Climate Science News
Since reaching its seasonal minimum on September 10 of 4.14 million square kilometers (1.60 million square miles), Arctic sea ice extent has increased at a rapid rate. Antarctic ice extent saw a sharp decline during the first half of September.Overview of conditions
Arctic sea ice extent during September 2016 averaged 4.72 million square kilometers (1.82 million square miles), the fifth lowest in the satellite record. Average September extent was 1.09 million square kilometers (421,000 square miles) above the record low set in 2012, and 1.82 million square kilometers (703,000 square miles) below the 1981 to 2010 long-term average. Extent remains especially low in the Beaufort, Chukchi and East Siberian Seas. The Northern Sea Route along the Russian coast appears to still be open, but the southern Northwest Passage route (Amundsen’s route) appears to be closed.Conditions in context
As of October 1, Arctic sea ice extent stood at 5.19 million square kilometers (2.00 million square miles), which is an increase of 1.05 million square kilometers (405,000 square kilometers) from the seasonal minimum of 4.14 million square kilometers (1.60 million square miles) recorded on September 10. Compared to some other years, the growth rate since the seasonal minimum has been quite rapid. The ice growth has been predominantly in the central Arctic Ocean and the East Siberian Sea sector. There has been little ice growth in the Laptev and Kara Seas, and ice has actually retreated in the Barents Sea.
September saw a shift in weather patterns. The summer of 2016 was characterized by unusually low pressure over the central Arctic Ocean, west of the dateline. While low pressure was still a dominant feature of September, the center of low pressure shifted towards North America, and a center of high pressure strengthened over north central Eurasia (Figure 2b). Conditions under the high pressure region were quite warm; temperatures at the 925 hPa level were up to 6 degrees Celsius (11 degrees Fahrenheit) above the 1981 to 2010 average (Figure 2c).September 2016 compared to previous years
Through 2016, the linear rate of decline for September is 87,200 square kilometers (33,700 square miles) per year, or 13.3 percent per decade. While the absolute seasonal minimum for 2016 was tied with 2007 as second lowest, the average extent for the month of September 2016 of 4.72 million square kilometers (1.82 million square miles) ends up being fifth lowest in the satellite record, behind both 2012 and 2007. This reflects the rapid growth of ice following the seasonal minimum recorded on September 10.Antarctic sea ice reaches winter maximum on a record early date
Antarctic sea ice extent reached 18.44 million square kilometers (7.12 million square miles) on August 31, 2016, and this appears to be the maximum extent for this year. This is the earliest maximum in the satellite record since 1979, and the first time the maximum has occurred in August. The maximum was 240,000 square kilometers (93,000 square miles) greater than the average extent for this date of 18.20 million square kilometers (7.03 million square miles). It is the tenth lowest maximum extent on record. On average, the maximum occurs much later (September 23 to 24).
The early maximum appears to be the result of an intense wind pattern in September, spanning nearly half of the continent from the Wilkes Land area to the Weddell Sea, and centered on the Amundsen Sea. Stronger than average low pressure in this area, coupled with high pressure near the Falkland Islands, and near the southern tip of New Zealand in the Pacific Ocean, created two regions of persistent northwesterly winds. Sea ice extent decreased in the areas where the northwesterly winds reached the ice front.
A comparison of sea ice extent from the date of the maximum (August 31) and the last day of September (one month later) shows that sea ice extent decreased through the month along a broad region west and east of the Antarctic Peninsula. It also decreased on the other side of the continent north of Wilkes Land. By comparison, this was partly offset by increases in the northern Amundsen Sea and north of Dronning Maud Land.The 2016 Arctic melt season in review
The winter of 2015/2016 was extremely warm over the Arctic Ocean. The maximum sea ice extent in March set a new low in the satellite record, barely beating out March 2015. Extent for the month of March as a whole ended up second lowest on record. In April, problems with the F-17 sensor forced a temporary cessation of sea ice updates until data from the newer F-18 satellite could be brought online. Data from other sources documented that during this time, ice was still tracking very low. The months of May and June set more record lows in ice extent.
Although the onset of surface melt was early over much of the Arctic Ocean, as the melt season progressed, a pattern of stormy weather set up. This ended up being a very persistent pattern; as averaged from June through August, sea level pressure was much lower than average over the central Arctic Ocean (Figure 5a), and air temperatures over most of the ocean were average or below average (Figure 5b). Such conditions have been previously shown to limit summer ice loss, and by the early August it became clear that a new record low for September extent was not in the offing. Two very strong storms crossed the central Arctic Ocean in August. In 2012, a strong storm contributed to accelerated ice loss, but this year, the overall influence of the storms remains unclear.
Despite the generally unfavorable weather conditions, the seasonal minimum of 4.14 million square kilometers (1.60 million square miles), reached on September 10, ended up in a statistical tie with 2007 as the second lowest in the satellite record. While previous analyses have shown that there is little correlation between the seasonal maximum extent and the season minimum extent, in large part because of the strong impacts of summer weather patterns, it is likely that the 2016 melt season started with a lot of fairly thin ice. This may help to explain why, despite summer weather unfavorable to sea ice loss, extent at the seasonal minimum ended up tied for second lowest.Sea ice age
Age is another indicator of the state of sea ice because older ice is generally thicker ice (Tschudi et al., 2016). As mentioned in previous posts, there has been an overall decline in ice age, particularly the oldest ice types—ice that has been in the Arctic for more than four years. Near-real-time updates (which are preliminary) indicate that at this year’s minimum, only 106,000 square kilometers (41,000 square miles) of 4+ year old ice remained, or 3.1 percent of the total ice extent. This is in stark contrast to the mid-1980s when over 2 million square kilometers (33 percent, or 772,000 square miles) of the summer minimum extent was composed of old ice that had survived at least four summer melt seasons.
Tschudi, M.A., J.C. Stroeve, and J.S. Stewart. 2016. Relating the age of Arctic sea ice to its thickness, as measured during NASA’s ICESat and IceBridge campaigns. Remote Sensing, 8, 457, doi:10.3390/rs8060457.
Arctic sea ice appears to have reached its seasonal minimum extent for 2016 on September 10. A relatively rapid loss of sea ice in the first ten days of September has pushed the ice extent to a statistical tie with 2007 for the second lowest in the satellite record. September’s low extent followed a summer characterized by conditions generally unfavorable for sea ice loss.
Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010. 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 10, Arctic sea ice extent stood at 4.14 million square kilometers (1.60 million square miles). This appears to have been the lowest extent of the year and is tied with 2007 as the second lowest extent on record. This year’s minimum extent is 750,000 square kilometers (290,000 square miles) above the record low set in 2012 and is well below the two standard deviation range for the 37-year satellite record. Satellite data show extensive areas of open water in the Beaufort and Chukchi seas, and in the Laptev and East Siberian seas.
During the first ten days of September, the Arctic lost ice at a faster than average rate. Ice extent lost 34,100 square kilometers (13,200 square miles) per day compared to the 1981 to 2010 long-term average of 21,000 square kilometers (8,100 square miles) per day. The early September rate of decline also greatly exceeded the rate observed for the same period in 2012 (19,000 square kilometers, or 7,340 square miles, per day). Recent ice loss has been most pronounced in the Chukchi Sea. This may relate to the impact of two strong cyclones that passed through the region during August.
Satellite passive microwave data and images from the Moderate Resolution Imaging Spectroradiometer (MODIS) suggest that the southern Northwest Passage routes are still open. While the passive microwave data show that the Northern Sea route is open, MODIS data reveal a narrow band of scattered sea ice blocking the passage near the Taymyr Peninsula.Conditions in context
Weather in early September was warm along the Siberian coast (up to 9 degrees Celsius or 16 degrees Fahrenheit above average), with high pressure over the same region and strong winds across the central Arctic. However, as discussed in previous posts, weather over the Arctic Ocean this past summer has been generally stormy, cool, and cloudy—conditions that previous studies have shown to generally limit the rate of summer ice loss. That September ice extent nevertheless fell to second lowest in the satellite record is hence surprising. Averaged for July through August, air temperatures at the 925 hPa level (about 2,500 feet above sea level) were 0.5 to 2 degrees Celsius (1 to 4 degrees Fahrenheit) below the 1981 to 2010 long-term average over much of the central Arctic Ocean, and near average to slightly higher than average near the North American and easternmost Siberian coasts. Reflecting the stormy conditions, sea level pressures were much lower than average in the central Arctic during these months.
Why did extent fall to a tie for second lowest with 2007? The 2016 Arctic melt season started with a record low maximum extent in March, and sea ice was measured at record low monthly extents well into June. Computer models of ice thickness, and maps of sea ice age both indicated a much thinner ice pack at the end of winter. Statistically, there is little relationship between May and September sea ice extents after removing the long-term trend, indicating the strong role of summer weather patterns in controlling sea ice loss. However, the initial ice thickness may play a significant role. As noted in our mid-August post, the upper ocean was quite warm this summer and ocean-driven melting is important during late summer. The science community will be examining these issues in more detail in coming months.Ice loss primarily in the northern Chukchi Sea
The late season ice loss appears to have been greatest in an extended area of patchy ice reaching from the eastern Beaufort Sea to the northern Chukchi Sea. This is in the area influenced by the two strong cyclones discussed in our August posts—the strong winds appear to have compacted the ice cover and may have led to an upward mixing of warm ocean water.
The Defense Meteorological Satellite Program (DMSP) F-17 satellite, which NSIDC ceased to use in May as its primary source for sea ice extent due to erratic data, has since re-stabilized and is providing more consistent day-to-day readings. While NSIDC will continue to use the DMSP F-18 satellite for data processing, it is instructive to examine the F-17 record. Early September extent from the F-17 record is slightly higher than from F-18. Both sensors indicate that the minimum extent for 2016 is slightly lower than the 2007 minimum, which was 4.15 million square kilometers (1.60 million square miles) and reached on September 18. However, the measurement accuracy is about ±25,000 square kilometers (±9,600 square miles) for a five-day trailing average daily extent measurement. This means that at the present levels, 2016 is a statistical tie for second lowest sea ice extent.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 4.15 1.60 Sept. 18 2008 4.59 1.77 Sept. 20 2009 5.12 1.98 Sept. 13 2010 4.62 1.78 Sept. 21 2011 4.34 1.67 Sept. 11 2012 3.39 1.31 Sept. 17 2013 5.06 1.95 Sept. 13 2014 5.03 1.94 Sept. 17 2015 4.43 1.71 Sept. 9 2016 4.14 1.60 Sept. 10 1979 to 2000 average 6.70 2.59 Sept. 13 1981 to 2010 average 6.22 2.40 Sept. 15 Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present) Table 2. Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present) RANK YEAR MINIMUM ICE EXTENT DATE IN MILLIONS OF SQUARE KILOMETERS IN MILLIONS OF SQUARE MILES 1 2012 3.39 1.31 Sept. 17 2
1.60 Sept. 10
Sept. 18 3 2011 4.34 1.67 Sept. 11 4 2015 4.43 1.71 Sept. 9 5 2008 4.59 1.77 Sept. 20 6 2010 4.62 1.78 Sept. 21 7 2014 5.03 1.94 Sept. 17 8 2013 5.06 1.95 Sept. 13 9 2009 5.12 1.98 Sept. 13 10 2005 5.32 2.05 Sept. 22
Note that the dates and extents of the minima have been re-calculated from what we posted in previous years. In June 2016, NSIDC transitioned to using data from the DMSP F-18 satellite, due to issues with the F-17 satellite. Data beginning April 1, 2016 are from F-18. In July 2016, Sea Ice Index data were updated to Version 2. These changes do not significantly affect sea ice trends and year-to-year comparisons, but in some instances users may notice small changes in values from the previous version of the data. Details on the changes are discussed in the Sea Ice Index documentation.
October 19, 2016: We revised the title for Table 2 from “Ten lowest minimum Arctic sea ice extents (1981 to 2010 average)” to “Ten lowest minimum Arctic sea ice extents (satellite record, 1979 to present)”
Throughout August, Arctic sea ice extent continued to track two or more standard deviations below the long-term average. The month saw two very strong storms enter the central Arctic Ocean from along the Siberian coast. In the Antarctic, ice extent remained near average.Overview of conditions
Average sea ice extent for August 2016 was 5.60 million square kilometers (2.16 million square miles), the fourth lowest August extent in the satellite record. This is 1.03 million square kilometers below the 1981 to 2010 average for the month and 890,000 square kilometers (344,000 square miles) above the record low for August set in 2012. As of September 5, sea ice extent remains below average everywhere except for a small area within the Laptev Sea. Ice extent is especially low in the Beaufort Sea and in the East Siberian Sea. With about two weeks of seasonal melt yet to go, it is unlikely that a new record low will be reached. However, since August 26, total sea ice extent is already lower than at the same time in 2007 and is currently tracking as the second lowest daily extent on record. In addition, during the first five days of September the ice cover has retreated an additional 288,000 square kilometers (111,000 square miles) as the tongue of sea ice in the Chukchi Sea has started to disintegrate.Conditions in context
The average ice loss rate through August was 75,000 square kilometers per day (29,000 square miles), compared to the long-term 1981 to 2010 average of 57,300 square kilometers per day (22,100 square miles per day), and a rate of 89,500 square kilometers per day for 2012 (34,500 square miles per day). Total ice extent loss in August was 2.34 million square kilometers (904,000 square miles).
Air temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average for a large area stretching from the northern Kara Sea, through the Laptev Sea, and into north-central Eurasia. Temperatures elsewhere over the Arctic Ocean were near average. Reflecting the generally stormy pattern through the month, sea level pressures were well below average (as much as 10 hPa) over the central and eastern Arctic Ocean. Two very strong cyclones entered the central Arctic Ocean in August from along the Siberian coast, bringing strong winds. On August 16, the central pressure of the first cyclone dropped to 968 hPa, nearly rivaling the storm in early August 2012 that attained a minimum central pressure of 966 hPa. On 22 August, the second storm started moving to the central Arctic Ocean along a similar track, and on August 23, attained a central pressure of 970 hPa.
Past studies have shown that stormy summers tend to end up with more sea ice at the end of the melt season than summers with high pressure over the central Arctic Ocean, primarily because stormy summers are both fairly cool and the wind pattern tends to spread the ice out. However, the impact of strong individual storms may be different—the 2012 event appears to have temporarily boosted ice loss by breaking up the ice cover, with the wave action tending to mix warmer waters from below to hasten melt. It may also be that, as the ice cover thins, its response to storms is changing.
It indeed appears that the August 2016 storms helped to break up the ice and spread it out, contributing to the development of several large embayments and polynyas. Some of this ice divergence likely led to fragmented ice being transported into warmer ocean waters, hastening melt. Whether warmer waters from below were mixed upwards to hasten melt remains to be determined, but as discussed below, these storms were associated with very high wave heights.August 2016 compared to previous years
Arctic sea ice extent averaged for August 2016 was the fourth lowest in the satellite data record. Through 2016, the linear rate of decline for August is 10.4 percent per decade.Cyclones, ocean wave heights, and ice retreat
Large waves are common at high latitudes; 10-meter wave heights (33 feet) are not unusual for the Nordic Seas, and 15-meter wave heights (49 feet) can occur in the high latitudes of the Southern Ocean. However, large waves are a relatively new feature of the western Arctic Ocean. The height of waves is in part determined by surface wind speed, as well as the fetch (distance over open water that the wind can travel) and the duration of a wind event. A moderate sea ice cover damps ocean waves by absorbing and dispersing the wave energy through jostling of the ice floes against one another. A dense ice pack cover acts as a shield between the ocean and the surface wind, preventing wave formation.
In the latter half of the twentieth century, 4 to 6 meter waves (13 to 20 feet) rarely occurred in the western Arctic Ocean, but with more open water they have become more frequent, especially when strong storms enter the Arctic Ocean in late summer or early autumn. During the first of the two August cyclones discussed above, waves up to 5.9 meters (19 feet) were predicted. This occurred during the early part of the cyclone’s lifecycle (1800 UTC August 14), in the eastern Kara Sea. Further east, north of the New Siberian Islands, wave heights were estimated as high as 4.3 meters (14 feet) late on August 15. In this region, the waves were directly incident on the ice edge. In response, the ice edge retreated following the 4.3 meter waves on August 15.Northwest Passage update
The Northwest Passage refers to the fabled shortcut between the Atlantic and Pacific through the Canadian Archipelago. However, it is not one route. There is a northern, deep-water route through the Parry Channel, entered from the west through the M’Clure Strait and a shallower southern route, known as Amundsen’s route. Sea ice in the Parry Channel route has shown a sharp decline since the middle of July, but the channel is still not entirely ice free. Considerable ice remains in the western (M’Clure Strait) region and there are lesser amounts in the eastern regions. This is mostly (~80 percent) multiyear ice. Low ice years in the Parry Channel are typically the result of early summer breakup associated with high sea level pressure over the Beaufort Sea and Canada Basin that displace the Arctic Ocean pack ice away from the western entrance. Conversely, low sea level pressure anomalies over the Beaufort Sea and Canada Basin keep the Arctic Ocean pack ice up against the western entrance. This has been the case for much of the 2016 melt season. The southern (Amundsen’s) route is open but it is still uncertain whether the northern route will open in the coming weeks.
Even during mild ice years, thick multiyear ice is typically advected into these routes during the summer months. Multiyear ice is a significant obstacle for ships. Nevertheless, taking advantage of mild sea ice conditions, the 68,000-ton Crystal Serenity set sail from Anchorage, Alaska on August 16 for its 32-day journey through the Northwest Passage via Amundsen’s route. This is the largest ship thus far to navigate the Northwest Passage and is accompanied by an icebreaker ship and two helicopters. The ship sailed through the Northwest Passage in less than three weeks—52 times faster than Amundsen’s nearly three-year voyage.
On the other side of the Arctic, the Northern Sea Route appears mostly ice free.Further reading
Collins, C. O., W. E. Rogers, A. Marchenko and A. V. Babanin. 2015. In situ measurements of an energetic wave event in the Arctic marginal ice zone. Geophysical Research Letters, 42, doi:10.1002/2015GL063063.
Haas, C., and S. E. L. Howell. 2015. Ice thickness in the Northwest Passage. Geophysical Research Letters, 42, 7673–7680, doi:10.1002/2015GL065704.
Hogan, T., et al. 2014. The Navy Global Environmental Model, Oceanography, 27(3), 116-125.
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. Journal of Geophysical Research, 118, 3595–3607, doi:10.1002/jgrc.20265.
Thomson, J., and W. E. Rogers. 2014. Swell and sea in the emerging Arctic Ocean, Geophysical Research Letters 41, doi:10.1002/2014GL059983.
Thomson, J. et al. 2016. Emerging trends in the sea state of the Beaufort and Chukchi seas, Ocean Modelling 105, doi:10.1016/j.ocemod.2016.02.009.
As of August 14, Arctic sea ice extent is tracking third lowest in the satellite record. The southern route through the Northwest Passage appears to be largely free of ice. Despite a rather diffuse ice cover in the Chukchi Sea, it is unlikely that Arctic sea ice extent this September will fall below the record minimum set in 2012.Overview of conditions
As of August 14, Arctic sea ice extent was 5.61 million square kilometers (2.17 million square miles). This is the third lowest extent in the satellite record for this date and slightly below the two standard deviation range. So far this month the rate of loss has been faster than average and has declined at a rate similar to that observed for 2012.
Ice loss has progressed quite rapidly in the Beaufort and Chukchi seas, where broken up ice floes are starting to melt away. However, large, thick multiyear ice floes persist in several areas; it remains to be seen if they will survive the melt season. A wedge of open water has also penetrated northward from the East Siberian Sea, yet ice remains extensive in the Laptev Sea, blocking the Northern Sea Route. Ice extent continues to be low in the Kara, Barents, and East Greenland seas. The southern (Amundsen’s) route through the Northwest Passage appears open in Advanced Scanning Microwave Radiometer 2 (AMSR2) data. However, data in visible wavelengths from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument still show some ice.Conditions in context
Ice loss from August 1 to 14 was faster than average, at 87,400 square kilometers (33,800 square miles) per day, and near the rates observed in 2012. Nevertheless, as has been the pattern this summer, atmospheric conditions through the first half of August have been generally cloudy and cool. Air temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below the 1981 to 2010 long-term average over the eastern part of the Arctic Ocean and near average elsewhere. The cool and cloudy conditions reflect a pattern of low atmospheric pressure over the Laptev and Kara seas.
As of August 16, a strong storm (central pressure of 968 hPa) was located over the Central Arctic Ocean at about 85 degrees North, near the dateline. The extent to which this strong storm will affect sea ice conditions remains to be seen.Ocean heat continues ice melt
The Arctic atmosphere is cooling now as the sun dips lower in the sky. However, sea ice loss will continue throughout August due primarily to melt from the ocean heat that has accumulated over the summer. Early ice retreat has allowed the ocean to warm, both from absorption of the sun’s energy and from northward-flowing warm water in the Chukchi Sea to the west of Alaska and in the Barents Sea to the north of Norway. Unusually strong ocean warming occurred in northern Baffin Bay (between northern Canada and Greenland), the Beaufort Sea (north of northwestern Canada and Alaska), the East Siberian Sea (north of far eastern Siberia), and the Barents and Kara seas (north of western Eurasia).
What is quite unusual this year is the early ice retreat and resulting ocean warming in the western Beaufort Sea and in the western East Siberian Sea. The extent of warming to the north of these two seas is also unusual, as well as the extent of this warming to the north. These two areas typically melt out later in the season, when atmospheric heating rates have declined from their mid-summer peak. Thus the exposed ocean warms, but not all that much. This pattern was true during the record-setting year of 2012, when by the end of summer, these areas were substantially cooler than surrounding seas that had melted out earlier.
This year, however, the melt out was early and extensive enough that the ocean has already warmed substantially in these two areas. More sea ice retreat is probable in the western Beaufort and East Siberian seas as well as areas in the coming weeks. But what about the ocean’s response? Some warm water might move northward via ocean currents and contribute to ice melt. However, further dramatic ocean surface warming is unlikely, given that the atmosphere is already cooling, especially in far northern latitudes.Ice loss rates indicate little chance for a record low this year
While there are still three to four weeks to go in the melt season, a new record low this September is highly unlikely. A simple projection method developed by Walt Meier at the NASA Goddard Space Flight Center uses daily ice loss rates from previous years to estimate possible trajectories of ice extent through the rest of the melt season.
This approach yields a range of minimum values based on how sea ice loss progressed in previous years. By selecting from an average of multiple years, or using loss rates from a specific previous year, the method yields an estimate of the likely range of the minimum sea ice extent. As of August 14, using daily ice loss rates based on the 2006 to 2015 average yields an average projected 2016 minimum extent of 4.33 million square kilometers (1.67 million square miles). Using the slowest (recent) August to September decline, which occurred in 2006, yields a 2016 minimum of 4.76 million square kilometers (1.84 million square miles). Using the fastest rate of decline, from 2012, yields a 2016 minimum extent of 4.06 million square kilometers (1.57 million square miles). These two years bracket a reasonable range of expected 2016 minima. It is possible that this year will have decline rates that fall outside the range of previous years. However, this approach indicates that it is very unlikely that 2016 will have a minimum below 2012’s value of 3.39 million square kilometers (1.31 million square miles). A projection from August 1 was submitted to the Sea Ice Outlook.Further reading
Lindsay, R.W. 1998. Temporal variability of the energy balance of thick Arctic pack ice, Journal of Climate, doi:10.1175/15200442(1998)011<0313:TVOTEB>2.0.CO;2.
Steele, M. and W. Ermold. 2015. Loitering of the retreating sea ice edge in the Arctic seas, Journal of Geophysical Research, doi:10.1002/2015JC011182.
Steele, M., J. Zhang, and W. Ermold. 2010. Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt, Journal of Geophysical Research, doi:10.1029/2009JC005849.
An extensive area of lower than average temperatures in the Central Arctic and the Siberian coast, attended by persistent low pressure systems in the same region, led to slightly slower than average sea ice decline through the month. The stormy pattern contributed to a dispersed and ragged western Arctic ice pack for July, with several polynyas beginning to form late in the month. A new record low September ice extent now appears to be unlikely.Overview of conditions
Arctic sea ice extent for July averaged 8.13 million square kilometers (3.14 million square miles), the third lowest July extent in the satellite record. This makes July only the second month so far this year that did not have a record low extent. July’s extent is 190,000 square kilometers (73,000 square miles) above the previous record low set in 2011, and 1.65 million square kilometers (637,000 square miles) below the 1981 to 2010 long-term average.
Ice extent continues to be far below average in the Kara and Barents seas, as it has been throughout the winter and spring. Extent also remains well below average in the Beaufort Sea, but in the Laptev and East Siberian seas, sea ice extent is near average.Conditions in context
The rate of ice loss during July 2016 was slightly below average at 83,800 square kilometers (32,400 square miles) per day. The 1981 to 2010 average rate of ice loss for July is 86,800 square kilometers (33,500 square miles) per day.
Warm conditions with temperatures at the 925 hPa level of 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) above average graced the northernmost coasts of Alaska, Canada, and Greenland, but the thick sea ice that is typical of this region is unlikely to melt out. Very warm conditions continued in the Kara and Barents seas, with temperatures as much as 3 to 6 degrees Celsius (5 to 11 degrees Fahrenheit) above average, consistent with the retreat of the ice cover to the northern edge of the Svalbard, Franz Josef, and New Siberian Islands. However, the main feature of the climate conditions for the month was a large area of below-average pressure centered over the Laptev Sea, and associated cooler than average conditions in the same area (1 to 4 degrees Celsius or 2 to 7 degrees Fahrenheit). This continues the pattern seen in June, with conditions unfavorable to pronounced sea ice retreat: cloudy and cool, with winds that tend to disperse the ice and increase its extent, rather than compact it.July 2016 compared to previous years
Through 2016, the rate of decline for the month of July is 72,700 square kilometers 28,070 square miles) per year, or 7.3 percent per decade. July extent remained above 2011 and 2012 levels throughout the month, but it was below the 2007 extent for the first half of the month.A shift in pressure
Beginning in June there was a significant change in the atmospheric circulation over the Arctic. May was characterized by high pressure over the Arctic Ocean which had persisted since the beginning of the year. However, in June the pattern shifted to lower than average pressure. This brought clouds and fairly low temperatures to the region, slowing ice loss. The change in circulation also shifted the pattern of ice motion, slowing the earlier movement of ice away from the coast in the Beaufort Sea (as depicted in our May 3rd post).
This pattern shift is associated with the development of a large and persistent area of moderate high pressure over the northeastern Pacific (south of Alaska) that formed beginning in mid-May. This may be related to an ongoing shift in the Pacific Decadal Oscillation over spring and early summer this year.Sea ice dances to the changing wind
The shift in air pressure pattern also resulted in a change in sea ice drift directions in the Arctic. Early in the year, sea ice drift had a strong clockwise pattern (Figure 5a, top). However, July conditions greatly reduced sea ice drift speed in the Beaufort Sea and produced a counterclockwise drift pattern in the Laptev Sea (Figure 5a, bottom).
Persistent low pressure and repeated cyclonic storms in the Siberian side of the Arctic tended to disperse the pack and move it away from the coast. By late July, several regions of thin pack and small polynyas were beginning to open in these areas (Figure 5b).The ice of our forefathers
Earlier this month, NOAA at NSIDC published a new compilation of Arctic sea ice extent using a variety of historical sources, including whaling ship reports and several historical ice chart series from Alaska, the Russian Arctic, Canada, and Denmark. The compilation provides a synthesized mid-monthly estimate extending back to 1850. The study concludes that the current downward trend in sea ice has no precedent in duration or scale of ice loss since 1850. With the exception of the Bering Sea, none of the areas have seen sea ice extents as low as in the past decade. Historical periods that show a decrease in summertime sea ice extent in the Arctic, such as the late 1930’s and 1940’s, are smaller in magnitude than the current downward-trending period.Further reading
Walsh, J. E., F. Fetterer, J. S. Stewart, and W. L. Chapman. 2016. A database for depicting Arctic sea ice variations back to 1850. Geographical Review. doi: 10.1111/j.1931-0846.2016.12195.x.
Through the first half of July, Arctic sea ice extent continued tracking close to levels in 2012, the summer that ended with the lowest September extent in the satellite record. The stormy weather pattern that characterized June has persisted into July. Nevertheless, sea ice melt began earlier than average over most of the Arctic Ocean.Overview of conditions
As of July 18, Arctic sea ice extent was 7.82 million square kilometers (3.02 million square miles). This is just below the two standard deviation value for the date, and just above the level observed on the same date in 2012, the year that ended up having the lowest September extent in the satellite record. Throughout the month, extent has closely tracked both the two standard deviation and 2012 levels.
Ice extent in the first half of July was well below average in the Kara and Barents seas, as it has been throughout the winter and spring. Extent is also below average in the Beaufort and Chukchi seas, between the East Siberian and Laptev seas by the New Siberian Islands, and along the southeast coast of Greenland. In the last several days, polynyas have formed in the northern Beaufort Sea. Compared to 2012 at this time of year, there is more ice in the southern Beaufort Sea, Baffin Bay, the Laptev Sea, and north of the New Siberian islands in the East Siberian Sea. There is less ice this year in the East Greenland Sea, extending through the Barents and Kara seas, and in the western Beaufort and Chukchi seas.Conditions in context
The average rate of ice loss through July 18 was 89,500 square kilometers (34,600 square miles) per day, which is close to the long-term average (1981 through 2010) rate of 86,800 square kilometers (33,500 square miles) per day. Recall from our last post that the month of June was characterized by a stormy pattern over the central Arctic Ocean, which likely acted to slow the rate of ice loss. This pattern has persisted into July. However, the rate of decline increased in the first two weeks of the month as very warm conditions spread around the Arctic coasts. Ice loss has slowed in the last few days. A number of low pressure systems, primarily generated over northern Eurasia, have migrated into the central Arctic Ocean, north of the East Siberian Sea. One of these was quite strong, with a central pressure dropping to as low as 979 hPa (Figure 3).
Cyclones found over the central Arctic Ocean in summer tend to be what is termed “cold cored.” Because of these cold-cored systems and their associated pattern of winds, air temperatures at the 925 hPa level for the first half of July have been well below average along and north of the East Siberian Sea. By sharp contrast, strongly above average temperatures have been the rule over the Barents and Kara seas, the Canadian Arctic Archipelago and northern Alaska (Figure 4). Local conditions can be quite variable, and not well captured by conditions at the 925 hPa level. On July 14, Deadhorse, on the North Slope of Alaska on the shores of the Beaufort Sea, saw a record high temperature. The reading of 85° Fahrenheit (through 7 p.m.) broke the record of 83° Fahrenheit set in 1991. It is also also the highest reading on record for any Alaska station within 50 miles of the Arctic Ocean coast north of the Brooks Range.Early melt onset
Seasonal onset of surface melt was early over most of the Arctic Ocean (Figure 5). This occurred under the high-pressure-dominated weather pattern that was present earlier in the spring. The onset of surface melt can be determined with the same passive microwave data used to determine sea ice extent and concentration. Melt began in late April/early May in the southern Beaufort Sea, which was about 6 weeks (more than 40 days) earlier than average. Melt also began a month earlier than average in the Barents Sea and northern Baffin Bay.
Early onset of melt is important because melt drops the surface albedo, allowing the sea ice and its overlying snow cover to absorb more solar radiation, which accelerates the melt process. Data from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument show many very large, multiyear ice floes in the Beaufort Sea, one of them about 50 miles across. It will be interesting to see if these large multiyear floes melt out this summer. NSIDC will be closely monitoring the situation.New insights into Antarctic sea ice conditions
Gerald Meehl of the National Center for Atmospheric Research led a new study shedding light on the upward trend in total Antarctic sea ice extent over the period of satellite observations. The overall view from climate models is that Antarctic sea ice extent should have decreased in response to the general warming of climate. This has led some scientists to suggest that the climate models are fundamentally flawed. However, an explanation for the expanding Antarctic sea ice appears to lie in the Interdecadal Pacific Oscillation (IPO), a natural mode of climate variability. The IPO transitioned from a positive to a negative phase in the late 1990s at the same time that the increase in total Antarctic sea ice extent accelerated. The negative IPO brought a cooling of tropical Pacific sea surface temperatures, and deepening of the Amundsen Sea Low near Antarctica. This has contributed to regional circulation changes in the Ross Sea region favoring expansion of the sea ice cover. Meehl’s study also shows that the negative phase of the IPO in coupled global climate models is characterized by patterns similar to the sea-level pressure and 850 hPa wind changes observed in all seasons near Antarctica since 2000, particularly in the Ross Sea region. Additional model experiments show that these atmospheric circulation changes are mainly driven by precipitation and convective heating anomalies related to the IPO in the equatorial eastern Pacific. They conclude that the models are not wrong, but instead can simulate the processes involved with natural climate variability that results in increased Antarctic sea ice, even when global temperatures are rising.Reference
Meehl, G.A., J.M. Arblaster, C. Bitz, C.T.Y. Chung, and H. Teng. 2016. Antarctic sea ice expansion between 2000-2014 driven by tropical Pacific decadal climate variability. Nature Geoscience, doi:10.1038/NGEO2751.
June set another satellite-era record low for average sea ice extent, despite slower than average rates of ice loss. The slow rate of ice loss reflects the prevailing atmospheric pattern, with low pressure centered over the central Arctic Ocean and lower than average temperatures over the Beaufort Sea.Overview of conditions
Arctic sea ice extent during June 2016 averaged 10.60 million square kilometers (4.09 million square miles), the lowest in the satellite record for the month. So far, March is the only month in 2016 that has not set a new record low for Arctic-wide sea ice extent (March 2016 was second lowest, just above 2015). June extent was 260,000 square kilometers (100,000 square miles) below the previous record set in 2010, and 1.36 million square kilometers (525,000 square miles) below the 1981 to 2010 long-term average.
Sea ice extent remains below average in the Kara and Barents seas, as it has throughout the winter and spring. Despite lower than average temperatures over the Beaufort Sea, sea ice extent there remains below average, and was the second lowest extent for the month of June during the satellite data record.Conditions in context
The average rate of ice loss during June 2016 was 56,900 square kilometers (22,000 square miles) per day, but was marked by two distinct regimes. First, there was a period of slow loss during June 4 to 14 of only 37,000 square kilometers (14,000 square miles) per day. This was followed by above average rates (74,000 square kilometers, or 29,000 square miles) for the rest of the month. For the month as a whole, the rate of loss was close to average (53,600 square kilometers per day). The slow ice loss during early June was a result of a significant change in the atmospheric circulation. May was characterized by high surface pressure over the Arctic Ocean, a basic pattern that has held since the beginning of the year. However, June saw a marked shift to low pressure over the central Arctic Ocean. This type of pattern is known to inhibit ice loss. A low pressure pattern is associated with more cloud cover, limiting the input of solar energy to the surface, as well as generally below average air temperatures. However, in June 2016, it was only in the Beaufort Sea where air temperatures at the 925 hPa level were distinctly below average (about 2 degrees Celsius below average, or 4 degrees Fahrenheit). The change in circulation also shifted the pattern of ice motion. In general, winds associated with such a low pressure pattern will tend to spread the ice out (that is, cause the ice to diverge).June 2016 compared to previous years
Through 2016, the rate of decline for the month of June is 44,600 square kilometers (17,200 square miles) per year, or 3.7 percent per decade. June extent remained below 2012 levels throughout the month, but it was above the 2010 extent for several days. 2010 had the lowest extent for several days during June.View from above
The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on the NASA Aqua and Terra satellites provide multiple views each day of the Arctic, and in summer the entire region is sunlit. Two mosaics for June 9 and June 28 show the seasonal progression in surface melting and darkening of the sea ice; the blue-green areas where surface ponding is present; and the movement of large sea ice floes in the Beaufort Sea. On June 9, the ponds are most evident in the Laptev Sea off the coast of Siberia; on June 28, the ponds are most evident in the Canadian Archipelago.
A quick look at sea ice thickness fields
Results from NASA’s Operation IceBridge aircraft missions conducted during late April and early May indicate that ice thicknesses from the Alaskan coast of the Beaufort Sea up to the North Pole were generally in the 2 to 3 meter range (7 to 10 feet), indicative of multiyear ice. However, substantial variations were found along the flight transects with several locations showing an ice thickness of 1.5 meters (5 feet) or less, indicative of first-year ice, while in other locations thicknesses were over 5 meters (16 feet), corresponding to either fairly thick multiyear ice or ridged first-year ice. This substantial variation is representative of a broken up and variegated ice pack with thick multiyear floes interspersed with thinner first-year ice.
The first-year thicknesses were found to be generally thinner than is typical at the end of winter, which is consistent with the usually high temperatures characterizing last winter. Very thin ice (less than 0.5 meters, or 1.6 feet) was found in places near the Alaskan coast, where leads opened up fairly late in the ice growth season. The IceBridge results are generally in agreement with the ice thickness surveys conducted in early April by researchers from York University, and with CryoSat-2 thickness maps discussed in our previous post.Sea Ice Outlook
Each summer the Sea Ice Prediction Network (SIPN) requests forecasts of the September average sea ice extent. Requests are made in June July and August. This year, thirty contributions to the June Sea Ice Outlook were received, employing a variety of methods, including statistical models, dynamical models, and informal polls. The median prediction for this year’s September sea ice extent is 4.28 million square kilometers (1.65 million square miles), similar to the extent observed in 2007. Dynamical models predict 4.58 million square kilometers (1.77 million square miles), compared to the slightly lower overall median extent prediction of 4.28 million square kilometers (1.65 million square miles) from statistical models. The lowest median extent comes from the heuristic contributions (4.0 million square kilometers, or 1.5 million square miles). Only one forecast points towards a new record low for 2016.Antarctic sea ice
Antarctic sea ice extent continues to track at near average levels, in sharp contrast to the previous two winters, which were above average. While the total ice extent in the Antarctic shows a small positive trend, particularly during the cold season, whether or not the total mass of the ice has changed depends on how much of the pack ice consists of consolidated ice, the extent of the marginal ice zone (the outer edge of the ice pack, which is lower in ice concentration), and coastal polynyas (open water areas near the coast). The marginal sea ice zone and the coastal polynyas have important biological implications. These are key regions for phytoplankton productivity and krill abundance that in turn feed Antarctic sea birds and nektonic fauna (things that swim).
A new study looks at how these regions are changing using two sea ice concentration algorithms distributed by NSIDC. While the algorithms give similar trends in the overall sea ice extent, they differ in terms of whether or not the sea ice cover is becoming more compacted (i.e., the consolidated ice pack is increasing in extent) or if the marginal ice zone is expanding (Figure 6). When sea ice is is growing seasonally, both algorithms indicate that it is due to an expansion of the consolidated ice pack, whereas during winter and spring, one measurement method (the NASA Team algorithm) finds the marginal ice zone is also expanding as well, and the other measurement (Bootstrap algorithm) shows no significant trend in the marginal ice. The algorithms also differ in how much of the total ice pack consists of pack ice or the marginal ice, with the NASA Team algorithm having on average twice as large of a marginal ice zone as the Bootstrap algorithm. As well, the NASA Team algorithm is known to underestimate ice concentration in the Antarctic. This highlights the need for further validation of sea ice concentrations derived from passive microwave satellite data.New Sea Ice Index version
As part of our quality control process, the Sea Ice Index, which supplies sea ice extent and concentration values, has been updated to Version 2. Changes include using the most recently available version of the Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data that provide final sea ice concentration data. The version update also adjusted three procedures in the Sea Ice Index processing routine that affected both the near-real-time data and the final data. These four updates affect different portions of the Sea Ice Index time series. Because of these updates, minor changes in some of the ice extent and area numbers will be seen. However, these changes are almost all quite small and do not alter current conclusions about Arctic or Antarctic sea ice conditions. More information on Version 2 is available in the Sea Ice Index documentation.Reference
Stroeve, J. C., Jenouvrier, S., Campbell, G. G., Barbraud, C., and Delord, K. 2016, in review. Mapping and assessing variability in the Antarctic Marginal Ice Zone, the pack ice and coastal polynyas. The Cryosphere Discuss., doi:10.5194/tc-2016-26.
Monthly mean of Sea Level Anomalies (annual and seasonal cycles removed)measured by altimetry over the Pacific for August 1997 (left) and August 2015 (right). Credits CNES/CLS.Further information:
- Indicators: ENSO
- Applications: Climate, ENSO
- Image of the month, July 2015 "El Niño's return, west side story".
- ENSO current conditions on CPC/NCEP website
- Météo France (2015/08/28): Vers un épisode El Niño de forte intensité (in french)