Arctic sea ice extent through most of April changed very little. Only at the end of the month did extent begin to decline. Because the month started with unusually low extent, however, the average extent for April ended up tied for ninth lowest in the satellite record. The situation in the Antarctic remained fickle. Extent at the end of the month was tracking near the levels recorded for 2024, but well above the record low in 2023.
Overview of conditions
April Arctic sea ice extent averaged 13.91 million square kilometers (5.37 million square miles) (Figure 1a), statistically tied with April 2006 for ninth lowest in the 47-year satellite record. It was 480,000 square kilometers (185,000 square miles) above the record low April extent set in 2019. Extent remained nearly constant at roughly 14 million square kilometers (5.41 million square miles) until the last few days of the month when it started to drop (Figure 1b). The fairly quick drop at the end of the month was the result of ice retreat along the coast of the Barents Sea and around Novaya Zemlya. During this time, the North Water Polynya in northern Baffin Bay also opened. While it is certainly unusual to have an overall static ice cover after the maximum extent is reached, similar periods with little change were observed in earlier years. The primary reason why April 2025 total extent remained largely flat was an increase in extent in the northeastern Barents Seas, which offset loss elsewhere. Total extent at month’s end was still 780,000 square kilometers (301,000 square miles) below the 1981 to 2010 average. Sea ice was also regionally low in the Barents Sea (despite the growth), Sea of Okhotsk, Bering Sea, and Labrador Sea.
Figure 1a. Arctic sea ice extent for April 2025 was 13.9 million square kilometers (5.4 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 May 5, 2025, along with daily ice extent data for four previous years and 2012, the year with the record-low summer minimum extent. 2025 is shown in blue, 2024 in green, 2023 in orange, 2022 in brown, 2021 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
Note: NSIDC has been using the National Centers for Environmental Prediction-National Center for Environmental Research (NCEP-NCAR) Reanalysis 1 for assessments of atmospheric circulation and temperature. However, this reanalysis code is old, and concerns have arisen over potentially erroneous features in the temperature fields in both the Arctic and Antarctic. NSIDC is therefore likely to shift to use data from either the NOAA Climate Forecast System Reanalysis (CFSR) or the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5). The final decision will depend on latency of the reanalyses and ease of data access. For this post, NSIDC is still using the NCEP-NCAR Reanalysis.
The notable feature of April 2025 was below average air temperatures over the northern Norwegian and Barents Seas; elsewhere over the Arctic Ocean temperatures were from 1 to 4 degrees Celsius (2 to 7 degrees Fahrenheit) above average (Figure 2a). The low temperatures in the Norwegian and Barents Seas clearly relate to the monthly averaged sea level pressure field, featuring unusually high pressure over the Northern Canada Basin and extending over Greenland and unusually low pressure centered over northern Eurasia and southern Alaska (Figure 2b). This combination points to strong and cold winds from the North over the northern Norwegian and Barents Seas. The especially strong pressure gradient across the Fram Strait, between northern Greenland and the Svalbard Archipelago, also points to a strong transport of sea ice out of the Arctic Ocean and into the East Greenland Sea.
April 2025 compared to previous years
The downward linear trend in Arctic sea ice extent through 2025 for April is 35,100 square kilometers (13,600 square miles) per year or 2.4 percent per decade relative to the 1981 to 2010 average (Figure 3). Based on the linear trend, since 1979, April has lost 1.64 million square kilometers (633,000 square miles) of sea ice, which roughly equivalent in size to the state of Alaska.
The fickle south
The situation in the Antarctic remained fickle. After approaching the record-low daily extents seen in 2023 at the beginning of April, sea ice extent rose fairly quickly, and by the end of the month stood just below the lowest decile (lowest 10 percent) of daily extents as assessed over the satellite record, and very close to the 2024 extent (Figure 4a). Growth was especially rapid in the Ross and western Amundsen sectors, but very low extents persisted in the Bellingshausen Sea and north of far eastern Dronning Maud Land (Figure 4b).
Figure 4a. The graph above shows Antarctic sea ice extent as of May 5, 2025, along with daily ice extent data for four previous years and 2014, the year of the record-high winter maximum extent. 2025 is shown in blue, 2024 in green, 2023 in orange, 2022 in brown, 2021 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
Figure 4b. Antarctic sea ice extent for April 2025 was 6.1 million square kilometers (2.4 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
Arctic sea ice extent during past interglacials
Brian Crow and Matthias Pange of the University of Bremen recently published a paper examining likely Arctic sea ice conditions over the past two interglacials. It is well accepted that past interglacials can be linked to Milankovitch forcings—periodic variations in Earth orbital parameters (obliquity, precession, and orbital eccentricity) that lead to summer warmth over northern high latitudes. Based on simulations using the Community Earth System Model (CESM), the authors conclude that while past studies have tried to explain the evolution of Arctic sea ice during these interglacial in terms of the amount of sunlight over high-latitude lands at the summer solstice, the energy integrated over the summer seems to be more important. During the peak of the last interglacial (about 127,000 years ago), there were likely ice-free summers, but the ice recovered after a few thousand years. Over the previous interglacial (from 423,000 to 408,000 years ago), the Milankovitch forcings were different. As a result, while summer ice extent during that period did not drop as low, extent over that span of 15,000 years may have been lower than those in the modern preindustrial period.
Further reading
Crow, B. R. and M. Prange. 2025. Long- and short-term variability of Arctic sea-ice cover during the Last Interglacial and Marine Isotope Stage 11c. Communications Earth Environment, 6:274. doi:10.1038/s43247-025-02267-4.