Climate Science News
Arctic sea ice continued to expand throughout the month of October, remaining at near-average levels on the Atlantic side and below average on the Pacific side. In the Southern Hemisphere, Antarctic sea ice has declined after reaching its record maximum in October and is now nearly within two standard deviations of the long-term average.Overview of conditions
Sea ice extent in October averaged 8.06 million square kilometers (3.11 million square miles). This is 850,000 square kilometers (328,000 square miles) below the 1981 to 2010 long-term average of 8.91 million square kilometers (3.44 million square miles) and 1.29 million square kilometers (498,000 square miles) above the record low for the month observed in 2007.
Arctic sea ice extent continued to increase throughout the month of October. Ice extent in the Pacific side remains below average. Areas in the Beaufort Sea along the Canadian and Alaskan coasts, and in the Chukchi Sea along the coast of Siberia were still ice free at the end of October. The image of monthly average sea ice extent (Figure 1) shows a large polynya within the East Siberian Sea, but this area is now covered by ice. On the Atlantic side, extent remains at near-average levels.Conditions in context
Through the month of October, the Arctic gained 3.39 million square kilometers (1.31 million square miles) of ice. This is faster than the average rate of ice gain for the month of October, but slower than the rate of ice gain seen in October 2012, after the record minimum of September 2012, and other recent Octobers.
Temperatures at the 925 hPa level show that the Arctic was 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) higher than average everywhere, except in the Kara and Barents seas where air temperatures were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) lower than average. Lower than average temperatures in this region were also a persistent feature of summer 2014 and helped maintain a more extensive ice cover in the region than in recent summers.
Warm conditions were partly a result of the ocean releasing the heat gained during summer back to the atmosphere. In addition, sea level pressures were higher than average over the central Arctic Ocean and the Barents Sea, reflecting the negative phase of the Arctic Oscillation .October 2014 compared to previous years
Due to the relatively rapid ice growth during October, Arctic sea ice extent for October 2014 was the 6th lowest in the satellite record. Through 2014, the linear rate of decline for October Arctic ice extent over the satellite record is -6.9% per decade.Amplified autumn warming
Projections of climate change through the rest of the century show amplified warming in the Arctic compared to the rest of the planet. While there are a number of reasons for this, sea ice loss plays a strong role. With less ice in spring and summer, the upper ocean (the top 20 meters, or 66 feet) gains more heat through absorption of solar radiation. For the ocean surface to refreeze in autumn and winter, the ocean must first lose this extra heat. This is manifested as strong surface warming over the areas of sea ice loss during autumn. While the warming is greatest near the surface, the warming can extend to a considerable height in the atmosphere.
This October shows the expected pattern of amplified warmth. Warming was greatest near the surface at high latitudes (5 degrees Celsius, or 9 degrees Fahrenheit above average) and extended upwards to the 700 hPa level, roughly 3,000 meters (9,842 feet) above the surface. This pattern is similar to that observed in October 2007 and 2009. However, in other recent years the location of the warmest surface conditions shifted further south, or did not extend as far up in the atmosphere. Such variations point to the influence of other factors, including patterns of atmospheric circulation, cloud cover, and atmospheric humidity.Arctic sea ice and the Madden-Julian Oscillation
Variations in large-scale atmospheric circulation patterns, such as the Arctic Oscillation , are known to affect the sea ice cover. These variations alter wind patterns that affect ice motion and bring in warm or cold air that influence ice melt and growth. For example, during a positive Arctic Oscillation phase, changes in the wind field help to push ice away from the coast of Siberia, allowing new ice to form and increasing the transport of ice out of Fram Strait. In the winters of the late 1980s and early 1990s, the Arctic Oscillation was in a persistent positive phase, helping to transport a large amount of thick, multiyear ice out of the Arctic through Fram Strait and leaving behind thinner ice that more easily melted the following summers.
A new study looks at the impact of a different mode of large-scale atmospheric variability, the Madden-Julian Oscillation, which appears to impact the ice cover on a shorter 30- to 90-day time scale. The Madden-Julian Oscillation is primarily driven by convection in the tropics, but causes changes in atmospheric circulation that impact the high latitudes. The impact on sea ice was found to be stronger during the winter season than in summer. It affected both the Atlantic and Pacific sectors and was confined to the marginal ice zone. The impact on sea ice also varies regionally, often showing opposing effects, such as between the Barents and Greenland seas in winter.Large Antarctic sea ice variability
After reaching a new record maximum extent this September, Antarctic sea ice extent has quickly declined, and is now back to levels seen in 2013 at this time of year. While almost the entire perimeter of Antarctica’s sea ice retreated slightly, two regions showed a larger retreat after the maximum: the eastern Weddell Sea (dotted ellipse marked A in Figure 5) and the eastern Ross Sea (dotted ellipse marked B in Figure 5). Both were areas of unusually extensive sea ice cover, and they contributed significantly to the record-setting level of ice extent in September. Weather patterns thirty days after the maximum changed markedly, with persistent warm northerly winds in these areas. Along the continent’s Pacific coast (Ross Ice Shelf and northern West Antarctic Ice Sheet) air temperatures at the 925 hPa level were 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit) above average. In the eastern Weddell Sea south of Africa, temperatures were 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) higher than average. Moreover, a series of intense storms in the first half of October dispersed an area of sea ice near the Amery Ice Shelf and the southern Indian Ocean.
We noted earlier that estimates from early satellites, such as Nimbus I and II, show some brief instances of very extensive and very reduced Antarctic sea ice. For example, in September 1964 ice extent was greater in most of the Southern Ocean than this year, the exception being the Ross Sea. Two years later, in 1966, the August extent shrank to a level smaller than any for that month in the modern satellite record. As seen in Figure 5, the largest variations between this early record and today occur around 180 degrees East in the South Pacific. This area is particularly sensitive to impacts of increased westerly winds and the Amundsen Sea Low, an atmospheric pressure pattern that tends to spread the sea ice cover northward in the Ross Sea. The change in winds and the Amundsen Sea Low over the past thirty-five years is well documented.Reference
Henderson, G. R., B. S. Barrett, and D. M. Lafleur. Arctic sea ice and the Madden-Julian Oscillation (MJO). Climate Dynamics , October 2014, Vol. 43, Issue 7-8, pp 2185-2196.
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.