The Arctic melt season has ended and sea ice extent is now increasing after reaching the fourth lowest minimum on record, on September 11. Sea ice extent in Antarctica has not yet reached its seasonal maximum.

Overview of conditions

Figure 1. Arctic sea ice extent for September 2015 was 4.63 million square kilometers (1.79 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Following the seasonal daily minimum of 4.41 million square kilometers (1.70 million square miles) that was set on September 11, which was the fourth lowest in the satellite record, Arctic sea ice has started its cycle of growth. Arctic sea ice extent averaged for the month of September 2015 was 4.63 million square kilometers (1.79 million square miles), also the fourth lowest in the satellite record. This is 1.87 million square kilometers (722,000 square miles) below the 1981 to 2010 average extent, and 1.01 million square kilometers (390,000 square miles) above the record low monthly average for September that occurred in 2012. As of this writing, Antarctica’s winter maximum has not yet occurred, but is anticipated within several days.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of October 5, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Note: This graph was updated to show the most recent years, in order to be consistent with our monthly posts. Sea Ice Index data.

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

For two weeks following the minimum extent on September 11, air temperatures at the 925 hPa level (about 3,000 feet above the surface) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) lower than average in the Chukchi and Beaufort seas, helping foster ice growth in those regions. Elsewhere over the Arctic Ocean, there has been fairly little ice growth, in part due to near average to slightly above average air temperatures. Both the Northern Sea Route and Roald Amundsen’s route through the Northwest Passage appeared to remain free of ice at the end of the month. The deeper northern route through Parry Channel, which consists of M’Clure Strait, Barrow Strait, and Lancaster Sound, never completely cleared of ice.

September 2015 compared to previous years

Figure 3. Monthly September ice extent for 1979 to 2015 shows a decline of 13.4% per decade relative to the 1981 to 2010 average.

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

Through 2015, the linear rate of decline for September Arctic ice extent over the satellite record is 13.4% per decade. The nine lowest September ice extents over the satellite record have all occurred in the last nine years.

Conditions leading to this year’s minimum

Figure 4a. The map at left shows multiyear ice fraction in mid-April derived from ASCAT, and the corresponding map at right shows ice age. ASCAT image courtesy of R. Kwok, NASA Jet Propulsion Laboratory. Ice age image derived from data provided by M. Tschudi, University of Colorado Boulder.

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

Figure 4b. The graphs show Arctic ocean air temperatures for May, June, July, and August at the 925 hPa level, ranked according to year from lowest (in blue colors) to highest (in red colors). Ranking of 2015 is given in yellow.

Credit: D. Slater, National Snow and Ice Data Center
High-resolution image

Figure 4c. The maps show Arctic sea surface temperature (SST) and anomaly in degrees Celsius, for September 2015. The image at left shows average temperature, with reds indicating higher temperatures and blues indicating lower temperatures. The map at right shows temperature anomaly, compared to the 1982 to 2006 average. Reds and oranges indicate higher than average temperatures, and blues lower than average. The grey line indicates the sea ice edge. SSTs are from from the NCDC OIv2 “Reynolds” data set, a blend of satellite (AVHRR) and in situ data designed to provide a “bulk” or “mixed layer” temperature. Ice edge is from NSIDC near real time passive microwave data.

Credit: M. Steele, Polar Science Center/University of Washington
High-resolution image

The summer melt season began earlier than average. The maximum winter extent, reached on February 25, 2015, was also the lowest recorded over the period of satellite observations. However, a relatively large amount of multiyear ice was transported into the southern Beaufort and Chukchi seas during the winter, as documented by images of multiyear ice fraction derived from the Advanced Scatterometer (ASCAT) instrument on the METOP-A satellite (Figure 4a). The corresponding ice age image shows that the multiyear ice largely consisted of floes that had survived several melt seasons, indicating that it was fairly thick. Thick ice is more difficult to melt out during summer than thinner ice; if not for this thicker ice, the September minimum extent would likely have been lower.

Melt onset began earlier than average in the Beaufort Sea, especially along the coast of Canada, leading to early development of open water in this area. Melt also began earlier than is usual in the Kara Sea, fostering early retreat of sea ice in the region. However, air temperatures at the 925 hPa level during May and June for the Arctic ocean region were not particularly high, ranking as the 26^th and 13^th warmest since 1979 (Figure 4b). As a result, although the winter maximum extent was the lowest in the satellite record, ice extent at the end of June was only the third lowest.

The pace of seasonal ice loss picked up rapidly in July, with Arctic ocean region temperatures at the 925 hPa level reaching the second highest during the satellite record (with 2007 ranked as the highest). Daily ice loss rates averaged 101,800 square kilometers (39,300 square miles) per day, the fourth largest rate of ice loss recorded for the month. Nevertheless, sea ice was slow to melt out of Baffin Bay and Hudson Bay, resulting in a July average extent for 2015 that was the eighth lowest on record. By the end of July however, the fast pace of ice loss during the month resulted in 2015 extent falling within 550,000 square kilometers (212,000 square miles) of the level recorded in 2012, and tracking below the levels recorded for 2013 and 2014. By the middle of August, the difference in extent between 2012 and 2015 had dropped to less than 500,000 square kilometers (193,000 square miles), hinting at the possibility that this year would rank among the lowest minimum extents recorded. However, temperatures for August were not particularly warm, and extent ended up fourth lowest.

Higher than average Arctic sea surface temperatures dominated the Arctic Ocean in September 2015 (Figure 4c), though not as high as seen in 2007 or 2012. Early melt onset as well as strong spring winds in the eastern Beaufort Sea led to early ice retreat in this area (Steele et al., 2015). These winds were particularly strong in April 2015, but then they abated, so that while the resulting summer sea surface temperatures were higher than surrounding waters, they were only around 2 to 3 degrees Celsius (4 to 5 degrees Fahrenheit) higher than average near the coast. The Kara Sea was also unusually warm this year, while sea surface temperatures were generally lower than average in the Nordic seas.

What happened to the old ice in the Beaufort and Chukchi Seas?

Figure 5a. The map shows Arctic sea ice age, in years, for the week of September 7 to 13, 2015.

Credit: M. Tschudi, University of Colorado Boulder
High-resolution image

Figure 5b. The plot shows survival rates of first-year, second-year, and older ice, in percentage of area that survived.

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

Maps of ice age at the beginning of the melt season and at the time of the September minimum extent (Figure 5a) reveal that most of the old ice transported into the southern Beaufort and Chukchi seas melted out this summer. This resulted in a 31% depletion of the multiyear ice cover this summer for the Arctic as a whole, compared to only 12% in 2013 and 38% in 2012. There was also more first-year ice lost this summer than during the last two summers. Sixty-two percent of the winter first-year ice was lost. Overall, this was the third largest amount of first-year ice lost in a melt season, behind 2012 (73%) and 2007 (67%).

References

Steele, M., S. Dickinson, J. Zhang, and R. Lindsay. 2015. Seasonal ice loss in the Beaufort Sea: Toward synchrony and prediction, J. Geophys. Res., 120, doi:10.1002/2014JC010247.

Erratum

A reader alerted us that Figure 5a was mislabeled. Instead of Mid-March 2015, it should have been labeled September 2015. On October 8, 2015, we corrected the label and its caption.

August saw a remarkably steady decline in Arctic sea ice extent, at a rate slightly faster than the long-term average. Forecasts show that this year’s minimum sea ice extent, which typically occurs in mid to late September, is likely to be the third or fourth lowest in the satellite record. All four of the lowest extents have occurred since 2007. In mid-August, Antarctic sea ice extent began to trend below the 1981 to 2010 average for the first time since November 2011.

Overview of conditions

Figure 1. Arctic sea ice extent for August 2015 was 5.61 million square kilometers (2.16 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Average sea ice extent for August 2015 was 5.61 million square kilometers (2.16 million square miles), the fourth lowest August extent in the satellite record. This is 1.61 million square kilometers (621,000 square miles) below the 1981 to 2010 average for the month, and 900,000 square kilometers (350,000 square miles) above the record low for August, set in 2012.

The rapid pace of daily ice loss seen in late July 2015 slowed somewhat in August. The pace increased slightly toward the end of the month, so that by August 31 Arctic sea ice extent was only slightly greater than on the same date in 2007 and 2011. The ice is currently tracking lower than two standard deviations below the 1981 to 2010 long-term average.

Sea ice extent remains below average in nearly every sector except for Baffin Bay and Hudson Bay, where some ice persists in sheltered coastal areas. A striking feature of the late 2015 melt season are the extensive regions of low-concentration ice (less than 70% ice cover) in the Beaufort Sea. A few patches of multi-year sea ice surrounded by open water remain in the central Beaufort Sea.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 31, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Ice loss rates were quite steady through most of the month of August. Sea ice loss for August averaged 75,100 square kilometers per day (29,000 square miles), compared to the long-term 1981 to 2010 average value of 57,300 square kilometers per day (22,100 square miles per day), and a rate of 89,500 square kilometers per day for 2012 (34,500 square miles per day).

Cool conditions prevailed in the East Siberian, Chukchi, and western Beaufort seas, where air temperatures at the 925 millibar level were 1.5 to 2.5 degrees Celsius (3 to 5 degrees Fahrenheit) below average. However, a broad region of higher-than-average temperatures extended from Norway to the North Pole, 1.5 to 2.5 degrees Celsius (3 to 5 degrees Fahrenheit) above average. Sea level pressures were up to 10 millibars above average over the central Arctic Ocean, paired with slightly below average values in north-central Siberia, similar to the dipole-like pattern seen for July. The Arctic Oscillation was in its negative phase for most of the month, again similar to July.

August 2015 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2015 shows a decline of 10.3% per decade.

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

Arctic sea ice extent averaged for August 2015 was the fourth lowest in the satellite data record. Through 2015, the linear rate of decline for August extent is 10.3% per decade.

Forecasting the minimum

Figure 4. The graph shows ice extent forecasts, based on ice extent as observed on August 31, 2015 and past years’ observed rates for selected years.

Credit: W. Meier, NASA Goddard Cryospheric Sciences Lab
High-resolution image

One way of estimating the upcoming seasonal minimum in ice extent is to extrapolate from the current extent, using previous years’ rates of daily sea ice loss. Assuming that past years’ daily rates of change indicate the range of ice loss that can be expected this year, this method gives an envelope of possible minimum extents for the September seasonal minimum. However, it is possible to have unprecedented loss rates, either slow or fast.

Starting with the ice extent observed on August 31 and then applying 2006 loss rates, the slowest rate in recent years, results in the highest extrapolated minimum for 2015 of 4.50 million square kilometers (1.74 million square miles), and a September monthly average extent of 4.59 million square kilometers (1.77 million square miles). The lowest daily minimum comes from using the 2010 pace, yielding an estimated 4.12 million square kilometers (1.67 million square miles) for the daily minimum, and a September monthly average extent of 4.33 million square kilometers (1.67 million square miles).

Using an average rate of ice loss from the most recent ten years gives a one-day minimum extent of 4.38 ± 0.11 million square kilometers (1.79 million square miles), and a September monthly average of 4.49 ± 0.09. As of August 31, the 5-day running daily average extent is 4.72 million square kilometers. If no further retreat occurred, 2015 would already be the sixth lowest daily ice extent in the satellite record.

The forecast places the upcoming daily sea ice minimum between third and fourth lowest, with fourth more likely. There is still a possibility that 2015 extent will be lower than 4.3 million square kilometers, the third lowest sea ice extent, surpassing the 2011 sea ice extent minimum, and a small chance of surpassing 2007, resulting in the second-lowest daily minimum. This assumes that we continue to have sea ice loss rates at least as fast as those of 2010. This was indeed the case for the final ten days of August 2015.

Northwest Passage icy; Northern Sea Route remains open

Figure 5. Click on the image to view an animation of sea ice concentration north of Canada for August 23 to September 1, 2015.

Credit: Canadian Ice Service Daily and Regional Ice Charts
High-resolution image

The southerly route through the Northwest Passage is open. The passage was discovered during 1903 to 1906 by Roald Amundsen, who made the first transit of the passage from Baffin Bay to the Beaufort Sea. This route passes south of Prince of Wales Island and Victoria Island before entering the Beaufort Sea south of Banks Island. Data from the AMSR-2 satellite, which uses passive microwave emission, suggests that this path is ice-free. The higher-resolution Multisensor Analyzed Sea Ice Extent (MASIE) product, based on several data sources and human interpretation, shows only a few areas of low-concentration ice. The broader and deeper passage through the Canadian Arctic Archipelago, between Lancaster Sound, Parry Channel, and McClure Strait, is still obstructed by ice, but at the end of August ice blocked only a short portion near Victoria Island. Before drawing conclusions about navigability, however, it is important to check with the operational services such as the National Ice Center (NIC) or the Canadian Ice Service (CIS). The Northern Sea Route, north of the European Russian and Siberian coasts, has remained largely clear of ice for the entire month.

Warm surface water near Alaska and the Kara Sea

Figure 6. The map shows average ocean sea surface temperature (SST) and sea ice concentration for August 30, 2015. SST is measured by satellites using thermal emission sensors (a global product, adjusted by comparison with ship and buoy data). Sea ice concentration is derived from NSIDC’s sea ice concentration near-real-time product. Also shown are drifting buoy temperatures at 2.5 meters depth in the ocean (about 8 feet deep: colored circles); gray circles indicates that temperature data from the buoys is not available.

Credit: M. Steele, Polar Science Center/University of Washington
High-resolution image

Strong winds from the east in spring of this year opened the ice pack in the eastern Beaufort Sea quite early, allowing early warming of the ocean surface. However, the winds shifted in later spring, forcing the warmed water layer against the North American mainland rather than dispersing it further into the Arctic Ocean. Sea surface temperatures (SSTs) were high as of late August 2015 in the Beaufort, Chukchi, and Laptev Seas, as well as in Baffin Bay and the Kara and northern Barents seas.

The remaining area of low concentration ice in the Beaufort Sea has large pockets of warming open water. This area is likely to melt out by the September ice minimum; however, maximum SSTs in this region will probably not be especially high (currently about 2.5 degrees Celsius, or 5 degrees Fahrenheit above the freezing point of seawater) owing to how late we are in the melt season.

NASA airborne mission flies over sea ice in 2015 to support ICESat-2

Figure 7. The map at left shows flight tracks flown by NASA to evaluate laser reflection characteristics over sea ice and land ice. The image at top right shows sea ice with melt ponds in the Lincoln Sea. The photo at bottom right shows the view from the aircraft window of moderately loose pack in the area.

Credit: K. Brunt/NASA
High-resolution image

In support of the upcoming Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission, NASA recently deployed two instrumented aircraft to Thule Air Force Base, Greenland (near Qaanaaq) to collect data for the development of software to process the satellite data. Instrumentation for the three-week campaign (July 28 to August 19) included a laser altimeter called SIMPL and an imaging spectrometer called AVIRIS-NG. ICESat-2 is a satellite-borne laser altimetry mission that uses a new approach to space-borne determination of surface elevation, based on a high measurement rate (10,000 times per second), multiple ground tracks of laser data, and closely spaced orbital tracks to provide more detailed mapping. Specific science goals of the airborne campaign include assessing how melting ice surfaces and snow-grain-size variability affect the surface return of green-wavelength light (the color of the ICESat-2 lasers).

Over sea ice, the aircraft data provide important information on sea ice freeboard (height of flotation) and snow cover on sea ice. Both are important parameters for correcting satellite measurements of sea ice thickness. Of the more than thirty-five science flight hours of data collected based out of Thule, four flights targeted sea ice in the vicinity of Nares Strait, where loose pack ice, covered in surface melt ponds, was found. These data will be available on the NASA ICESat-2 Web site later in the year.

Arctic sea ice extent is well below average for this time of year, although ice has persisted in Baffin Bay and Hudson Bay. The Northern Sea Route appears to be mostly open, except for a narrow section along the Taymyr Peninsula. The Northwest Passage is still clogged with ice. Antarctic sea ice extent remains high, but the growth rate has slowed and extent is now closer to its long-term average for this time of year.

Overview of conditions

Figure 1. Arctic sea ice extent for July 2015 was 8.77 million square kilometers (3.38 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

July 2015 average ice extent was 8.77 million square kilometers (3.38 million square miles), the 8th lowest July extent in the satellite record. This is 920,000 square kilometers (355,000 square miles) below the 1981 to 2010 average for the month.

While Arctic sea ice retreated at near average rates during the month of June, the pace of ice loss quickened in July such that the extent at the end of the month was within 550,000 square kilometers (212,000 square miles) of the extent recorded on the same date in 2012, and is now tracking below 2013 and 2014. Ice extent was at below average levels within the Kara, Barents, Chukchi, East Siberian, and Laptev seas, while extent was near average in the Beaufort Sea and the East Greenland Sea. Sea ice extent remained more extensive than average within Baffin Bay and Hudson Bay. While the ice extent remained overall higher than in 2012, this is largely a result of the higher extent within Baffin and Hudson bays. Despite average sea ice extent within the Beaufort Sea, higher resolution passive microwave satellite imagery from AMSR-2 and visible-band imagery from MODIS (Figure 6) reveals that the ice has become rather diffuse (low ice concentrations) with many large broken ice floes surrounded by open water.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 2, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Although the pace of ice loss is almost always faster in July than in June, the July rate of loss for 2015 has been pronounced. The rate of ice loss for July 2015 averaged 101,800 square kilometers (39,300 square miles) per day, compared to 97,400 square kilometers (37,600 square miles) in 2012 and 86,900 square kilometers (33,500 square miles) per day in the long-term 1981 to 2010 average. This rapid loss is in part a result of fairly high air temperatures over most of the Arctic Ocean. Temperatures at the 925 hPa level (3,000 feet above sea level) reached nearly 6 degrees Celsius (11 degrees Fahrenheit) above average directly north of Greenland, and up to 5 degrees Celsius (9 degrees Fahrenheit) above average in the East Siberian Sea. In contrast, temperatures were up to 5 degrees Celsius (9 degrees Fahrenheit) cooler than average in the Barents Sea. Sea level pressure was above average over most of the Arctic Ocean, most pronounced near the pole, and over the Greenland Ice Sheet. This was paired with below average pressures over Siberia. Overall, this pattern is very similar to what has come to be known as the Dipole Anomaly.

July 2015 compared to previous years

Figure 3. July ice extent for 1979 to 2015 shows a decline of 7.2% per decade relative to the 1981 to 2010 average.

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

Arctic sea ice extent averaged for July 2015 was the 8th lowest in the satellite data record. Through 2015, the linear rate of decline for July extent is 7.2% per decade.

Seasonal ice hanging on in Baffin and Hudson bays

Figure 4. The graphs show daily sea ice extent from July 1, 2015 to August 3, 2015 (solid green line) compared to previous years, for the Baffin and Hudson bays. Data are from the Multisensor Analyzed Sea Ice Extent (MASIE) product.

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

This summer, the ice has been slow to retreat in the Baffin and Hudson bays, as highlighted by the Multisensor Analyzed Sea Ice (MASIE) product. Throughout July, ice in the bays remained more extensive than in recent summers, adding an extra 500,000 square kilometers (193,000 square miles) of ice to the Arctic total. These areas, normally navigable at this time of year, are reported to be clogged with ice. The heavy ice conditions made fuel resupply difficult for some coastal communities in Nunavut and Nunavik. A supply ship was delayed three weeks attempting to reach Nunavik, and Arctic research projects have been delayed as well. More extensive ice than usual in the eastern part of Hudson Bay also resulted in delays of resupply for communities in Northern Quebec. Polar bears, which are usually farther out on the ice edge at this time of year, were observed in Iqaluit.

Melt started early in 2015

Figure 5. The map at left shows melt onset dates for 2015. The map at right shows anomalies (departure from average) compared to the 1981 to 2010 long-term average. Data are from the Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) passive microwave time series.

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

The timing of seasonal melt onset plays an important role in the amount of ice that can be melted each summer. When melt begins, the surface albedo drops, meaning that more of the sun’s energy is absorbed by the surface, favoring further melt and a further decline in albedo. Because microwave emissions are sensitive to liquid water in the snowpack, the timing of melt onset can be detected using the same satellite passive microwave data that is used for determining the sea ice extent, but with a different algorithm. This summer, melt began a month earlier than average in the Kara Sea, where the ice cover retreated early in the summer, and in the southern Beaufort Sea, where the ice cover is now very diffuse. In contrast, melt came later than average in Baffin Bay where the ice has been slow to completely melt out this summer. Melt also came later than average in parts of the East Siberian and Laptev seas.

Breakup of old, thick ice in the Beaufort Sea

Figure 6. The map at top, left shows ice age, in years, for the beginning of July 2015 (Week 27, June 29 to July 5). The MODIS satellite image (bottom, left) of the Beaufort Sea area, from July 22, 2015, shows a mélange of very large and smaller multiyear ice floes surrounded by open water. The AMSR-2 satellite image from July 22 (top, right) shows ice percent concentration. Ice age data are from C. Fowler and J. Maslanik, University of Colorado Boulder. MODIS data are from the Land Atmosphere Near-Real Time Capability for EOS (LANCE) System, NASA/GSFC. Sea ice concentration image courtesy University of Bremen from the JAXA AMSR-2 sensor.

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

Multiyear ice, which is ice that has survived at least one melt season, tends to be fairly thick. The location of multiyear ice and its age can be determined through tracking the ice motion from year to year. Ice age data from the beginning of July show a tongue of old multiyear ice extending from the southern Beaufort Sea towards Alaska into the Chukchi Sea. However, passive microwave imagery from AMSR-2 reveals that the ice pack has become very diffuse within the Beaufort Sea, with ice concentrations dropping below 50%. Corresponding visible-band imagery from MODIS shows a mélange of very large and smaller multiyear ice floes surrounded by open water. The presence of open water surrounding the floes allows for enhanced lateral and basal ice melt, raising the possibility that much of the multiyear ice in this region will melt out during the remainder of the summer.

Antarctic sea ice extent pauses, still high

Figure 6. The graph above shows Antarctic sea ice extent as of August 3, 2015, along with daily ice extent data for 2010, 2013, and 2015. 2015 is shown in solid blue, 2014 in green, 2013 in dashed blue, and 2010 in pink. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

July average extent for Antarctica was 17.06 million square kilometers (6.59 million square miles). Sea ice extent grew at approximately 150,000 square kilometers per day (58,000 square miles per day) for the first half of July, but then growth slowed to just 10,000 square kilometers (3,900 square miles) per day for much of the rest of the month. The change was due to regional ice retreats in the northern Weddell Sea and northwestern Ross Sea,  almost balanced by continued growth in the northern Bellingshausen Sea west of the Antarctic Peninsula. The slower growth in sea ice extent places 2015 now at around 4th highest in terms of daily extent, below 2014, 2013, and 2010.

Relatively warm conditions prevailed for much of the month in the two regions of ice edge retreat, the northern Weddell Sea and northwestern Ross Sea, with average air temperatures at the 925 hPa level (3,000 feet above sea level) at approximately 4 degrees Celsius (7 degrees Fahrenheit) above average. However, sea surface temperatures just north of the ice edge were 0.5 to 1 degree Celsius (1 to 2 degrees Fahrenheit) cooler than average, raising the potential for rapid ice growth through the remainder of the winter season.

Melt season is underway, and sea ice in the Arctic is retreating rapidly. At the end of May, ice extent was at daily record low levels. By sharp contrast, sea ice extent in the Southern Hemisphere continues to track at daily record high levels.

Overview of conditions

Figure 1. Arctic sea ice extent for May 2015 was 12.65 million square kilometers (4.88 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Arctic sea ice extent for May 2015 averaged 12.65 million square kilometers (4.88 million square miles), the third lowest May ice extent in the satellite record. This is 730,000 square kilometers (282,000 square miles) below the 1981 to 2010 long-term average of 13.38 million square kilometers (5.17 million square miles) and 70,000 square kilometers (27,000 square miles) above the record low for the month, observed in 2004.

The below average extent for this month is partly a result of early melt out of ice in the Bering Sea and the persistence of below-average ice conditions in the Barents Sea. Early breakup of sea ice in the Bering Sea also occurred last spring. Elsewhere, ice is tracking at near-average levels. By the end of May, several openings had appeared in the ice pack, most notably in the southern Beaufort Sea near Banks Island, off the coast of Barrow, Alaska, and in the Kara Sea. Now that we are entering the month of June, the rate of ice loss is likely to quicken, but how fast will depend on the weather conditions and the date of ice surface melt onset across the high Arctic.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of June 1, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2011 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Figure 2b. In this satellite image, captured on June 2, 2015, broken up ice over the eastern Beaufort Sea is apparent. Eastern Russia is snow covered, while the Seward Peninsula is relatively snow free. Sea level pressures were high over the Arctic Ocean at this time. Greenland is seen clearly at the lower left. Image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Terra satellite.

Credit: Land Atmosphere Near-Real Time Capability for EOS (LANCE) System, NASA/GSFC
High-resolution image

Overall, May was cooler than average over the central Arctic Ocean, the East Greenland Sea and the East Siberian and Laptev seas, notably north of the Greenland Ice Sheet where air temperatures at the 925 millibar level (about 3,000 feet above the surface) were 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) below average. However, temperatures were 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) above average in the Beaufort Sea and the Barents and Kara seas, with surface temperatures rising above the freezing point in Barrow, Alaska. These temperature patterns were linked to below-average sea level pressures over the Bering Sea, Baffin Bay and the North Atlantic, coupled with above average pressures over Siberia, Alaska, and Canada. Associated wind patterns also helped to push ice offshore from the coast of Alaska, leading to the formation of open water off the coast of Barrow, Alaska.

Temperature conditions during May may prove to be important, given the potential role that melt ponds in spring play in the evolution of the ice cover throughout summer. For example, during years with fewer melt ponds in May, September sea ice extent tends to be higher than during years with more melt ponds. (See our May 2014 discussion of the importance of spring melt ponds.)

Overall the total ice extent for May 2015 declined at a fairly rapid pace, losing 1.69 million square kilometers (653,000 square miles). This was slightly faster than the 1981 to 2010 average rate of decline of 1.41 million square kilometers (544,000 square miles). The ice extent is now tracking at more than two standard deviations below the 1981 to 2010 long-term average.

May 2015 compared to previous years

Figure 3. Monthly May ice extent for 1979 to 2015 shows a decline of 2.33% per decade relative to the 1981 to 2010 average.

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

Arctic sea ice extent averaged for May 2015 was the third lowest in the satellite record for the month. Through 2015, the linear rate of decline for May extent is 2.33% per decade.

Weather versus preconditioning

Figure 4. The images above compare patterns of winter (January-February-March) sea ice concentration anomalies (SIC, in percent concentration) with sea surface temperature anomalies (SST, in Kelvin) and sea level air pressures (SA, in pressure altitude), for a pre-industrial control model simulation.

Credit: M. Bushuk et al., Geophys. Res. Lett.
High-resolution image

The shrinking summer sea ice cover has fostered increased socioeconomic activity in the Arctic, such as resource extraction and ship traffic, leading to a focus on developing reliable methods to predict the summer minimum sea ice extent several months in advance.

Key to improving our ability to accurately forecast September sea ice conditions is a better understanding of the physical mechanisms underlying sea ice variability from year to year. An area of growing interest is sea ice reemergence: the observation that lower-than-average or higher-than-average sea ice extent tends to recur at time lags of 5 to 12 months. This reemergence phenomenon appears to be related to sea surface temperatures in the seasonal ice zones (from melt season to growth season), sea ice thickness in the central Arctic (from growth season to melt season) and atmospheric circulation (from melt season to growth season).

For example, a new study shows that when winter sea ice concentrations are above average in the East Greenland, Barents and Kara seas, ice concentrations tend to be below average in the Bering Sea. This spatial pattern of anomalies linking the North Atlantic and North Pacific is related to the sea level pressure pattern that drives surface winds and their associated movement of atmospheric heat. These conditions are in turn linked to cooler or warmer than average sea surface temperatures that provide memory, influencing regional sea ice concentrations the following autumn. Thus, while the atmosphere is critical in setting the spatial patterns of sea ice variability, the ocean provides the memory for reemergence.

Figure 4 shows the leading winter (January-February-March) patterns of sea ice reemergence in the Arctic, based on model output from a pre-industrial control simulation of the Community Climate System Model version 4 (CCSM4). The reemerging sea ice concentration (SIC) pattern is characterized by below-average SIC in the Bering Sea and above-average SIC in the Barents-Greenland-Iceland-Norwegian (Barents-GIN) seas. Local sea surface temperature anomalies (SSTs) have the opposite sign and provide memory that allows melt season SIC conditions to reemerge the following growth season. The sea level pressure (SLP) pattern drives winds that provide for communication between the North Atlantic and North Pacific.

The Sea Ice Prediction Network provides a forum for the sea ice forecasting community to share predictions of September mean sea ice extent using a variety of methods.

Down below, Antarctica above

Figure 5. The graph above shows Antarctic sea ice extent as of June 1, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Beginning in late April, Antarctic sea ice extent surpassed the previous satellite-era record set in 2014, and for the entire month of May it has set daily record high ice extents. This makes May 2015 the record high month for the 1979 to 2015 period. As has been the case for several months, ice extent is unusually high in areas of the eastern Ross Sea – western Amundsen Sea, and in the northern and northeastern Weddell Sea. Unusually high extent has developed over the Davis Sea area of the far southern Indian Ocean.

Antarctic sea ice extent for May 2015 averaged 12.10 million square kilometers (4.67 million square miles). The linear rate of increase for May is now 2.88% per decade for the period 1979 to 2015.

Despite the record sea ice extent, air temperatures at the 925 millibar level (about 3,000 feet above the surface) remained generally above average for most of the continent and coastal areas of the surrounding ocean. Air temperatures were as much as 5 degrees Celsius (9 degrees Fahrenheit) above the 1981 to 2010 average over the West Antarctic ice sheet and central Ross Sea. The region of high ice extent near the northeastern Ross Sea had near-average air temperatures in the vicinity of the ice edge. Cooler than average temperatures were observed near the ice edge in the northeastern Weddell Sea (2 degrees Celsius, or 4 degrees Fahrenheit, below average) and Davis Sea (4 degrees Celsius, or 7 degrees Fahrenheit, below average). Air circulation patterns were variable for the month. The Southern Annular Mode, a north-south movement of the westerly wind belt that circles Antarctica, was in a near neutral state for the month as a whole.

Further reading

Bushuk, M., D. Giannakis, and A. J. Majda (2015). Arctic sea-ice reemergence: The role of large-scale oceanic and atmospheric variability. J. Climate, doi:10.1175/JCLI-D-14-00354.1, in press.

Bushuk, M. and D. Giannakis (2015). Sea-ice reemergence in a model hierarchy. Geophys. Res. Lett., doi:10.1002/2015GL063972, in press.

Schroeder, D., D.L. Feltham, D. Flocco and M. Tsmados, (2014). September Arctic sea ice minimum predicted by spring melt pond fraction. Nature Climate Change, doi:10.1038/nclimate2203.

Stroeve, J., E. Blanchard-Wrigglesworth, V. Guemas, S. Howell, F. Massonnet and S. Tietsche, (2015). Developing user-oriented seasonal sea ice forecasts in a changing Arctic. EOS, doi:10.1175/JCLI-D-14-00354.1, in press.

After reaching its seasonal maximum on February 25, the beginning of the melt season was interrupted by late-season periods of ice growth, largely in the Bering Sea, Davis Strait and around Labrador. Near the end of March, extent rose to within about 83,000 square kilometers (32,000 square miles) of the February 25 value. The monthly average Arctic sea ice extent for March was the lowest in the satellite record.

Overview of conditions

Figure 1. Arctic sea ice extent for March 2015 was 14.39 million square kilometers (5.56 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Arctic sea ice extent for March 2015 averaged 14.39 million square kilometers (5.56 million square miles). This is the lowest March ice extent in the satellite record. It is 1.13 million square kilometers (436,000 square miles) below the 1981 to 2010 long-term average of 15.52 million square kilometers (6.00 million square miles). It is also 60,000 square kilometers (23,000 square miles) below the previous record low for the month observed in 2006.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of April 5, 2015, along with daily ice extent data for four previous years. 2015 is shown in blue, 2014 in green, 2013 in orange, 2012 in brown, and 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

The change in total Arctic sea ice extent for March is typically quite small. It tends to increase slightly during the first part of the month, reach the seasonal maximum, and then decline over the remainder of the month. Following the seasonal maximum recorded on February 25, this year instead saw a small decline over the first part of March, and then an increase, due largely to periods of late ice growth in the Bering Sea, Davis Strait and around Labrador. On March 26, extent had climbed to within 83,000 square kilometers (32,000 square miles) of the seasonal maximum recorded on February 25. Despite this late-season ice growth, analysts at the Alaska Ice Program report in their April 3 post that ice in the Bering Sea was very broken up.

March 2015 compared to previous years

Figure 3. Monthly March ice extent for 1979 to 2015 shows a decline of 2.6% per decade relative to the 1981 to 2010 average.

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

The monthly average Arctic sea ice extent for March was the lowest in the satellite record. Through 2015, the linear rate of decline for March extent is 2.6% per decade.

Overview of the winter season

Figure 4. The plot shows Arctic air temperature anomalies at the 925 hPa level in degrees Celsius for March 2015. 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

As discussed in our previous post, the winter of 2014/2015 was characterized by an unusual pattern of atmospheric circulation, with the jet stream lying well north of its usual location over Eurasia and the North Pacific, and then plunging southwards over eastern North America. This pattern was associated with unusually warm conditions extending across northern Eurasia, the Bering Sea and Sea of Okhotsk, Alaska and into the western part of the United States, contrasting with cold and snowy conditions over the eastern half of the United States. The record low seasonal maximum in ice extent recorded on February 25, 2015 was largely due to low extent in the unusually warm Bering Sea and Sea of Okhotsk. This pattern of atmospheric circulation and temperatures largely continued through March.

Recent work by Dennis Hartmann of the University of Washington suggests that this unusual jet stream pattern was driven, at least in part, by a particular configuration of sea surface temperatures over the tropical Pacific known as the North Pacific Mode, or NPM. The NPM pattern consists of above-average sea surface temperatures in the western Tropical Pacific that extend north and east towards the California coast and across the far northern Pacific Ocean. While the better-known El-Nino-Southern Oscillation (ENSO) pattern has been in a neutral state for the past few winters, the NPM has been in an extreme positive state since the summer of 2013.

The pattern of air temperatures seen this past winter has persisted through March; note the unusually warm conditions over northern Eurasia, Alaska and western North America, contrasting with unusually cold conditions over eastern North America.

Snow cover update

Figure 5. This map shows the rank of snow water equivalent measured at SNOTEL sites across the western U.S. A rank of 1 (black dots) corresponds to the lowest SWE in the SNOTEL record; a rank of 31 (magenta dots) is the highest.

Credit: Andrew Slater, NSIDC
High-resolution image

The unusual atmospheric circulation pattern just discussed also helps to explain the snow drought over the western United States. NSIDC scientist Andrew Slater maintains regular updates of western U.S. mountain snowpack conditions using data from the SNOTEL (snowpack telemetry) system – a network of automated sensors that measure snow water equivalent. The automated SNOTEL sites are complemented by snowcourses, where snow water equivalent is measured manually on a periodic basis.

Typically, the snowpack peaks around April 1. As seen in Figure 5, the April 1 snowpack over most of the western United States is far below average. At many sites, snow water equivalent is at historic lows for this time of year. Conditions are somewhat better along the Front Range of Colorado and in Arizona, Wyoming and Montana.

Record warmth in Antarctica

Air temperatures reached record high levels at two Antarctic stations last week, setting a new mark for the warmest conditions ever measured anywhere on the continent. On March 23, at Argentina’s base Marambio, a temperature of 17.4° Celsius (63.3° Fahrenheit) was reached, surpassing a previous record set in 1961 at a nearby base, Esperanza. The old record was 17.1° Celsius (62.8° Fahrenheit). However, Esperanza quickly reclaimed the record a few hours later on March 24, reaching a temperature of 17.5° Celsius (63.5° Fahrenheit).

The cause of these warm conditions is familiar to people living in mountainous regions: a foehn or chinook wind, in which air flows up and over a steep mountain ridge. On the windward side, moisture is wrung out of the air mass in the form of rain or snow. As the air descends on the leeward (downwind) side, it compresses and warms.

This airflow pattern is a key part of the climate conditions that led to past ice shelf disintegrations in the region, such as the dramatic break-up of the Larsen B Ice Shelf in 2002. Air pressure patterns during the event indicated a near-stationary high pressure center in the Drake Passage north of the Antarctic Peninsula, and a strong area of low pressure at the base of the Peninsula, favoring the foehn pattern. Events like this have been recorded by a network of sensors installed by the National Science Foundation LARISSA project.  This network recorded temperatures as high as 16.9° Celsius (62.4° Fahrenheit), westerly winds up to 23 meters per second (45 miles per hour), and a ~100 hour period of temperatures above freezing over the Larsen B area. A recent publication by a colleague at the Scripps Institute of Oceanography describes the impact of foehn or chinook patterns on ice shelf and sea ice stability in the region, making use of the network of Automated Meteorology-Ice-Geophysics Observing Systems (AMIGOS) and other weather sensors in the region.

Further reading

Cape, M., M. Vernet, P. Skvarca, S. Marinsek, T. Scambos, and E. Domack. 2015. Foehn winds link climate-driven warming to coastal cryosphere evolution in Antarctica. Jour. Geophys. Res., Atmospheres, submitted.

Scambos, T., R. Ross, T. Haran, R. Bauer, D.G. Ainley, K.-W. Seo, M. Keyser, A. De, Behar, D.R. MacAyeal. 2013. A camera and multisensor automated station design for polar physical and biological systems monitoring: AMIGOS. Journal of Glaciology, 59 (214), 303-314, doi: 10.3189/2013JoG12J170.

Arctic sea ice extent was the third lowest for the month of January. Ice extent remained lower than average in the Bering Sea and Sea of Okhotsk, while ice in the Barents Sea was near average. Antarctic sea ice extent declined rapidly in late January, but remains high.

Overview of conditions

Figure 1. Arctic sea ice extent for January 2015 was 13.62 million square kilometers (5.26 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Sea ice extent in January averaged 13.62 million square kilometers (5.26 million square miles). This is 910,000 square kilometers (351,000 square miles) below the 1981 to 2010 long-term average of 14.53 million square kilometers (5.61 million square miles), and 50,000 square kilometers (19,000 square miles) above the record low for the month observed in 2011.

This below-average Arctic extent is mainly a result of lower-than-average extent in the Bering Sea and the Sea of Okhotsk. On the Atlantic side, Barents Sea ice extent is near average. This is in sharp contrast to the general pattern seen since 2004 of below average extent in this region, but above average extent in the Bering Sea. Ice extent is also near average in the East Greenland Sea, Baffin Bay and the Labrador Sea.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of February 2, 2015, along with daily ice extent data for four previous years. 2014 to 2015 is shown in blue, 2013 to 2014 in green, 2012 to 2013 in orange, 2011 to 2012 in brown, and 2010 to 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

During most of January, the Arctic Oscillation (AO) was in a strongly positive phase. When the AO is in a positive phase, sea level pressure in the Arctic is particularly low, and sea level pressure is relatively high in the middle latitudes of the Northern Hemisphere. Variability in Arctic sea ice conditions is strongly influenced by the phase of the AO. Typically, during the positive phase of the AO, surface winds push ice away from the shores of Siberia, leading to the formation of more young, thin ice that is prone to melting out in summer. The positive phase also tends to increase the transport of thick, multiyear ice out of the Arctic through Fram Strait.

Air temperatures (at the 925 millibar level, about 3,000 feet above the surface) were mostly above average over most of the Arctic Ocean, with positive anomalies of 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit) over the Chukchi and Bering seas on the Pacific side of the Arctic, and also over the East Greenland Sea on the Atlantic side.

January 2015 compared to previous years

Figure 3. Monthly January ice extent for 1979 to 2015 shows a decline of 3.2% per decade relative to the 1981 to 2010 average.

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

Arctic sea ice extent for January was the third lowest in the satellite record. Through 2015, the linear rate of decline for January extent over the satellite record is 3.2% per decade.

Barents Sea ice variability

Figure 4. The graph shows Barents Sea ice area (blue line) and ocean temperatures in the Barents Sea Opening (red line) from 1980 to 2015. The sea ice area tends to be smaller for higher Atlantic water temperatures, with a lag of 1 to 2 years (note the reversed scale for Atlantic water temperatures). The data are based on Årthun et al. (2012), who find that the ocean temperature largely reflects changes in volume of Atlantic water inflow. Sea ice area anomalies are from the NASA Team algorithm (Cavalieri et al., 1996), provided by the National Snow and Ice Data Center. Ocean temperature has been sampled by the Institute of Marine Research (IMR), Norway, and is a section between Norway and Bear Island (BSO; 71.5-73.5N, 20E).

Credit: Ingrid Onarheim, Bjerknes Centre for Climate Research
High-resolution image

Variability in winter sea ice in the Barents Sea largely reflects ocean heat transport. The inflow of Atlantic water between Norway and Bear Island (the Barents Sea Opening or BSO) is the Barents Sea’s main oceanic heat source. Because there are no significant freshwater sources reaching the central Barents Sea, this warm Atlantic water extends to the surface and readily impacts the sea ice. This contrasts with the rest of the Arctic Ocean, where the Atlantic water lies well beneath the slightly fresher polar surface layer. The import of sea ice in the northern straits is also small, around 20% of the sea ice area exported southwards in the Fram Strait, meaning that the Barents Sea primarily consists of thin, first-year ice. Thus, periods with large volumes of warm Atlantic water entering into the Barents Sea are correlated with less sea ice formation and overall less sea ice extent.

Variations in winter ice extent in the Barents Sea are well correlated with variations in overall Arctic sea ice extent, as assessed over the satellite record. This winter is an exception. Sea ice extent in the Barents Sea is fairly high compared to recent years, while it is low for the Arctic as a whole. According to colleagues at the University of Bergen, this is due to a reduced overall inflow of Atlantic waters. A maximum in the ocean heat transport occurred in the mid 2000s, yet since then, the inflow has in general lessened, both along the Norwegian coast, through the Fram Strait, and through the Barents Sea Opening between Norway and Bear Island. Variations in Atlantic inflow is a focus of ongoing research at the Bjerknes Centre in Bergen, as well as in other research centers in Europe.

Antarctic sea ice declines rapidly, still high

Figure 5a. The graph above shows Antarctic sea ice extent as of February 2, 2015, along with daily ice extent data for four previous years. 2014 to 2015 is shown in blue, 2013 to 2014 in green, 2012 to 2013 in orange, 2011 to 2012 in brown, and 2010 to 2011 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Antarctic sea ice extent reached record high levels for late December 2014 and early January 2015, peaking around January 10 at more than 2.5 million square kilometers (965,000 square miles) above the 1981 to 2010 average, and 1.05 million square kilometers (580,000 square miles) above the previous record (2014) for that date. As noted last month, the largest excursions are occurring in the northern Weddell Sea and the northern Ross Sea. After January 10, and particularly after January 19, sea ice extent dropped rapidly (~250,000 square kilometers, or 96,500 square miles, per day), and large areas of the northern Ross Sea became ice free. The northern Weddell region still has a very large ice extent relative to average conditions.

Figure 5b. These images show Antarctic wind vector (top) and air temperature (bottom) anomalies for late December 2014 to early January 2015, compared to 1981 to 2010 averages.

Credit: NOAA ESRL Physical Sciences Division
High-resolution image

Weather conditions during late December and January help to explain these changes. In the northern Weddell Sea, southerly winds (more so than average) and cool conditions relative to the 1981 to 2010 average prevailed for late December and all of January, and sea ice there remained high relative to long-term averages for the month. For the northern Ross Sea, air temperatures at the 925 hPa level have been slightly above average for the entire period, but winds in this area shifted during January, from southerly (pushing ice outward) to northwesterly. The combination of northerly winds and slightly warm conditions seems to have reduced the ice extent anomaly significantly in this sector.

Further reading

Smedsrud, L.H., I. Esau, R. B. Ingvaldsen, T. Eldevik, P. M. Haugan, C. Li, V. S. Lien, A. Olsen, A. M. Omar, O. H. Otterå, B. Risebrobakken, A. B. Sandø, V. A. Semenov, and S. A. Sorokina. 2013. The role of the Barents Sea in the Arctic climate system.
Reviews of Geophysics, 51, doi:10.1002/rog.20017.

Årthun, M., T. Eldevik, L. H. Smedsrud, Ø. Skagseth, and R. B. Ingvaldsen. 2012.
Quantifying the Influence of Atlantic Heat on Barents Sea Ice Variability and Retreat. Journal of Climate, Volume 25, pp. 4736-4743, doi:10.1175/JCLI-D-11-00466.1.

Schauer, U. and A. Beszczynska-Möller. 2009. Problems with estimation and interpretation of oceanic heat transport – conceptual remarks for the case of Fram Strait in the Arctic Ocean, Ocean Sci., 5, 487–494.

While the U.S. experienced extreme weather in November, conditions in the Arctic were fairly ordinary. Arctic sea ice in November followed a fairly average growth pace. Ice extent was near average over much of the Arctic with only the Chukchi Sea and Davis Strait showing below average ice conditions.

Overview of conditions

Figure 1. Arctic sea ice extent for November 2014 was 10.36 million square kilometers (4.00 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Sea ice extent in November averaged 10.36 million square kilometers (4.00 million square miles). This is 630,000 square kilometers (243,000 square miles) below the 1981 to 2010 long-term average of 10.99 million square kilometers (4.24 million square miles) and 520,000 square kilometers (201,000 square miles) above the record low for the month observed in 2006.

Arctic sea ice extent continued to increase throughout the month of November. By the end of the month, most of the Arctic Ocean was covered by ice, the exception being the Chukchi Sea that remained unusually ice free for this time of year. Ice also began to extend into Hudson Bay and Baffin Bay, although ice growth was slower than average in Davis Strait. The near-average ice conditions in the East Greenland, Barents and Kara seas have not been seen in the last few winters, and is the reason that overall extent for November is higher than in recent years.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of November 30, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Sea ice extent grew 2.15 million square kilometers (830,000 square miles) during the month of November. This was about average for the month and substantially slower than observed in 2012. While the month started with 1.17 million square kilometers (452,000 square miles) more ice in 2014 than on November 1, 2012, by the end of the month, the difference between 2014 and 2012 had closed to only 416,000 square kilometers (161,000 square miles). The difference in November ice growth between 2012 and 2014 reflects the larger area of open water at the end of summer 2012. With more open water, there was a larger area for new ice to grow.

November 2014 compared to previous years

Figure 3. Monthly November ice extent for 1979 to 2014 shows a decline of 4.7% per decade relative to the 1981 to 2010 average.

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

Arctic sea ice extent for November was the 9th lowest in the satellite record. Through 2014, the linear rate of decline for November extent over the satellite record is 4.7% per decade.

Arctic amplification and mid-latitude weather extremes

Figure 4. This plot of average surface air temperatures from November 17 to 19, 2014 over North America during a polar outbreak shows unusually cold air reaching down into the U.S. Temperatures are in degrees Kelvin. Blues and purples indicate sub-freezing temperatures.

Credit: NSIDC/NOAA ESRL Physical Sciences Divisionr
High-resolution image

Last month we discussed how the extra heat stored in ice-free areas of the ocean during recent summers is released back to the atmosphere as the ice begins to re-form, leading to amplified warming in the Arctic atmosphere. The impact of this warming and its potential impacts on mid-latitude weather patterns and extreme weather events is an active area of research.

This November has been particularly notable for severe weather in the U.S., with a very strong storm in the Bering Sea affecting the Aleutian Islands of western Alaska* (a remnant of Typhoon Nuri that tracked from the tropics through the Aleutians), record-setting low temperatures in the upper plains, and epic lake-effect snow near Buffalo, N.Y. Such individual events cannot be directly linked to climate change, let alone specifically to sea ice loss.

*Correction, December 16, 2014: Adjusted the wording here to make clear that the storm did not affect mainland Alaska, but only the Aleutians.

New research this year from Japanese scientists (Mori et al., 2014) provides support for the hypothesis, put forward by Jennifer Francis of Rutgers University and Steve Vavrus of the University of Wisconsin, that the warming Arctic is contributing to an increasing waviness of the jet stream with the potential for more extreme weather events, including cold outbreaks in the lower 48 U.S. and Eurasia that have been seen in recent years. However, while there is some evidence of this connection, it is not conclusive and many scientists remain skeptical of a link between Arctic sea ice and mid-latitude weather.

Antarctica watch

Figure 5. Antarctic sea ice extent for November 2014 was 16.63 million square kilometers (6.42 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic South Pole. Sea Ice Index data. About the data

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

Antarctic sea ice has continued to decline at a faster-than-average pace (approximately 122,000 square kilometers, or 47,100 square miles per day through the month of October, compared to the average rate of 112,000 square kilometers or 43,200 square miles per day), and is now about 650,000 square kilometers (251,000 square miles) below the level for the date recorded in 2013. Currently ice extent remains about 700,000 square kilometers (270,000 square miles) higher than the 1981 to 2010 average for this time of year. Large reductions in the Bellingshausen Sea and the southern Indian Ocean were the main causes of the Antarctic-wide decrease, driven in large part by persistent northerly winds. Air temperatures over the Southern Ocean for the month were near average in nearly all areas. On the icy continent itself, cool conditions prevailed over the Antarctic Peninsula and West Antarctica (1 to 2 degrees Celsius, or 1.8 to 3.6 degrees Fahrenheit below average) while warm conditions were the rule in the Eastern Hemisphere section (2 to 4 degrees Celsius, or 3.6 to 7.2 degrees Fahrenheit above average).

Reference

Mori, M., M. Watanabe, H. Shiogama, J. Inoue, and M. Kimoto, 2014. Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades. Nature Geoscience, vol. 7, pp. 869-873.

The sun has set over the central Arctic Ocean and Arctic sea ice extent is now increasing. Sea ice extent in Antarctica appears to have passed its seasonal maximum. The peak Antarctic value recorded so far of over 20 million square kilometers (7.7 million square miles) sets a new record over the period of satellite observations.

Overview of conditions

Figure 1. Arctic sea ice extent for September 2014 was 5.28 million square kilometers (2.04 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Following the seasonal daily minimum of 5.02 million square kilometers (1.94 million square miles) that was set on September 17, 2014 (6th lowest in the satellite record), Arctic sea ice has started its seasonal cycle of growth. Arctic sea ice extent averaged for the month of September 2014 was 5.28 million square kilometers (2.04 million square miles), also the 6th lowest in the satellite record. This is 1.24 million square kilometers (479,000 square miles) below the 1981 to 2010 average extent, and 1.65 million square kilometers (637,000 square miles) above the record low monthly average for September that occurred in 2012.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of October 2, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Because ice extent falls through the first part of September and rises in the latter part, statistics on the average daily rate of ice loss or gain through the month are largely meaningless. More relevant is the total ice loss through the melt season. Between the seasonal maximum extent that occurred on March 21, 2014 and the September 17 minimum, the Arctic Ocean lost a total of 9.89 million square kilometers (3.82 million square miles) of ice, which is the 9th largest in the satellite record, but the least amount of seasonal loss since 2006. This year’s loss was 1.92 million square kilometers 741,000 square miles) less than the total loss that occurred in 2012.

September 2014 compared to previous years

Figure 3. Monthly September ice extent for 1979 to 2014 shows a decline of 13.3% per decade relative to the 1981 to 2010 average.

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

Through 2014, the linear rate of decline for September Arctic ice extent over the satellite record is 13.3% per decade, relative to the 1981 to 2010 average. The ten lowest September ice extents over the satellite record have all occurred in the last ten years.

Summer weather conditions in 2014

Figure 4. These images show June to August sea level pressure anomalies, compared to the 1981 to 2010 average, (left) and June to August temperature anomalies at the 925 hPa level, compared to the 1981 to 2010 average (right). At left, blues and purples indicate lower than average pressures, while greens, yellows, and reds indicate higher than average pressures. At right, reds and yellows indicate warmer than average temperatures, and blues and purples indicate lower than average temperatures.

Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Division
High-resolution image

Weather conditions prevailing over the summer of 2014 were unremarkable. Compared to the long term (1981 to 2010) climatology, sea level pressure over the period June through August was higher than average over much of the central Arctic Ocean, the Atlantic sector of the Arctic, and Greenland. While air temperatures at the 925 hPa level (approximately 3000 feet altitude) were slightly above average over part of the central Arctic Ocean, they were below average over the Kara Sea and just north of Alaska. The summer of 2013, which is now the 7th lowest ice extent in the satellite record, was also generally unremarkable in terms of temperature. Both of these years contrast sharply with 2012, which saw unusually warm conditions across the Arctic Ocean. The one significant weather pattern over the summer was a larger than normal pressure gradient over the Laptev Sea that drove southerly winds, brought warmer air, and helped drive sea ice northward. This led to the tongue of open water that reached to within 5 degrees latitude of the pole. However, this pressure gradient was not particularly extreme so thinner ice cover in the area was also a significant contributor to the open water near the pole. Sea surface temperatures may also have played a role, as we discussed in a previous post.

Ice age

Figure 5. These images show the ages of ice in the Arctic at the end of September 2013 and 2014.

Credit: NSIDC courtesy M. Tschudi, University of Colorado
High-resolution image

The distribution of sea ice age at the time of the minimum provides some insights into the summer evolution of the ice cover. For ice that is three years and older, the distribution is similar to recent years, with most of this ice along the northern coast of Greenland and northwestern coast of the Canadian Archipelago. Through the winter, older ice moved across the Beaufort and Chukchi seas due to the typical clockwise circulation of the Beaufort Gyre. Similar to recent summers, much of this ice melted away, though this year it lasted through most of the summer, contributing to the relatively late development of open water along the Alaskan coast.

One notable feature this year compared to last year is that a tongue of second-year ice (ice that is 1 to 2 years old) persisted north and east of the East Siberian Sea. This likely helped limit the loss of ice in this region and kept the ice edge much farther southward than in the neighboring Laptev Sea to the east. The predominance of thinner first-year ice in the Laptev region, along with persistent southerly winds, led to seasonal retreat of the ice edge to north of 85 degrees North latitude.

Sea Ice maximum in Antarctica

Figure 6a. Antarctic sea ice extent for September 22, 2014 was 20.11 million square kilometers (7.76 million square miles). The orange line shows the 1981 to 2010 median extent for that day. The black cross indicates the geographic South Pole. Sea Ice Index data. About the data

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

Figure 6b. The graph above shows Antarctic sea ice extent as of October 2, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

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

Figure 6c. Monthly Antarctic September ice extent for 1979 to 2014 shows an increase of 1.3% per decade relative to the 1981 to 2010 average.

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

As we reported in our Arctic minimum announcement, sea ice in Antarctica has remained at satellite-era record high daily levels for most of 2014. On September 22, 2014, Antarctic ice extent increased to 20.11 million square kilometers (7.76 million square miles). This was the likely maximum extent for the year.

This year’s Antarctic sea ice maximum was 1.54 million square kilometers (595,000 square miles) above the 1981 to 2010 average maximum extent, which is nearly four standard deviations above this average. The 2014 ice extent record is 560,000 square kilometers (216,000 square miles) above the previous record ice extent set on October 1, 2013. Each of the last three years (2012, 2013, and 2014) has set new record highs for extent in the Antarctic.

The monthly average Antarctic ice extent for September 2014 is 20.03 million square kilometers (7.73 million square miles). This is 1.24 million square kilometers (479,000 square miles) above the 1981 to 2010 average for September ice extent. The Antarctic sea ice trend for September is now +1.3% per decade relative to the 1981 to 2010 average.

Monthly averaged ice extent for September is well above average in the western Pacific (northern Ross Sea) and Indian Ocean (Enderby Land) sectors.

Antarctic extent patterns

Figure 7. This image shows sea ice concentration trends for the month of September 2014. Oranges and reds indicate higher concentration trends; blues indicate lower concentration trends. Sea Ice Index data. About the data

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

A comparison of ice extent (Figure 6a) with ice concentration trends (Figure 7) illustrates that the areas of unusual ice growth are in the same places that have been showing ongoing trends of increased ice extent. This suggests that wind patterns play a significant role in the recent rapid growth in Antarctic ice extent. However, another possible reason is that recent ice sheet melt, caused by warmer, deep ocean water reaching the coastline and melting deeper ice, is making the surface water slightly less dense. While the change in saltiness is too small to significantly affect the freezing temperature, the increase in slightly less dense water surrounding Antarctica inhibits mixing, creating conditions that favor ice growth (as we discussed in our July 17 post).

Late season growth patterns

Figure 8a. This image series shows Antarctic sea ice concentration from September 1 to September 30, 2014. Click on the image to view the animated image series. Data are from the AMSR2 satellite instrument.

Credit: NSIDC/University of Bremen
View animated images

The period between September 10 and September 22 saw very rapid late-season ice growth in Antarctica, pushing the total sea ice extent upward by nearly 60,000 square kilometers per day (23,000 square miles). An animation of Antarctic sea ice concentrations from AMSR2 satellite data shows that a pulse of increased sea ice growth in several areas, but especially in the northern Weddell Sea, was the cause of the rapid rise in extent. A look at the weather for mid-September in the south indicates that a band of southerly winds swept from west to east across the northern Weddell Sea, favoring both ice growth and ice advection to the north.

For the mid-winter period, climate patterns for 2014 evolved in a similar way to 2013, as discussed in previous posts and in a paper led by our colleague, Phillip Reid. Sea ice growth in the Ross, Amundsen, and Bellingshausen seas for the austral winter of 2014 was favored by moderately strong low pressure anomalies in the Amundsen Sea, the northern Weddell Sea, and the central Indian Ocean region in mid-winter (late July and August). But at the period of the sea ice maximum, higher pressures over the continent reduced the intensity of westerly winds, and resulted in cooler southerly winds over the Weddell Sea and the Amundsen Sea. This helped to create the very large ice extent values seen in September. The Antarctic sea ice maximum period, as described above, had a further push from southerly winds over the far southern Atlantic (northernmost Weddell Sea) and Indian Ocean regions.

A related note

Last year, a vessel became trapped in ice south of Australia in an incident that highlighted the need for better local ice forecasts. The International Ice Charting Working Group will meet later this month in Punta Arenas, Chile. Members will work on improving the collective capability of ice services to provide ice information in the interests of marine safety.

Reference

Reid, P., S. Stammerjohn, R. Massom, T. Scambos, and J. Lieser. 2015, in press. The record 2013 Southern Hemisphere sea-ice extent maximum. Annals of Glaciology 56 (69), doi:10.3189/2015AoG69A892.

The Arctic summer of 2014 is nearing an end. Overall, the rate of ice loss during August was near average. Regions of low concentration ice remain in the Beaufort and East Siberian seas that may yet melt out or compress by wind action. While the Northwest Passage continues to be clogged with ice and is unlikely to open, the Northern Sea Route along the Siberian coasts appears open except for some ice around Severnaya Zemlya. As the end of the southern winter draws closer, Antarctic sea ice extent remains higher than average.

Overview of conditions

Figure 1. Arctic sea ice extent for August 2014 was 6.22 million square kilometers (2.40 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

Sea ice extent in August 2014 averaged 6.22 million square kilometers (2.40 million square miles). This is 1.00 million square kilometers (386,000 square miles) below the 1981 to 2010 August average, but well above the 2012 August average of 4.71 million square kilometers (1.82 million square miles). Extent was below average throughout the Arctic except for a region in the Barents Sea, east of Svalbard. The ice edge continued to retreat north of the Laptev Sea, and is now within 5 degrees latitude of the North Pole.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of September 1, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. Sea Ice Index data.

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

August ice extent declined at an average rate of 54,300 square kilometers (21,000 square miles) per day. This was slightly less than the average rate for the month. Generally, the decline slows in August as the Arctic sun dips lower in the sky. Recent years have been an exception, with relatively fast ice loss rates in August.

August 2014 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2014 shows a decline of 10.3% per decade relative to the 1981 to 2010 average.

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

Despite the near-average rate of decline in ice extent through the month, August 2014 ended up with the 7th lowest extent in the satellite record. It is 1.51 million square kilometers (583,000 square miles) above the record low for August 2012 and is also higher than August of 2007, 2008, 2010, 2011, and 2013. The monthly linear rate of decline for August over the satellite record is now 10.3 percent per decade.

The Northwest Passage: closed for business

Figure 4. This time series shows the total sea ice area for selected years within the Western Parry Channel route of the Northwest Passage. The cyan line shows 2014, and other colors show ice conditions in different years.

Credit: S. Howell/Environment Canada
High-resolution image

Several recent years have seen remarkably open conditions in the Northwest Passage by the end of August. This year, however, much of the passage is clogged with ice, and even the circuitous Amundsen route is not entirely open. (Note that Amundsen required two summers to navigate this route in 1905; Amundsen wintered over in the hamlet of Gjoa Haven—now called Uqsuqtuuq).

The recent openings of the Northwest Passage in 2007, 2008, 2010, and 2011 were associated with high sea level pressure anomalies over the Beaufort Sea and Canadian Basin. This atmospheric pattern essentially displaces the polar pack away from the M’Clure Strait, resulting in minimal ice inflow from the Arctic Ocean. In contrast, weather patterns this year have been more moderate, and as a result, more ice remains in the Northwest Passage. As of the end of August 2014, ice area in the passage was tracking above the 1981 to 2010 average. Ice area over the summer of 2013 tracked slightly below the 1981 to 2010 average, but was considerably higher than the years prior. The summer of 2011 saw the lowest ice area in the Northwest Passage since 1968.

On the other side of the Arctic Ocean, conditions are much more open along the Northeast Passage (also known as the Northern Sea Route). There are wide areas of open water along much of the Russian Arctic coast, the lone exception being the area around Severnaya Zemlya.

Reference

Howell, S. E. L., T. Wohlleben, M. Dabboor, C. Derksen, A. Komarov, and L. Pizzolato. 2013. Recent changes in the exchange of sea ice between the Arctic Ocean and the Canadian Arctic Archipelago, J. Geophys. Res. Oceans, 118, 3595-3607, doi:10.1002/jgrc.20265.

Overview of conditions

Arctic sea ice extent declined at a fairly rapid rate through the first three weeks of July, but the loss rate then slowed due to a shift in weather patterns. In Antarctica, the advance of sea ice nearly halted for about a week in early July, and then resumed. At the end of the month, Antarctic extent was at or near a record high for this time of year.

Overview of conditions

Figure 1. Arctic sea ice extent for July 2014 was 8.25 million square kilometers (3.19 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

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

July 2014 average ice extent was 8.25 million square kilometers (3.19 million square miles). This is 1.85 million square kilometers (714,000 square miles) below the 1981 to 2010 average for the month.

Ice extent is below average in nearly all sectors of the Arctic. Open water continued to grow in the Laptev and Beaufort Seas, reaching well north of 80^oN in the Laptev Sea. By the end of the month, the Alaskan Coast was essentially free of ice except for small patches of very diffuse ice off Barrow. The Barents Sea, Hudson Bay, and Baffin Bay/Davis Strait are now essentially ice free. Large areas of low concentration ice in the central Beaufort Sea are likely to melt out in coming weeks. The Northwest Passage through the channels of the Canadian Arctic Archipelago remains choked with ice. Parts of the Northern Sea Route are still difficult to traverse because of high-concentration, near-shore ice between the Laptev and East Siberian seas and also north of the Taymyr Peninsula.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of August 4, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. Sea Ice Index data.

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

For July 2014 as a whole, ice extent declined at an average rate of 86,900 square kilometers (33,600 square miles) per day, close to the 1981 to 2010 average July rate of 86,500 square kilometers (33,400 square miles) per day. However, this averages together a fairly fast rate of decline over the first three weeks of the month with a slower rate of decline over the remainder of the month.

The slower ice loss later in the month reflects a shift in weather patterns. For much of the month, high pressure at sea level dominated the central Arctic Ocean and the Barents Sea. However, this pattern broke down and was replaced by lower-than-average pressure over the central Arctic Ocean. A low pressure pattern tends to bring cool conditions and the counterclockwise winds associated with this pattern also tend to spread the ice out.

July 2014 compared to previous years

Figure 3. Monthly July ice extent for 1979 to 2014 shows a decline of 7.4% per decade relative to the 1981 to 2010 average.

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

July 2014 is the 4th lowest Arctic sea ice extent in the satellite record, 340,000 square kilometers (131,000 square miles) above the previous record lows in July 2011, 2012, and 2007. The monthly linear rate of decline for July is 7.4% per decade.

More news on the Antarctic

Figure 4a. Antarctic sea ice extent for July 2014 was 17.40 million square kilometers (6.72 million square miles). The magenta line shows the 1981 to 2010 median extent for that month. The black cross indicates the geographic South Pole. Sea Ice Index data. About the data

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

Figure 4b. The graph above shows Antarctic sea ice extent as of August 4, 2014, along with daily ice extent data for four previous years. 2014 is shown in blue, 2013 in green, 2012 in orange, 2011 in brown, and 2010 in purple. The 1981 to 2010 average is in dark gray. Sea Ice Index data.

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

In our previous post, we noted that on July 1, Antarctic sea ice extent was growing rapidly, and could surpass the September 2013 record high extent (over the period of satellite observations). During early July, the advance of Antarctic sea ice extent nearly halted, but toward the end of the month, there was another period of rapid ice growth. Maximum extent is usually reached in September or October, at the end of the austral winter.

Many readers may be familiar with NSIDC’s Charctic interactive sea ice graph that allows one to plot daily Arctic ice extent for any year in the satellite record (1979 to present) and make quick comparisons with average conditions and between different years. NSIDC has recently added an Antarctic option to Charctic. We have done so in response to growing interest in Antarctic sea ice conditions and the very different behavior of Arctic and Antarctic sea ice. Just go to the Charctic site and click the button marked “Antarctic.”

Questions about data processing

Figure 5. This graph shows the differences in Antarctic sea ice extent between Version 2 and Version 1 of the Bootstrap algorithm. Blue indicates when Version 2 derived values were lower than Version 1; red indicates when Version 2 derived values were higher than Version 1. The vertical dashed lines indicate satellite sensor changes.
Credit: I. Eisenman et al., The Cryosphere
High-resolution image

A recent paper investigated the processing of Antarctic sea ice data and how this affects the interpretation of Antarctic ice extent trends. While their findings do not affect NSIDC’s analysis of Antarctic sea ice extent, as we use a different data set, it is an interesting example of scientific rigor regarding data, and it does affect other reports of Antarctic sea ice trends.

The paper studied the Bootstrap algorithm, which has been used in several published reports of Antarctic trends, including the last two IPCC Assessment Reports. These reports suggested that the Antarctic sea ice extent shifted from a small, statistically insignificant upward trend in the early 2000s to a more substantial, and statistically significant upward trend in recent years. (NSIDC uses a different algorithm, called NASA Team, to estimate sea ice extent.)

The paper found that following an update to the algorithm in 2007, using the newer Version 2 of the Bootstrap algorithm produced Antarctic sea ice extent trends that were approximately two times larger than those derived using Version 1. Closer examination of the data showed a noticeable step change in extent at the point of transition to a new satellite sensor in 1991. This step change appeared to be related to an error in calibration between the sensors, rather than actually being an abrupt shift in Antarctic sea ice.

Trends derived from both versions for time periods either before or after the sensor transition are similar. However, the two algorithms produce different results when trends that span the 1991 sensor transition are calculated. Using Version 2 of the algorithm produces a markedly higher trend.

Using the newer version of the algorithm, Antarctic extent trends agree much more closely with the trends from the NASA Team algorithm used by NSIDC. Regardless, the expansion in Antarctic sea ice is confirmed by other groups using different techniques.

References

Eisenman, I., W. N. Meier, and R. J. Norris. 2014. A spurious jump in the satellite record: has Antarctic sea ice expansion been overestimated?, The Cryosphere 8, 1289-1296, doi:10.5194/tc-8-1289-2014.