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Satellite data shows that Arctic sea ice was 50 per cent thicker in Autumn 2013 than it was in Autumn 2012, according to the US National Snow and Ice Data Center (NSIDC).
Data from the European Space Agency's (ESA's) CryoSat satellite which is equipped to measure the thickness of sea ice using radars shows that Arctic sea ice volumes grew by 50 per cent last year. This is due to an increase in ice thickness, since sea ice extent declined by around 3 per cent.
In a statement issued on 5 February, the NSIDC said: “Preliminary measurements from the CryoSat show that the volume of Arctic sea ice in autumn 2013 was about 50% higher than in the autumn of 2012. In October 2013, CryoSat measured approximately 9,000 cubic kilometers (approximately 2,200 cubic miles) of sea ice compared to 6,000 cubic kilometers (approximately 1,400 cubic miles) in October 2012.”
NSIDC data also shows that the decline in Arctic sea ice extent in January slowed to below the long-term rate of decline.
Over the last few decades, satellites have shown a downward trend in the area of Arctic Ocean covered by ice. However, the actual volume of sea ice has proven difficult to determine because it moves around and so its thickness can change.
According to ESA, CryoSat was designed to measure sea-ice thickness across the entire Arctic Ocean, and has allowed scientists, for the first time, to monitor the overall change in volume accurately.
About 90 per cent of the increase is due to growth of multiyear ice – which survives through more than one summer without melting – with only 10 per cent growth of first year ice. Thick, multiyear ice indicates healthy Arctic sea-ice cover, says ESA.
Multiyear ice at the end of 2013 was on average about 20 per cent, or around 30 cm, thicker than 2012.
“One of the things we’d noticed in our data was that the volume of ice year-to-year was not varying anything like as much as the ice extent – at least in 2010, 2011 and 2012... We didn’t expect the greater ice extent left at the end of this summer’s melt to be reflected in the volume. But it has been, and the reason is related to the amount of multiyear ice in the Arctic.” said Rachel Tilling from the UK’s Centre for Polar Observation and Modelling, who led the study into Arctic sea ice thickness, and was quoted in an ESA press release.
The ESA press release also quoted Professor Andrew Shepherd from University College London, who also worked on the research as saying:“It’s estimated that there was around 20 000 cubic kilometres of Arctic sea ice each October in the early 1980s, and so today’s minimum still ranks among the lowest of the past 30 years.”
Meanwhile Antarctic sea ice levels continue to expand. Antarctic sea ice extent continues to track very high in January, reaching the second-highest monthly extent in the 36-year satellite monitoring record, according to the NSIDC. New monthly extent records were set for each month between August and November, and December was tied for the record (within the limits of the precision).
Here is the full NSIDC report issued today, 5 February 2014:
Arctic sea ice extent remained lower than average in January, and just within two standard deviations of the long-term average. Arctic temperatures remained above average, even as cold winter air embraced North America. The retention of more sea ice in September 2013 has increased the overall thickness and volume of the ice pack compared to recent years. Antarctic sea ice remains significantly more extensive than average.
Arctic sea ice extent continued to track below average during January, remaining just within two standard deviations of the long-term average. The average extent for January was 13.73 million square kilometers (5.30 million square miles). This is 800,000 square kilometers (309,000 square miles) less than the 1981 to 2010 average, and 160,000 square kilometers (61,800 square miles) above the previous record low for the month of January set in 2011. Sea ice extent remains below average in the Barents Sea, the Sea of Okhotsk, and the Bering Sea. While recent winters have seen more extensive sea ice in the Bering Sea, this is the first January since 2005 for which below average conditions have been observed there. Extent is close to average in Baffin Bay, the Labrador Sea, and the Gulf of St. Lawrence.
Air temperatures for January were higher than average over most of the Arctic Ocean, helping to keep daily ice growth rates at near average values. Air temperatures at the 925 hPa level were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average over the central Arctic Ocean and 7 to 8 degrees Celsius (13 to 14 degrees Fahrenheit) higher than average over the North Atlantic region, Greenland, Baffin Bay, and Alaska. Cooler than average conditions prevailed over Siberia (−4 to −8 degrees Celsius, or −7 to −14 degrees Fahrenheit) and the southern Beaufort Sea (−2 to −4 degrees Celsius, or −4 to −7 degrees Fahrenheit). This temperature pattern is consistent with a negative Arctic Oscillation pattern, which dominated the month of January. This is in contrast to the positive Arctic Oscillation pattern, which dominated December 2013, leading to anomalously warm conditions over Siberia and Eurasia and colder than average conditions over Greenland, Alaska, and Canada.
Including 2014, sea ice extent for January is declining at a rate of 3.2% per decade relative to the 1981 to 2012 average, or at a rate of 47,800 square kilometers (18,500 square miles) per year. January 2014 is the fourth lowest extent in the satellite record, behind 2005, 2006, and the record low January 2011.
While satellite observations have shown a decline in Arctic Ocean sea ice extent since the late 1970s, sea ice is highly mobile, and a decrease in extent does not necessarily imply a corresponding decrease in ice volume. Observations of thickness (which allows calculation of volume) have been limited, making it difficult to estimate sea ice volume trends. The European Space Agency (ESA) CryoSat satellite was launched in October 2010 and has enabled estimates of sea ice thickness and volume for the last three years.
Preliminary measurements from CryoSat show that the volume of Arctic sea ice in autumn 2013 was about 50% higher than in the autumn of 2012. In October 2013, CryoSat measured approximately 9,000 cubic kilometers (approximately 2,200 cubic miles) of sea ice compared to 6,000 cubic kilometers (approximately 1,400 cubic miles) in October 2012. About 90% of the increase in volume between the two years is due to the retention of thick, multiyear ice around Northern Greenland and the Canadian Archipelago. However, this apparent recovery in ice volume should be considered in a long-term context. It is estimated that in the early 1980s, October ice volume was around 20,000 cubic kilometers (approximately 4,800 cubic miles), meaning that ice volume in October 2013 still ranks among the lowest of the past 30 years. CryoSat will continue to monitor sea ice through the current growth season, and the data will reveal the effect of this past autumn’s increase on ice volume at the end of winter.
Antarctic sea ice extent continues to track very high in January, reaching the second-highest monthly extent in the 36-year satellite monitoring record. New monthly extent records were set for each month between August and November, and December was tied for the record (within the limits of the precision). Trend maps of sea ice concentration (Figure 5b), however, reveal that the increase is not uniform around the Antarctic continent, nor is the strength of the monthly trends (in percent increase per decade) as great as those for the Arctic, in either winter or summer. While sea ice has increased in the western Ross Sea and the Weddell Sea, it has declined in the Amundsen and Bellingshausen seas.
Most efforts to explain these regional patterns of sea ice variability and trends have focused on variations in patterns of atmospheric circulation around the Antarctic continent, and how these patterns are driven by variations in sea surface temperature in the tropical Pacific Ocean (such as those associated with El Niño and La Niña). While these patterns show large variations seasonally and year-to-year, the longer-term trend in Pacific sea surface temperature is small, and does not appear to explain the long-term overall sea ice increases that have been observed. A new study published in Nature by Li and colleagues may provide the missing link. They argue that changes in the north Atlantic and tropical Atlantic sea surface temperatures may be driving long-term, subtle trends in Southern Ocean winds that would explain the regional trends in sea ice cover. Their results link higher Atlantic sea surface temperatures since 1979 to reduced sea level pressure in the Amundsen Sea, contributing to the resulting dipole-like sea ice pattern between the northern Ross Sea (where sea ice is increasing) and the northern Bellingshausen Seas (where it is decreasing).
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