Approaching autumn, pace slows

After declining rapidly through July, sea ice extent decline slowed during the first two weeks of August. A new record September minimum is highly unlikely. Our 2018 projection for the sea ice minimum extent falls between the fourth and ninth lowest in the 39-year satellite record. Two NSIDC scientists are studying ice and ocean conditions in the western Arctic aboard an icebreaker.

Overview of conditions

Figure 1. Arctic sea ice extent for August 15, 2018 was 5.7 million square kilometers (2.2 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

As of August 15, Arctic sea ice extent was 5.7 million square kilometers (2.2 million square miles). This is 1.58 million square kilometers (610,000 square miles) below the 1981 to 2010 average, but 868,000 square kilometers (335,000 square miles) above the record low at this time of year recorded in 2012. Ice retreated recently in the Kara, Laptev, and Beaufort Seas. The ice edge was relatively unchanged near Greenland and Svalbard, and in the East Siberian Sea. Much of the Northwest Passage through Canada remains choked with ice. The Northern Sea Route appears open, according to the Multisensor Analyzed Sea Ice Extent (MASIE) analysis, though ice is lingering near the coast in the East Siberian Sea. Scattered ice floes are likely present along the route. A large patch of sea ice, separated from the main pack, persists in the southern Beaufort Sea. Such patterns of ragged patchiness or large polynyas have been a more frequent feature of Arctic summers since 2006.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of August 15, 2018, along with daily ice extent data for four previous years and the record low year. 2018 is shown in blue, 2017 in green, 2016 in orange, 2015 in brown, 2014 in purple, and 2012 in dotted red. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
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Figure 2b. This plot shows average sea level pressure in the Arctic, in millibars, for July 1 to 15, 2018. Yellows and reds indicate higher than average sea level pressure; blues and purples indicate lower than average sea level pressure. Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division High-resolution image

Figure 2b. This plot shows average sea level pressure in the Arctic, in millibars, for August 1 to 14, 2018. Yellows and reds indicate higher than average sea level pressure; blues and purples indicate lower than average sea level pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 2c. This plot shows departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for June 2018. Yellows and reds indicate higher than average temperature; blues and purples indicate lower than average temperature. Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division High-resolution image

Figure 2c. This plot shows departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for August 1 to 14, 2018. Yellows and reds indicate higher than average temperature; blues and purples indicate lower than average temperature.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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This a true-color composite from MODIS on the NASA Terra satellite. August 13, 2018.

Figure 2d. This shows a true color composite image of Cape Morris Jesup off of northern Greenland, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite on August 13, 2018.

Credit: W. Meier, NSIDC/NASA
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Through the first two weeks of August, ice extent declined at approximately 65,000 square kilometers (25,100 square miles) per day, slightly faster than the 1981 to 2010 average of 57,000 square kilometers (22,000 square miles) per day. Sea level pressure was above average over the central Arctic Ocean, a change from last month, flanked by areas of below-average pressure in the Kara Sea and northern Canada (Figure 2b). Temperatures at 925 hPa (about 2,500 feet altitude) were generally 1 to 5 degrees Celsius (2 to 9 degrees Fahrenheit) above average over much of the Arctic Ocean for this period, with the area just north of Greenland reaching 5 to 7 degrees Celsius (9 to 13 degrees Fahrenheit) above average (Figure 2c). Below average air temperatures persisted over the Kara Sea, 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit), and the Beaufort Sea, 1 to 5 degrees Celsius (2 to 9 degrees Fahrenheit). Another feature of note is the region of open water (Figure 2d) along the north coast of Greenland, around Cape Morris Jesup, which is visible on August 13 in Moderate Resolution Imaging Spectroradiometer (MODIS) Terra true color imagery from NASA WorldView. The region normally consists of thick, consolidated ice from a general pattern of on-shore ice motion. Even when winds blow offshore, the strength of the thick ice would hold in place along the coast. However, current ice conditions appear more broken up and likely thinner, and over the past couple of weeks, offshore winds have succeeded in pushing ice off of the coast.

Estimating the September minimum extent

Figure 3. This graph shows potential sea ice minimum extents for 2018 based on ice loss rates from previous years. 2018, through August 15, is shown in blue. Projections based on 2008 rates are shown in purple dots, and 2006 rates are shown in blue dots.

Credit: W. Meier, NSIDC
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A simple way to project the upcoming annual minimum extent involves using the daily rates of change from previous years and applying them to the current sea ice extent. Following the 2005 to 2017 average rate of change between August 15 and the minimum, the extent is projected to drop to an annual low of 4.55 million square kilometers (1.76 million square miles), with a standard deviation range of 4.32 to 4.78 million square kilometers (1.67 to 1.85 million square miles). If sea ice extent continues at the rate of ice loss seen in 2008, the fastest recorded, the minimum at the end of summer would be 4.20 million square kilometers (1.62 million square miles), or the fourth lowest minimum in the satellite record. If sea ice extent continues with the rate for ice loss from 2006, the slowest recorded, the minimum would be 4.90 million square kilometers (1.89 million square miles), or the ninth lowest in the satellite record. It is possible that the rate of change through the remaining summer will be unprecedented in the satellite record (either faster or slower), yielding a final minimum extent outside of this range, but our estimates provide a window of the most likely minimum extent this year. Another possibility is that winds will consolidate the ice and reduce the overall extent. This was a factor contributing to the record low recorded in 2012.

Sea ice up close and personal

Figure 5a. This photograph, off the starboard side of the Araon on 9 August 2018 (21:00 UTC) at 76N/179W, shows dirty ice amidst bright white ice. Photo credit: J. Stroeve

Figure 4a. This photograph, off the starboard side of the RV Araon on August 9, 2018 (21:00 UTC) at 76 degrees N and 179 degrees W, shows dirty ice amidst bright white ice.

Credit: J. Stroeve, NSIDC
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Figure 5b. The team has spotted their first sighting of a polar bear. |Credit: A. Khan ||

Figure 4b. The team’s first sighting of a polar bear.

Credit: A. Khan, NSIDC
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Two NSIDC scientists are currently aboard the Korean icebreaker Araon as it travels through the Chukchi Sea. NSIDC scientist Julienne Stroeve wants to better understand how changes in the sea ice regime (e.g. ice thickness, snow depth, date of melt onset) influence the availability of sunlight under the ice, which plays a key role in phytoplankton blooms and grazing habits of zooplankton. Another objective is to quantify how layering of salty and fresh water in melt ponds evolves over time. To meet these objectives, the researchers will deploy several instrumented to measure seasonal snow accumulation, salinity, and temperature within selected salty and fresh melt ponds. A bio-optical buoy will measure the light and oxygen below the ice, and other buoys will measure the ice growth and melting on different types of ice floes.

As the icebreaker travels through the Arctic Ocean, NSIDC scientist Alia Khan is measuring the amount of sunlight that reaches the ice surface to assess the accuracy of incoming solar energy from weather models. Additionally, she is collecting atmospheric aerosol particles, such as smoke and dust, to measure their size distribution. On the ice, she will collect spectral reflectance measurements (reflectance of the surface in different solar energy wavelengths) of different ice types, such as thin first-year versus thick multiyear ice, snow-covered versus bare ice, and melt ponds. Lastly, she will collect snow and ice samples for analysis of black carbon and algal biomass. Black carbon comes from the incomplete combustion of biomass and fossil fuels. When the dark particles are deposited on snow and ice surfaces, the darker surface absorbs more solar radiation than the surrounding, lighter surface, reducing reflectance of solar energy and enhancing melt. The pigment of ice algae has a similar impact. Collecting these data will help scientists better understand the effects of ship traffic and long-range atmospheric transport that deposit black carbon on the sea ice.

The team left Nome, Alaska, on August 4, and is currently traveling eastwards between 74 and 75 degrees N and 167 degrees W. Before reaching the ice camp where the instruments will be deployed, the ship is retrieving and installing moorings. Ice conditions have been varied since the first sightings of sea ice occurred at 72 degrees 58 minutes N/168 degrees 18.2 minutes W. The first ice sighted mostly consisted of small multiyear ice remnants about 1 meter thick (3.3 feet) and less than 20 meters (66 feet) in size. Now the majority of the ice floes are thin, first-year ice floes between 50 to 200 meters (164 to 656 feet) in size, and 50 to 100 centimeters (1.6 to 3.3 feet) thick. While most of the ice is level ice, some large ridging has been observed. Almost all the ice floes have melt ponds, some discrete and some linked, especially on the thinner first-year ice. Most melt ponds have thaw holes. So far, the majority of melt ponds have a thin top ice layer as air temperatures are hovering around -3 degrees Celsius (27 degrees Fahrenheit). However, once the ship reached 179 degrees W, air temperatures approached 0 degrees Celsius (32 degrees Fahrenheit) and the melt ponds thawed. The most interesting feature thus far has been dirty ice in the midst of bright white ice (see Figure 4a). It is unclear if these dirty ice floes are a result of ice algae, dust, or soot deposits from this summer’s forest fires. The team has also been rewarded with sightings of polar bears (see Figure 4b).

Erratum

Readers alerted us to an error. On August 16, we reported the August 15 sea ice extent as 7.3 million square kilometers (2.82 million square miles) below the 1981 to 2010 average. Instead, it is 1.58 million square kilometers (610,000 square miles) below the 1981 to 2010 average. On August 17, 2018, we corrected the number.

Ice loss speeds up during second half of July

Arctic sea ice extent declined rapidly the latter half of July, despite the persistence of low sea level pressure over the Arctic Ocean and generally cool conditions. At the same time, unusually high sea level pressure persisted over the United Kingdom and Scandinavia, where several new record high temperatures were reached, fostering extensive wildfires.

Overview of conditions

Figure 1. Arctic sea ice extent for July 2018 was 8.22 million square kilometers (3.2 million square miles). The magenta line shows the 1981 to 2010 average extent for that month.

Figure 1. Arctic sea ice extent for July 2018 was 8.22 million square kilometers (3.20 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for July 2018 averaged 8.22 million square kilometers (3.20 million square miles). This was 1.25 million square kilometers (483,000 square miles) below the 1981 to 2010 long-term average sea ice extent, and 550,000 square kilometers (212,000 square miles) above the record low for the month set in July 2012. July 2018 was the ninth lowest July extent in the satellite record.

Despite finishing ninth lowest in the monthly average, ice loss was rapid during the month. As a result, by July 31 daily extent tracked fourth lowest in the satellite record, just below the extent seen last year at this time, and also just above that seen in 2007, 2011, and 2012. Extent remained unusually low in the Atlantic sector of the Arctic, including the Barents, Kara, Laptev, and East Greenland Seas, whereas the ice edge in the Beaufort and East Siberian Seas remained near average. By the end of July, the ice within Hudson Bay had all melted out and the ice edge in the Chukchi Sea had also retreated far north of its average position for this time of year. This pattern is in stark contrast to last year when by July’s end, the ice edge was located far north of its usual position in the Beaufort and East Siberian Seas while with ice on the Atlantic side, extent was near average.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of July 31, 2018, along with daily ice extent data for four previous years and the record low year. 2018 is shown in blue, 2017 in green, 2016 in orange, 2015 in brown, 2014 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data.

Figure 2. The graph above shows Arctic sea ice extent as of July 31, 2018, along with daily ice extent data for four previous years and the record low year. 2018 is shown in blue, 2017 in green, 2016 in orange, 2015 in brown, 2014 in purple, and 2012 in dotted brown. The 1981 to 2010 median is in dark gray. The gray areas around the median line show the interquartile and interdecile ranges of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image

Total ice loss during July was 3.27 million square kilometers (1.26 million square miles), or a rate of -105,400 square kilometers (-41,000 square miles) per day. This was faster than the 1981 to 2010 long-term average rate of retreat for the month of -86,800 square kilometers (-34,000 square miles) per day. Ice retreat occurred primarily within Hudson Bay and the Kara, Laptev, and Chukchi Seas, and to a lesser extent within Baffin Bay, the East Greenland Sea and the East Siberian coastal regions. In contrast, ice expanded slightly in parts of the Beaufort Sea. While there was little overall change in ice extent in the Beaufort Sea, ice concentration remained low over much of the region, with large areas of open water developing between ice floes. Open water areas between floes readily absorb the sun’s energy and help to enhance lateral (from the side) and basal (from the bottom) melting. However, by the end of July the sun is lower in the sky as compared to June, so this effect is diminishing.

Continuing the pattern of the last two summers, low sea level pressure persisted over the central Arctic Ocean during July, a pattern that historically has tended to slow summer ice loss. Low sea level pressure also persisted over Greenland, paired with high sea level pressure over northern Europe and Siberia to the east, and high sea level pressure over Alaska and Canada to the west. This led to air temperatures at the 925 hPa level (approximately 2,500 feet above the surface) ranging from -0.5 to -4.0 degrees Celsius (-0.9 to -7.0 degrees Fahrenheit) below average over the Kara and Laptev, and from -0.5 to -2.0 degrees Celsius (-0.9 to -4.0 degrees Fahrenheit) over the Beaufort Sea. Near the pole, air temperatures were near average or slightly above average (+0.5 to +1.0 degrees Celsius or +0.9 to +2.0 degrees Fahrenheit). Air temperatures -0.5 to -3 degrees Celsius (-0.9 to +5.0 degrees Fahrenheit) below average also persisted over central and northern Greenland.

Meanwhile, over in Scandinavia several new record high temperatures were observed during the month. In Turku, Finland, temperatures soared to 33.3 degrees Celsius (91.9 degrees Fahrenheit) on July 17, the highest temperature recorded since 1914. In central Norway, the Trondheim airport reported a temperature of 32.4 degrees Celsius (90.3 degrees Fahrenheit) on July 16, the highest on record, while Bardufoss, just south of Tromsø within the Arctic circle, saw a new record of 33.5 degrees Celsius (92.3 degrees Fahrenheit) on July 18. In Sweden, more than forty forest fires raged across the country during the unprecedented heatwave in mid-July. Fires were also burning within Lapland and Latvia. However, it was not only Scandinavia experiencing hot and dry conditions. Western Europe continued to experience prolonged heatwaves. Wildfires in Greece have already killed nearly ninety people, while Japan declared their extreme heatwave as a natural disaster, as more than sixty-five people have died and 22,000 have been treated in hospitals.

July 2018 compared to previous years

Figure 3. Monthly July ice extent for 1979 to 2018 shows a decline of 7.2 percent per decade.

Figure 3. Monthly July ice extent for 1979 to 2018 shows a decline of 7.2 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for July sea ice extent is 68,700 square kilometers per year (27,000 square miles per year) or 7.2 percent per decade relative to the 1981 to 2010 average.

Beaufort on the brink?

Figure 4a. This shows a true color composite image of the Beaufort Sea in the Arctic, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite.

Figure 4a. This shows a true color composite image of the Beaufort Sea in the Arctic, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite.

Credit: W. Meier, NSIDC/NASA
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Figure 4b. This image shows sea ice concentration in the Arctic, based on data from the Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2).

Figure 4b. This image shows sea ice concentration in the Arctic, based on data from the Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2).

Credit: University of Bremen
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Ice concentration over much of the Beaufort Sea has rapidly declined over the past couple of weeks. July 27 imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the NASA Terra satellite showed a large off-shore region with broken-up ice and small ice floes vulnerable to rapid melt by the surrounding ocean (Figure 4a). Sea ice concentration data provided by the University of Bremen from the higher resolution Japan Aerospace Exploration Agency (JAXA) Advance Microwave Scanning Radiometer 2 (AMSR2) showed an expanding open water area within the ice pack between mid-July and August 1 (Figure 4b). By August 1, substantial open water was found throughout the Beaufort. On the other hand, near the coast to the east of Utqiaġvik (formerly Barrow), more compact and likely thicker ice remains, which is less likely to rapidly melt away. How much of the Beaufort ice cover survives the summer and how much more melts away will depend considerably on the weather conditions over the next four to six weeks.

Melt onset a mixed bag

Figure 5. These maps show preliminary melt onset (left) and melt onset anomaly (right) in the Arctic relative to the 1981 to 2010 average. White areas are open ocean or areas with no melt detected.

Figure 5. These maps show preliminary melt onset (left) and melt onset difference from average (right) in the Arctic relative to the 1981 to 2010 average. White areas are open ocean or areas with no melt detected.

Data courtesy Jeffrey Miller, NASA GSFC.
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This summer the ice retreated quite early in the Bering Sea in late April and early May, leading to record low extent in the region. This is partly because the melt started nearly two months earlier than average in certain parts of the Bering Sea, while the regional average melt onset date was 38 days earlier. Melt also began several weeks earlier than average in the Barents Sea, stretching up through the Kara Sea and the southern Laptev Sea. In contrast, melt was later than average in most of the Chukchi and East Siberian Seas as well as parts of the Beaufort Sea. While melt onset generally happens earlier in the southern parts of the Arctic and later as one moves further north, exceptions do occur. For example, already in March some melt onset was detected over the central Arctic Ocean, but it did not continuously melt since that date.

Reconstructing sea ice extent in the Kara and Barents Seas

Figure 6. This graph shows reconstructions of sea ice extent in the Barents and Kara Seas from 1289 to 1993 (red line). The gray line shows the 30-year average, the blue line shows observed sea ice extent, and the green line shows the trend.

Figure 6. This graph shows reconstructions of sea ice extent in the Kara and Barents Seas from 1289 to 1993 (red line). The gray line shows the 30-year average, the blue line shows observed sea ice extent, and the green line shows the trend.

Credit: Qi Zhang (Institute of Polar Meteorology, Chinese Academy of Meteorological Sciences, Bejing, China) and Cunde Xiao (Stake Key Laboratory of Earth Surface and Resources Ecology, Beijing Normal University, Bejing, China)
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While we now have forty years of consistent sea ice observations from satellite, this data record is still relatively short, especially for trying to better understand drivers of current sea ice loss and issues such as potential impacts on mid-latitude weather. A new study from a team of Chinese researchers relied on climate proxies from ice cores and tree ring data from coastal forests to provide estimates of autumn sea ice within the Kara and Barents Seas back to 1289. This new data record suggests that between the 13th and 18th centuries, sea ice extent in the Kara and Barents Seas was more extensive than today and was increasing slightly. This period coincides with the Little Ice Age. After the end of the 18th century, sea ice in this region began to decline and the downward trend became significant during the second half of the 19th century until about the 1930s to 1940s. The sea ice then expanded until the 1970s, after which it has continually declined. Based on this reconstruction, current ice loss in the Kara and Barents Seas is viewed as unprecedented, both in duration and rate of change. While the study is only regional and does not indicate overall Arctic-wide sea ice changes, it provides useful context for the recent decline relative to the long-term variability.

Antarctic sea ice update

Sea ice in the Southern Hemisphere grew at a slightly faster-than-average pace from June through mid-July, but then slowed through the second half of July. At mid-July, ice extent was near average in all sectors except the region north of Dronning Maud Land. In the last two weeks of July, an area of below-average ice extent developed north of Wilkes Land in response to warm winds from the northeast, reducing the overall ice growth and bringing the Southern Hemisphere ice extent down relative to the 1981 to 2010 average (below the range of 90 percent of the past observational years). Above average temperatures at the 925 hPa level (about 2,500 feet above sea level) of 4 to 5 degrees Celsius (7 to 9 degrees Fahrenheit) occurred over the northern West Antarctic coast and the southern Peninsula, where the Peninsula high pressure ridge brought winds from the north. Temperatures 3 to 6 degrees Celsius (5 to 11 degrees Fahrenheit) above average also occurred along the Wilkes Land coast.

References

Divine, D. V. and C. Dick. 2007. March through August ice edge positions in the Nordic Seas, 1750-2002, Version 1. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: https://doi.org/10.7265/N59884X1.

Zhang, Q., C. Xiao, M. Ding, and T. Dou. 2018. Reconstruction of autumn sea ice extent changes since AD1289 in the Barents-Kara Sea, Arctic. Science China Earth Sciences, doi:10.1007.s11430-017-9196.4.