Air temperatures in December 2024 were above average over the entire Arctic Ocean, continuing the pattern set in November. Average Arctic sea ice extent for December was the lowest in the satellite record because of delayed ice growth in Hudson Bay and low extent in the northern Barents Sea. Antarctic sea ice has declined at a below average pace since mid-November, erasing the record and near-record low extents of October and November and finishing the year very close to the 1981 to 2010 average.
Overview of conditions
Arctic sea ice extent for December averaged 11.42 million square kilometers (4.41 million square miles), the lowest extent in the satellite record for the month (Figure 1a). This comes on the heels of the third lowest extent for the month in November 2024 (Figure 1b). The December extent was 40,000 square kilometers (15,000 square miles) below the previous record low for the month set in 2016, and 1.42 million square kilometers (548,000 square miles) below the 1981 to 2010 average.
By the end of December, ice extent remains well below average in Hudson Bay, as well as off the Labrador coast, continuing the pattern seen in November. Extent also remains low in the northern Barents Sea, most likely caused by the import of warm Atlantic waters into the region and favorable atmospheric circulation patterns.
Figure 1a. Arctic sea ice extent for December 2024 was 11.42 million square kilometers (4.41 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 January 6, 2025, along with daily ice extent data for four previous years and the record low 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 2012 to 2013 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
December air temperatures at the 925 millibar level (approximately 2,500 feet above the surface) were above average over essentially all of the Arctic Ocean, and with a spatial pattern very similar to that observed for November (Figures 2a and 2b). Especially notable is a continuation of the prominent area of warmth north off the Canadian Arctic Archipelago and Greenland, where similar to November, temperatures were up to 8 degrees Celsius (14 degrees Fahrenheit) above average. Less prominent but also worth noting is the area of unusual warmth centered over eastern Hudson Bay, where sea ice has yet to form. This feature manifests large heat and moisture fluxes from the open water to the atmosphere.
At least in a qualitative sense, such persistence seems unusual. Given that regional temperature patterns are strongly driven by regional patterns of atmospheric circulation, patterns of sea level pressure for the two months were also very similar. Both months were characterized by strong centers of low pressure over the Atlantic and Pacific sides of the Arctic, with a ridge of relatively high pressure extending across the Chukchi and Beaufort Seas (Figures 2c and 2d). However, it is not clear how these patterns relate to the persistent band of unusual warmth north of the Canadian Arctic Archipelago and Greenland.
Figure 2a. This plot shows the departure from average air temperature in the Arctic at the 925 hPa level, in degrees Celsius, for December 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
Figure 2b. 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
Figure 2c. This plot shows average sea level pressure in the Arctic in millibars for December 2024. Yellows and reds indicate high air pressure; blues and purples indicate low pressure. — Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
Figure 2d. This plot shows average sea level pressure in the Arctic in millibars for November 2024. Yellows and reds indicate high air pressure; blues and purples indicate low pressure. — Credit: NSIDC courtesy NOAA Earth System Research Laboratory Physical Sciences Laboratory
December 2024 compared to previous years
Including 2024, the downward linear trend in Arctic sea ice extent for December is 44,000 square kilometers (17,000 square miles) per year, or 3.4 percent per decade relative to the 1981 to 2010 average. Based on the linear trend, since 1979, December has lost 1.98 million square kilometers (764,000 square miles) of sea ice, which is equivalent to three times the size of Texas.
Recovery in the Antarctic
Antarctic sea ice loss has slowed after a prolonged period of record to near-record daily lows set in 2023 and 2024. During November and December, which is mid to late spring in the Southern Hemisphere, the average rate of decline fell well below average. In 2024, the daily loss was 140,000 square kilometers (54,000 square miles) compared to 165,000 square kilometers (64,000 square miles) for the 1981 to 2010 average, erasing a 1.6 million square kilometer (618,000 square mile) deficit seen at the beginning of November (Figure 4a). By the end of December, extent was roughly at the 1981 to 2010 average extent (Figure 4b). This provides a sharp illustration of the high variability of Antarctic sea ice extent.
After significant below-average extents became persistent in August 2016, scientists began speculating that Antarctic sea ice had entered a new regime of strongly reduced extent related to oceanic influences. Following the 2017 and 2023 record low minimum extents, a dramatic record-low maximum extent in 2023, and near-record low maximum in 2024, the regime-shift idea took hold. The recent slowdown in extent loss during December gives some pause to this idea. However, though sea ice extents have been substantially below average since 2016, period of near- or even above-average extents occurred in 2021 and 2022. Thus, while the 2016 to 2024 timeline is too short to definitively determine that a regime shift has occurred, one month where extent approached average extent is too short to contradict the idea of a regime shift.
Regionally, sea ice extent was above average over the western Weddell and Amundsen Seas, and slightly below average in the Ross Sea, with near-average extents in other areas. Notably, a polynya, or persistent area of open water, formed in the north-central Weddell Sea in mid-December, near 65 degrees South, 45 degrees West. Overall, sea ice concentrations are generally low over large areas of the pack. This, combined with indications of a warm spring with high surface melting on the continent itself, will make for an interesting upcoming summer.
Figure 4a. The graph above shows Antarctic sea ice extent as of January 6, 2025, 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 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
Figure 4b. Antarctic sea ice extent for December 31, 2024, was 7.32 million square kilometers (2.83 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
The year in review
The most anticipated event in the seasonal cycle of Arctic sea ice is the September seasonal minimum extent. The daily minimum extent for 2024 of 4.28 million square kilometers (1.65 million square miles) was set on September 11, and was the seventh lowest in the satellite record. The last 18 years, from 2007 to 2024, are the lowest 18 sea ice extents in the satellite record.
It is often asked “Why was there no new record low?” The answer largely lies with the summer weather patterns. The annual sea ice maximum for 2024, set on March 14, was the fourteenth lowest in the satellite record at 15.01 million square kilometers (5.80 million square miles). Seasonal ice loss through spring and early summer was modest. Through July and the first half of August, ice loss was fairly rapid compared to recent years, but by the end of August, it was clear that no new record would be set. It never got warm enough in the summer to raise concerns of a record September minimum extent. From past experience, especially rapid summer ice loss is favored by high pressure over the Arctic Ocean, which fosters warm conditions due both to the clear skies and wind patterns that bring warm air into the Arctic Ocean. The atmospheric circulation for summer 2024 is best described as highly variable, with patterns temporarily favoring rapid ice loss interspersed with less favorable patterns.
However, 2024 was not without its highlights. A unique feature of 2024 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. At the end of the melt season, both the Northern (deep water) and Southern (Amundsen’s) Northwest Passage routes were essentially unblocked by ice, which can be tied to the warm conditions that prevailed over the channels of the Canadian Arctic Archipelago. In turn, there was an unusually early melt out in Hudson Bay that proceeded from east to west because of warm conditions and favorable winds. As noted above, part of Hudson Bay has yet to freeze over.
Turning briefly to Antarctica, as discussed above, speculation that the Antarctic had entered a new regime of strongly reduced Antarctic sea ice related to oceanic influences, has, at least temporarily, come to an end.