Analysis - Sea Ice Today
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The new abnormal

Since 2007, the Arctic sea ice minimum has dropped below 5 million square kilometers (1.93 million square miles) every year, except in 2009, 2013, and 2014, when extent barely crossed the 5 million square kilometer mark. Such low extents would have been hard to imagine in the 1990s, when extent averaged 6.46 million square kilometers (2.49 million square miles). This persistent new normal, and the related losses of most of the old and thick ice, are prominent characteristics of the new, warmer Arctic—resiliently low in ice cover despite more than a decade of variations in seasonal climate patterns and ocean conditions. Arctic climate warming continues to lead an unfortunate path of change for the planet. Here, NSIDC researchers summarize this year’s events in the Arctic, and touch upon Antarctica sea ice extent at the end of its austral winter.

Overview of conditions

Average Arctic sea ice extent for the month of September was 4.38 million square kilometers (1.69 million square miles), sixth lowest in the 46-year-satellite passive microwave record (Figure 1a). Ice extent was particularly low in the Beaufort Sea and the Kara and East Siberian Seas. A unique feature of this year was the region of compact, first-year ice along far northeastern Russia, near Wrangel Island that survived the melt season. This ice is “dirty” and appears to have been transported from the continental shelves of the Laptev Sea. Sea ice in the Northwest Passages (NWP) through the channels of the Canadian Archipelago dropped rapidly through September, despite an influx of ice from the north. Both NWP routes and the Northern Sea Route along the Russian coast are presently clear of ice via satellite imagery—with the exception of the coastal area near Wrangel Island.

The rate of change of Arctic sea ice extent in September was relatively low at the beginning of the month with an approximate 24,000 square kilometers (9,000 square miles) per day loss through September 10 (Figure 1b). The rate of growth following the minimum was also low at 14,000 square kilometers (5,000 square miles) per day between September 12 and September 30.

extent map and graph for Arctic September sea ice extent
Figure 1a. The map on the left shows Arctic sea ice extent for September 2024 at 4.38 million square kilometers (1.69 million square miles). The magenta line shows the 1981 to 2010 average extent for that month. Figure 1b. The graph on the right shows Arctic sea ice extent as of October 2, 2024, along with daily ice extent data for four previous years and the record low year. 2024 is shown in blue, 2023 in green, 2022 in orange, 2021 in brown, 2020 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. — Credit: National Snow and Ice Data Center

Conditions in Context

Air temperatures at the 925 hPa level (approximately 2,500 feet above the surface) were 2 to 3 to degrees Celsius (4 to 5 degrees Fahrenheit) above average over the eastern Beaufort Sea, Canadian Archipelago, and Greenland, and reached 5 degrees Celsius (9 degrees Fahrenheit) above average in northern Baffin Bay and northern Greenland (Figure 2a). Conditions were also quite warm over the Barents Sea with temperatures 2 to 5 degrees Celsius above average (4 to 9 degrees Fahrenheit) and up to 6 degrees Celsius (11 degrees Fahrenheit) above average in westernmost Russia near Finland.

The atmospheric pattern for the month at sea level was dominated by strong high pressure over western Russia that brought warm air northward to Eastern Europe and the Barents Sea (Figure 2b). Relatively high pressure over Greenland and Baffin Bay also drove warm winds northward into the Canadian Archipelago, supporting the rapid loss of sea ice in the Northwest Passage region. Lower air pressure (near 1,000 millibars) was the rule over a wide area from Alaska to eastern Russia.

Plots for Arctic air temperature and sea level pressure for September 2024
Figure 2a. The left plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for September 2024. Yellows and reds indicate above average temperatures; blues and purples indicate below average temperatures. Figure 2b. The plot on the right shows average sea level pressure in the Arctic in millibars for September 2024. Yellows and reds indicate above average air pressures; blues and purples indicate below average air pressures. — Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory

September 2024 compared to previous years

Including 2024, the downward linear trend in Arctic sea ice extent for September is 78,000 square kilometers (30,000 square miles) per year, or 12.13 percent per decade relative to the 1981 to 2010 average. Based on the linear trend, since 1979, September has lost 1.61 million square kilometers (622,000 square miles) of sea ice, which is roughly equivalent to the state of Alaska or the country of Iran.

September sea ice extent since 1979
Figure 3. Monthly September ice extent for 1979 to 2024 shows a decline of 12.1 percent per decade. — Credit: National Snow and Ice Data Center

Wrangel Island sea ice feature

A unique feature in the Arctic sea ice this summer was durable, compacted, and apparently sediment-laden, first-year ice that persisted between the far northeastern Siberian coast and Wrangel Island. This feature, apparent in June, persisted through the entire melt season. It appears to have formed from strong motion of first-year ice from the east and south that compacted and ridged the ice, as well as scouring and upturning sediment. The thickness of the ice prevented it from melting completely even though the rest of the surrounding ice pack melted back several hundred kilometers. The sediment gave the ice surface an unusual brownish-gray tint.

Wrangel Island on September 21, 2024
Figure 4. This Visible Infrared Imaging Radiometer Suite (VIIRS) instrument captures a true color image from September 21, 2024, showing the persistent ice floe near Wrangel Island in the Chukchi Sea. — Credit: NASA Worldview

Northwest Passage

Our colleague Steven Howell provided an update on the late-season conditions and causes of low ice cover in the Northwest Passage (NWP). As of October 1, 2024, sea ice area in the northern (deepwater) route was at an all-time record low extent, besting the previous record low that occurred on September 17, 2011 (Figure 5a). At the beginning of September, there was southward ice advection through channels between the northern islands of the Canadian Archipelago from higher latitude regions, as indicated by the up-tick of sea ice area in the NWP tracking area on September 10. However, wind patterns changed mid-September, limiting southward advection, and bringing in warmer air. Melting from the combined effects of ocean and air resulted in the northern route being virtually sea ice free by late in the month (Figure 5b). The southern route is also sea ice free, a more typical occurrence in recent Septembers.

Graphs showing sea ice area for Northwest Passage routes as of October 1, 2024 and other years
Figure 5a. These graphs show total sea ice area for 2024, 2023, 2022, 2021, 2011 and the 1991 to 2020 average within the northern route, on the left, and southern route, on the right, of the Northwest Passage. The 2024 year ends on October 1. — Credit: Data from Canadian Ice Service; Steve Howell, Environment and Climate Change Canada

 

GIF showing changes to Hudson Bay throughout September 2024, through the 1991 to 2010 average, and as a difference from average
Figure 5b. Click to play. This animation shows the spatial distribution of sea ice concentration in the Western Canadian Arctic from the week of June 24, 2024, to the week of September 30, 2024. 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 time period; and the map on the right shows the difference in sea ice concentrations between the 1991 to 2020 average and the weeks displayed. Red shows a stark decline from the average. — Credit: Data from Canadian Ice Service; Steve Howell, Environment and Climate Change Canada

Arctic sea ice continues to be young and thin

One characteristic of the “new abnormal Arctic” is a lack of multiyear ice, particularly the oldest and generally thickest ice (greater than four-years old). Multiyear ice was once the dominant sea ice type in the Arctic Ocean (Figure 6). At the end of summer in the mid-1980s, there was over 4 million square kilometers (1.54 million square miles) of multiyear ice and over 2 million square kilometers (772,000 square miles) of ice greater than four-years old. At the end of the 2024 melt season, there was only 1.48 million square kilometers (571,000 square miles) of multiyear ice and only 120,000 square kilometers (46,000 square miles) of ice greater than four-years old. Phrased differently, the Arctic Ocean has lost 95 percent of its oldest and thickest ice. 

Ice Age in Arctic map and graph comparing 2024 to 1985
Figure 6. 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 2024 on the right. The bottom time series shows extent of multiyear ice in black and ice greater-than-four-years old in red at the seasonal minimum for 1985 to 2024. The oldest (four or more years old) ice is in red. — Credit: Tschudi et al., 2019a and 2019b

Another strange year for Antarctic sea ice

Antarctic sea ice continued to track at exceptionally low extent levels for late winter, and appears to have reached its maximum on September 19 at 17.16 million square kilometers (6.63 million square miles). Averaged for September, sea ice extent stood at 17.06 million square kilometers (6.59 million square miles), just 260,000 square kilometers (100,000 square miles) above last year’s record-setting low monthly average. The last two years have had lower maximum extents than any other years in the modern satellite record by nearly 1 million square kilometers (386,000 square miles). Extent for the past two years has fallen well below levels before the modern satellite era, based on estimates derived from climate indices (Fogt et al., 2022), as well as an estimate for 1966 based on early visible-band, satellite imagery from Nimbus-II.  

Antarctic sea ice extent for multiple decades
Figure 7. 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 2024. The Nimbus-II 1966 value is marked as a gold diamond within the uncertainty range, which is drawn as a vertical gold line. — Credit: Walt Meier, NSIDC

Review of the Arctic’s seasonal retreat in 2024 

Starting from a relatively high winter peak as the fourteenth lowest extent, Arctic sea ice remained higher than the previous 12 years until July, when the rate of decline accelerated, pushing ice extent to third lowest by late July. However, in early September, the rate of loss slowed, and the daily minimum finished at seventh lowest in the 46-year-satellite record. Because of slow ice growth after the daily minimum, the September average extent was the sixth lowest. Key aspects of the 2024 decline were an early loss of ice in eastern Hudson Bay, driven by unusually strong winds from the east that pushed the ice towards the west. This was followed by a rapid loss of ice along the Siberian coast in July as winds and warm conditions opened much of the Kara and Laptev Seas. In August, losses in the Beaufort Sea, which had lagged in the beginning of the melt season, began to dominate the rate of retreat. As already discussed, an unusual area of compact, first-year ice persisted near Wrangel Island.

Overall, the Arctic climate of the summer of 2024 (June through September) was characterized by a fairly strong Icelandic low. Owing to slack winds, ice transport in the Transpolar Drift Stream was relatively slow. Air temperatures at the 925 hb level over the same period were high in the Barents Sea at 4 degrees Celsius (7 degrees Fahrenheit) above average and Hudson Bay at 3 degrees Celsius (5 degrees Fahrenheit), but notably below average in the vicinity of northeastern-most Siberia and Wrangel Island. Overall, the Arctic Ocean was about 1 degree Celsius (2 degrees Fahrenheit) above average for the four warmest months.

Further reading

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 10-02-2024.

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 10-02-2024.

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 10-02-2024.