Following the pattern of recent years, autumn freeze up has been slow in the Arctic, reflecting the growing heat in the ocean mixed layer during summer and higher air temperatures. In the Antarctic, the rate of spring ice loss slowed somewhat during November, ending the month above the extreme low levels of 2016 and 2023.
Overview of conditions
Arctic sea ice extent for November averaged 9.11 million square kilometers (3.52 million square miles), and was the third lowest in the 46-year-satellite record (Figure 1a). The November extent was 450,000 square kilometers (174,000 square miles) higher than the record low for the month set in 2016 (Figures 1a and 1b), but was 1.59 million square kilometers (614,000 square miles) below the 1981 to 2010 average (Figure 1b). Since 2012, the two largest departures from average extent in any month have occurred in autumn—November 2016 and October 2020—and November 2024 is similarly extreme.
While ice extent overall grew at a steady pace for most of November, growth slowed towards the end of the month. Regionally, ice growth primarily occurred in the Kara, Beaufort, and Chukchi Seas, as well as Baffin Bay and the Canadian Archipelago. However, the ice edge remains farther north than average in the Barents and Kara Seas. In Hudson Bay, no appreciable sea ice has formed, though lower temperatures towards the month’s end allowed some coastal ice formation around Churchill and in northern Foxe Basin. Ice extent also remained below average in Baffin Bay, Davis Strait, and in the Bering Sea.
Figure 1a. Arctic sea ice extent for November 2024 was 9.11 million square kilometers (3.52 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
Figure 1b. The graph above shows Arctic sea ice extent as of December 3, 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. Sea Ice Index data. — Credit: National Snow and Ice Data Center
Conditions in Context
Air temperatures over the Arctic Ocean in November were mixed (Figure 2a). At the 925 millibar level (approximately 2,500 feet above the surface), temperatures were up to 10 degrees Celsius (18 degrees Fahrenheit) above the 1991 to 2020 average north of Greenland, while areas from coastal Canada to northern Scandinavia experienced temperatures 3 to 6 degrees Celsius (5 to 11 degrees Fahrenheit) above average. In contrast, the Beaufort, Bering, and Laptev Seas experienced relatively cool conditions, 1 to 3 degrees Celsius (2 to 5 degrees Fahrenheit) below average. Over Hudson Bay, where the winter ice has yet to form, air temperatures were 1 to 5 degrees Celsius (2 to 9 degrees Fahrenheit) above average .
The generally warm conditions reflect unusually high sea level pressure over the central Arctic Ocean coupled with below average sea level pressure over Eurasia and North America (Figure 2b). While a prominent feature of the general atmospheric circulation pattern is an anticyclone (high pressure cell) in the Beaufort Sea, this pressure cell has shifted somewhat towards the pole. The strong pressure gradient between the high pressure and the low pressure over Eurasia funneled warmer continental air from Siberia towards the Kara and Barents Seas, where it has then circulated clockwise north of Greenland.
Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for November 2024. 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
November 2024 compared to previous years
Including 2024, the downward linear trend in Arctic sea ice extent for November is 51,000 square kilometers (20,000 square miles) per year, or 4.8 percent per decade relative to the 1981 to 2010 average. Based on the linear trend, since 1979, November has lost 2.28 million square kilometers (880,000 square miles) of sea ice, which is equivalent to 8.4 times the size of the state of Colorado.
A long open water season for southeastern Hudson Bay?
This past summer saw an unusually early ice retreat in eastern and southern Hudson Bay. When the ice retreats early, there is more time for the ocean to absorb solar energy that otherwise would be reflected by the brighter, white sea ice. Since the sea ice had already broken up in southeastern Hudson Bay by May, ocean temperatures started to rise early, with much of southeastern Hudson Bay experiencing marine heat waves, especially in June, July, and October. A marine heat wave occurs when the sea surface temperature exceeds the ninetieth percentile for that time of year for at least five consecutive days. Between June and October, this part of Hudson Bay had experienced more than 60 percent of days with a marine heat wave—a new record. Marine heat waves can have major ecological implications, contributing to declines in species like eelgrass (Zostera marina), which play important roles in the region’s coastal and estuarine ecosystems.
Since the ocean heat gained during summer must be released to the atmosphere ice before sea ice can form, the excess ocean heat is likely to delay the freeze up. This lengthens the ice-free period, with adverse consequences to the local polar bear populations as they will have to fast for a longer period. Polar bears prefer to feed by waiting on sea ice for seals to appear at breathing holes. They eat very little—basically fasting—while remaining on land in the ice-free season. A longer ice-free season means they must fast for longer. This is a concern for the southern Hudson Bay polar bear populations. Using the date of ice retreat together with the current ocean heat content, it is estimated that new ice formation may not occur until mid-December this year, which would extend the ice-free period, and hence the fasting period, to more than 190 days.
Another potentially endangered species
Mandt’s black guillemots (Cepphus grylle mandtii), a subspecies of the black guillemot, are medium-sized seabirds that make the Arctic Ocean their home. They live wedged between Alaska and Russia along the sea ice edge and specialize in one fish: Arctic cod. One well-studied colony resides on Cooper Island near Utqiaġvik (formerly Barrow), Alaska. During winter, the guillemots spend time on the sea ice in the marginal ice zone to forage for Arctic cod. However, as sea ice has started to retreat earlier and form later and ocean temperatures have increased, Arctic cod populations have declined or shifted further north. Consequently, guillemots are forced to travel greater distances from their breeding grounds to find food.
George Divoky, a researcher at the Cooper Island Arctic Research Center, has been monitoring and counting birds in this colony for nearly 50 years. His observations reveal a strong decline in the population. Reduced foraging opportunities have led to lower chick survival rates, and the number of breeding pairs has dropped dramatically. Based on data collected since 1975, his work predicts the likely quasi-extinction of this colony within the next two decades.
Figure 5a. This map shows the location of the Cooper Island Mandt’s black guillemot colony, along with their presumed source colonies on Herald and Wrangel Islands as well as two other colonies that are monitored at Cape Lisburne and Herschel Island. The gray area shows the summering (July to August) location of nonbreeding birds and the fall (September to November) location of breeders. The delimited light blue area shows the Bering Sea wintering (December to April) area. — Credit: Divoky Et al., 2024
Figure 5b. A pair of black guillemots sit together on Cooper Island. — Credit: US Environmental Protection Agency
Antarctica still tracking low
Antarctic sea ice extent averaged 14.19 million square kilometers (5.48 million square miles) for November, with 1.71 million square kilometers (660,000 square miles) below the 1981 to 2010 average (Figure 6a). While the Antarctic sea ice extent at the start of November was tracking as the second lowest, it has since fallen to third lowest as extent is now tracking above 2016. (Figure 6b). In 2016, the fastest austral spring retreat was recorded at a rate of 92,000 square kilometers (36,000 square miles) per day as averaged from October 1 to November 30. As of November 30, the 2024 extent is 457,000 square kilometers (176,000 square miles) above the record low set in 2016 and 172,000 square kilometers (66,000 square miles) above 2023 on the same date, and the decline rate has been only 72,000 square kilometers (28,000 square miles) per day. However, the 2024 summer maximum was much lower than in 2016. Compared to the record low in 2016, the pattern of areas with below average ice conditions are broadly similar, with low ice extent found largely in the Indian Ocean, Davis Sea, and the Ross Seas, although the ice edge is also a bit more poleward in the Weddell Sea this November.
Figure 6a. Antarctic sea ice extent for November 2024 was 14.19 million square kilometers (5.48 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
Figure 6b. The graph above shows Antarctic sea ice extent as of December 3, 2024, along with daily ice extent data for four previous years and the record high year. 2024 to 2025 is shown in blue, 2023 to 2024 in green, 2022 to 2023 in orange, 2021 to 2022 in brown, 2020 to 2021 in magenta, and 2014 to 2015 in dashed brown. The 1981 to 2010 median is depicted 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
Further reading
Divoky, George J., P. L. Jan, and C. Barbraud. 2024. An Ice-Obligate Seabird Responds to a Multi-Decadal Decline in Arctic Sea Ice. Ecosphere 15(8): e4970. doi:10.1002/ecs2.4970.
Johnson, M. R., S. L. Williams, C. H. Lieberman, et al. 2003. Changes in the abundance of the seagrasses Zostera marina L. (eelgrass) and Ruppia maritima L. (widgeongrass) in San Diego, California, following an El Niño event. Estuaries 26, 106–115. doi:10.1007/BF02691698.
Leblanc, M.-L., et al. 2023. Limited recovery following a massive seagrass decline in subarctic eastern Canada. Global Change Biology, 29, 432–450. doi:10.1111/gcb.16499.
Stroeve, J. C., A. D. Crawford, and S. Stammerjohn. 2016. Using timing of ice retreat to predict timing of fall freeze-up in the Arctic. Geophysical Research Letters, 43, 6332–6340. doi:10.1002/2016GL069314.
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, 6868–6875. doi:10.1002/2017GL073656.