On September 19 and 23, Arctic sea ice appeared to have reached its seasonal minimum extent for the year, at 4.59 million square kilometers (1.77 million square miles). This ties 2018 with 2008 and 2010 for the sixth lowest minimum extent in the nearly 40-year satellite record. 

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

Figure 1a. Arctic sea ice extent for September 23, 2018 was 4.59 million square kilometers (1.77 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
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Figure 1b. The map above compares Arctic sea ice extent on September 19, 2018 and September 23, 2018, when Arctic sea ice reached its minimum extent for the year. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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On September 19 and 23, 2018, sea ice extent dropped to 4.59 million square kilometers (1.77 million square miles), tying for the sixth lowest minimum in the satellite record along with 2008 and 2010. This appears to be the lowest extent of the year. In response to the setting sun and falling temperatures, ice extent will begin expanding 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 5 and 9 days later than the 1981 to 2010 median minimum date of September 14. The interquartile range of minimum dates is September 11 to September 19. This year’s minimum date of September 23 is one of the latest dates to reach the minimum in the satellite record, tying with 1997. The lateness of the minimum appears to be at least partially caused by southerly winds from the East Siberian Sea, which brought warm air into the region and prevented ice from drifting or growing southward.

This year’s minimum extent ranked behind 2015 (fifth lowest), 2011 (fourth lowest), 2007 and 2016 (tied for second lowest), and 2012 (lowest). Moreover, the twelve lowest extents in the satellite era have all occurred in the last twelve years.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent on September 23, 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
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This year’s minimum set on September 23 was 1.20 million square kilometers (463,000 square miles) above the record minimum extent in the satellite era, which occurred on September 17, 2012, and 1.63 million square kilometers (629,000 square miles) below the 1981 to 2010 average minimum extent.

Twelve lowest minimum Arctic sea ice extents (satellite record, 1979 to present)

Values within 40,000 square kilometers (15,000 square miles) are considered tied. The 2017 value has changed from 4.64 to 4.67 million square kilometers (1.80 million square miles) when final analysis data updated near-real time data.

With the waning of Arctic summer, the seasonal decrease in sea ice extent has slowed. At this time of the year, the extent is the highest it has been since 2014. Nevertheless, sea ice extent remains well below the interdecile range (lowest 10 percent for ice extent years). The minimum is expected to be one of the ten lowest in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for August 2018 was 5.61 million square kilometers (2.17 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
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Arctic sea ice extent for August 2018 averaged 5.61 million square kilometers (2.17 million square miles). This was 1.59 million square kilometers (614,000 square miles) below the 1981 to 2010 long-term average sea ice extent, and 890,000 square kilometers (344,000 square miles) above the record low for the month set in August 2012. August 2018 was the seventh lowest August extent in the satellite record, but the highest August extent since 2014.

At the end of the month, sea ice extent stood at 4.97 million square kilometers (1.92 million square miles). Sea ice extent remained low along the coastal seas of the Arctic Ocean with the exception of the East Siberian Sea. The Northern Sea Route nevertheless appears to be navigable. Low sea ice concentrations persist in the northern Beaufort and Laptev Seas; these areas may still retreat further north before the melt season ends. The Northwest Passage is still choked with ice and is likely to remain so.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of September, 4, 2018, along with daily ice extent data for four previous years and 2012, the year with record low minimum extent. 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
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Figure 2b. This plot shows departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for August 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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Figure 2c. This plot shows average sea level pressure in the Arctic, in millibars, for August 2018. Yellows and reds indicate high sea level pressure; blues and purples indicate low sea level pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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The average ice loss rate for August was 57,500 square kilometers (22,200 square miles) per day. This was slightly faster than the 1981 to 2010 average, but substantially slower than August loss rates in recent years, particularly 2008, 2012, 2015, and 2016.

Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were up to 4 degrees Celsius (7 degrees Fahrenheit) above average over much of the Arctic Ocean and the Laptev Sea, but up to 4 degrees Celsius (7 degrees Fahrenheit) below average over the Canadian Archipelago (Figure 2b). Higher temperatures over the ocean were related to high sea level pressure east of the Laptev Sea and low pressure over the Barents and Kara Seas, funneling in warm air from Eurasia (Figure 2c).

August 2018 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2018 shows a decline of 10.4 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for August sea ice extent is 75,000 square kilometers (29,000 square miles) per year, or 10.4 percent per decade relative to the 1981 to 2010 average. Ice loss during the month was 1.78 million square kilometers (687,000 square miles), which is nearly the same as the 1981 to 2010 average August decrease.

Sea ice off the Alaskan coast

Figure 4. This map of the Arctic Ocean shows sea surface temperatures (SST) from the University of Washington Polar Science Center UpTempO project. The image shows SSTs from the National Oceanic and Atmospheric Administration (NOAA) and sea ice concentrations from the National Snow and Ice Data Center (NSIDC). The numbered circles denote the location of UpTempO buoys, which are measuring the temperature in the near-surface ocean layer. Data from the buoys is available from the UpTempO website.

Credit: University of Washington
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Ice that has persisted along the Alaskan coast is starting to rapidly disintegrate. However, some remnants consist of thick floes. Sea surface temperatures obtained from the University of Washington’s UpTempO website indicate that waters in the area are near the freezing point. As such, some ice in this region may survive the melt season. These temperatures are consistent with those collected during the cruise of the South Korean icebreaker Aaron (see From the field, a wrap up below). Sea surface temperatures ranged between -1 and +1 degrees Celsius (30 and 34 degrees Fahrenheit) when the ship was traveling through the ice, and more than 4 degrees Celsius (39 degrees Fahrenheit) within the open waters of the Chukchi and Bering Seas.

Opening north of Greenland, closed Northwest Passage

Figure 5a. This map shows sea ice conditions in the western part of the Canadian Archipelago. The colors in the color bar correspond to sea ice concentration in tenths. Dark blue is low concentration (less than 10 percent), white is high concentration (100 percent).

Credit: Canadian Ice Service
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Figure 5b. This chart shows total sea ice area for selected years and the 1981 to 2010 average within the northern route of the Northwest Passage. The dotted red line shows 2018 and the other colors show ice conditions in different years.

Credit: Canadian Ice Service
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As noted in our previous post, an unusual area of open water formed off the northern coast of Greenland. It reached a maximum size of about 23,000 square kilometers (about 8,900 square miles) in mid-August—about the size of the state of New Jersey or the country of Wales. The opening has closed somewhat since then, but an ice-free region remains east of Cape Morris Jesup.

In contrast to northern Greenland, substantial amounts of ice remain in the channels of the Canadian Archipelago, thus the Northwest Passage is not open (Figure 5a). As of the end of August, sea ice area in the northern route of the Northwest Passage is currently tracking just above the 1981 to 2010 average (Figure 5b). The region is far from being free of sea ice; high ice concentrations are still present, about half of which is multiyear ice. Below average air temperature over the western Canadian Arctic Archipelago has limited ice melt. Low sea level pressures over the Beaufort Sea and Canadian Basin have packed ice against the western entrance of the Northwest Passage. The southern route of the Northwest Passage also contains relatively high ice concentrations, although mainly first-year ice. In the unlikely event that the southern route does open in the coming weeks it will be short-lived since multi-year ice from the northern regions would quickly move southward to fill the open water gaps.

From the field, a wrap up

Figure 6a. These graphs show the evolution of snow depth, in meters, from August 20 to August 30, 2018 as recorded by two MetOcean snow buoys, which NSIDC scientist Julienne Stroeve deployed.

Credit: J. Stroeve, NSIDC
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Figure 6b. This photograph shows the MetOcean Snow Buoy set up on sea ice in the Chukchi Sea.

Credit: J. Stroeve, NSIDC
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Figure 6c. NSIDC scientist Alia Khan collects snow samples for black carbon analysis, and measures snow grain size, snow depth, and spectral albedo.

Credit: A. Khan, NSIDC
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NSIDC scientists Julienne Stroeve and Alia Khan have returned from their Arctic expedition on the South Korean icebreaker Aaron. Both successfully deployed their instruments and collected scientific measurements. Now the work of data analysis begins. Since the buoy deployment by Stroeve and others, two of the melt pond buoy systems have already shown 20 centimeters (7.9 inches) of ice melt. Both snow buoys deployed by Stroeve (Figure 6b) are sending back good data (Figure 6a), with a mean snow depth for the last ten days in August of around 9.5±3.3 centimeters (3.74±1.3 inches for buoy #1 and 8.6±1.8 centimeters (3.4±0.7 inches) for buoy #2. While snow depth at the second buoy remained relatively constant, buoy #1 shows the effect of a snowfall event that likely occurred on August 30. Both buoys have drifted considerably eastwards since deployment, with buoy #1 drifting 104 kilometers (65 miles) in ten days (from 79.0 degrees N, longitude 164.5 degrees W to 79.0 degrees N, longitude 159.6 degrees W), and buoy #2 drifting 132 kilometers (82 miles) in nine days (from 78.4 degrees N, longitude 167.9 degrees W to 78.5 degrees N, longitude 162.0 degrees W).

Khan collected snow and ice samples (Figure 6c) for the analysis of black carbon (BC), which comes from the incomplete combustion of biomass and fossil fuels. When the dark particles are deposited on snow and ice surfaces, they absorb more solar radiation than the surrounding surface, reducing the albedo and enhancing melt. Over the course of the five-day ice camp, her team collected 133 snow samples. The team is interested in exploring local BC signals from shipping traffic, transport and deposition from regional Arctic wildfires, and background concentrations of long-range atmospheric transport of BC. They will compare BC concentrations in snow and sea ice with spectral albedo measurements, as well as results from a global aerosol atmospheric transport model to look at potential source regions of the aerosols.

Antarctic Report

Figure 7. This graph shows daily Antarctic sea ice extent for the austral winter season from the past seven years, 2012 to 2018. 2012 is shown in red, 2013 in a dashed green line, 2014 in solid green, 2015 in yellow, 2016 in magenta, 2017 in purple, and 2018 in orange. 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.

Credit: NSIDC
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Antarctic sea ice has increased at a faster-than-average pace in the later part of August. The sea ice maximum is typically reached in late September. Overall sea ice extent is still in the bottom quartile (the lowest 25 percent of years) of the satellite record (Figure 7). Ice extent is below the median of the past 40 years in several regions, including the northern Weddell, far northeastern Weddell, and southern Indian Ocean.

The past seven austral winter seasons for Antarctic sea ice extent have been remarkably variable. In 2012, 2013, and 2014, Antarctic sea ice extent set consecutive satellite-era record highs for the annual maximum. However, 2015 had a near-average seasonally maximum ice extent, while 2016 saw ice extent plunge in late August to reach unprecedented low levels by austral spring in November. Since 2016, ice has remained below the 1981 to 2010 average extent, setting the second-lowest winter maximum extent in October 2017.

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
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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 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 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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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 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 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.

Arctic sea ice extent declined at a slightly slower-than average pace in June. Despite the slow loss, warm conditions and winds from the south developed a large area of open water in the Laptev Sea.

Overview of conditions

Figure 1. Arctic sea ice extent for June 2018 was 10.7 million square kilometers (4.1 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 June 2018 averaged 10.7 million square kilometers (4.1 million square miles). This was 1.05 million square kilometers (405,000 square miles) below the 1981 to 2010 average and 360,000 square kilometers (139,000 square miles) above the record low June extent set in 2016. This was the fourth lowest June average extent in the satellite record.

Extent at the end of June remained below average in the Chukchi Sea, but because of slow retreat through June in the region, extent in the Chukchi is now closer to average than was the case at the end of May. The Barents Sea and East Siberian Sea also have extents well below average at the end of June. Most of the ice in the Sea of Okhotsk has melted. Ice has been retreating in the west side of Hudson Bay where extent is below average. However, this is countered by above average extent in the eastern side of the bay. Notably, a large area of open water has developed in the Laptev Sea, leading to record low extents in that region during the first half of June.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of July, 4, 2018, along with daily ice extent data for four previous years and 2012, the year with record low minimum extent. 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
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Figure 3a. This plot shows the average sea level pressure in the Arctic at the 925 hPa level, in millibars, for June 2018. Yellows and reds indicate higher than average air pressure; blues and purples indicate lower than average air pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 3b. 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

The salient features of the atmospheric pattern for June include a region of low sea level pressure centered over the northern Barents Sea, and a high pressure cell centered over the Laptev Sea. A ridge of high pressure also extends eastward into northern Canada (Figure 3a). Winds from the south between the low pressure area in the Barents Sea and the high pressure area in the Laptev Sea gave rise to a pronounced region of above-average temperatures centered over Central Siberia and extending over the Laptev and East Siberian Seas (Figure 3b). However, elsewhere over the Arctic Ocean, temperatures were near average or slightly below average.

The temperature pattern is consistent with the early development of open water in the Laptev Sea. Extents in this area oscillated between slightly above and below the record low extent set in June 2014. Parts of the Laptev Sea opened as early as mid-April, likely due to winds transporting ice away from the fast ice zone (ice that is locked to the shoreline). While new ice formed in these open water areas, this ice was thin and prone to melting out once the summer melt season started.

Also of note was the passage of a strong cyclone in early June. This system moved into the Kara Sea on June 6, and reached a minimum central pressure of less than 970 hPa on June 7. By June 10, it had migrated into the Beaufort Sea. It dissipated on June 13.

June 2018 compared to previous years

Figure 4. Monthly June ice extent for 1979 to 2018 shows a decline of 4.1 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for June sea ice extent is 48,000 square kilometers (18,500 square miles) per year, or 4.1 percent per decade relative to the 1981 to 2010 average. Ice loss during the month was 1.6 million square kilometers (618,000 square miles), somewhat slower than the 1981 to 2010 average loss of 1.7 million square kilometers (656,000 square miles) for the month. Clearly the early ice losses in the Laptev Sea, associated with warm conditions over the region, could not make up for slower retreats elsewhere.

New insights into warming in the northern Barents Sea

An interesting feature of recent years is a region of unusually high winter air temperatures, or a winter hotspot, over the northern Barents Sea. Previous studies have provided evidence linking the hotspot to a halocline retreat, which is a retreat or weakening of the cold, fresh waters at the ocean surface that prevent ocean heat imported from the Atlantic from mixing upwards. A new paper by Lind et al. (2018) argues that the hotspot is driven by the lack of sea ice transport. Sea ice is mostly fresh water (low salinity) and less is being transported into that region. Hence the ocean surface becomes less fresh over the northern Barents Sea, allowing the warm Atlantic water to mix upwards.

Antarctica in June

Figure 5. This plot shows departure from average air temperature in Antarctica 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
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Sea ice expanded at a faster-than-average pace in June in the Southern Hemisphere, bringing Antarctic sea ice extent closer to typical ice extents for this time of year. This follows on the heels of a period of below-average ice extent since austral winter in 2016. Sea ice extent is near average in all sectors except the northeastern Weddell Sea, and a small area in the northern Davis Sea. Higher-than-average air temperatures prevailed in these regions, and cool conditions prevailed over the northern Ross Sea.

Antarctica’s sea ice and ice shelf disintegration

A new study in the Journal Nature found that reduced sea ice in the northwestern Weddell Sea and southern Bellingshausen Sea likely contributed to the weakening of major ice shelves prior to their disintegration in the 1990s and early 2000s. Loss of the sea ice buffer near Antarctica’s coast allows long-period ocean swell to flex ice shelves. Under ordinary conditions, this flexing has little effect. However, if the ice shelves have been pre-conditioned by seasonal melt-water flooding, the flexing by wave action in late summer can have a devastating effect. Minor flexure of the ice shelf plate allows water to infiltrate existing cracks and initiate fracturing of the ice.

Four major ice shelf break-up events in 1995 (Larsen A), 2002 (Larsen B), and 2008 and 2009 (Wilkins) all occurred after multiple weeks where no sea ice was present near the ice shelf fronts to dampen ocean swell. In the case of the Larsen A and B events, the loss of the ice shelves initiated a significant acceleration of the tributary glaciers. The study demonstrates that sea ice—a component of the cryosphere that is very sensitive to changing climate and ocean—has an important protective effect on the Antarctic ice sheet.

Further Reading

Lind, S., R. B. Ingvaldsen, and T. Furevik. 2018. Arctic warming hotspot in the Northern Barents Sea linked to declining sea-ice import. Nature Climate Change, doi:10.1038/s41558-018-0205-y.

Massom, R., T. A. Scambos, L. G. Benetts, P. Reid, V. A. Squire, and S. Stammerjohn. 2018. Antarctic ice shelf disintegration triggered by sea ice loss and ocean swell. Nature, 558, 383-389, doi:10.1038/s41586-018-0212-1.

Sea ice extent in the Bering Sea remains at record low levels for this time of year. Total ice extent over the Arctic Ocean also remains low.

Overview of conditions

Figure 1. Arctic sea ice extent for April 2018 was 13.71 million square kilometers (5.29 million square miles). The magenta line shows the 1981 to 2010 average extent for the month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Arctic sea ice extent for April 2018 averaged 13.71 million square kilometers (5.29 million square miles). This was 980,000 square kilometers (378,400 square miles) below the 1981 to 2010 average and only 20,000 square kilometers (7,700 square miles) above the record low April extent set in 2016. Given the uncertainty in measurements, NSIDC considers 2016 and 2018 as tying for lowest April sea ice extent on record. As seen throughout the 2017 to 2018 winter, extent remained below average in the Bering Sea and Barents Sea. While retreat was especially pronounced in the Sea of Okhotsk during the month of April, the ice edge was only slightly further north than is typical at this time of year. Sea ice extent in the Bering Sea remains the lowest recorded since at least 1979. The lack of sea ice within this region created many coastal hazards this past winter.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of April 30, 2018, along with daily ice extent data for four previous years and 2012, the year with record low minimum extent. 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
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Overall, sea ice extent for April 2018 declined by 920,000 square kilometers (355,000 square miles). The amount of ice lost for the month was less than the 1981 to 2010 average of 1.1 million square kilometers (424,700 square miles). The ice edge retreated everywhere except in Hudson Bay and Baffin Bay/Davis Strait. The sea ice expanded slightly within Davis Strait during the month. Sea ice in the Hudson Bay usually does not begin to retreat until the end of May.

Air temperatures at 925 hPa (about 2,500 feet above sea level) for April were up to 10 degrees Celsius (18 degrees Fahrenheit) higher than average in the East Siberian Sea and stretching towards the pole. Air temperatures were also up to 5 degrees Celsius (9 degrees Fahrenheit) above average within the East Greenland Sea and 3 degrees Celsius (5 degrees Fahrenheit) above average over Baffin Bay. By contrast, air temperatures were near average within the Barents and Kara seas and lower than average over Canada and the Hudson Bay. The pattern of temperature departures from average resulted from higher than average sea level pressure over the Beaufort Sea as well as the North Atlantic, combined with below average sea level pressure over Eurasia and western Greenland through eastern Canada. On the Pacific side of the Arctic, this pressure pattern drove warm air from the south over the East Siberian and Chukchi Seas, while bringing cold air into northern Canada. The pattern of above average sea level pressure over the North Atlantic was combined with lower than average sea level pressure over western Greenland and the Canadian Archipelago, bringing in warm air in from the south over Greenland and Baffin Bay.

April 2018 compared to previous years

Figure 3. Monthly April ice extent for 1979 to 2018 shows a decline of 2.6 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of decline for April sea ice extent is 37,500 square kilometers (14,500 square miles) per year, or 2.6 percent per decade relative to the 1981 to 2010 average.

Continued loss of the oldest sea ice, five-years or older

Figure 4a-d. These maps show the ice age distribution during week nine in 1984 (a) and 2018 (b). The time-series (c) shows total sea ice extent for different age classes as is outlined in the Arctic Ocean Domain (d).

Credit: Preliminary analysis courtesy M. Tschudi, University of Colorado Boulder. Images by M. Tschudi, S. Stewart, University of Colorado, Boulder, and W. Meier, J. Stroeve, NSIDC
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An updated assessment of ice age changes in the Arctic through week nine (early March) in 2018 shows a substantial amount of first-year ice within the Beaufort, Chukchi, East Siberian, Laptev, Kara and Barents Seas (Figure 4b). Multiyear ice near the Alaskan and Siberian coast is limited to scattered regions off shore in the Beaufort and Chukchi Seas. A tongue of second- and third-year ice extends from near the pole toward the New Siberian Islands, and a region of second-year ice extends toward Severnaya Zemlya. As averaged over the Arctic Ocean domain (Figure 4d), the multiyear ice cover has declined from 61 percent in 1984 to 34 percent in 2018. In addition, only 2 percent of the ice age cover is categorized as five-plus years, the least amount recorded during the winter period. While the proportion of first-year versus multiyear ice will largely depend on how much ice melted during summer, how much ice is exported out of Fram Strait each winter also plays a role. First-year ice grows to about 1.5 to 2 meters (5 to 6.5 feet) thick over a winter season, while older ice is often 3 to 4 meters (9.8 to 13.1 feet) thick.

Note: The ice age fields originally posted on Thursday, May 3, were incorrect. The ice age field has its “birthday” each September after the minimum, when all of the age values are incremented by one after the end of the summer melt season. For example, first-year ice becomes second-year ice after the minimum, second-year ice becomes third-year ice, and so on. However, in the original post, the near-real-time age fields were not incremented after the 2017 minimum. The ice age fields are now corrected (as of Monday, May 7). However, as these are near-real-time data, minor adjustments may occur during final processing. Final numbers will be available in the next few months.

Is winter warming resulting in less winter ice growth?

Figure 5a. These maps show the cumulative number of freezing degree day anomalies from the Climate Forecast System version 2 (CFSv2).

Credit: A. Barrett, National Snow and Ice Data Center
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Figure 5b. This time-series (a) from 1985 to 2017 shows the mean winter ice growth (mid-November to mid-April) simulated by the Los Alamos sea ice model (CICE) forced by the National Center for Environmental Prediction (NCEP-2) atmospheric reanalysis. Also shown are the mean 2 meters NCEP-2 air temperature averaged over the Arctic Ocean (b), cumulative freezing degree days (FDDs) (c), and CICE-simulated November ice thickness (d).

See Stroeve et al. (2018) for more details.
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The last three winters have seen air temperatures at the North Pole surge above 0 degrees Celsius (32 degrees Fahrenheit). While heat transport associated with individual storms can result in high air temperatures persisting over several days, a more important metric in regard to how winter warming impacts the sea ice cover is the cumulative number of freezing degree days. This is defined as the number of days below freezing multiplied by the magnitude of the temperatures below the freezing point. Widespread reductions in the total number of freezing degree days (as compared to average) are apparent for the last three winters, being most pronounced this past winter (Figure 5a).

Previous studies evaluated how the low number of cumulative freezing degree days in the 2015 to 2016 winter over the Barents and Kara Seas impacted the ice thickness and sea ice extent in that region. A newer study looks at the effects of warm winters for a larger area. NSIDC scientist Julienne Stroeve found that in response to the warm winter of 2016 to 2017, ice growth over the Arctic Ocean was likely reduced by 13 centimeters (5 inches). Generally, one does not expect variations in winter air temperature to have a significant impact on winter ice growth—temperatures still generally remain well below freezing and the rate at which ice grows (thickens) is greater for thin ice than thick ice. Thus, despite an overall increase in winter air temperatures, thermodynamic ice growth over winter has generally increased in tandem with thinning at the end of summer (Figure 5b). However, since 2012, this relationship appears to be changing. Overall winter ice growth in the 2016 to 2017 winter was similar to that in 2003, despite having a mean November ice thickness well below that seen in 2003. A similar analysis is not yet available for the 2017 to 2018 winter, but given the very warm conditions, it is likely that thermodynamic ice growth was reduced compared to average.

Unusual polynya opening north of Greenland

Figure 6a. This sequence of high-resolution images from the NASA Advanced Microwave Scanning Radiometer 2 (AMSR2) show the formation of a large polynya north of Greenland.

Credit: J. Stroeve, National Snow and Ice Data Center
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Figure 6b. This graph shows average daily temperatures at Cape Morris Jesup, Greenland’s northernmost station.

Credit: J. Stroeve, National Snow and Ice Data Center
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During the middle of February, a large polynya opened north of Greenland and persisted through the first week of March (Figure 6a). Development of the polynya was driven in part by strong winds from the south and unusually high air temperatures. On February 24, during the peak of the polynya opening, air temperatures at Cape Morris Jesup, Greenland’s northernmost station, surged well above freezing, reaching 6.1 degrees Celsius (43 degrees Fahrenheit), while the daily average temperature hovered just above freezing (Figure 6b). Such periods of extremely warm winter temperatures have been unusual since the beginning of the Cape Morris Jesup record in 1981. During the month of February, only a few years exhibited hourly air temperatures rising above 0 degrees Celsius (32 degrees Fahrenheit): once in 1997, five times in 2011, seven in 2017 and 59 times in 2018.

References

Beitsch, A., L. Kaleschke, and S. Kern. 2014. Investigating high-resolution AMSR2 sea ice concentrations during the February 2013 fracture event in the Beaufort Sea. Remote Sensing 6, 3841-3856, doi.org/10.3390/rs6053841.

Boisvert, L.N., A.A. Petty, and J. Stroeve. 2016. The impact of the extreme winter 2015/16 Arctic cyclone on the Barents–Kara Seas, Bulletin of the American Meteorological Society, doi:10.1175/MWR-D-16-0234.1.

Ricker, R., S. Hendricks, F. Girard-Ardhuin, L. Kaleschke, C. Lique, X. Tian-Kunze, M. Nicolaus, and T. Krumpen. 2017a. Satellite observed drop of Arctic sea ice growth in winter 2015-2015, Geophysical Research Letters, doi:10.1002/2016GL072244.

Stroeve, J., D. Schroeder, M. Tsamados, and D. Feltham. 2018. Warm winter, thin ice? The Cryosphere, doi:10.5194/tc-2017-287, accepted.

Further reading

Thompson, A. “Shock and thaw—Alaskan sea ice just took a steep, unprecedented dive.” Scientific American. https://www.scientificamerican.com/article/shock-and-thaw-alaskan-sea-ice-just-took-a-steep-unprecedented-dive.

Hansen, K. “Historic low sea ice in the Bering Sea.” NASA Earth Observatory. https://earthobservatory.nasa.gov/IOTD/view.php?id=92084.