A few days after the annual Arctic sea ice minimum extent was reached on September 19, the sun set at the North Pole, aiding sea ice growth. Arctic sea ice extent has grown at a fairly slow pace, leading to the fifth lowest September in the 45-year passive microwave satellite record. Antarctic sea ice extent has had an uptick in growth, but remains at record low levels for this time of year.

Overview of conditions

Figure 1a. Arctic sea ice extent for September 2023 was 4.37 million square kilometers (1.69 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 1b. The graph above shows Arctic sea ice extent as of October 3, 2023, along with daily ice extent data for four previous years and the record low year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 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
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Figure 1c. This image from the Japan Aerospace Exploration Agency (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) shows sea ice concentration in the Arctic Ocean on October 2, 2023, highlighting the openings of sea ice north of Alaska within the Beaufort and Chukchi Seas.

Credit: Japan Aerospace Exploration Agency, courtesy University of Bremen
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Average Arctic sea ice extent for September 2023 was 4.37 million square kilometers (1.69 million square miles), placing it fifth lowest in the 45-year satellite record (Figure 1a). Following the annual minimum of 4.23 million square miles (1.63 million square kilometers), the growth in Arctic sea ice extent has been slower than average (Figure 1b). The image plot for October 2 from the Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument provided by the University of Bremen shows that with the cessation of melt, the ice edge has become more sharply defined (Figure 1c). The lack of ice in the longitudes spanning the Laptev Sea eastward to the Beaufort Sea is striking; before ice forms in these areas the upper ocean will have to lose its remaining heat through radiation and convective transfer to the atmosphere and space. The Northern Sea Route remains essentially free of ice. While both the Northern (deepwater) and Southern (Amundsen’s) routes of the Northwest Passage appear largely ice free, some ice still remains in the northern route, notably at the eastern entrance of M’Clure Strait. This is discussed further below.

Conditions in context

Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for September 2023. Yellows and reds indicate above average temperatures; blues and purples indicate below average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Figure 2b. This plot shows average sea level pressure in the Arctic in millibars for September 2023. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Air temperatures at the 925 hPa level (approximately 2,500 feet above the surface) for September were modestly above average, with temperatures 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) over most of the Arctic Ocean (Figure 2a). Warm conditions prevailed in the ice-free Norwegian, Barents, and Kara Seas. Over land, Canada and northwestern Eurasia experienced warm conditions, as much at 5 degrees Celsius (9 degrees Fahrenheit) above average.

The atmospheric circulation for September was characterized by fairly low pressure over most of the Arctic Ocean, notably north of the Barents and Laptev Seas and east of Greenland (Figure 2b). Over land, high pressure prevailed over Eurasia and eastern Canada.

September 2023 compared to other years

Figure 3. Monthly September ice extent for 1979 to 2023 shows a decline of 12.2 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend in Arctic sea ice extent for September over the 45-year satellite record is 78,500 square kilometers (20,300 square miles) per year, or 12.2 percent per decade relative to the 1981 to 2010 average (Figure 3). Based on the linear trend, since 1979, September has lost 3.45 million square kilometers (1.33 million square miles) of ice. This is roughly equivalent to twice the size of Alaska or Iran.

The Northern Hemisphere’s summer 2023 in review

Figure 4a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from April to August 2023. Yellows and reds indicate above average temperatures; blues and purples indicate below average temperatures.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Figure 4b. The top maps show Arctic sea ice age at the end of summer, a week before the seasonal minimum, for 1985 on the left and 2023 on the right. The bottom time series shows extent of multiyear ice in black and ice >4 years old in red at the seasonal minimum for 1985 to 2023. The oldest (4+ year old) ice is in red.

Credit: Data and images from Tschudi et al., 2019a and 2019b
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With the passing of the seasonal maximum in Arctic sea ice extent on March 6, the melt season started slowly, but daily extents remained among the third to sixth lowest in the satellite record. The pattern of slow ice loss persisted through April—average extent for April ranked tied with 2002 as tenth lowest in the satellite record. The rate of ice loss picked up towards the end of May, dropping extent below the interdecile range after spending most of the month just above the lower part of the inter-decile range. Nevertheless, extent for the month as a whole ranked only thirteenth lowest in the satellite record. June sea ice loss proceeded at only an average rate and by month’s end, it was clear that a record low September ice extent was highly unlikely. While the rate of Ice loss picked up in August, the sea ice minimum reached on September 19 ended up as sixth lowest in the satellite record. The April through August average air temperate map at the 925 hPa level tells the basic story of 2023—temperatures were below average over much of the Arctic Ocean, limiting melt (Figure 4a). The year nevertheless ended up as notable for the combination of ice-fee conditions in the southern (Amundsen’s) Northwest Passage route and very mild ice conditions in the northern (deepwater) route; this is consistent with the above average temperatures at the 925 hPa level over the Canadian Arctic Archipelago.

Multiyear ice extent at the end of summer was quite low, as has been the case for the last several years (Figure 4b). A band of multiyear ice persists on the Atlantic side, extending from the Laptev Sea across the Arctic north of the Kara and Barents Seas. Much of this ice will likely drift out of the Arctic Ocean with the Transpolar Drift Stream over the next several months to a year. Very little of the oldest (4+ years old) ice remains in the Arctic, with small patches north of Greenland and an area north of the Beaufort Sea. The total extent of the oldest sea ice is 93,000 square kilometers (36,000 square miles), the second lowest in the satellite record since 1985, only higher than 55,000 square kilometers (21,000 square miles) in 2019. This is in stark contrast to the 1980s when old ice covered over 2.5 million square kilometers (965,000 square miles) of the Arctic Ocean.

Note that operational ice services track sea ice daily primarily for the safety of on-ice operations and ships at sea. These services use data sources that go beyond the single source used here. For example, analysts at the US National Ice Center (USNIC) depend on radar and visible-band data when mapping Arctic ice. USNIC tracks Arctic-wide sea ice extent using charts they produce. NSIDC archives these charts. Currently, the USNIC analysis indicates a minimum of 5.05 million square kilometers (1.95 million square miles) on September 27. The USNIC extent values differ from the Sea Ice Index values used by ASINA because of the different imagery and analysis techniques employed.

The Southern Hemisphere’s winter 2023 in review

Figure 5a. The graph above shows Antarctic sea ice extent as of October 3, 2023, along with daily ice extent data for four previous years and 2014, the record maximum year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 2014 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
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Figure 5b. Click on image to begin the animation. From 2013 through 2023, Antarctic sea ice exhibited its highest and lowest extents in the satellite record dating back to 1979. From 2013 through 2015, extents were mostly above the 1981 to 2010 average, including the record-high 2014 winter maximum. Beginning in 2016, extents were mostly below the 1981 to 2010 average. Antarctic sea ice extent fell to the lowest minimum on record in March 2023 and the lowest maximum in September 2023.

Credit: Animation by Michon Scott, based on NSIDC’s Charctic Interactive Sea Ice Graph
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Figure 5c. This image show the sea ice edge for the last week of August 1966 using the minimum Advanced Vidicon Camera System on the NASA Nimbus satellite. Superimposed is the sea ice edge, depicted as a black line, from the manual analysis.

Credit: Gallagher et al. 2014
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Figure 5d. This graph shows the average Antarctic extent for June through August for multiple decades. The blue line depicts the “best fit” from 1905 to 2020; the grey line depicts the upper and lower 95 percent range for the same time period; and the red line depicts the modern satellite data from the Sea Ice Index from 1979 to 2023. The Nimbus-II 1966 value is marked as a gold diamond within the uncertainty range, which is drawn as vertical gold line.

Credit: W. Meier, NSIDC
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The story for the southern hemisphere was very different. After a record low minimum extent in February 2023, the seasonal increase in ice extent was near average through March, but then began to slow in April (Figure 5a). By May, it became clear that Antarctic sea ice extent, while of course growing in response to seasonal cooling, was lagging far below previous daily lows in the satellite record. Extent was particularly low in the Bellingshausen Sea, Weddell Sea, and western Ross Sea regions. By the middle of July, the heart of austral winter, extent stood at more than 2.60 million square kilometers (1.00 million square miles) below the 1981 to 2010 average, an area nearly as large as Argentina or the combined areas of Texas, California, New Mexico, Arizona, Nevada, Utah, and Colorado. August saw particularly low extent in the Ross Sea and eastern Weddell Sea sectors, but with some recovery in the Bellingshausen Sea. On September 10, 2023, Antarctic extent reached an annual maximum of 16.96 million square kilometers (6.55 million square miles). This year’s maximum was 1.03 million square kilometers (398,000 square miles) below the previous record low set in 1986. There is growing evidence that the Antarctic sea ice system has entered a new regime, featuring a much stronger influence of warm ocean waters limiting ice growth (Figure 5b).

Average Antarctic sea ice extent for September was 16.80 million square kilometers (6.49 million square miles), also far below the previous record for the month. Average September sea ice extent was 1.69 million square kilometers (653,000 square miles) below the 1981 to 2010 average extent of 18.49 million square kilometers (7.14 million square miles). More remarkably, it was 880,000 million square kilometers (340,000 square miles) below 1986, the previous lowest September.

The extents this year have been far outside anything observed in the 45-year modern satellite record that began in 1979. However, some earlier satellite data, including that from the Nimbus satellites in the mid-1960s, point to extents that may rival 2023. Estimates derived from Nimbus-II data suggest that extent for 1966 may have been only slightly higher than 2023 (Gallaher et al., 2014). However, Nimbus-II carried only a visible sensor, which could not collect data during cloudy conditions, resulting in sparse coverage of the Antarctic sea ice region (Figure 5c).

Data was not collected for September when the maximum generally occurs, but only for May through August. In addition, the data quality was limited, making discrimination between ice and ocean difficult. It seems clear that while the 1966 May, June, and July estimates are on par with the 1979 to 2022 values, August 1966 was an outlier with lower extent than July 1966. This is not reasonable given the seasonality of the ice cover. The recovery of such old satellite data is valuable for providing long-term context; however, as just discussed data quality issues preclude making quantitative comparisons with the modern satellite record.

As discussed in the August 2 post, another source of pre-1979 data was recently published at NSIDC (Fogt et al., 2023). It is based on the reconstruction of sea ice extent from climate indices, atmospheric reanalyses, and other information (Fogt et al., 2022). A reconstruction approach uses relationships between observed sea ice extent from satellites and the collection of climate indices to derive a relationship between the two. This relationship is then extrapolated to the pre-satellite period. The reconstruction data set encompasses 1905 to 2020 as seasonal 3-month averages. Comparing the June to August average from that product with the satellite data indicates that this year is well outside average ranges of the 115-year reconstruction (Figure 5d). Like the Nimbus-II data, such reconstructions also have high uncertainty and depend on the assumption that the relationships between satellite data and climate indices are valid over the pre-satellite period.

Sea ice conditions in the Northwest Passage routes during the 2023

Figure 6a. This time series shows total sea ice area for 2023, 2022, 2021, 2029, 2011, and the 1991 to 2020 average within the northern route of the Northwest Passage. Data are from the Canadian Ice Service.

Credit: S. Howell, Environment and Climate Change Canada
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Figure 6b. These maps show sea ice concentration in the Northwest Passage for the week of September 25, 2023. The left map shows spatial distribution of total sea ice concentration; the middle map shows the 1991 to 2020 average sea ice concentration for the same week; and the map on the right shows the difference in sea ice concentrations between the 1991 to 2020 average and the week of September 25, 2023. Red shows a stark decline from the average. Data are from the Canadian Ice Service.

Credit: S. Howell, Environment and Climate Change Canada
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Figure 6c. The time series shows total sea ice area for 2023, 2022, 2021, 2029, 2011, and the 1991 and 2020 average within the southern route of the Northwest Passage. Data are from the Canadian Ice Service.

Credit: S. Howell, Environment and Climate Change Canada
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Our colleague Steve Howell at Environment and Climate Change Canada (ECCC) has provided an up-to-date summary of sea ice conditions in the Northwest Passage based on ice charts created by the Canadian Ice Service. While ice conditions at the end of the 2023 melt season were certainly remarkable, the northern route of Northwest Passage route did not break record low conditions of 2011, but still ranks second lowest since 1968 and is well below the 1991 to 2020 average (Figure 6a). Preliminary analysis indicates that the atmospheric circulation over the Canadian Arctic Archipelago during August and September of 2023 was not favorable to Arctic Ocean ice advection, which typically prevents the northern route from clearing. Interestingly, sea ice extent on September 25 is lower than in 2011 during the same time period (Figure 6b). Although the northern route was virtually sea ice free, complete transit without icebreaker escort would be difficult because of sea ice blocking the opening at M’Clure Strait. By contrast, the southern route is sea ice free from end to end (Figure 6c).

Further reading

Fogt, R. L., A. M. Sleinkofer, M. N. Raphael, H. S. and Handcock. 2022. A regime shift in seasonal total Antarctic sea ice extent in the twentieth century. Nature Climate Change 12, 54– 62, doi:10.1038/s41558-021-01254-9.

Fogt, R., M. N. Raphael, and M. S. Handcock. 2023. Seasonal Antarctic Sea Ice Extent Reconstructions, 1905-2020, Version 1 [Data Set]. Boulder, Colorado USA. National Snow and Ice Data Center, doi:10.7265/55×7-we68. Date Accessed 09-28-2023.

Gallaher, D., G. G. Campbell, W. N. Meier. 2014. Anomalous variability in Antarctic sea ice extents during the 1960s with the use of Nimbus data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 3(7), 881-887, doi:10.1109/JSTARS.2013.2264391.

Tschudi, M., W. N. Meier, J. S. Stewart, C. Fowler, and J. Maslanik. 2019a. EASE-Grid Sea Ice Age, Version 4 [Data Set]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center, doi:10.5067/UTAV7490FEPB. Date Accessed 10-02-2023.

Tschudi, M., W. N. Meier, and J. S. Stewart. 2019b. Quicklook Arctic Weekly EASE-Grid Sea Ice Age, Version 1 [Data Set]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center, doi:10.5067/2XXGZY3DUGNQ. Date Accessed 10-02-2023.

On September 10, Antarctic sea ice likely reached its annual maximum extent of 16.96 million square kilometers (6.55 million square miles). This is the lowest sea ice maximum in the 1979 to 2023 sea ice record by a wide margin.

Please note that this is a preliminary announcement. Changing winds or late-season growth could still increase the Antarctic ice extent. NSIDC scientists will release a full analysis of the Antarctic and Arctic September conditions in early October.

Overview of conditions

Figure 1. Antarctic sea ice extent for September 10 2023, was 16.96 million square kilometers (6.55 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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On September 10, 2023, sea ice in the Antarctic reached an annual maximum extent of 16.96 million square kilometers (6.55 million square miles), setting a record low maximum in the satellite record that began in 1979 (Figure 1). This year’s maximum is 1.03 million square kilometers (398,000 square miles) below the previous record low set in 1986. It is also 1.75 million square kilometers below (676,000 square miles) below the 1981 to 2010 average Antarctic maximum extent. Sea ice extent is markedly below average north of Queen Maud Land and west of the Antarctic Peninsula. Other low areas include the Indian Ocean and Ross Sea. Extent is above average stretching out of the Amundsen Sea.

The Antarctic maximum extent is one of the earliest on record, having reached it 13 days earlier than the 1981 to 2010 median date of September 23. The interquartile range for the date of the Antarctic maximum is September 18 to September 30.

Conditions in context

Figure 2. The graph above shows Antarctic sea ice extent as of September 10, 2023, along with daily ice extent data for four previous years and the record maximum year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 2014 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
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This year marks a significant record low maximum in Antarctic sea ice extent (Figure 2). Since early April 2023, sea ice maintained record low ice growth. From early to mid-August, growth slowed considerably, maintaining a difference of nearly 1.5 million square kilometers (579,000 square miles) between 2023 and 1986, the second lowest year on satellite record. After that period, ice growth quickened and narrowed the gap to about 1 million square kilometers (386,000 square miles). This is the first time that sea ice extent has not surpassed 17 million square kilometers (6.56 million square miles), falling more than one million square kilometers below the previous record low maximum extent set in 1986. 

Ten lowest maximum Antarctic sea ice extents (satellite record, 1979 to present)

Values within 40,000 square kilometers (15,000 square miles) are considered tied.

References

Purich, A. and E. W. Doddridge. 2023. Record low Antarctic sea ice coverage indicates a new sea ice state. Communications Earth and Environment 4, 314, doi:10.1038/s43247-023-00961-9.

Turner, J., T. Phillips, G. J. Marshall, J. S. Hosking, J. O. Pope, T. J. Bracegirdle, and P. Deb. 2017. Unprecedented springtime retreat of Antarctic sea ice in 2016. Geophysical Research Letters, 44(13), 6868-6875, doi:10.1002/2017GL073656.

Turner, J., C. Holmes, T. Caton Harrison, T. Phillips, B. Jena, T. Reeves‐Francois, R. Fogt, E. R. Thomas, C. C. and Bajish. 2022. Record low Antarctic sea ice cover in February 2022. Geophysical Research Letters, 49(12), e2022GL098904, doi:10.1029/2022GL098904.

Zhang, L., T. L. Delworth, X. Yang, F. Zeng, F. Lu, Y. Morioka, and M. Bushuk. 2022. The relative role of the subsurface Southern Ocean in driving negative Antarctic Sea ice extent anomalies in 2016–2021, 3, 302, Communications Earth and Environment doi:10.1038/s43247-022-00624-1.

For more information

NASA visualization of 2023 Arctic sea ice minimum extent

On September 19, Arctic sea ice likely reached its annual minimum extent of 4.23 million square kilometers (1.63 million square miles). The 2023 minimum is sixth lowest in the nearly 45-year satellite record. The last 17 years, from 2007 to 2023, are the lowest 17 sea ice extents in the satellite record.

In the Antarctic, sea ice extent set unprecedented record lows through most of the growth season. Highly variable conditions are typical of Antarctic sea ice extent near the seasonal maximum, and ice may still continue to grow but will unlikely avoid setting a record low. The previous five lowest maximums on record include 1986, 2002, 2017, 1989, and 2022. The maximum for Antarctic sea ice typically occurs in late September or early October, but has been as early as August 30.

Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010. NSIDC scientists will release a full analysis of the Arctic melt season, and discuss the Antarctic winter sea ice growth, in early October.

Overview of conditions

Figure 1. Arctic sea ice extent for September 19 2023, was 4.23 million square kilometers (1.63 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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On September 19, sea ice reached its annual minimum extent of 4.23 million square kilometers (1.63 million square miles) (Figure 1). As the sun continues to lower on the horizon, air temperatures will drop further, expanding ice extent through autumn and winter. However, with significant patches of low ice concentration a late season storm may compress the sea ice and push the ice extent lower.

The minimum extent was reached five days later than the 1981 to 2010 median minimum date of September 14. The interquartile range of minimum dates is September 11 to September 19.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of September 19, 2023, along with daily ice extent data for four previous years and the record low year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 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
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This year’s minimum set on September 19 was 840,000 square kilometers (324,000 square miles) above the satellite-era record minimum extent of 3.39 million square kilometers (1.31 million square miles), which occurred on September 17, 2012 (Figure 2). It is also 1.99 million square kilometers (770,000 square miles) below the 1981 to 2010 average minimum extent, which is equivalent to nearly three times the size of Texas.

In the 45-year-satellite record, 17 of the lowest minimums have all occurred in the last 17 years.

The overall, downward trend in the minimum extent from 1979 to 2023 is 12.5 percent per decade relative to the 1981 to 2010 average. The loss of sea ice is about 77,800 square kilometers (30,000 square miles) per year, equivalent to losing the state of Nebraska or the Czech Republic annually.

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

Values within 40,000 square kilometers (15,000 square miles) are considered tied. The 2022 value has changed from 4.67 to 4.70 million square kilometers (1.81 million square miles) and the date of the minimum moved from September 18 to September 19 when final analysis data updated near-real-time data. 

For more information

NASA visualization of 2023 Arctic sea ice minimum extent

While the first half of August saw a rapid pace of Arctic sea ice loss, the pace slowed during the latter half of the month as mostly cooler conditions set in. Antarctic sea ice extent increased during the second half of the month.

Overview of conditions

Figure 1a. Arctic sea ice extent for August 2023 was 5.57 million square kilometers (2.15 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 1b. The graph above shows Arctic sea ice extent as of September 4, 2023, along with daily ice extent data for four previous years and the record low year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 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
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August Arctic sea ice extent averaged 5.57 million square kilometers (2.15 million square miles), or the eighth lowest in the 45-year satellite record (Figure 1a). Extent was 1.63 million square kilometers (629,000 square miles) below the 1981 to 2010 reference period and 850,000 square kilometers (328,000 square miles) above the previous record low for the month set in 2012. As of the end of August, 2.24 million square kilometers (860,000 square miles) of sea ice was lost in the Arctic.

As is typical during the latter half of August, the pace of ice loss slowed (Figure 1b).  Nevertheless, the daily ice loss rate of 72,100 square kilometers (27,800 square miles) per day was faster than the 1981 to 2010 average of 57,200 square kilometers (22,100 square miles) per day.

At month’s end, the ice edge remained considerably farther north than average in the Beaufort, Chukchi and East Siberian Seas, while in the Kara and Barents Seas the ice edge was near its typical location, albeit farther north in a few scattered regions. In the East Greenland Sea the ice was also well north of its usual position, in large part because of reduced ice export out of Fram Strait. While the ice edge in the Laptev Sea was near average, large areas of low ice concentration and open water were present.

The southern Northwest Passage, known as Amundsen’s route, remains nearly ice free, and the northern deepwater route between M’Clure Strait and Lancaster Sound has less ice than the previous record low for this time of year set in 2011. However, some ice still clogs M’Clure Strait and ice in the Beaufort Sea hinders easy access.

Conditions in context

Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from August 15 to 31, 2023. 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 Laboratory
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Figure 2b. This plot shows average sea level pressure in the Arctic in millibars from August 15 to 31, 2023. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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During the second half of August, air temperatures at the 925 millibar level (about 2,500 feet above the surface) averaged 1 to 5 degrees Celsius (2 to 9 degrees Fahrenheit) below average in the Chukchi and East Siberian Seas, whereas above-average air temperatures prevailed in northern Greenland at 1 to 6 degrees Celsius (2 to 11 degrees Fahrenheit) (Figure 2a). Patches of warm conditions persisted in the Kara and Barents Seas of 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average, though cool conditions were nearby. This contrasts with the pattern observed in the first half of the month when temperatures were below average north of Greenland, above average in the Chukchi and East Siberian Seas, and considerably above average in the Kara and Barents Seas.

Conditions shifted with the development of prominent areas of low sea level pressure over northern Canada and the Central Arctic Ocean; the latter feature is typical for this time of year (Figure 2b). By contrast, high pressure lingered over Greenland, the Norwegian Sea, and extended eastward along the Russian coast into the Laptev Sea. The high pressure over the Norwegian Sea and the implied winds from the south helped to transport warm air northward and also inhibited ice transport out of Fram Strait. Low pressure over the central Arctic Ocean helped to transport cold air southwards, contributing to the cool conditions over the Chukchi Sea.

August 2023 compared to previous years

Figure 3. Monthly August ice extent for 1979 to 2023 shows a decline of 9.9 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend in Arctic sea ice extent in August over the 45-year satellite record is 71,400 square kilometers (27,600 square miles) per year, or 9.9 percent per decade relative to the 1981 to 2010 average (Figure 3). Based on the linear trend, since 1979, August has lost 3.14 million square kilometers (1.21 million square miles) of ice. This is roughly equivalent to twice size of state of Alaska or the country of Iran.

Cascading impacts of changing sea ice conditions on marine ecosystems

Figure 4. The top illustration shows the current seasonal cycle in the diel vertical migration (DVM), also known as diurnal vertical migration of zooplankton and its links to sunlight. The bottom panel shows a possible future scenario of the impact of earlier spring light penetration and later autumn freeze up on the DVM within the surface layer, up to 50 meters (164 feet) of the Arctic Ocean. This assumes a ‘business-as-usual’ (SSP5-8.5) emission scenario. The intensity of the green-brown shading in the sea ice reflects potential changes in sea ice algae while the green shading of phytoplankton blooms is not scaled to productivity or biomass.

Credit: Based on scenarios shown in Soreide et al. 2010, Leu et al. 2011, Wassmann and Reigstad 2011, and Ardyna and Arrigo 2020
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The largest biomass migration on Earth each day happens within our oceans. Zooplankton, including tiny copepods and krill, migrate during the night towards the ocean surface to feed and then retreat to deeper depths during daylight to avoid predation. In the Arctic, however, the alternation of winter’s polar night and summer’s polar day results in a seasonal migration pattern. During the polar day, zooplankton primarily feed on phytoplankton blooms but during the polar night, they travel to the underside of the ice to feed on ice algae. As sea ice shrinks and thins, more light enters the ocean and shifts the seasonal migration. According to researchers at the Alfred Wegener Institute (AWI) and National Snow and Ice Data Center (NSIDC) scientist Julienne Stroeve, zooplankton prefer to stay at depths where light levels are below a certain intensity. Using mooring data deployed at the end of the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, they quantify this critical light threshold. Using this threshold in climate model simulations, they conclude that as sea ice continues to thin, the ocean level at which this critical light threshold is reached deepens earlier in the year, resulting in zooplankton remaining at depth for longer before coming to the surface to feed on sea ice algae. Currently, the zooplankton begin their springtime downward migration after nauplius larvae of the copepod C. hyperboreus have migrated to the surface and developed to copepodites. As the ice cover reduces, this springtime migration will start earlier. This will change their feeding habits, perhaps feeding on the C. hyperboreus nauplii before they have fully developed. Changing light levels will also shift the biomass and seasonality of ice algae and phytoplankton, the food sources for zooplankton. Since zooplankton feed the fish that feed the seals and whales, this change can cascade through the marine ecosystem.

Northwest Passage

Figure 5a. This time series graph shows total sea ice area for 2023, 2022, 2021, 2020, 2011, and the 1991 to 2020 average within the southern route of the Northwest Passage.

Credit: S. Howell, Canadian Ice Service
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Figure 5b. This time series graph shows total sea ice area for 2023, 2022, 2021, 2020, 2011, and the 1991 to 2020 average within the northern route of the Northwest Passage.

Credit: S. Howell, Canadian Ice Service
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As of August 28, the southern route of the Northwest Passage, known as Amundsen’s route, is almost completely free of sea ice (Figure 5a). The sea ice area in the northern route (deep water) is currently tracking just above 2011 record low conditions (Figure 5b). The route is almost sea ice free with the exception of the vicinity of the western end of M’Clure Strait. Although ice conditions have been very light this year as well as in 2022, it is important to note that ice conditions can be highly variable. While light ice years in the Northwest Passage may occur more frequently as the Arctic continues to warm, the processes of sea ice transport and the aging of seasonal first year ice that lead to heavy ice years in the Northwest Passage, such as in 2021 and 2020, still continue to operate.

Floe-ing with the landscape

Figure 6. These three satellite images show buoy positions in red and sea ice conditions from the Moderate Resolution Imaging Spectroradiometer (MODIS) on July 12, July 26, and August 6, from left to right. The blue star shows the location of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Central Observatory where one of the buoys was deployed.

Credit: Watkins, D. M. et al, 2023
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A recent paper led by colleagues at Brown University highlights the tight coupling between sea ice and ocean dynamics in the Fram Strait region. Fram Strait—the passage between Greenland and the Svalbard archipelago—is the key deepwater connection between the Arctic and Atlantic Oceans. It is also the primary region where sea ice is exported from the Arctic Ocean into the Atlantic. Figure 6 shows an ensemble of drifting buoys that were deployed as part of the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in Fall 2019 in the Laptev Sea. The buoys were carried westward by the Transpolar Drift Stream, and then flushed through Fram Strait and into the East Greenland Sea during spring and summer 2020. The authors documented clear changes in sea ice dynamics as the buoys crossed over undersea features, such as the Yermak Plateau north of Svalbard and the East Greenland Continental Shelf. These changes are concentrated at frequencies corresponding to tides and inertial oscillations, which show how the seafloor topography influences sea ice. The importance of ocean currents for the sea ice drift was further shown using a new ice tracking algorithm called Ice Floe Tracker. The team showed an increased role for ocean forcing relative to wind forcing on marginal ice zone sea ice in shallow seas and near the edge of the continental shelf.

Antarctic growth accelerates

Figure 7. The graph above shows Antarctic sea ice extent as of September 4, 2023, along with daily ice extent data for four previous years and the record high year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 2014 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
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After a brief period of slow growth during the first half of August, ice growth quickened in the Southern Hemisphere. While the total Antarctic sea ice extent is still tracking at record low levels, the ice extent has increased more than average in the Bellingshausen and Amundsen Seas as well as in the Pacific Ocean. Elsewhere the ice edge remains further poleward than average.

References

Flores, H., G. Veyssière, G. Castellani, et al. 2023. Sea-ice decline could keep zooplankton deeper for longer. Nature Climate Change, doi:10.1038/s41558-023-01779-1

Howell, S. E. L., D. G. Babb, J. C. Landy, and M. Brady. 2022. Multi-year sea ice conditions in the Northwest Passage: 1968-2020. Atmosphere-Ocean, 1, 15, doi:10.1080/07055900.2022.2136061

Howell, S. E. L., D. G. Babb, J. C. Landy, G. W. K. Moore, B. Montpetit, and M. Brady. 2023. A comparison of Arctic Ocean sea ice export between Nares Strait and the Canadian Arctic Archipelago. Journal of Geophysical Research: Oceans, 128, e2023JC019687, doi:10.1029/2023JC019687

Watkins, D. M., A. C. Bliss, J. K. Hutchings, and M. M. Wilhelmus. 2023. Evidence of abrupt transitions between sea ice dynamical regimes in the East Greenland marginal ice zone. Geophysical Research Letters, 50, e2023GL103558, doi:10.1029/2023GL103558

After declining at a near-average pace for much of the summer, Arctic sea ice loss accelerated during early August. Antarctic sea extent continues to increase but at an unusually slow pace, exacerbating the record low extent levels seen throughout the austral autumn and winter.

Overview of conditions

Figure 1a. The graph above shows Arctic sea ice extent as of August 15, 2023, along with daily ice extent data for four previous years and the record low year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 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
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Figure 1b. Arctic sea ice extent for August 15, 2023, was 5.74 million square kilometers (2.22 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 1c. This map shows a swath of low concentration within the sea ice extent north of the Laptev Sea on August 15, 2023. Sea ice concentration data are from Advanced Microwave Scanning Radiometer 2 (AMSR2) imagery.

Credit: University of Bremen
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The decline in Arctic sea ice extent through the first half of August was faster than average (Figure 1a). Over the period August 1 to 15, 2023, extent decreased at a rate of 81,000 square kilometers (31,000 square miles) per day, compared to the 1981 to 2010 average of 69,000 square kilometers (27,000 square miles) per day. As of August 15, extent stood at 5.74 million square kilometers (2.22 million square miles) (Figure 1b), 1.56 million square kilometers (600,000 square miles) below the 1981 to 2010 average for that date. The mid-August extent is the ninth lowest in the 45-year satellite record.

At mid-month, extent remains near average on the Atlantic side of the Arctic, but elsewhere is well below average other than a tongue of ice extending toward the coast in the East Siberian Sea just west of Wrangel Island. There is also a small area of ice extending near the shore along the western part of the Northern Sea Route near Severnaya Zemlya in the Kara Sea. Both of these regions of ice may melt out within the next couple of weeks.

The Northwest Passage appears to be on the verge of becoming nearly ice free, particularly the southern route, known as Amundsen’s route. The northern route through the relatively wide Parry Channel, is still blocked by ice, but at relatively low concentration.

Elsewhere, a swath of low concentration extended into the ice pack north of the Laptev Sea (Figure 1c). This may represent a response to a low-pressure system that moved into the region on August 14. While not particularly strong (994 millibar), such storms tend to cause divergent flow in the sea ice pack and increase wave action that break up the ice.

Conditions in context

Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from August 1 to 14, 2023. 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 Laboratory
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Figure 2b. This plot shows average sea level pressure in the Arctic in millibars from August 1 to 14, 2023. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Through the first half of August, air temperatures conditions at the 925 millibar level (about 2,500 feet above the surface) varied widely across the Arctic (Figure 2a). Temperatures prevailed at 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average over the Pole and north of Greenland, while temperatures were above average over most of the rest of the Arctic Ocean. Conditions over the Barents Sea were unusually warm during the first two weeks of August, with temperatures up to 8 degrees Celsius (14 degrees Fahrenheit) above average. The Beaufort and Chukchi Sea regions saw temperatures 1 to 6 degrees Celsius (2 to 11 degrees Fahrenheit) above average.

The sea level pressure pattern during the first half of the month featured low pressure over the pole and high pressure elsewhere (Figure 2b). As noted above, a low-pressure system, a cyclone, did move in the Laptev Sea area on August 14, but the region was still under high pressure as averaged for August 1 to 14.

Extreme ice conditions in the Southern Ocean persist

Figure 3a. The graph above shows Antarctic sea ice extent as of August 15, 2023, along with daily ice extent data for four previous years and the record high year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 2014 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
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Figure 3b. Antarctic sea ice extent for August 15, 2023 was 15.12 million square kilometers (5.84 million square miles). The orange line shows the 1981 to 2010 average extent for that day. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Record low levels of Antarctic sea ice extent have persisted and have even become more extreme. Since the beginning of August, the growth in extent has begun to level off (Figure 3a). Highly variable conditions are typical of Antarctic sea ice extent near the seasonal maximum, but the present situation is clearly remarkable. While there will likely be further increases in extent the second half of the month, close attention to the progression of ice growth or retreat is warranted.

On August 15, extent was 15.12 million square kilometers (5.84 million square miles) (Figure 3b), which is 2.54 million square kilometers (980,000 square miles) below the 1981 to 2010 average extent for August 15. Even more remarkable, this year’s extent on August 15 was 1.73 million square kilometers (670,000 square miles) below the previous record low for the date, in 1986. Ice extent is particularly low in the Ross Sea and eastern Weddell Sea sectors, but has recovered somewhat in the Bellingshausen Sea. The Amundsen Sea and western Bellingshausen Sea are now slightly above average.

Melt onset

Figure 4. The map on the left shows the melt onset of Arctic Sea Ice for 2023. Different in 2023 melt onset date with the 1981 to 2010 melt date. Red indicates earlier than average melt onset; blue indicates later than average melt onset.

Credit: Data processed by Jeff Miller, NASA Goddard; image by Julienne Stroeve, NSIDC; data based on Markus et al. (2009)
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The onset of surface melt is a potential harbinger of ice conditions later in the melt season. When melt begins, the reflectivity, known as albedo, of the surface decreases, allowing more of the sun’s energy to be absorbed. This means more energy is available to promote further melting the ice and a greater potential for areas of sea ice to melt out completely by the end of summer. Melt onset data are based on the Markus et al. 2009 method, and were provided by Jeff Miller at NASA Goddard. This year, melt started 10 to 20 days earlier than average along the coastal seas around nearly all of the Arctic, while over the central Arctic, melt started 10 to 20 day later than average (Figure 4).

Hudson Bay

Figure 5. The map of Hudson Bay Complex on the left shows the average ice-free period (sea ice concentration is continuously below 15 percent) from 1979 to 2013 based on the Bootstrap Algorithm applied to passive microwave satellite retrievals. The chart on the right compares the satellite record to 37 historical climate model simulations of the ice-free period averaged for the Hudson Bay Complex (1979 to 2013). Each model is represented by a single ensemble member.

Credit: Alex Crawford, University Manitoba and Crawford, A. D. et al. 2023
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As in many recent years, Hudson Bay melted out earlier than the 1981 to 2010 average date, and there is a trend toward a longer summer ice-free period. There is interest in knowing how long Hudson Bay will be seasonally ice free in the future. A recent study by Alex Crawford and colleagues at the University of Manitoba highlights a common problem in many climate models used to make future projections: The ice-free periods are too long (Figure 5). On average, models simulate sea ice retreating 19 days too early in summer and advancing 9 days too late in autumn, meaning the average model simulates an ice-free period that is about a month longer than is observed by satellite. After accounting for uncertainty in satellite observations, 73 percent (27 of 37) of models significantly overestimate the ice-free period. This performance is the worst for any Arctic sub-region.

The main culprit is how models simulate the atmosphere. Models that overestimate the ice-free period tend to depict overly warm conditions over Hudson Bay, especially in August to October. This warmth links back to winds blowing too often from the south and east. Extra warmth delays autumn freeze up, which leads to thinner ice that melts more readily in summer. Improving the atmospheric components of these models might improve the simulation of Hudson Bay sea ice and provide more confidence in projections of the future.

References

Crawford, A. D., E. Rosenblum, J. V. Lukovich, and J. C. Stroeve. 2023. Sources of Seasonal Sea Ice Bias for CMIP6 Models in the Hudson Bay Complex. Annals of Glaciology, First View, 1-18, doi:10.1017/aog.2023.42.

Markus, T., J. C. Stroeve, and J. Miller. 2009. Recent changes in Arctic sea ice melt onset, freezeup, and melt season length. Journal Geophysical Research, 114, C12024, doi:10.1029/2009JC005436.

While large parts of the world saw record breaking heat in July, and Antarctic sea ice extent remained at record daily lows as assessed over the satellite record, Arctic sea ice extent for July was only the twelfth lowest in the satellite record. At month’s end, ice concentrations were low north of the Laptev Sea; however, the Northern Sea Route and the Northwest Passage retained considerable ice.

Overview of conditions

Figure 1a. Arctic sea ice extent for July 2023 was 8.18 million square kilometers (3.16 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 1b. This map shows a large opening on August 1, 2023, in the Laptev and East Siberian Seas and extensive open water north of Alaska and the Mackenzie River Delta. Sea ice concentration data are from Advanced Microwave Scanning Radiometer 2 (AMSR2) imagery.

Credit: University of Bremen
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For the month of July, Arctic sea ice extent declined at a pace of 93,300 square kilometers (36,000 square miles) per day, near the 1981 to 2010 average of 86,900 square kilometers (33,600 square miles) per day (Figure 1a). The July average Arctic sea ice extent of 8.18 million square kilometers (3.16 million square miles) was the twelfth lowest in the satellite record, and 1.29 million square kilometers (498,000 square miles) below the 1981 to 2010 reference period. By stark contrast, Antarctic sea ice extent remained far below previous record daily lows throughout the month. While there is speculation that a fundamental change in the Antarctic sea ice system is afoot, there is some evidence from early satellite data that extent may have been similarly low in 1966.

The sea ice concentration image on August 1, 2023, from the Advanced Microwave Scanning Radiometer 2 (AMSR2) offers a detailed view of Arctic sea ice conditions (Figure1b). Large parts of the Laptev and East Siberian seas are largely ice free, and a large area of fairly low ice concentration extends north of the Laptev Sea. However, ice is still present along much of the Northern Sea Route, noting of course that Russian ice breakers are quite capable of keeping routes open. The ice edge has retreated to well north of the Alaskan and Mackenzie Delta coasts, but it is clear that the southern (Amundsen’s) route through the Northwest Passage is still choked with ice. To date since July 1, 2.86 million square kilometers (1.10 million square miles) of sea ice have melted.

Conditions in context

Figure 2a. The graph above shows Arctic sea ice extent as of August 1 2023, along with daily ice extent data for four previous years and the record low year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 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
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Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, from July 1 to 29, 2023. 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 Laboratory
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Figure 2c. This plot shows average sea level pressure in the Arctic in millibars from July 1 to 29, 2023. Yellows and reds indicate high air pressure; blues and purples indicate low pressure.

Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
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Air temperatures at the 925 hPa level (approximately 2,500 feet above the surface) averaged for July 2023 were with one exception unremarkable (Figure 2). This contrasts sharply with the record high global average surface air temperature (2 meters or 6.6 feet above the surface) for the month as shown in records compiled by NASA, the National Oceanic and Atmospheric Administration (NOAA) and other agencies. Arctic temperatures at the 925 hPa level were from 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) above average across much of the Arctic Ocean but below average by 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) over the Laptev Sea, which as noted above is largely ice free. The one area of pronounced warmth is centered over the Mackenzie River Delta, with temperatures up to 7 degrees Celsius (13 degrees Fahrenheit) above average. The atmospheric circulation pattern for the month was by contrast quite interesting, with low pressure over the Eurasian side of the Arctic and high pressure over the North American side (Figure 2c). As a result, there was a strong pressure gradient across the central Arctic Ocean extending to the east of Svalbard and then towards Iceland, pointing to strong winds and hence strong sea ice transport.

July 2023 compared to previous years

Figure 3. Monthly July ice extent for 1979 to 2023 shows a decline of 7.0 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend for Arctic sea ice extent in July over the 45-year satellite record is 66,500 square kilometers (25,700 square miles) per year, or 7.0 percent per decade relative to the 1981 to 2010 average (Figure 3). Based on the linear trend, since 1979, July has lost 2.92 million square kilometers (1.13 million square miles) of ice. This is roughly equivalent to four times the size of Texas.

An update on the Southern Hemisphere

Figure 4a. Antarctic sea ice extent for July 2023 was 13.49 million square kilometers (5.21 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 4b. The graph above shows Antarctic sea ice extent as of August 1, 2023, along with daily ice extent data for four previous years and the record high year. 2023 is shown in blue, 2022 in green, 2021 in orange, 2020 in brown, 2019 in magenta, and 2014 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
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While Arctic sea ice is in the midst of the melt season, Antarctic sea ice is growing, but only slowly for this time of year. Antarctic sea ice extent averaged for July was at a record low at 13.49 million square kilometers (5.21 million square miles), and 1.50 million square kilometers (579,000 square miles) below the previous satellite record low set in 2022 (Figure 4a and 4b). As discussed in the previous post, there is speculation that the Antarctic sea ice system has entered a new regime, in which ocean heat is now playing a stronger role in limiting autumn and winter ice growth and enhancing spring and summer melt.

While this very low extent has garnered much attention, as well as consternation, a study led by colleague Dave Gallaher several years ago provides evidence from early Nimbus satellite data that sea ice extent in the winter of 1966 may have rivaled the very low level seen today. There are caveats. First, the Nimbus data for 1966 is for August, not September, the month with the annual highest average extent in the Antarctic. Second, there is substantial uncertainty in the 1966 extent because of the limited data from the low resolution visible-band Nimbus images (notably cloud cover) and challenges in interpreting the imagery. The estimated August 1966 sea ice extent from Nimbus is 15.90 million square kilometers (6.14 million square miles). A simple projection, based on data through July 1, yields an August 2023 extent of August 15.07 million square kilometers (5.82 million square miles), still significantly lower than the 1966 data suggest. Despite these uncertainties, the Nimbus data is consistent with observations from the satellite passive microwave record that Antarctic sea ice extent is highly variable.

A second information source, from a reconstruction of Antarctic sea ice led by Ryan Fogt, a professor at Ohio University, suggests that the present level is well below anything seen since the earliest Southern Ocean weather observations, back to 1905. Fogt and colleagues first established how weather station data are correlated with observed sea ice extent from 1979 through 2020. Using this information together with weather station records that go back to the early 1900s, they deduce what sea ice extent was likely to have been between 1905 and 2020, along with what its variability was likely to have been.

Further reading

Fogt, R. L., A. M. Sleinkofer, M. N. Raphael, H. S. and Handcock. 2022a. A regime shift in seasonal total Antarctic sea ice extent in the twentieth century. Nature Climate Change 12, 54– 62. doi:10.1038/s41558-021-01254-9.

Gallaher, D. W., G. G. Campbell, W. N. and Meier. 2013. Anomalous variability in Antarctic sea ice extents during the 1960s with the use of Nimbus data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 7(3), 881-887. doi:10.1109/JSTARS.2013.2264391.

Sunlight has returned to the highest latitudes in the Arctic, while in the Antarctic autumn is settling in. The seasonal decline of Arctic sea ice extent since the March 6 annual maximum has been slow, but daily extent has remained among the third to sixth lowest in the satellite record. Since the seasonal minimum reached on February 21, Antarctic sea ice has expanded at a fairly typical pace.

Overview of conditions

Figure 1. Arctic sea ice extent for March 2023 was 14.44 million square kilometers (5.58 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Figure 1b. The graph above shows Arctic sea ice extent as of April 4, 2023, along with daily ice extent data for four previous years and the record low year. 2022 to 2023 is shown in blue, 2021 to 2022 in green, 2020 to 2021 in orange, 2019 to 2020 in brown, 2018 to 2019 in magenta, and 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
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The March 2023 average Arctic sea ice extent was 14.44 million square kilometers (5.58 million square miles), the sixth lowest March in the satellite record (Figure 1a). March monthly average extent was 990,000 square kilometers (382,000 square miles) below the 1981 to 2010 average of 15.43 million square kilometers (5.96 million square miles), but 150,000 square kilometers (57,900 square miles) above the record low set in March 2017 (Figure 1b).

After the March 6 seasonal maximum, extent declined for a week, but then remained almost constant during the second half of the month. Ice extent was slightly below average in almost all areas, but particularly in the Sea of Okhotsk and in the Gulf of St. Lawrence, with smaller retreats in the Barents and Bering Seas. Sea ice concentration within the ice pack was generally quite high in all areas, with the exception of the Sea of Okhotsk and the northern Barents Sea where the ice pack was more open.

Overall, extent decreased 170,000 square kilometers (65,600 square miles) during March 2023, compared to the 1981 to 2010 average March decrease of 220,000 square kilometers (84,900 square miles).

Conditions in context

Figure 2a. This plot shows average sea level pressure in the Arctic in millibars for March 2023. 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 Laboratory
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Figure 2b. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for March 2023. 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 Laboratory
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March weather conditions were dominated by persistent high sea level pressure over northern Canada and Greenland, and low sea level pressure over northern Europe and European Russia (Figure 2a). This led to winds from the south and warm conditions over Baffin Bay and western Greenland with temperatures up to 6 to 7 degrees Celsius above average (11 to 13 degrees Fahrenheit) (Figure 2b). Cool conditions extended from Iceland to Franz Josef Land, where temperatures were 4 to 6 degrees Celsius below average (7 to 11 degrees Fahrenheit).

March 2023 compared to previous years

Figure 3. Monthly March ice extent for 1979 to 2023 shows a decline of 2.5 percent per decade.

Credit: National Snow and Ice Data Center
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The downward linear trend for Arctic sea ice extent in March over the 45-year satellite record is 38,900 square kilometers (15,000 square miles) per year, or 2.5 percent per decade relative to the 1981 to 2010 average. Based on the linear trend, since 1979, March has lost 2.28 million square kilometers (880,000 square miles). This is roughly eight and a half times the size of Colorado or six and a half times the size of Germany.

Arctic sea ice age

Figure 4. The top maps show sea ice age for the week of February 26 to March 4 for (a) 1985  and (b) 2023. The bottom graph is a timeseries of the percent of the sea ice extent within the Arctic Ocean domain (inset map) for the week of February 26 to March 4, 1985, through 2023; color categories are the same as in the maps. Data and images from NSIDC EASE-Grid Sea Ice Age, Version 4 (Tschudi et al., 2019a) and Quicklook Arctic Weekly EASE-Grid Sea Ice Age, Version 1 

Credit: Tschudi et al., 2019b
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An important indicator of sea ice conditions is the sea ice age. As in recent years, there is far less multiyear ice (ice that has survived at least one summer melt season) and the oldest ice (ice that has survived several or more melt seasons) is nearly gone. Multiyear ice covered 33.9 percent of the Arctic Ocean domain in the week of February 26 through March 4, 2023, slightly less than the 34.3 percent during the same week in 2022. This is much less than in the late 1980s when multiyear ice covered 60 to 65 percent of the Arctic Ocean.

A rapid decline in multiyear ice coverage occurred after the then record 2007 September sea ice extent minimum. The multiyear ice coverage has been variable since then, with no significant trend. Overall, there is almost no ice over four years old remaining—it now comprises just 3 percent of the total ice cover. This is the same percentage as last year and contrasts starkly with the late 1980s when 30 to 35 percent of the Arctic Ocean’s ice was older than 4 years. Since 2011, the older-than-four-year-old ice has comprised less than 5.5 percent of the Arctic Ocean. These results are consistent with a new study that evaluated the thickness of ice from moorings in Fram Strait, finding a shift in the ice thickness after 2007 and a decline of the average residence time of ice in the Arctic Ocean.

Autumn in the Antarctic

Figure 5. Antarctic sea ice extent for March 2023 was 2.80 million square kilometers (1.08 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
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Antarctic sea ice extent expanded at a near-average pace in March following its record low extent on February 21. At the end of the month, the Ross Sea and Amundsen Sea were covered again with ice, and significant expansion of ice had begun in the Weddell Sea. However, large areas of the coast, such as the southern Bellingshausen Sea coastline were still ice free; other areas of open water persisted along the boundary between the Amundsen and Ross Seas. Despite regrowth, the Weddell Sea ice cover is well below its typical extent for the end of March.

The March 2023 average sea ice extent around Antarctica was 2.80 million square kilometers (1.08 million square miles), the second lowest March on record. This is 100,000 square kilometers (38,600 square miles) more than the record low extent for March set in 2017.

Ocean circulation changes in the Southern Ocean

Figure 6a. This map shows global ocean circulation, including the major areas of ocean water sinking and upwelling. This is often called the global ocean conveyor belt.

Credit: Modified from National Geographic
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Figure 6b. This schematic diagram of the Southern Ocean portion of the global ocean circulation shows the changes in the recent decades, on the right, relative to the earlier pattern, on the left.

Credit: Lee et al., 2023
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The ocean circulation, which includes well-known surface and subsurface currents and the vertical motion of ocean water, appears to have changed in a major way over the Southern Hemisphere in recent decades. Increased contributions of meltwater from the Antarctic Ice Sheet, mostly from melting at depth due to increased warm deep water reaching the edge of the continent, has added freshwater to the sea currents, making the water less dense. This lighter water flows up to the surface, increasing the stratification in the near-surface layer. Because the stratification is stronger, the vertical ocean circulation has slowed.

These changes reflect changing winds around the continent, resulting from both the ozone hole, which cools the Antarctic stratosphere, increasing the westerly circumpolar winds, and increased carbon dioxide and methane in the air, which warms the tropics, again making the far southern winds stronger.

Great Scott! The Great Lakes in 2023

Figure 7a. This map of the Great Lakes shows ice cover on February 4th, 2023, the date of maximum ice cover for 2023. 

Credit: US National Ice Center
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Figure 7b. This plot shows the departure from average air temperature in the Great Lakes Region at the 925 hPa level, in degrees Celsius, from December 1, 2022, to March 29, 2023, relative to the 1991 to 2020 average. 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 Laboratory
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This year, the maximum ice cover area of the Great Lakes, as monitored by the US National Ice Center in Suitland Maryland, was 23.35 percent on February 4, 2023, and for much of the winter ice cover was below 10 percent (Figure 7a). Winter temperatures over the Great Lakes ranged from 0.5 degrees Celsius (1 degree Fahrenheit) above the 1991 to 2020 average over Lake Superior to more than 2 degrees Celsius (4 degrees Fahrenheit) above average over Lake Ontario (Figure 7b).

Although the year-to-year variability in Great Lakes ice cover is high, an analysis led by Jia Wang, an ice climatologist at the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL), found that average winter ice cover on the Great Lakes has declined 69 percent between1973 and 2017, with the greatest losses in Lake Superior and Lake Ontario. However, nearly complete ice cover was seen as recently as 2019. Historically, widespread ice cover over Lake Michigan and Lake Erie (and many other areas) supported ice harvesting for refrigeration.

In memoriam: Josh King

Figure 8. This photograph is a portrait of Josh King.

Credit: Steve Howell, Environment and Climate Change Canada
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It is with great sadness that another colleague of ours recently passed away. Josh King was a dedicated snow field scientist who collected invaluable snow observations throughout the Arctic region during his career. In 2017, NSIDC scientist Julienne Stroeve and others worked with King to collect snow and ice data in the Lincoln Sea, the region of the Arctic known as the Last Ice Area. Stroeve remembers how professional King was in leading the data collection efforts, keeping the team motivated while working tirelessly after returning back to base each night to keep instruments operational and quality control the data collected. It is a great loss for the scientific community to lose a colleague at such a young age.

References

Holling, H. C. 1941. Paddle-to-the-Sea. Boston, Houghton Mifflin

Ice Harvesting in Sandusky

Lee, S. K., R. Lumpkin, F. Gomez, S. Yeager, H. Lopez, F. Takglis, S. Dong, W. Aguiar, D. Kim, and M. Baringer. 2023. Human-induced changes in the global meridional overturning circulation are emerging from the Southern Ocean. Nature Communications Earth and Environment 4, 69, doi:10.1038/s43247-023-00727-3.

National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL) Annual Max Ice Cover Animation

Sumata, H., de Steur, L., Divine, D.V. et al. 2023. Regime shift in Arctic Ocean sea ice thickness. Nature 615, 443–449, doi:10.1038/s41586-022-05686-x.

Tschudi, M., W. N. Meier, J. S. Stewart, C. Fowler, and J. Maslanik. 2019a. EASE-Grid Sea Ice Age, Version 4 [Data Set]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center, doi:10.5067/UTAV7490FEPB. Date Accessed 03-31-2023.

Tschudi, M., W. N. Meier, and J. S. Stewart. 2019. Quicklook Arctic Weekly EASE-Grid Sea Ice Age, Version 1 [Data Set]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center, doi:10.5067/2XXGZY3DUGNQ. Date Accessed 03-31-2023.

Wang, J., J. Kessler, F. Hang, H. Hu, A. Clites, and P. Chu. 2017. Great Lakes ice climatology update of winters 2012-2017: Seasonal cycle, interannual variability, decadal variability, and trend for the period 1973-2017. NOAA Technical Memorandum GLERL-170.

Arctic sea ice has likely reached its maximum extent for the year, at 14.62 million square kilometers (5.64 million square miles) on March 6. The 2023 maximum is the fifth lowest in the 45-year satellite record. NSIDC scientists will present a detailed analysis of the 2022 to 2023 winter sea ice conditions in the regular monthly post in early April.

Overview of conditions

Figure 1. This image shows Arctic sea ice extent on March 7, 2023, which was 14.62 million square kilometers (5.64 million square miles) like the extent on March 6, 2023. The March 7 image is being used because of missing data on the prior day’s map. 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 6, 2023, Arctic sea ice likely reached its maximum extent for the year, at 14.62 million square kilometers (5.64 million square miles), the fifth lowest extent in the satellite record. This year’s maximum extent is 1.03 million square kilometers (398,000 square miles) below the 1981 to 2010 average maximum of 15.65 million square kilometers (6.04 million square miles) and 210,000 square kilometers (81,000 square miles) above the lowest maximum of 14.41 million square kilometers (5.56 million square miles) set on March 7, 2017.

The date of the maximum this year, March 6, was six days earlier than the 1981 to 2010 average date of March 12.

Conditions in context

Figure 2. The graph above shows Arctic sea ice extent as of March 6, 2023, along with daily ice extent data for four previous years and the record low year. 2022 to 2023 is shown in blue, 2021 to 2022 in green, 2020 to 2021 in orange, 2019 to 2020 in brown, 2018 to 2019 in magenta, and 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 below average sea ice extent in the Bering Sea, Sea of Okhotsk, Barents Sea, and Labrador Sea. Above average extent was in the Greenland Sea. Extent was well below average in the Gulf of St. Lawrence for a second year in row.

Since the maximum on March 6, extent has dropped about 200,000 square kilometers (77,000 square miles), with losses primarily in Labrador Sea, Gulf of St. Lawrence, and the Barents Sea.

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

For the Arctic maximum, which typically occurs in March, the uncertainty range is ~34,000 square kilometers (13,000 square miles), meaning that extents within this range must be considered effectively equal.

On February 21, Antarctic sea ice likely reached its annual minimum extent of 1.79 million square kilometers (691,000 square miles). This the lowest sea ice extent in the 1979 to 2023 sea ice record, setting a record low for the second straight year.

Please note that this is a preliminary announcement. Changing winds or late-season melt could still reduce the Antarctic ice extent. NSIDC scientists will release a full analysis of the Antarctic and Arctic February conditions in early March.

Overview of conditions

Figure 1. Antarctic sea ice extent for February 21, 2023, was 1.79 million square kilometers (691,000 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 February 21, 2023, sea ice in the Antarctic reached an annual minimum extent of 1.79 million square kilometers (691,000 square miles), setting a record low in the satellite record that began in 1979. This year’s minimum is 1.05 million square kilometers (405,000 square miles) below the 1981 to 2010 average Antarctic minimum extent. It is 136,000 square kilometers (52,500 square miles) below the previous record low from February 25, 2022. Nearly all of the remaining ice is in the Weddell Sea, with isolated patches along the coasts of Princess Astrid and Princess Ragnild and regions of eastern Wilkes Land and the Pine Island Bay.

The Antarctic minimum extent was reached three days earlier than the 1981 to 2010 median date of February 24. The interquartile range for the date of the Antarctic minimum is February 20 to February 27.

Conditions in context

Figure 2a. The graph above shows Antarctic sea ice extent as of February 21, 2023, along with daily ice extent data for four previous years and the record high year. 2022 to 2023 is shown in blue, 2021 to 2022 in green, 2020 to 2021 in orange, 2019 to 2020 in brown, 2018 to 2019 in magenta, and 2013 to 2014 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
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Figure 2b. This graph shows Antarctic annual sea ice minimum extent, depicted as black diamonds, from 1979 to 2023, based on a 5-day running average of daily extent. The linear trend line is in blue with a 1.0 percent per decade downward trend, which is not statistically significant. A five-year running average is shown in red.

Credit: W. Meier, NSIDC
High-resolution image

This year marks a second consecutive record low in Antarctic sea ice extent (Figure 2a). In recent years, 2017 and 2018 also reached very low extents, third and fourth lowest, respectively. With this series of low years, it is natural to speculate if there is now a downward trend. However, a trend computed over such a short time period is not especially meaningful. Note in this respect that 2013 through 2015 saw near record high minimum extents.

Overall, the downward trend in the annual Antarctic sea ice minimum extent computed over the complete satellite record is 2,800 square kilometers (1,100 square miles) per year, or 1.0 percent per decade relative to the 1981 to 2010 average. This trend is not statistically significant (Figure 2b). This is in stark contrast to the Arctic where the trend in the sea ice minimum is larger in magnitude and has strong statistical significance.

Antarctic sea ice extent appears to have broken the record low set last year. With a couple more weeks likely left in the melt season, the extent is expected to drop further before reaching its annual minimum. Much of the Antarctic coast is ice free, exposing the ice shelves that fringe the ice sheet to wave action and warmer conditions.

Overview of conditions

Figure 1a. This map of Antarctica shows many low areas of sea ice concentration, depicted as darker blues, surrounding the continent, rendering extent likely to decrease in the coming days or weeks. Antarctic sea ice extent for February 13, 2023, was 1.91 million square kilometers (737,000 square miles). The orange line shows the 1981 to 2010 median extent for that day. Sea Ice Index data. About the data

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

Figure 1b. The graph above shows Antarctic sea ice extent as of February 13, 2023, along with daily ice extent data for four previous years and the record high year. 2022 to 2023 is shown in blue, 2021 to 2022 in green, 2020 to 2021 in orange, 2019 to 2020 in brown, 2018 to 2019 in magenta, and 2013 to 2014 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

On February 13, 2023, Antarctic sea ice extent fell to 1.91 million square kilometers (737,000 square miles) (Figure 1a). This set a new record low, dropping below the previous record of 1.92 million square kilometers (741,000 square miles) set on February 25, 2022 (Figure 1b). This year represents only the second year that Antarctic extent has fallen below 2 million square kilometers (772,000 square miles). In past years, the annual minimum has occurred between February 18 and March 3, so further decline is expected.

Conditions in context

Figure 2. This graph shows Antarctic annual sea ice minimum extent, depicted as black diamonds, from 1979 to 2023, based on a 5-day running average of daily extent. The grey diamond data point depicts the 2023 minimum, which is still preliminary, with further loss expected. The linear trend line is in blue with a 0.9 percent per decade downward trend, which is not statistically significant. A five-year running average is shown in red. As the Antarctic melt season is still in progress, depicted as a grey downward arrow, the linear trend and running average will change slightly.

Credit: W. Meier, NSIDC
High-resolution image

Extent has tracked well below last year’s melt season levels since mid-December. As noted in our previous post, a positive Southern Annular Mode has led to stronger-than-average westerly winds. Along with a strong Amundsen Sea Low, the weather conditions have brought warm air to the region on both sides of the Antarctic Peninsula. This has largely cleared out the ice cover in the Amundsen and Bellingshausen Seas, and reduced the sea ice extent in the northwestern Weddell Sea. Sea ice is patchy and nearly absent over a long stretch of the Pacific-facing coastline of Antarctica.  Earlier studies have linked low sea ice cover with wave-induced stresses on the floating ice shelves that hem the continent, leading to break up of weaker areas.

Antarctic sea ice extent has been highly variable over the last several years. While 2022 and 2023 have had record low minimum extent, four out of the five highest minimums have occurred since 2008. Overall, the trend in Antarctic minimum extent over 1979 to 2023 is near zero. The current downward linear trend in the Antarctic minimum extent from 1979 to 2023 is 2,400 square kilometers (930 square miles) per year, or 0.9 percent per decade, which is currently not statistically significant. Nevertheless, the sharp decline in sea ice extent since 2016 has fueled research on potential causes and whether sea ice loss in the Southern Hemisphere is developing a significant downward trend.