The seasonal minimum of Arctic sea ice extent is imminent; extent at the minimum is likely to be the sixth lowest in the satellite record, tied with 2008.

Overview of conditions

Figure 1. Arctic sea ice extent for September 17, 2018 was 4.60 million square kilometers (1.78 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

On September 17, Arctic sea ice extent stood at 4.60 million square kilometers (1.78 million square miles). This was 1.69 million square kilometers (653,000 square miles) below the 1981 to 2010 long-term average extent for this day of year, but 1.21 million square kilometers (467,000 square miles) above the record low for this day of year set in 2012. With the onset of autumn, air temperatures are dropping across the Arctic. The seasonal minimum extent is imminent. The Arctic’s minimum sea ice extent is likely to be the 6th lowest in the 39-year satellite record. Cool conditions in July played a large role in slowing the rate of summer ice loss. The Northern Sea Route nevertheless appears to be navigable. The Northwest Passage, including both the Northern and Southern routes, will not open this year. A remnant island of sea ice north of Alaska—well separated from the main area of pack ice and discussed in our previous post—is almost certain to survive the melt season.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of September 17, 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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Figure 2b. This plot shows the difference from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for September 1 to 16, 2018. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Figure 2c. This plot shows the average sea level pressure in the Arctic in millibars (hPa) for September 1 to 16, 2018. Yellows and reds indicate high average air pressures; blues and purples indicate low air pressures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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The average rate of ice loss from September 1 through September 17 was 25,000 square kilometers per day (10,000 square miles per day), similar to average rate of loss for the first half of September over the period 1981 to 2010. Sea ice retreat primarily occurred in the northern Chukchi, East Siberian, and Laptev Seas. The ice edge retreated slightly in the Kara and Barents Seas. Air temperatures at the 925 hPa level (about 2,500 feet above the surface) were near average over much of the Arctic Ocean, the obvious exception being in the East Siberian Sea, where temperatures were as much as 7 to 9 degrees Celsius (13 to 16 degrees Fahrenheit) above average. These high temperatures helped to reduce the sea ice extent in this region. The sea level pressure pattern for this same period is dominated by an area of low pressure extending from central Siberia, across the pole, and into the Canadian Arctic, and is most pronounced north of the Laptev Sea. The feature north of the Laptev Sea, in conjunction with the area of high pressure centered over the Bering Sea, has acted to transport warm air from the south over the East Siberian Sea, helping to explain the high temperatures there.

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 (3.20 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. 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.

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.

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).

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 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.
High-resolution image

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 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)
High-resolution image

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.

Sea ice declined at a near average rate through the first half of July as low sea level pressure dominated the Arctic Ocean. Wind patterns caused smoke from Siberian forest fires to sweep over the ice.

Overview of conditions

Figure 1. Arctic sea ice extent for July 15, 2018 was 8.5 million square kilometers (3.3 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 July 15, Arctic sea ice extent was 8.5 million square kilometers (3.3 million square miles). This is 1.24 million square kilometers (479,000 square miles) below the 1981 to 2010 average, but 670,000 square kilometers (259,000 square miles) above the record low for this day in 2011. While total Arctic sea ice extent was tracking at record low levels during winter, the rate of summer ice loss has been unremarkable thus far. Thus far in July, ice retreat has been most pronounced in the Kara Sea, whereas in the Beaufort Sea, the ice edge expanded slightly southwards. The ice edge has changed little within the Barents and East Greenland Seas on the Atlantic side, and retreat has been sluggish in the Chukchi Sea on the Pacific side of the Arctic Ocean.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of July 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 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

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

Through the first two weeks of July, ice extent declined at a rate of 134,000 square kilometers (52,000 square miles) per day, which is near the 1981 to 2010 average. The spatial pattern of ice loss has not changed much since the end of June, with minimal ice loss around the entire ice edge. The Beaufort Sea saw some increase in extent due to the transport of ice from the north. Low sea level pressure dominated the central Arctic Ocean and Greenland. Typically, this pattern, associated with counterclockwise (cyclonic) winds is associated with cool conditions and also causes ice divergence, helping to spread the ice cover over a larger area. However, air temperatures over the pole and the East Siberian and Chukchi Seas at the 925 hPa level (approximately 2,500 feet above the surface) ranged 1 to 2 degrees Celsius (2 to 4 degrees Fahrenheit) above average for the first part of July. Regions with below average air temperatures were found in the Kara, Laptev, and Beaufort Seas (-1 to -3 degrees Celsius or -2 to -5 degrees Fahrenheit below average).

The passive microwave data show a decrease in ice concentration in several areas of the Arctic Ocean, particularly in northern areas of the Beaufort and Chukchi Seas. This is not necessarily a real decrease—it manifests as surface melt and the development of melt ponds on the ice surface. Microwave emission is sensitive to the freeze-thaw state of water. Liquid water atop the ice surface changes the returned signal, mimicking a reduced sea ice concentration. Because the calculation of ice extent does not consider concentration (except for the 15 percent concentration threshold), extent values are much less sensitive to this melt effect. During the melt season, ice extent provides a more consistent and reliable measure of total ice cover.

Siberian smoke over the Arctic Ocean

Figure 3. These images from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) sensor show the Arctic Ocean and surrounding land from July 3 to 6, 2018. Blue arrows indicate smoke that had drifted from fires in Siberia.

Credit: NASA
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Fires in the western United States have been much in the news lately. Less noted are significant fires in Siberia. Over several days at the beginning of July, smoke from these fires was brought into the Arctic Ocean by winds associated with the pattern of low pressure in the region. The smoke streamed over the East Siberian, Chukchi, and Beaufort Seas and eventually across Alaska into northern Canada.

The smoke has two potential effects on sea ice. First, as it drifts over the ice, the smoke particles scatter solar radiation and reduce how much is received at the surface. This has a cooling effect that will tend to reduce the rate of ice loss. However, smoke particles that settle onto the ice will darken the surface, thus decreasing the reflectivity of the surface, or albedo. This increases the amount of solar energy absorbed by the ice and enhances melt. The atmospheric scattering effect of the smoke is short term and dissipates after the smoke drifts away. The surface albedo effect has a longer-term impact and could serve to enhance melt rates through the summer. The magnitude of the effect will depend on how many smoke particles are deposited on the surface, the albedo of the surface that the particles fall on, and the amount of cloud cover which reduces the incoming sunlight. The biggest effect would be on bright, snow-covered ice. It would be smaller on darker melting ice and melt ponds, and there would be no effect in open water areas.

The Defense Meteorological Satellite Program (DMSP) F18 satellite will be undergoing testing from June 25 to 29 and from July 9 to 12. During this time, data from the Special Sensor Microwave Imager/Sounder (SSMIS) sensor on F18 may have degraded quality or may not be collected. DMSP F18 is the primary sensor that provides NSIDC with near-real-time data for sea ice monitoring (nsidc-0081, the Sea Ice Index, and the Arctic Sea Ice News and Analysis web page). If the data quality does not meet operational standards, NSIDC will remove the resulting sea ice fields or NSIDC may not distribute data from the F18 SSMIS during the test periods.

Arctic sea ice extent for May 2018 was the second lowest in the satellite record. Above average temperatures and high sea level pressure prevailed over most of the Arctic Ocean, while some surrounding continental regions were colder than usual.

Overview of conditions

Figure 1. Arctic sea ice extent for May 2018 was 12.2 million square kilometers (4.7 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 May 2018 was 12.2 million square kilometers (4.7 million square miles). This was the second lowest May extent in the 39-year satellite record, and is 310,000 square kilometers (120,000 square miles) above May 2016, the record low for the month. Compared to May 2016, the ice cover remained slightly more extensive in the Barents and Kara Seas, within Baffin Bay, Davis Strait, and the southern Beaufort Sea, but less extensive in the Chukchi and East Greenland Seas.

In Svalbard, the average temperature for May 2018 was 6 degrees Celsius (11 degrees Fahrenheit) above average. By the end of the month, the north and west coasts of Svalbard were largely ice-free and a tongue of open water east of the islands extended northeast to Franz Joseph Land. According to NSIDC data, open water stretched as far north as ~82 degrees N at the end of May.

In the Chukchi Sea, open water developed to the west of Point Barrow, Alaska throughout the month. This may be in part a result of the inflow of warm waters from the Pacific, where sea surface temperatures were higher than average. It may also be due to the general lack of sea ice in the region that allows the ocean to readily absorb the sun’s energy. Ice retreat was also substantial within the Sea of Okhotsk, and little ice remains in the region. Hudson Bay began to open up, with a significant area of open water in the northwest sector of the bay.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of June 3, 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
High-resolution image

Figure 2b. This plot shows departure from average sea level pressure in the Arctic, in millibars, for May 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 2c. This plot shows air temperatures at the 925 mb level averaged over the Arctic Ocean region. This region covers only ocean areas in the Arctic, bounded by the Bering Strait on the Pacific side, and Fram Strait and roughly the 20 degree E meridian between Svalbard and Norway.

Credit: A. P. Barrett, NSIDC
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The atmospheric pattern (Figure 2b) for May was characterized by a region of above average sea level pressure centered over the Fenno-Scandinavian Peninsula and below average pressure centered over Greenland. This pattern helped to funnel warm winds from the south into the Barents Sea sector favoring retreat of ice. Air temperatures at the 925 hPa level (about 2,500 feet above sea level) in the Barents Sea were up to 5 degrees Celsius (9 degrees Fahrenheit) above average (not shown). On the Pacific side, departures from average sea level pressure were small and a fairly typical Beaufort Sea High and Aleutian Low pattern reigned for much of the month. Overall it was warm across the Arctic Ocean with temperatures at the 925 hPa level ranging between 2 to 5 degrees Celsius (4 to 9 degrees Fahrenheit) above average for the month. By contrast, conditions over land regions surrounding the Arctic were relatively cool. Parts of Central Siberia and Nunavut in northern Quebec saw temperatures more than 5 degrees Celsius (9 degrees Fahrenheit) below average. However, Europe, eastern Asia and western North America were warmer than usual.

Air temperatures at the 925 mb level (about 2,500 feet above sea level) over the Arctic Ocean have been above average through most this year (Figure 2c). Temperatures were extremely high compared to typical conditions from January through early March. After a brief cold period in March, temperatures returned to near average and increased at typical rates through most of May.

While it is still relatively early in the melt season, images from the Moderate Resolution Imaging Spectroradiometer (MODIS) show considerable fracturing of multiyear ice floes in the Beaufort Sea. The early development of open water around these large ice floes can help accelerate melt through absorption of solar energy. Some of these ice floes appear already partially covered by melt ponds.

May 2018 compared to previous years

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

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

The linear rate of decline for May sea ice extent is 36,000 square kilometers (14,000 square miles) per year, or 2.6 percent per decade relative to the 1981 to 2010 average. Ice loss during the month was 1.7 million square kilometers (656,000 square miles), which was faster than the 1981 to 2010 average loss of 1.5 million square kilometers (579,000 square miles) for the month.

Another season for the Sea Ice Outlook

The Sea Ice Prediction Network is once again soliciting contributions to the Sea Ice Outlook predicting the September 2018 sea ice extent. This effort is coordinated by the Arctic Research Consortium of the United States (ARCUS). This is the second phase of the Sea Ice Prediction Network, and is currently funded by the National Science Foundation, the Office of Naval Research, and the United Kingdom’s National Environment Research Council. While all prediction methods are welcome, a new focus of the project is to assess the economic value of seasonal ice forecasts. To make the forecasts more useful to stakeholders, there is an increased emphasis on predicting the spatial pattern of the ice cover for September, not just the total extent. The Sea Ice Outlook will summarize contributions and assess the seasonal evolution of conditions each month through summer and in post-season reports at https://www.arcus.org/sipn.

Autumn in Antarctica

Figure 4a. Arctic sea ice extent for June 1, 2018 was 11.0 million square kilometers (4.2 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

Sea ice extent in the Southern Ocean grew steadily in May at the rate of 123,000 square kilometers (47,000 square miles) per day, somewhat faster than the 1981 to 2010 average growth rate of 108,000 square kilometers (42,000 square miles) per day. This pushed Antarctic ice extent from third lowest at the start of the month to sixth lowest by June 1. Ice extent was near average for all regions except for a broad section of the far eastern Weddell Sea, where ice extent was less than the 1981 to 2010 average. The eastern Ross, Amundsen, and Bellingshausen Seas began the month with less ice cover than average, but rapid growth in these regions brought ice extent to near average by the end of the month.

Reference

Nilsen, T. “Warmest May ever on Arctic Islands,” The Barents Observer, June 3, 2018, 11:00 a.m., MST, https://thebarentsobserver.com/en/ecology/2018/06/warmest-may-ever-arctic-islands.

The 2018 winter sea ice maximum has passed, and the melt season has begun. The most notable aspect of the 2017 to 2018 winter ice extent was the persistently low ice extent in the Bering Sea. While December, January, and February were characterized by very warm conditions over the Arctic, March temperatures were mixed, with cool conditions over the Eurasian side and moderately warm conditions over the North American side.

Overview of conditions

Figure 1. Arctic sea ice extent for March 2018 was 14.30 million square kilometers (5.52 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
High-resolution image

Arctic sea ice extent for March 2018 averaged 14.30 million square kilometers (5.52 million square miles), the second lowest in the 1979 to 2018 satellite record. This was 1.13 million square kilometers (436,300 square miles) below the 1981 to 2010 average and 30,000 square kilometers (11,600 square miles) above the record low March extent in 2017. Extent at the end of the month was far below average in the Bering Sea, as it has been for the past several months, and slightly below average in the far northern Atlantic Ocean and Barents Sea. Ice extent was slightly above average in the Sea of Okhotsk.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of April 4, 2018, along with daily ice extent data for four previous years, and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 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

Figure 2b. This plot shows departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 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 the average sea level pressure in the Arctic at the 925 hPa level, in millibars, for March 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
High-resolution image

Overall, ice extent for March 2018 changed little. Extent reached the annual maximum on March 17 and declined by March 31 to nearly the same level as at the beginning of the month. Ice loss following the seasonal maximum has been almost entirely restricted to the Bering Sea and the Sea of Okhotsk, with slight increases in extent in the Barents Sea and near Svalbard.

Air temperatures at the 925 hPa level (about 2,500 feet above sea level) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) higher than average in regions near Greenland and Alaska. Cooler conditions prevailed over Scandinavia, the Kara Sea, and far eastern Siberia, where temperatures were generally 4 to 7 degrees Celsius (7 to 13 degrees Fahrenheit) below average.

Higher than average sea level pressure was present over the western Arctic, including Canada, the Beaufort Sea, and Greenland, while lower than average sea level pressure prevailed over most of Europe and Siberia. This pattern was associated with winds from the south in the Bering Sea and Alaska, helping to push ice toward the pole. Conversely, over Scandinavia and the Barents Sea this pressure pattern resulted in winds from the northeast that pushed Arctic air onto the northern Eurasian landmass leading to colder air temperatures.

The Arctic Oscillation (AO), an indicator for general wind, precipitation, and temperature patterns in the Arctic, was strongly negative in early March, reflecting the higher than average sea level pressure in the western Arctic. This negative phase is characterized by a weakening of the circumpolar wind pattern, a pattern that favors cold air outbreaks over much of the United States as well as parts of Europe and Asia.

March 2018 compared to previous years

Figure 3. Monthly March ice extent for 1979 to 2018 shows a decline of 2.7 percent per decade.

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

The linear rate of decline for March ice extent is 42,200 square kilometers (16,400 square miles) per year, or 2.7 percent per decade relative to the 1981 to 2010 average.

Review of winter season 2017 to 2018

Figure 4. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for December 2017 and January and February in 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

Unusually warm conditions and some prominent warm air intrusions characterized the 2017 to 2018 winter over the Arctic Ocean. Mean air temperature for the months of December, January, and February combined (the climatological winter season) was as much as 7 degrees Celsius (13 degrees Fahrenheit) higher than average, and nearly the entire Arctic Ocean was 4 degrees Celsius (7 degrees Fahrenheit) higher than average. This is the fourth year in a row that unusual jet stream patterns have led to warm air intrusions over the Arctic Ocean. However, some Arctic and subarctic land areas experienced unusually cold periods during the winter. Recent studies show that the frequency and intensity of warm air intrusions has increased in the last few years, particularly in the Atlantic sector, helping to reduce ice growth in the Barents Sea. The winter of 2017 to 2018 marks the second year in a row of pronounced warming events in the Pacific sector.

Deep snow in Russia and Europe

Figure 5. These images show Northern Hemisphere water equivalent of snow cover in millimeters (top) and Northern Hemisphere total snow mass in gigatons (bottom) from October 2017 to March 31, 2018.

Credit: GlobSnow Project and the Finnish Meteorological Institute
High-resolution image

Snow cover extent on the land masses surrounding the Arctic Ocean was average this past winter. However, an analysis of the snow cover thickness and density showed that the total snow mass this past winter was high. Estimates of total snow mass as of March 31 showed that the Northern Hemisphere had nearly 700 billion tons more snow this winter than the 1982 to 2012 average. Many areas of Russia and northern Europe had more than 150 millimeters (6 inches) of water-equivalent on the ground, present as deep snow cover. Snow extent had been above average the entire autumn-winter season but grew to exceptional levels beginning in February. Although the total snow mass has begun to decrease, it is still far above average. The analysis is based on many sources of snow and snow depth data, including passive microwave data produced by NSIDC (EASE-Grid Snow Water Equivalent and Daily Snow Cover), and data derived from several other groups from the European Space Agency and the National Oceanographic and Atmospheric Administration.

Sea ice drift in the Arctic Ocean

Figure 6. This plot shows monthly average sea ice motion in the Arctic, in centimeters per second, for the months of January, February, and March in 2018.

Credit: Alek Petty/NASA Goddard Space Flight Center (GSFC) and the Ocean and Sea Ice Satellite Application Facility (OSI-SAF)
High-resolution image

Plots of monthly average sea ice motion for January, February, and March 2018 reveal pronounced changes in drift direction, since sea ice movement is largely controlled by winds, and therefore storms and pressure patterns. The maps include averages of sea surface temperature outside of the ice-covered area, and indicate that the surface of both the northern Pacific and northern Atlantic were substantially warmer relative to a 1982 to 2015 reference period. Strong Beaufort Gyre and Transpolar Drift patterns were present for January and March of 2018. Ice motion and sea surface temperature data are based on a multi-sensor estimate created by the Ocean and Sea Ice Satellite Application Facility (OSI-SAF), a European meteorological consortium.

Seasonal increase in Antarctic sea ice

After reaching a minimum extent for the year on February 20 and 21, Antarctic sea ice grew rapidly in March 2018. Sea ice extent averaged 3.53 million square kilometers (1.36 million square miles) for the month, not far below the 1981 to 2010 average of 4.03 million square kilometers (1.56 million square miles). Growth was especially rapid in the Amundsen and Ross Seas, nearly erasing the area of below-average sea ice extent that had been in the eastern Ross Sea and western Amundsen in early March.

Rapid sea ice growth in the Amundsen and eastern Ross Seas was reflected in temperatures at the 925 hPa level that were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average across the Pine Island Bay region. This is likely related to cool winds from the south coming up against the west side of a low-pressure area over the Bellingshausen Sea. By comparison, temperatures 2.5 to 4.5 degrees Celsius (4 to 8 degrees Fahrenheit) higher than average were the rule over much of the continental interior from Dronning Maud Land to northern Victoria Land along the Transantarctic Mountains. The index of the strength of the circumpolar vortex (or Southern Annular Mode) was near-neutral for March.

References

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.

Graham, R. M., L. Cohen, A. A. Petty, L. N. Boisvert, A. Rinke, S. R. Hudson, M. Nicolaus, and M. A. Granskog. 2017. Increasing frequency and duration of Arctic winter warming events, Geophysical Research Letters, 44, 6974–6983, doi:10.1002/2017GL073395.

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

Rinke, A., M. Maturilli, R. M. Graham, H. Matthes, D. Handorf, L. Cohen, S. R. Hudson, and J. C. Moore. 2017. Extreme cyclone events in the Arctic: Wintertime variability and trends , Environmental Research Letters, 12 (9), 094006, doi:10.1088/1748-9326/aa7def.

Correction

On April 20, we revised a sentence under the section Seasonal increase in Antarctic sea ice. The sentence originally read “Growth was especially rapid in the Amundsen and eastern Ross Sea, where sea ice was nearly absent at the time of the minimum extent, and along the East Antarctic coast, where many areas now exceed the daily median extent for the end of March.” We revised it to “Growth was especially rapid in the Amundsen and Ross Seas, nearly erasing the area of below-average sea ice extent that had been in the eastern Ross Sea and western Amundsen in early March.”

Arctic sea ice appears to have reached its annual maximum extent on March 17. This is the second lowest Arctic maximum in the 39-year satellite record. The four lowest maximum extents in the satellite record have all occurred in the past four years. NSIDC will post a detailed analysis of the 2017 to 2018 winter sea ice conditions in our regular monthly post in early April.

Overview of conditions

Figure 1. Arctic sea ice extent for March 17, 2018 was 14.48 million square kilometers (5.59 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

On March 17, 2018, Arctic sea ice likely reached its maximum extent for the year, at 14.48 million square kilometers (5.59 million square miles), the second lowest in the 39-year satellite record, falling just behind 2017. This year’s maximum extent is 1.16 million square kilometers (448,000 square miles) below the 1981 to 2010 average maximum of 15.64 million square kilometers (6.04 million square miles).

The four lowest seasonal maxima have all occurred during the last four years. The 2018 maximum is 60,000 square kilometers (23,200 square miles) above the record low maximum that occurred on March 7, 2017; 40,000 square kilometers (15,400 square miles) below the 2015 and 2016 maxima (now tied for third lowest); and is 190,000 square kilometers (73,400 square miles) below the 2011 maximum, which is now fifth lowest.

In March 2017, we reported a new record maximum being set, with 2016 sliding to the second lowest, and 2015 the third lowest. In November 2017, we updated our calculation of the monthly average sea ice extent in the NSIDC Sea Ice Index, resulting in 2016 tying with 2015.

The date of the maximum this year, March 17, was five days later than normal compared to the 1981 to 2010 median date of March 12.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of March 22, 2018, along with daily ice extent data for four previous years and the record low year. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in magenta, and the record low year 2011 to 2012 in dashed 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

The ice growth season ended with very low sea ice extents in the Bering Sea in the Pacific side of the Arctic, and in the Barents Sea in the Atlantic side of the Arctic. The regions of reduced ice cover reflect the combined influences of late autumn freeze-up as well as persistent high air temperatures throughout the winter. Freeze-up was especially late in the Chukchi Sea, due in part to the effects of strong ocean heat transport into the area through the Bering Strait. February then saw an early retreat of sea ice in the Bering Sea. Sea ice extent on the Atlantic side remained below average throughout the winter, which also appears linked to warm ocean waters. While air temperatures at the 925 hPa level (about 2,500 feet above sea level) remained well above average through most of winter, February saw an extreme heat wave over the Arctic Ocean. This is the fourth winter in a row that such heat waves have been recorded over the Arctic Ocean.

A late spurt in sea ice growth just prior to the maximum occurred in the Barents Sea near Novaya Zemlya; sea ice retreat just after the maximum was led by ice loss in the Bering Sea.

Table 1. Ten lowest maximum Arctic sea ice extents (satellite record, 1979 to present)

The Antarctic minimum

As noted in our previous post, in the Southern Hemisphere, sea ice reached its minimum extent for the year on February 20 and 21, at 2.18 million square kilometers (842,000 square miles). This year’s minimum extent was the second lowest in the satellite record, 70,000 square kilometers (27,00 square miles) above the record low set on March 3, 2017. The Antarctic minimum extent is 670,000 square kilometers (259,000 square miles) below the 1981 to 2010 average minimum of 2.85 million square kilometers (1.10 million square miles).

The February 20 and 21 timing of the minimum (the same extent was recorded on both dates) was just slightly earlier than the 1981 to 2010 median date of February 24 for the minimum. Over the satellite record, the Antarctic minimum has occurred as early as February 15 and as late as March 6.

Compared to the Arctic, air temperatures over the sea ice regions of Antarctica over the past season (austral summer) have been closer to their climatological average, hovering within 2 degrees Celsius (4 degrees Fahrenheit) of the 1981 to 2010 average. Relatively rapid and early growth of ice along the eastern Weddell Sea ice edge led the beginning of the autumn sea ice expansion.

Final analysis pending

Please note this is a preliminary announcement. At the beginning of April, NSIDC scientists will release a full analysis of winter conditions in the Arctic, along with monthly data for March.

As temperatures at the North Pole approached the melting point at the end of February, Arctic sea ice extent tracked at record low levels for this time of year. Extent was low on both the Atlantic and Pacific sides of the Arctic, with open water areas expanding rapidly in the Bering Sea during the latter half of the month. On the other side of the globe, Antarctic sea ice has reached its minimum extent for the year, the second lowest in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for February 2018 was 13.95 million square kilometers (5.39 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

Winter continues to be mild over the Arctic Ocean. Sea ice extent remained at record low daily levels for the month. Arctic sea ice extent for February 2018 averaged 13.95 million square kilometers (5.39 million square miles). This is the lowest monthly average  recorded for February, 1.35 million square kilometers (521,000 square miles) below the 1981 to 2010 average and 160,000 square kilometers (62,000) below the previous record low monthly average in 2017.

Extent was especially low in the Bering Sea where sea ice declined during the first three weeks of the month. The eastern part of the Bering Sea was largely ice-free for most of the month; extent was low on the western side, with the ice edge further north than normal. In the Chukchi Sea, extent also retreated during part of February, with open water developing north of the Bering Strait on both the Siberian and Alaskan coasts. As seen all winter, ice extent continued to be below average in the Barents Sea, and at the end of February, a wedge of open water formed north of Svalbard that extended well into the Arctic Ocean.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of March 4, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 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

Figure 2b. This plot shows the average sea level pressures at the 925 hPa level for February 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c. This figure shows differences from average temperature in degrees Celsius, and wind conditions for the period February 22 to 26, 2018. In addition, the North Atlantic Oscillation (NAO) index is shown in the lower left. This is a measure of the strength of the westerly winds in the North Atlantic. When the index is negative, the flow is wavier, which increases the probability of transport of warm air to Greenland from the south.

Credit: European Centre for Medium-Range Weather Forecasts (ECMWF) IFS forecast model
High-resolution image

Low pressure centered just east of the Kamchatka Peninsula and high pressure centered over Alaska and the Yukon during February set up southerly winds that brought warm air and warm ocean waters into the Pacific side of the Arctic Ocean, impeding southward ice growth. This helps to explain the rapid loss of ice extent in the Bering Sea and the ice-free regions within the Chukchi Sea during the month. The warm air intrusion is evident in the 925 mb air temperatures, with monthly temperatures 10 to 12 degrees Celsius (18 to 22 degrees Fahrenheit) above average in the Chukchi and Bering Sea.

On the Atlantic side, low pressure off the southeast coast of Greenland and high pressure over northern Eurasia helped to funnel warm winds into the region and may have also enhanced the northward transport of oceanic heat. At the end of the month, this atmospheric circulation pattern was particularly strong, associated with a remarkable inflow of warm air from the south, raising the temperatures near the North Pole to above freezing, around 20 to 30 degrees Celsius (36 to 54 degrees Fahrenheit) above average. Air temperatures at Cape Morris Jesup in northern Greenland (83°37’N, 33°22’W) exceeded 0 degrees Celsius for several hours and open water formed to the north of Greenland at the end of the month. This is the third winter in a row in which extreme heat waves have been recorded over the Arctic Ocean. A study published last year by Robert Graham from the Norwegian Polar Institute showed that recent warm winters represent a trend towards increased duration and intensity of winter warming events within the central Arctic. While the Arctic has been relatively warm for this time of year, northern Europe was hit by extreme cold conditions at the end of February.

February 2018 compared to previous years

Figure 3. Monthly 2018 ice extent for 1979 to 2018 shows a decline of 3.1 percent per decade.

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

The linear rate of decline for February is 47,000 square kilometers per year (18,000 square miles per year), or 3.1 percent per decade.

Late freeze-up

Figure 4. These graphs show the average Arctic Ocean ice freeze-up dates for 1979 to 2017 (top) and the number of days that freeze-up occurred earlier (cool colors) or later (warm colors) than average (bottom).

Credit: J. Miller, NASA Goddard Space Flight Center
High-resolution image

This year, the freeze-up started earlier than average over much of the central Arctic Ocean, near average within Hudson and Baffin Bays, but significantly later than average elsewhere. Freeze-up was delayed by more than a month later than average within the Chukchi and Bering Seas on the Pacific side, and within the Barents and East Greenland Seas on the Atlantic side. In these regions freeze-up happened after December. Later freeze-up impacts sea ice thickness, reducing the number of days over which sea ice can grow during winter.

Winter navigation in the Arctic without an icebreaker

Figure 5. This figure shows the distribution of Arctic sea ice according to stage of development, , as of February 22, 2018. Pink shows new ice; purple shows young ice; blue shows first year thin ice; orange shows first year medium ice, red shows first year thick ice, brown shows old ice, and while shows glacial ice.

Credit: U.S. National Ice Center
High-resolution image

The Arctic Ocean is becoming more accessible for shipping. Most of the increase in commercial shipping traffic has been during summer, primarily through the Northern Sea Route along the coast of Siberia. However, this February a commercial tanker, the Eduard Toll, made the first crossing of the Northern Sea Route in winter. Improvements in ship-building and the development of ice-strengthened hull technology is a major factor in enabling winter access. Previous ice-strengthened ships could only navigate safely through 0.5 meter thick ice, compared to the 1.8 meter thick ice that the Eduard Toll cruised through. A fleet of six ships with similar technology is being constructed by a South Korean shipbuilder.

While the Northern Sea Route has tended to be dominated by first-year ice, which typically reaches a maximum of around 2 meters, thicker (3- to 4-meter) multi-year ice would be a hazard even to the newer, stronger ships. According to analysis by the U.S. National Ice Center, this year’s old ice (multi-year ice) has pulled completely away from the coast and the Northern Sea Route is dominated by first-year medium (0.7- to 1.2-meter) or first-year thick (1.2- to 2-meter) ice.

Opposite pole, same near-record low extent

Figure 6a. The graph above shows Antarctic sea ice extent as of March 1, 2018, along with daily ice extent data for four previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2016 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2011 to 2012 in dotted magenta. 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

Figure 6b. This figure shows Antarctic sea ice extent for February 28, 2018. Sea Ice Index data. About the data

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

In the Antarctic, sea ice extent reached its daily seasonal minimum, 2.18 million square kilometers (842,000 square miles), on February 20 and 21. This is the second lowest minimum extent in the satellite record, 70,000 square kilometers (27,000 square miles) above the record low, which was set on March 3, 2017. The February average was 2.29 million square kilometers (884,000 square miles), second lowest in the satellite record, and 20,000 square kilometers (7,700 square miles) above the record low February in 2017.

Sea ice in the Antarctic is highly variable from year to year—much more so than in the Arctic. This is clearly seen in the February extent values, where low 2011 values were followed by record or near-record highs in 2013, 2014, and 2015. This was then followed by record or near-record lows in 2017 and this year.

Sea ice extent is particularly low in the Ross and western Amundsen Sea region, and along the southern reaches of the Bellingshausen Sea. Patchy sea ice areas along the East Antarctic coast are near-average in extent.

Further reading

Graham, R. M., L. Cohen, A. A. Petty, L. N. Boisvert, A. Rinke, S.R. Hudson, M. Nicolaus, and M. A. Granskog. 2017. Increasing frequency and duration of Arctic winter warming events, Geophys. Res. Lett., 16, 6974-6983, doi:10.1002/2017GL073395.

Kretschmer, M., D. Coumou, L. Agel, M. Barlow, E. Tziperman, and J. Cohen. 2017. More persistent weak stratospheric polar vortex states linked to cold extremes, Bull. Amer. Meteor. Soc., doi:10.1175/BAMS-D-16-0259.1.

Arctic sea ice extent in December 2017 was below average in both the far northern Atlantic and the Bering Sea, and notably high temperatures prevailed over most of the Arctic, especially over Central Alaska. We look back at the year’s events, and examine Arctic sea ice trends since 1850 based on a new compilation of data from maps, ship reports, and other records.

Overview of conditions

Figure 1. Arctic sea ice extent for December 2017 was 11.75 million square kilometers (4.54 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 December 2017 averaged 11.75 million square kilometers (4.54 million square miles), the second lowest in the 1979 to 2017 satellite record. This was 1.09 million square kilometers (420,900 square miles) below the 1981 to 2010 average and 280,000 square kilometers (108,100 square miles) above the record low December extent recorded in 2016. Extent at the end of the month was below average in the far northern Atlantic Ocean and Barents Sea, slightly above average in western Hudson Bay, and continued to be below average in the Bering and Chukchi Seas. Near-average conditions prevailed along the eastern coast of Greenland and in the Sea of Okhotsk.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of January 2, 2018, along with daily ice extent data for five previous years. 2017 to 2018 is shown in blue, 2016 to 2017 in green, 2015 to 2014 in orange, 2014 to 2015 in brown, 2013 to 2014 in purple, and 2012 to 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

Figure 2b. This plot shows the departure from average air temperatures at the 925 hPa level in degrees Celsius for December 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c. This plot shows the departure from average sea level pressures at the 925 hPa level in degrees Celsius for December 2018. Yellows and reds indicate higher than average air pressures; blues and purples indicate lower than average air pressures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Ice growth during December 2017 averaged 59,800 square kilometers (23,100 square miles) per day. This was fairly close to the average rate for the month of 64,100 square kilometers (24,800 square miles) per day. Ice growth in the Chukchi Sea (very late compared to previous years), the Kara Sea, and the eastern Hudson Bay areas were the main regions of change in December. In contrast, the ice edge slightly retreated in the Barents Sea near Franz Josef Land.

December air temperatures at the 925 hPa level (about 2,500 feet above sea level) throughout the Arctic Ocean were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above average. Prominent warm spots were found over north Central Asia and Central Alaska (more than 10 degrees Celsius, or 18 degrees Fahrenheit above average), as well as over Svalbard and Central Siberia (nearly 6 degrees Celsius or 11 degrees Fahrenheit above average). Temperatures were 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) below average in Eastern Siberia.

The air temperature pattern in December was similar to that seen in November, driven in part by the arrangement of high and low air pressure regions surrounding the Arctic. Below-average pressure over easternmost Siberia and above-average pressure over the Gulf of Alaska drove southwesterly winds into Central Alaska and the Yukon region. Warmth in the Central Arctic and in Svalbard was consistent with southerly winds arising from low pressure over Scandinavia and higher pressure in the Laptev Sea and Central Siberia.

The Arctic Oscillation (AO) is a key climate indicator for general wind, precipitation, and temperature patterns in the Arctic. The AO index was moderately positive through most of 2017, indicating a tendency toward strong circumpolar winds at high latitude and warm conditions in the mid-latitudes. December 2017 had a mix of conditions, resulting in a near-neutral AO state (as measured by the index).

December 2017 compared to previous years

Figure 3. Monthly December ice extent for 1979 to 2017 shows a decline of 3.7 percent per decade.

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

The linear rate of sea ice decline for December is 47,400 square kilometers (18,300 square miles) per year or 3.7 percent per decade. Recall from our previous post that NSIDC has revised the way in which monthly average extents are computed, which has some impacts on computed trends.

2017 year in review

Figure 4. These figures show trends for ice-over dates in the Beaufort (top) and Chukchi (bottom) Seas. Sea Ice Index data.

Credit: R. Thoman, NOAA
High-resolution image

The winter of 2016 to 2017 saw record low winter sea ice extent and higher than average temperatures. Indeed, the first four months of 2017 set or tied record low extents for the month. However, the melt season progressed somewhat slowly from May through July, as storminess and relatively cool conditions began to prevail. As such, sea ice extent at the seasonal minimum, on September 13, ended up as eighth lowest.

Assessments of sea ice thickness modeled by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), as well as sea ice age near the seasonal minimum extent indicate that Arctic sea ice remains very low in overall volume. As the year ended, ice extent remained especially low in the Chukchi and Bering Seas. As discussed in an earlier post, the unusually early seasonal ice retreat in the Chukchi Sea this past summer likely relates to a strong inflow of oceanic heat into the region via the Bering Strait. With more heat in the upper ocean at summer’s end, it takes longer for sea ice to form in autumn and winter. Colleague Rick Thoman of the National Oceanic and Atmospheric Administration (NOAA) National Weather Service has assembled a time series of the ice-over dates in both the Chukchi and Beaufort Seas based on the satellite passive microwave record (Figure 4). The ice-over date is defined as the first day that the ice concentration exceeds 95 percent in the region. The trends towards later freeze up in both seas is striking. This has an impact on sea ice thickness as the growth season is shortened, which may lead to thinner ice by the end of winter. On the other hand, later freeze up also means less time for snow accumulation on the sea ice. Since sea ice grows faster for a thinner snowpack, this may partially offset the impacts of late ice formation.

A longer record of Arctic sea ice extent

Figure 5a. This figure shows departures from 1850 to 2013 calendar-month averages of Arctic sea ice extent as a function of year (x-axis) and calendar month (y-axis). The color bar at the right shows magnitudes of departures from the average.

Credit: J. E. Walsh, F. Fetterer, J. S. Stewart, W. L. Chapman. 2016. Geographical Review; after a figure by J. Stroeve, National Snow and Ice Data Center
High-resolution image

Figure 5b. These sea ice concentration maps compare the lowest September minimum Arctic sea ice extents for the periods 1850 to 1900, 1901 to 1950, 1951 to 2000, and 2000 to 2013.

Credit: F. Fetterer/National Snow and Ice Data Center, NOAA
High-resolution image

Using a compilation of maps, ship reports, and other records, NOAA has published monthly estimates of Arctic sea ice extent spanning 1850 to 2013. While data in the earlier part of the record is limited, the carefully constructed time series helps to put the more recent satellite record in a longer-term context. Figure 5a shows the decline in extent over the period of satellite observations standing out prominently in comparison with the rest of the record, especially in late summer and early autumn. An earlier period of unusually low summer sea ice extent around 1937 to 1943 (as compared to the 1850 to 2013 average) did not extend to the winter season, and was followed by a few years of significantly higher-than-average summer ice extents. Early in the record (1850 to 1900), winter ice extent was not particularly elevated relative to the 1850 to 2013 average, but summer sea ice extent was quite a bit higher higher than the average. As another way to place recent conditions into a longer context using this data set, we show the years of the lowest September extent recorded within the 50-year periods 1850 to 1900, 1901 to 1950, 1951 to 2000, along with the lowest over the period 2000 to 2013 (Figure 5b). The decline in extent is apparent.

Low sea ice extent in the Antarctic

Figure 6. Antarctic sea ice extent for December 2017 was 9.34 million square kilometers (3.61 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

In the Southern Hemisphere, sea ice for December 2017 averaged 9.34 million square kilometers (3.61 million square miles) and was the fourth lowest in the satellite record. Sea ice extent was far below average in the eastern Weddell Sea, but above average in the northwestern Weddell Sea. The East Antarctic coastline had near-average ice extent. As the Southern Hemisphere entered into the summer months, sea ice declined steeply. Temperatures at the 925 hPa level were 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) higher than average in Dronning Maud Land and the northern Ross Sea, and generally lower than average over the ice sheet. Near-average temperatures have prevailed over the fringing Southern Ocean. Pressures were slightly above average over the continent and below average in the surrounding ocean. Consistent with this pattern, the Southern Annular Mode index, a measure of the strength of westerly winds, was moderately positive for December.

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.

Rapid expansion of the Arctic sea ice cover is the norm for October as solar input dwindles and the remaining heat in the upper ocean is released upwards, warming the lower atmosphere and escaping to space. Because of late season growth, the seasonal Antarctic maximum we previously reported as occurring on September 15 was exceeded, with a new maximum set on October 11 and 12. This is the second-lowest and second-latest seasonal maximum extent in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for October 2017 was 6.71 million square kilometers (2.60 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 October 2017 averaged 6.71 million square kilometers (2.60 million square miles), the fifth lowest in the 1979 to 2017 satellite record. This was 1.64 million square kilometers (633,000 square miles) below the 1981 to 2010 average and 820,000 square kilometers (317,000 square miles) above the record low October extent recorded in 2012. By the end of October, extent remained below average throughout most of the Arctic except within the Laptev Sea, which is fully ice covered. Ice growth over the month was most prominent within the Beaufort, East Siberian, and Laptev Seas and within Baffin Bay. In the Chukchi, Kara, and Barents Seas, the rate of ice growth was slower. Ice extent also remains far below average in the East Greenland Sea.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of November 2, 2017 along with daily ice extent data for five previous years. 2017 is shown in blue, 2016 in green, 2015 in orange, 2014 in brown, 2013 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

Figure 2b. This plot shows Arctic air temperature anomalies at the 925 hPa level in degrees Celsius for October 2017. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
High-resolution image

Figure 2c. This plot shows Arctic air temperatures as a function of height and latitudes. Above average air temperatures for the Arctic as a whole extend up to approximately 9,200 meters (30,000 feet) altitude. Yellows and reds indicate higher than average temperatures; blues and purples indicate lower than average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Division
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Ice growth during October 2017 averaged 94,200 square kilometers (36,000 square miles) per day. This was 5,100 square kilometers (2,000 square miles) per day faster than the average rate of ice growth for the month. Total ice extent for the month remains more than 2 standard deviations below the 1981 to 2010 average.

October air temperatures at 925 hPa (about 3,000 feet above sea level) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above average over most of the Arctic Ocean and up to 7 degrees Celsius (13 degrees Fahrenheit) above average over the East Greenland Sea. Unusually high temperatures over the East Greenland Sea appear to largely reflect the transport of warm air from Eurasia, driven by the combination of above average sea level pressure over the Kara and Barents Seas, and below average pressure over the North Atlantic and Greenland. Elsewhere, above average near surface air temperatures reflect in part the exchange of heat from the ocean to the atmosphere as the ocean cools and sea ice forms, such as within the Chukchi Sea. A plot of temperatures as a function of both height and latitudes shows that the above average air temperatures for the Arctic as a whole extend up to approximately 9,200 meters (30,000 feet) high in the atmosphere.

October 2017 compared to previous years

Figure 3. Monthly October ice extent for 1979 to 2017 shows a decline of 9.3 percent per decade.

Credit: National Snow and Ice Data Center
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The linear rate of sea ice decline for October is 77,600 square kilometers (30,000 square miles) per year, or 9.3 percent per decade relative to the 1981 to 2010 average. While this appears as an increase in the rate of October ice retreat compared to the trend reported last year, it is not a climate signal but is rather largely a result of using a different averaging method to derive the monthly average sea ice extent values (see below).

Effects of snow salinity on CryoSat-2 ice freeboard estimates

Figure 4. This schematic illustrates how salinity shifts the source of the radar signature in the icepack. Ice thickness can be over-estimated by radar satellites (CryoSat-2) when snow conditions are more saline.

Credit: V. Nandan
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After the end of sea ice melt season, the ocean cools and new sea ice forms. The ice crystals that form expel salt into the water. Some of this salt, or brine, is also expelled upwards to the surface of the ice or into snow that has fallen since the ice formed. The brine is then wicked upwards into the snowpack, leading to a slightly saline snowpack, ranging from 1 to 20 parts per thousand (standard seawater is about 35 parts per thousand). This saline snow is a strong reflector of radar energy.

A recent study led by the Cryosphere Climate Research Group at the University of Calgary investigated the impact of snow salinity on retrieving sea ice thickness from radar altimeters, such as CryoSat-2. The study shows that the snow layers observed over much of the Arctic’s first-year ice are salty enough to reflect the radar pulse from CryoSat-2, a radar altimeter used to measure sea ice thickness and ice sheet elevation. They calculate that a correction factor could compensate for this effect, and improve sea ice thickness measurements. While snow salinity is important, other factors, such as surface roughness and ice density also contribute to uncertainties in ice thickness, and they can potentially cancel each other out. Continued comparisons to observed thickness data is crucial to better quantify these uncertainties.

Antarctica’s double-humped sea ice maximum

Figure 5a. This graph shows the first and second peaks in extent during the 2017 Antarctic sea ice freeze up. The extent line for the year 2002 is also shown and has a similar pattern to 2017. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 5b. This map shows Antarctic sea ice concentration on October 31, 2017. Note the Maud Rise polynya at the top of the image. Data are from the Advanced Microwave Scanning Radiometer 2 (AMSR2).

Credit: Institute of Environmental Physics, University of Bremen
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In our last post, we noted that Antarctic sea ice may have reached its maximum extent for the year on September 15, at 17.98 million square kilometers (6.94 million square miles). However, after two weeks of decline, extent increased again reaching a second and final maximum of 18.03 million square kilometers (6.96 million square miles) on October 11 and 12. This is tied with 2002 for the latest maximum on record and is the second lowest Antarctic maximum extent in the satellite data record, slightly higher than 1986. Interestingly, 2002 had a similar Bactrian maximum pattern.

The Maud Rise polynya (or Weddell Sea polynya) continues to be a significant feature of the sea ice cover near 5°E longitude and 65°S. The feature appeared around September 13 and grew to its approximate current extent by September 17. Its current size remains about 30,000 square kilometers (12,000 square miles).

Winds and ocean temperatures continue to drive Antarctic sea ice variability. Since there is no land boundary to the north of the Antarctic continent, sea ice in the Southern Hemisphere is free to expand toward the equator until it reaches water temperatures that are high enough to melt sea ice. As a result, changes in winds or ocean temperatures can have a large influence on the amount of sea ice year to year. Changes in winds related to the positive phase of the Southern Annular Mode (SAM) appear to explain the positive trend in total Antarctic sea ice extent. When the SAM is in a positive phase during austral summer, stronger than average westerly winds blow around the Antarctic continent, and sea ice is pushed both westward and slightly northward due to the Coriolis effect. In addition, below average sea surface temperatures persist through the summer and lead to increased sea ice growth the following autumn, while the negative phase precedes higher sea surface temperatures and reduced sea ice growth. A new study suggests the negative SAM mode during 2016/2017 austral summer largely explained the record minimum Antarctic sea ice extent observed in March 2017.

Revised computation of the monthly mean extent

Figure 6. This chart compares the monthly October Arctic sea ice extents generated from the old (black dashed line) and the new (solid black line) averaging method. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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We have updated the way the monthly average sea ice extent is calculated in the NSIDC Sea Ice Index, the source for our sea ice extent estimates. The monthly average total extent (and area) are now computed as an average of the daily values over the month. Historically, the monthly mean sea ice extent has been calculated based on the monthly mean averaged sea ice concentration field. While there is a rationale for both approaches, the new method is more intuitive and eliminates unusual and unexpected results in months when there is rapid ice growth and retreat. Most of the new monthly mean extents are smaller than the previous values with a mean extent difference between -0.45+0.24 and -0.23+0.16 million square kilometers for the Arctic and Antarctic, respectively. The largest differences for the Arctic occur during the month of October due to the rapid ice growth rates typical at that time of year, with the largest difference of -1.20 million square kilometers in October 2012. Changes in rankings and trends were much smaller because the new method tends to affect all years of a given month in a similar manner. October is also the month with the largest trend difference, increasing in magnitude from -7.4 percent per decade to -9.3 percent per decade. Changes in Arctic trends for other months are much smaller.

Similarly, in the Antarctic, differences in averaging methods results in the largest changes during the month of December when the ice cover is rapidly receding. The largest difference of -1.27 million square kilometers occurs in December 1981. The largest changes in the trends are for January and December with a change in value from +2.7 to +3.5 and +1.2 to +1.9 percent per decade, respectively. For more detailed information on the impacts of the revised averaging methods on trends and rankings, please see NSIDC Special Report 19.

Further reading

Nandan, V., T. Geldsetzer, J. Yackel, M. Mahmud, R. Scharien, S. Howell, J. King, R. Ricker, and B. Else. 2017. Effect of snow salinity on CryoSat-2 Arctic first-year sea ice freeboard measurements: Sea ice brine-snow effect on CryoSat-2. Geophysical Research Letters. doi:10.1002/2017GL074506.

Doddridge, E. W. and J. Marshall. 2017. Modulation of the seasonal cycle of Antarctic sea ice extent related to the Southern Annular Mode. Geophysical Research Letters, 44, 9761–9768. doi: 10.1002/2017GL074319.

Windnagel, A., M. Brandt, F. Fetterer, and W. Meier. 2017. Sea Ice Index Version 3 Analysis. NSIDC Special Report 19. https://nsidc.org/sites/nsidc.org/files/files/NSIDC-special-report-19.pdf.