Climate Science News
The sun has set over the central Arctic Ocean and Arctic sea ice extent is now increasing. Sea ice extent in Antarctica appears to have passed its seasonal maximum. The peak Antarctic value recorded so far of over 20 million square kilometers (7.7 million square miles) sets a new record over the period of satellite observations.Overview of conditions
Following the seasonal daily minimum of 5.02 million square kilometers (1.94 million square miles) that was set on September 17, 2014 (6th lowest in the satellite record), Arctic sea ice has started its seasonal cycle of growth. Arctic sea ice extent averaged for the month of September 2014 was 5.28 million square kilometers (2.04 million square miles), also the 6th lowest in the satellite record. This is 1.24 million square kilometers (479,000 square miles) below the 1981 to 2010 average extent, and 1.65 million square kilometers (637,000 square miles) above the record low monthly average for September that occurred in 2012.Conditions in context
Because ice extent falls through the first part of September and rises in the latter part, statistics on the average daily rate of ice loss or gain through the month are largely meaningless. More relevant is the total ice loss through the melt season. Between the seasonal maximum extent that occurred on March 21, 2014 and the September 17 minimum, the Arctic Ocean lost a total of 9.89 million square kilometers (3.82 million square miles) of ice, which is the 9th largest in the satellite record, but the least amount of seasonal loss since 2006. This year’s loss was 1.92 million square kilometers 741,000 square miles) less than the total loss that occurred in 2012.September 2014 compared to previous years
Through 2014, the linear rate of decline for September Arctic ice extent over the satellite record is 13.3% per decade, relative to the 1981 to 2010 average. The ten lowest September ice extents over the satellite record have all occurred in the last ten years.Summer weather conditions in 2014
Weather conditions prevailing over the summer of 2014 were unremarkable. Compared to the long term (1981 to 2010) climatology, sea level pressure over the period June through August was higher than average over much of the central Arctic Ocean, the Atlantic sector of the Arctic, and Greenland. While air temperatures at the 925 hPa level (approximately 3000 feet altitude) were slightly above average over part of the central Arctic Ocean, they were below average over the Kara Sea and just north of Alaska. The summer of 2013, which is now the 7th lowest ice extent in the satellite record, was also generally unremarkable in terms of temperature. Both of these years contrast sharply with 2012, which saw unusually warm conditions across the Arctic Ocean. The one significant weather pattern over the summer was a larger than normal pressure gradient over the Laptev Sea that drove southerly winds, brought warmer air, and helped drive sea ice northward. This led to the tongue of open water that reached to within 5 degrees latitude of the pole. However, this pressure gradient was not particularly extreme so thinner ice cover in the area was also a significant contributor to the open water near the pole. Sea surface temperatures may also have played a role, as we discussed in a previous post.Ice age
The distribution of sea ice age at the time of the minimum provides some insights into the summer evolution of the ice cover. For ice that is three years and older, the distribution is similar to recent years, with most of this ice along the northern coast of Greenland and northwestern coast of the Canadian Archipelago. Through the winter, older ice moved across the Beaufort and Chukchi seas due to the typical clockwise circulation of the Beaufort Gyre. Similar to recent summers, much of this ice melted away, though this year it lasted through most of the summer, contributing to the relatively late development of open water along the Alaskan coast.
One notable feature this year compared to last year is that a tongue of second-year ice (ice that is 1 to 2 years old) persisted north and east of the East Siberian Sea. This likely helped limit the loss of ice in this region and kept the ice edge much farther southward than in the neighboring Laptev Sea to the east. The predominance of thinner first-year ice in the Laptev region, along with persistent southerly winds, led to seasonal retreat of the ice edge to north of 85 degrees North latitude.Sea Ice maximum in Antarctica
As we reported in our Arctic minimum announcement, sea ice in Antarctica has remained at satellite-era record high daily levels for most of 2014. On September 22, 2014, Antarctic ice extent increased to 20.11 million square kilometers (7.76 million square miles). This was the likely maximum extent for the year.
This year’s Antarctic sea ice maximum was 1.54 million square kilometers (595,000 square miles) above the 1981 to 2010 average maximum extent, which is nearly four standard deviations above this average. The 2014 ice extent record is 560,000 square kilometers (216,000 square miles) above the previous record ice extent set on October 1, 2013. Each of the last three years (2012, 2013, and 2014) has set new record highs for extent in the Antarctic.
The monthly average Antarctic ice extent for September 2014 is 20.03 million square kilometers (7.73 million square miles). This is 1.24 million square kilometers (479,000 square miles) above the 1981 to 2010 average for September ice extent. The Antarctic sea ice trend for September is now +1.3% per decade relative to the 1981 to 2010 average.
Monthly averaged ice extent for September is well above average in the western Pacific (northern Ross Sea) and Indian Ocean (Enderby Land) sectors.Antarctic extent patterns
A comparison of ice extent (Figure 6a) with ice concentration trends (Figure 7) illustrates that the areas of unusual ice growth are in the same places that have been showing ongoing trends of increased ice extent. This suggests that wind patterns play a significant role in the recent rapid growth in Antarctic ice extent. However, another possible reason is that recent ice sheet melt, caused by warmer, deep ocean water reaching the coastline and melting deeper ice, is making the surface water slightly less dense. While the change in saltiness is too small to significantly affect the freezing temperature, the increase in slightly less dense water surrounding Antarctica inhibits mixing, creating conditions that favor ice growth (as we discussed in our July 17 post).Late season growth patterns
The period between September 10 and September 22 saw very rapid late-season ice growth in Antarctica, pushing the total sea ice extent upward by nearly 60,000 square kilometers per day (23,000 square miles). An animation of Antarctic sea ice concentrations from AMSR2 satellite data shows that a pulse of increased sea ice growth in several areas, but especially in the northern Weddell Sea, was the cause of the rapid rise in extent. A look at the weather for mid-September in the south indicates that a band of southerly winds swept from west to east across the northern Weddell Sea, favoring both ice growth and ice advection to the north.
For the mid-winter period, climate patterns for 2014 evolved in a similar way to 2013, as discussed in previous posts and in a paper led by our colleague, Phillip Reid. Sea ice growth in the Ross, Amundsen, and Bellingshausen seas for the austral winter of 2014 was favored by moderately strong low pressure anomalies in the Amundsen Sea, the northern Weddell Sea, and the central Indian Ocean region in mid-winter (late July and August). But at the period of the sea ice maximum, higher pressures over the continent reduced the intensity of westerly winds, and resulted in cooler southerly winds over the Weddell Sea and the Amundsen Sea. This helped to create the very large ice extent values seen in September. The Antarctic sea ice maximum period, as described above, had a further push from southerly winds over the far southern Atlantic (northernmost Weddell Sea) and Indian Ocean regions.
A related note
Last year, a vessel became trapped in ice south of Australia in an incident that highlighted the need for better local ice forecasts. The International Ice Charting Working Group will meet later this month in Punta Arenas, Chile. Members will work on improving the collective capability of ice services to provide ice information in the interests of marine safety.
Reid, P., S. Stammerjohn, R. Massom, T. Scambos, and J. Lieser. 2015, in press. The record 2013 Southern Hemisphere sea-ice extent maximum. Annals of Glaciology 56 (69), doi:10.3189/2015AoG69A892.
On September 17, Arctic sea ice reached its likely minimum extent for 2014. This is now the sixth lowest extent in the satellite record and reinforces the long-term downward trend in Arctic ice extent. Sea ice extent will now begin its seasonal increase through autumn and winter. Meanwhile, sea ice in the Antarctic has surpassed the previous record maximum extent set in 2013 and is now more than 20 million square kilometers (7.72 million square miles) for the first time in the past thirty-five years. It is too soon to determine if Antarctic sea ice has reached its annual maximum.
Please note that this is a preliminary announcement. Changing winds in the Arctic could still push ice floes together, reducing Arctic ice extent below the current yearly minimum. NSIDC scientists will release a full analysis of the Arctic melt season, and discuss the Antarctic winter sea ice growth, in early October.Overview of conditions
On September 17, 2014, sea ice extent dropped to 5.02 million square kilometers (1.94 million square miles). This appears to have been the lowest extent of the year. In response to the setting sun and falling temperatures, ice extent will now climb through autumn and winter. However, a shift in wind patterns or a period of late season melt could still push the ice extent lower. The minimum extent was reached two days later than the 1981 to 2010 average minimum date of September 15.Conditions in context
This year’s minimum was 1.61 million square kilometers (622,000 square miles) above the record minimum extent in the satellite era, which occurred on September 16, 2012, and 1.20 million square kilometers (463,000 square miles) below the 1981 to 2010 average minimum.Varying distribution of ice in 2014 versus 2013
This year, the ice cover remained more extensive over the Barents and Kara seas compared to last year. The most notable feature was the lack of ice north of the Laptev Sea that at one point in the melt season extended beyond 85 degrees North latitude, within 550 kilometers (342 miles) of the North Pole. This year was also unusual compared to recent years in that the Northwest Passage remained closed. On the other side of the Arctic, the Northern Sea Route or Northeast Passage opened with little ice near most of the shipping route along the coast of Siberia.Antarctic overview and conditions
While it is too soon to tell if sea ice around Antarctica has reached its annual maximum for the winter, it remained at record high daily levels for most of the year. On September 19, the five-day average ice extent surpassed 20 million square kilometers (7.72 million square miles) for the first time in the satellite record. Ice extent is above average in almost all sections of the Antarctic, particularly in the northern Ross Sea and Indian Ocean sectors. Near-average ice extent occurs south of South America in the northern Bellingshausen Sea and in a small region south of Australia.
Previous minimum Arctic sea ice extents Table 1. Previous minimum Arctic sea ice extents YEAR MINIMUM ICE EXTENT DATE IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES 2007 4.17 1.61 September 18 2008 4.59 1.77 September 20 2009 5.13 1.98 September 13 2010 4.63 1.79 September 21 2011 4.33 1.67 September 11 2012 3.41 1.32 September 16 2013 5.10 1.97 September 13 2014 5.02 1.94 September 17 1979 to 2000 average 6.70 2.59 September 13 1981 to 2010 average 6.22 2.40 September 15
The end of this year’s Arctic sea ice melt season is imminent and the minimum extent will be slightly lower than last year’s, making it the sixth lowest extent in the satellite record. Earlier in the month, a small area of the Laptev Sea ice edge was within five degrees of the North Pole. This appears to be the result of persistent southerly winds from central Siberia. Meanwhile, Antarctic sea ice is poised to set a record maximum this year, now at 19.7 million square kilometers (7.6 million square miles) and continuing to increase.Overview of Conditions
Arctic sea ice extent for September 15 was 5.07 million square kilometers (1.96 million square miles). This is only 30,000 square kilometers (11,600 square miles) below the same date last year, yet sea ice extent remains low compared to the long-term 1981 to 2010 average. As is typical for this time of year, weather conditions near the ice edge heavily influence the timing of the minimum, which has occurred as late as September 23. We are now a day past the 1981 to 2010 average minimum date of September 15.Conditions in context
Sea ice extent declined at a rate of 28,700 square kilometers (11,100 square miles) per day through the first half of September. This is nearly twice as high as the 1981 to 2010 average rate of decline for this period of 16,200 square kilometers (6,200 square miles) per day. As was the case for the beginning of the month, extent remains below average in all sectors of the Arctic except for a region in the Barents Sea, east of Svalbard. There are areas of fairly low concentration ice north of the East Siberian and Chukchi seas that may still melt out or compact from wind-driven drifting.
However, as in 2013, a large area in the East Siberian Sea remains ice covered, helping to keep the overall extent higher for this time of year than observed since 2007. Last summer that area was covered by first-year ice that did not melt out under cooler-than-average conditions. This year, a region of second-year ice appears to have helped stabilize ice loss there.
The Northwest Passage remains closed, while the Northern Sea Route is still largely clear of ice.A new ice edge
Through the first half of September, the ice edge slowly retreated north of the Laptev Sea and is now within five degrees latitude of the North Pole. This is the most northerly position that the ice edge has been recorded over the period of satellite observations in this region. A large part of this region was also ice free in 2007. The reasons for the strong ice retreat in this sector are, at present, not entirely clear but we offer some initial insights.
In April, we discussed the pattern of ice age across the Arctic as the melt season began. In general, younger ice tends to be thinner ice. Areas of young ice are more likely to melt out during the summer than areas of old ice. The ice age figure from that post, reproduced here (Figure 3a), shows a strong northward extension of ice less than one year of age along the same general longitudes that open water has developed. Given the general circulation of the sea ice away from the Siberian shores, this area of thin ice prone to melting out would have tended to advance further northward through the melt season. Indeed, average sea level pressures this summer featured a pattern of surface winds particularly conducive to transporting thinner ice northward in the Laptev Sea sector (Figure 3b). To the east, winds were calmer and an arm of older, thicker second-year ice there may have helped to limit melt out and northward advection.Sea surface temperature update
As one may expect with an early retreat of sea ice, sea surface temperatures in the Laptev Sea were higher than average by up to 5 degrees Celsius (9 degrees Fahrenheit), with up to 3 degrees Celsius (5 degrees Fahrenheit) anomalies extending north of 80 degrees North for the first time since 2007. Early ice retreat and high sea surface temperatures are not unusual for this area and have appeared every summer since 2007, with the exception of 2008. The date of ice opening in the Laptev Sea is not particularly unusual in 2014 either. Open water and warming ocean temperatures started in early June. However, this summer there was a rapid northward progression of the ice edge in this area, especially along about longitude 140 degrees East, which allowed the sun to warm the resulting open water.
Over other parts of the Arctic, sea surface temperatures were not particularly noteworthy, except for cooler-than-average conditions in the northern Barents and Kara seas where the ice has remained extensive compared to recent summers. This reverses a recent trend toward warming and ice retreat in these areas, noted in last year’s sea surface temperature update. Preliminary analysis indicates that these changes are forced by local meteorological conditions, rather than oceanic heat transport by Atlantic water.Further reading
Steele, M., S. Dickinson, and J. Zhang. 2014. Seasonal ice loss in the Beaufort Sea: Toward synchronicity and prediction. Journal of Geophysical Research-Oceans. In review.
The Arctic summer of 2014 is nearing an end. Overall, the rate of ice loss during August was near average. Regions of low concentration ice remain in the Beaufort and East Siberian seas that may yet melt out or compress by wind action. While the Northwest Passage continues to be clogged with ice and is unlikely to open, the Northern Sea Route along the Siberian coasts appears open except for some ice around Severnaya Zemlya. As the end of the southern winter draws closer, Antarctic sea ice extent remains higher than average.Overview of conditions
Sea ice extent in August 2014 averaged 6.22 million square kilometers (2.40 million square miles). This is 1.00 million square kilometers (386,000 square miles) below the 1981 to 2010 August average, but well above the 2012 August average of 4.71 million square kilometers (1.82 million square miles). Extent was below average throughout the Arctic except for a region in the Barents Sea, east of Svalbard. The ice edge continued to retreat north of the Laptev Sea, and is now within 5 degrees latitude of the North Pole.Conditions in context
August ice extent declined at an average rate of 54,300 square kilometers (21,000 square miles) per day. This was slightly less than the average rate for the month. Generally, the decline slows in August as the Arctic sun dips lower in the sky. Recent years have been an exception, with relatively fast ice loss rates in August.
August 2014 compared to previous years
Despite the near-average rate of decline in ice extent through the month, August 2014 ended up with the 7th lowest extent in the satellite record. It is 1.51 million square kilometers (583,000 square miles) above the record low for August 2012 and is also higher than August of 2007, 2008, 2010, 2011, and 2013. The monthly linear rate of decline for August over the satellite record is now 10.3 percent per decade.The Northwest Passage: closed for business
Several recent years have seen remarkably open conditions in the Northwest Passage by the end of August. This year, however, much of the passage is clogged with ice, and even the circuitous Amundsen route is not entirely open. (Note that Amundsen required two summers to navigate this route in 1905; Amundsen wintered over in the hamlet of Gjoa Haven—now called Uqsuqtuuq).
The recent openings of the Northwest Passage in 2007, 2008, 2010, and 2011 were associated with high sea level pressure anomalies over the Beaufort Sea and Canadian Basin. This atmospheric pattern essentially displaces the polar pack away from the M’Clure Strait, resulting in minimal ice inflow from the Arctic Ocean. In contrast, weather patterns this year have been more moderate, and as a result, more ice remains in the Northwest Passage. As of the end of August 2014, ice area in the passage was tracking above the 1981 to 2010 average. Ice area over the summer of 2013 tracked slightly below the 1981 to 2010 average, but was considerably higher than the years prior. The summer of 2011 saw the lowest ice area in the Northwest Passage since 1968.
On the other side of the Arctic Ocean, conditions are much more open along the Northeast Passage (also known as the Northern Sea Route). There are wide areas of open water along much of the Russian Arctic coast, the lone exception being the area around Severnaya Zemlya.Reference
Howell, S. E. L., T. Wohlleben, M. Dabboor, C. Derksen, A. Komarov, and L. Pizzolato. 2013. Recent changes in the exchange of sea ice between the Arctic Ocean and the Canadian Arctic Archipelago, J. Geophys. Res. Oceans, 118, 3595-3607, doi:10.1002/jgrc.20265.
Arctic sea ice extent is well below average, and large areas of low concentration ice are observed in the Beaufort Sea and along the Siberian coast. However, it is highly unlikely to set a record low at the end of this year’s melt season. Antarctic sea ice extent remains at record highs.Overview of conditions
Sea ice declined at slightly slower than average rates through the first part of August. By mid-August, extent was similar to this time last year, which makes it unlikely that this year’s minimum extent will approach the record low level observed in September 2012. On August 17, sea ice extent was 1.03 million square kilometers (398,000 square miles) below the 1981 to 2010 long-term average and 1.42 million square kilometers (548,000 square miles) above that observed in 2012 on the same date. Ice extent remains below average everywhere, except near Franz Joseph Land and in the northern part of the Barents Sea. Extent is particularly low in the Laptev Sea where open water now extends to about 85 degrees latitude, less than 560 kilometers (350 miles) from the North Pole. This is the one region of the Arctic where ice loss has been exceptional in 2014 compared to recent summers. Ice extent is also very low in the East Greenland Sea, possibly as a result of reduced ice transport through Fram Strait.Conditions in context
The first part of August was dominated by anomalously low sea level pressure over the Kara Sea, combined with anomalously high pressure over the central Arctic Ocean and Greenland, as well as the Beaufort and Chukchi seas. This led to warm air advection from the south over the East Siberian and Chukchi seas and extending into the central Arctic Ocean, with air temperatures at the 925 millibar height being nearly 8 degrees Celsius (14 degrees Fahrenheit) higher than average off the coast of Siberia near the New Siberian Islands. Sea ice concentrations in this region dropped compared to the beginning of August, and the waters along the coast of eastern Siberia are now mostly ice free. Ice concentrations are also low in the Beaufort Sea. Ice has continued to break up in the Kara Sea where it has been slow to melt out this summer. Nevertheless, air temperatures in the Kara Sea remain lower than average by 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit). As of mid-August, sea ice extent remains on track to end up somewhere between the sixth and the tenth lowest sea ice minimum.Low ice concentration as seen from MODIS
Visible satellite imagery from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) reveal a diffuse ice cover in the Beaufort Sea, as well as in areas of the Laptev and East Siberian seas. Despite low ice concentrations, ice extent is right at the long-term average for the region, in stark contrast to 2012 when the ice edge had already retreated to north of 75 degrees latitude. Ice remains extensive in the Northwest Passage through the channels of the Canadian Arctic Archipelago. On the Eurasian side, the Northern Sea Route is mostly open except that some ice still blocks Vilkitsky Strait, the narrow strait between the Siberian coast and the islands of Severnya Zemlya separating the Kara and Laptev seas.No new record low in 2014
During August, sea ice extent declines more slowly as the sun starts to set in the Arctic and the sea ice minimum approaches. Thus, the window is closing on potential ice loss through the remaining summer. A simple way to estimate how much ice loss may occur during the rest of the summer is to extrapolate daily ice loss, using rates of ice loss from previous years. The approach provides a reasonable bracket on possible scenarios through September. Using the 1980 rate of ice loss yields the highest potential minimum this year, because the end of summer rate of ice loss in 1980 was very slow. The lowest potential minimum is estimated using the 2012 rate of ice loss, as there was rapid ice loss in 2012. No scenario suggests a minimum near the record low year of 2012. Most likely this year’s minimum will be between 5.0 and 5.5 million square kilometers (1.9 and 2.1 million square miles).Antarctic sea ice trend
Antarctic sea ice remains at a daily record high, and 1.19 million square kilometers (459,000 square miles) above the 1981 to 2010 average. Sea ice extent is now higher than average nearly everywhere around the continent, except for a portion of the northwestern Weddell Sea. This has occurred despite the fact that air temperatures at the 925 hPa level in the Ross and western Amundsen Sea have been much higher than average, by up to 8 degrees Celsius (14 degrees Fahrenheit), for the past two weeks. Longer term, the preceding three months (mid-May to mid-August) have been slightly warmer than average over most of the Antarctic sea ice areas. This supports the idea that the record or near record high Antarctic ice extents of 2014 have been driven by wind patterns and ocean conditions as discussed in our July post.
Arctic sea ice extent declined at a fairly rapid rate through the first three weeks of July, but the loss rate then slowed due to a shift in weather patterns. In Antarctica, the advance of sea ice nearly halted for about a week in early July, and then resumed. At the end of the month, Antarctic extent was at or near a record high for this time of year.Overview of conditions
July 2014 average ice extent was 8.25 million square kilometers (3.19 million square miles). This is 1.85 million square kilometers (714,000 square miles) below the 1981 to 2010 average for the month.
Ice extent is below average in nearly all sectors of the Arctic. Open water continued to grow in the Laptev and Beaufort Seas, reaching well north of 80oN in the Laptev Sea. By the end of the month, the Alaskan Coast was essentially free of ice except for small patches of very diffuse ice off Barrow. The Barents Sea, Hudson Bay, and Baffin Bay/Davis Strait are now essentially ice free. Large areas of low concentration ice in the central Beaufort Sea are likely to melt out in coming weeks. The Northwest Passage through the channels of the Canadian Arctic Archipelago remains choked with ice. Parts of the Northern Sea Route are still difficult to traverse because of high-concentration, near-shore ice between the Laptev and East Siberian seas and also north of the Taymyr Peninsula.Conditions in context
For July 2014 as a whole, ice extent declined at an average rate of 86,900 square kilometers (33,600 square miles) per day, close to the 1981 to 2010 average July rate of 86,500 square kilometers (33,400 square miles) per day. However, this averages together a fairly fast rate of decline over the first three weeks of the month with a slower rate of decline over the remainder of the month.
The slower ice loss later in the month reflects a shift in weather patterns. For much of the month, high pressure at sea level dominated the central Arctic Ocean and the Barents Sea. However, this pattern broke down and was replaced by lower-than-average pressure over the central Arctic Ocean. A low pressure pattern tends to bring cool conditions and the counterclockwise winds associated with this pattern also tend to spread the ice out.July 2014 compared to previous years
July 2014 is the 4th lowest Arctic sea ice extent in the satellite record, 340,000 square kilometers (131,000 square miles) above the previous record lows in July 2011, 2012, and 2007. The monthly linear rate of decline for July is 7.4% per decade.More news on the Antarctic
In our previous post, we noted that on July 1, Antarctic sea ice extent was growing rapidly, and could surpass the September 2013 record high extent (over the period of satellite observations). During early July, the advance of Antarctic sea ice extent nearly halted, but toward the end of the month, there was another period of rapid ice growth. Maximum extent is usually reached in September or October, at the end of the austral winter.
Many readers may be familiar with NSIDC’s Charctic interactive sea ice graph that allows one to plot daily Arctic ice extent for any year in the satellite record (1979 to present) and make quick comparisons with average conditions and between different years. NSIDC has recently added an Antarctic option to Charctic. We have done so in response to growing interest in Antarctic sea ice conditions and the very different behavior of Arctic and Antarctic sea ice. Just go to the Charctic site and click the button marked “Antarctic.”Questions about data processing
A recent paper investigated the processing of Antarctic sea ice data and how this affects the interpretation of Antarctic ice extent trends. While their findings do not affect NSIDC’s analysis of Antarctic sea ice extent, as we use a different data set, it is an interesting example of scientific rigor regarding data, and it does affect other reports of Antarctic sea ice trends.
The paper studied the Bootstrap algorithm, which has been used in several published reports of Antarctic trends, including the last two IPCC Assessment Reports. These reports suggested that the Antarctic sea ice extent shifted from a small, statistically insignificant upward trend in the early 2000s to a more substantial, and statistically significant upward trend in recent years. (NSIDC uses a different algorithm, called NASA Team, to estimate sea ice extent.)
The paper found that following an update to the algorithm in 2007, using the newer Version 2 of the Bootstrap algorithm produced Antarctic sea ice extent trends that were approximately two times larger than those derived using Version 1. Closer examination of the data showed a noticeable step change in extent at the point of transition to a new satellite sensor in 1991. This step change appeared to be related to an error in calibration between the sensors, rather than actually being an abrupt shift in Antarctic sea ice.
Trends derived from both versions for time periods either before or after the sensor transition are similar. However, the two algorithms produce different results when trends that span the 1991 sensor transition are calculated. Using Version 2 of the algorithm produces a markedly higher trend.
Using the newer version of the algorithm, Antarctic extent trends agree much more closely with the trends from the NASA Team algorithm used by NSIDC. Regardless, the expansion in Antarctic sea ice is confirmed by other groups using different techniques.
Eisenman, I., W. N. Meier, and R. J. Norris. 2014. A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?, The Cryosphere 8, 1289-1296, doi:10.5194/tc-8-1289-2014.
Arctic sea ice extent continued a rapid retreat through the first two weeks of July as a high pressure cell moved over the central Arctic Ocean, bringing higher temperatures. Antarctic sea ice extent increased rapidly through June and early July, and reached new daily record highs through most of this year.Overview of conditions
During the second half of June, the rate of sea ice loss in the Arctic was the second fastest in the satellite data record. As a result, by the beginning of July extent fell very close to two standard deviations below the long-term (1981 to 2010) average.
The rate of ice loss for the first half of July averaged 104,000 square kilometers (40,000 square miles) per day, 21% faster than the long-term average for this period.
Ice loss during the first two weeks of July 2014 was dominated by retreat within the Laptev Sea, and within the Kara and Beaufort seas. Open water areas now exist north of 80 degrees North in the Laptev Sea. Ice cover remains fairly extensive in the Beaufort and Kara seas compared to recent summers.
By July 15, ice extent had fallen to within 440,000 square kilometers (170,000 square miles) of that seen in 2012 (the modern satellite-era record minimum) on the same date, and was 1.54 million square kilometers (595,000 square miles) below the 1981 to 2010 average. However, ice concentration remains high within the central Arctic Ocean, particularly compared to 2012.Conditions in context
The first half of July 2014 was dominated by anomalously high sea level pressure over the Arctic Ocean and the Barents Sea, coupled with below-average sea level pressure over Iceland. Air temperatures at the 925 millibar level (or about 2,500 feet above the surface) were mostly 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average over parts of the Arctic Ocean, leading to surface melting. Air temperatures were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average in the Kara and Barents seas, where melt has generally been off to a slower start than average this summer. Ice extent remains below average in the Laptev and East Greenland seas and Baffin Bay, and is near average to locally below average in the Beaufort, Chukchi and Kara seas.Onset of summer melt
In general there has been a trend over the satellite data record towards earlier melt onset in the Arctic. Melt usually now begins an average of 7 days earlier than in the late 1970s and early 1980s, or at a rate of about 2 days earlier per decade. However, in regions such as the Kara and Barents seas, melt has begun on average 5 to 7 days per decade earlier, totaling 18 to 25 days earlier since 1979, helping to foster earlier development of open water in those regions.
Despite statistically significant trends towards earlier melt onset, there remains a lot of year-to-year variability. For example, in 2013, melt was slow to start, particularly over the Arctic Ocean, the Laptev and East Siberian seas, Hudson Bay, and the Bering Sea. By contrast, melt onset in 2012 was generally earlier than average over most of the Arctic Ocean, including the Beaufort, Chukchi, Laptev, and Kara seas, as well as Hudson Bay and Baffin Bay, and later than normal in the East Siberian Sea, the Greenland and Bering seas. While melt began earlier than average this summer in the Beaufort, Chukchi, Bering, and Laptev seas, it has been somewhat slower to start in the East Siberian Sea and in the Kara Sea, as well as in large parts of the central Arctic Ocean.Conditions in Antarctica
On July 1, Antarctic sea ice extent was at 16.16 million square kilometers (6.24 million square miles), or 1.37 million square kilometers (529,000 square miles) above the 1981 to 2010 average. More notably, sea ice extent on that date was 760,000 square kilometers (293,000 square miles) higher than the 2013 extent for the same day, and thus is on pace to possibly surpass the record high extent over the period of satellite observations that was recorded last September.
For June, sea ice concentration and extent were higher than average for the Amundsen, Southern Indian Ocean, and far southern Atlantic (Weddell and eastward) sectors. (See Antarctic reference map.) The regions on either side of the Antarctic Peninsula were among the few sections with lower-than-average concentration and lower sea ice extent. Cooler-than-average ocean conditions are present near the ice edge along the Wilkes Land, Amundsen Sea, and Weddell Sea ice edge, which will favor continued expansion of sea ice in these areas.
Weather patterns over Antarctica during June were characterized by a strong low-pressure pattern over the Amundsen Sea, and lower-than-average air temperatures (1 to 6 degrees Celsius, or 2 to 11 degrees Fahrenheit below average) in the same region. Cool conditions (2 to 3 degrees Celsius or 4 to 5 degrees Fahrenheit below average) surrounded most of the coastal areas of the Antarctic, with the exception of the Peninsula region where, as has also been seen in the first two weeks of July, northerly winds brought warmer-than-average conditions and reduced sea ice extent.Antarctica’s positive trend in sea ice extent
Antarctic sea ice extent also shows a small, long-term upward trend over the period of satellite observations. Antarctica and the Southern Ocean are geographically very different from the Arctic, and are governed by different atmospheric and ocean circulation patterns. Nevertheless, Antarctica has experienced many of the same general signals of Earth’s changing climate as in the Arctic, including general warming, ice sheet loss and faster-flowing glaciers. This makes the small, long-term upward trend in Antarctic sea ice extent rather puzzling. The record sea ice maxima over the past two years (relative to the modern satellite era) have added to the puzzle.
Two recent studies, focused on the back-to-back satellite-era record maxima of 2012 and 2013 (Turner et al., 2013; Reid et al., 2014 in press), point to unusual short-term wind patterns that both fostered ice growth and spread the ice out. In both years, the record-setting extents are related to the size and strength of the Amundsen Sea low pressure area late in the growth season. The more recent study also notes cool ocean water (1 to 2 degrees Celsius or 2 to 4 degrees Fahrenheit below average) persisting near the sea ice edge in the Amundsen-Bellingshausen region in July and August 2013.
Leading ideas regarding the long-term upward trend as assessed over the thirty-five-year satellite record are: (1) persistent changes in wind patterns, resulting from increased westerly winds, which have changed both how much ice is formed and how it is moved around after formation (Holland and Kwok, 2012); and (2) that meltwater from the underside of deep floating ice shelves surrounding the continent (greater than 350 meters, or 1,150 feet thick) has risen to the surface and contributed to a slight freshening of the surface ocean layer (Bintanja et al., 2012). The extra melting results from the changing wind patterns, which act to draw deep warm ocean water inward to the continent to replace surface water and sea ice that is pushed outward and eastward by the stronger westerlies. By thickening, spreading, and stabilizing the polar surface ocean layer (which is comprised of cool, near-freezing water) the increased melt from the ice sheet edges helps sea ice grow around the Antarctic continent.Early satellite data
Antarctica’s sea ice extent has also been highly variable. For example, austral summer minimum ice extents have varied by as much as 25% over the 1979 to 2014 modern satellite record. The June 1979 extent was the highest for a month by a significant margin. Then in 2002, June sea ice extent was the lowest ever recorded. Nine years later, in June 2011, extent tracked below the 1981 to 2010 average.
This variability is underscored by recent assessments of very early satellite images from the Nimbus program of the late 1960s (Gallaher et al., 2014). Mapping of the September 1964 ice edge (at the austral winter sea ice maximum) indicates that 1964 likely exceeded both the 2012 and 2013 record monthly-average maximums, at 19.7±0.3 million square kilometers (7.60±0.11 million square miles). This was followed in August 1966 by an extent estimated at 15.9±0.3 million kilometers (6.13±0.11 million square miles), considerably smaller than the record low August monthly extent set in 1986. It hence appears that Antarctica’s sea ice variability may be greater than the 35-year modern satellite record would indicate, and that the current growth trend, while important, is not yet reaching unprecedented levels seen within the past century.Further reading
Bintanja, R., G. J. Van Oldenborgh, S. S. Drijfhout, B. Wouters, and C. A. Katsman. 2013. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion, Nature Geoscience, 6, 376–379, doi:10.1038/ngeo1767.
Gallaher, D., G. G. Campbell, and W. N. Meier. 2014. Anomalous variability in Antarctic sea ice extents during the 1960s with the use of Nimbus data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 7(3), 881-887, doi:10.1109/JSTARS.2013.2264391.
Holland, P., and R. Kwok. 2012. Wind-driven trends in Antarctic sea-ice drift. Nature Geoscience, 5(12), 872-875, doi:10.1038/ngeo1627.
Reid, P., S. Stammerjohn, R. Massom, T. Scambos, and J. Leiser. 2014 in press. The record 2013 Southern Hemisphere sea-ice extent maximum. Annals of Glaciology, in press, 64(69).
Turner J., J. S. Hosking, T. Phillips, and G. J. Marshall. 2013. Temporal and spatial evolution of the Antarctic sea ice prior to the September 2012 record maximum extent. Geophysical Research Letters, 40, 5894–5898, doi:10.1002/2013GL058371.
Ssalto/Duacs maps of Seal Level Anomalies (in cm) made from 4 altimetry mission (Jason-2, Cryosat-2, Saral and HY-2A), on 2014/07/07 when the typhoon is max. The typhoon path is shown by colored circles (the intensity scale is purple for a tropical depression, blue for cat. 1, green for cat. 2, yellow for cat. 3, orange for cat.4 and red for category 5. The dates near the path indicates the date when the hurricane passed. Credits Cnes/CLS Ssalto/Duacs.
Maps of significant wave height (in m) measured along-track by HY-2A over the ocean. Only the ground tracks between the 2014/07/04 and the 2014/07/09 are represented. Credits Cnes/CLS Ssalto/Duacs.Further information:
- Applications: Hurricanes
- Altimetry applications in videos: Monitoring hurricanes
- Nasa Earth Observatory: Typhoon Neoguri
Arctic sea ice extent continues its seasonal decline. Through most of June the pace of decline was near average, but increased towards the end of the month.Overview of conditions
June 2014 averaged 11.31 million square kilometers (4.37 million square miles). This is 580,000 square kilometers (224,000 square miles) below the 1981 to 2010 average for the month.
Large areas of open water quickly opened up in the Laptev Sea at the beginning of June and continued to expand through the month. The southern part of the Beaufort Sea has also opened and melt ponds are apparent on the open drift first-year ice and extending into the pack ice (see Figure 5 below). Nevertheless, ice extent in this region continued to be above the levels of recent years through much of the month. Extent was lower than average in the Barents Sea, Hudson Bay, and the East Greenland Sea, but higher than in recent years in the Kara Sea.Conditions in context
Ice extent during June declined by an average of 78,900 square kilometers (30,500 square miles) per day, faster than the 1981 to 2010 average June rate of 57,200 square kilometers (22,100 square miles) per day. Last March’s relatively low maximum extent helped set the stage for June’s low extent. June is a month that has seen large variability in the rate of ice loss in recent years. In 2012, a period of rapid acceleration occurred during the first half of the month, kick-starting the decline towards the eventual record low extent that September. So far, 2014 has failed to match the 2012 loss rates. However, ice extent on June 30th came within 300,000 square kilometers (115,800 square miles) of that in 2012. The 2014 rate of ice decline also accelerated toward the end of June as wide areas of low-concentration ice on the peripherial areas of the Arctic Ocean opened up, especially in the Hudson and Baffin bays. This increased rate of loss is typical of late June and early July, and is visible in the 30-year mean trend for Arctic sea ice (see the ChArctic interactive sea ice chart).June 2014 compared to previous years
June 2014 is the 6th lowest Arctic sea ice extent in the satellite record, 490,000 square kilometers (189,000 square miles) above the previous record low in June 2010. The monthly linear rate of decline for June is 3.6% per decade.A cooler June
At the 925 mb level (approximately 3000 feet above sea level) average June temperatures over parts of the Arctic Ocean were from 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) below the 1981 to 2010 average, but with a warming trend over the latter half of the month; the last week of June saw temperatures of 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average over the central Arctic Ocean. June 2013 was also slightly cooler than average.This is in stark contrast to the unusually warm summers of many recent years, particularly 2012 and 2007 when air temperatures over the Arctic Ocean were up to 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit), respectively, above average.
The cool conditions in June 2013 were attributed to a generally cyclonic pattern of atmospheric circulation. However, by late June 2014 the more typical pattern of high pressure over the Beaufort Sea had developed, coupled with low pressure over Alaska and Eurasia.Landsat 8 expands Arctic Sea Ice coverage
Landsat 8, launched in February of 2013, has been regularly acquiring images of the world’s daylit land surface since May of that year. The mission recently increased the pace of image acquisition, covering nearly all available daylit areas each day, and expanded coverage of sea ice areas in the Arctic and coastal areas of Greenland (the latter with ascending node, or evening hour, coverage). Coverage for the Arctic Ocean is focused on the far western and far eastern Arctic, that is, the Beaufort, Chukchi, and East Siberian Sea, although substantial coverage of sea ice is included in the acquisition of all Arctic land areas. Ascending (evening) and decending (morning, the typical acquisition time) coverage of coastal Greenland permits better tracking of glacier flow and in particular sea ice break-up and glacier retreat in the fjord areas.
The images, and the historical (somewhat variable) record of Arctic coverage provide information on ice type, surface melting and melt ponds, ice motion, coastal fast ice break-up, lead fraction and shear zones within the ice.More on seasonal thickness evolution of Arctic sea ice
As noted in last month’s post, satellite and airborne sensors are now able to provide good coverage of the Arctic ice thickness. However, as with any remote sensing estimate, the observations come with uncertainty. Direct measurements, even though they do not provide wide-coverage, are important for validation. They can also provide a useful indication of general ice conditions (thickness, temperature) at the beginning of the ice season. Such direct observations, in concert with available satellite and airborne data, can improve seasonal forecasts of sea ice, such as those provided in the recently released Sea Ice Outlook.
In March, the U.S. Navy’s Office of Naval Research (ONR) Marginal Ice Zone project deployed three clusters of mass balance buoys on the sea ice, complementing ongoing similar deployments by the U.S. Army Cold Regions Research and Engineering Laboratory. These mass balance buoys not only provide a simple thickness measurement, but can also provide a time series of the evolution of the ice, both at the top and bottom surface. The ONR buoys additionally include air temperatures sensors, which are useful for monitoring atmospheric conditions, as well as temperatures through and below the ice.
ONR deployed three clusters of buoys in the Beaufort Sea at three different latitudes. Initial ice thickness at the sites was between 1.5 and 2 meters (5 and 6.5 feet). During April and May, there were brief incursions of above freezing air temperatures leading to some melt, but temperatures mostly remained below freezing until early June. All three clusters show continuous above freezing air temperatures starting by the second week of June. With the higher temperatures, melt has commenced on both the top and bottom surfaces.
The Beaufort Sea has been a region of dramatic summer ice loss in recent years, particularly 2012, with regions dominated by thicker, multi-year ice melting out completely. While vigorous melt has begun, it remains to be seen how the ice cover will evolve over the rest of the melt season.