-term decline in extent. However, since then there has been a marked 41% and 9% recovery in autumn and spring sea ice volume, respectively, more than offsetting losses of the previous three years. The recovery was driven by the retention of thick ice around north Greenland and Canada during summer 2013 which, in turn, was associated with a 6% drop in the number of days on which melting occurred – climatic conditions more typical of the early 1990’s. Such a sharp increase in volume after just one cool summer indicates that the Arctic sea ice pack may be more resilient than has been previously considered.

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