This story is an update to the Arctic sea ice feature in our World of Change series, which tracks long-term change on Earth’s surface through satellite imagery.

A layer of frozen seawater caps the Arctic Ocean. This sea ice grows through the long polar winter, usually peaking in March, then melts through the summer to its annual low in September. It is a natural fluctuation that has persisted for millennia. But satellite records show the ice now covers less of the Arctic Ocean at its annual maximum and minimum than it did a few decades ago.

Sea ice in 2026 reached its annual minimum extent on September 12 (above), when it covered an estimated 4.6 million square kilometers (1.78 million square miles), according to NASA and the National Snow and Ice Data Center (NSIDC). That ties 2008, 2010, and 2025 for the 10th-lowest minimum in the satellite record.

The maps below pair each September since 1990 (left), around the ice’s annual minimum, with the following March (right), near its annual maximum, through March 2026.

Lower Lows, Thinner Ice

Scientists have used satellites to observe the annual growth and retreat of Arctic sea ice continuously since late 1978. While sea ice extent has declined overall during that time, the downward trend steepened in the 2000s and set off a run of record and near-record lows. Each of the past 20 summers, from 2007 through 2026, ranks among the 20 lowest minimum extents in the satellite record. The lowest occurred in September 2012.

More recently, the September sea ice extent has been relatively steady. Weather can make a big difference in how much ice melts from one summer to the next. For example, over the past decade, increased cloud cover has prevented sunlight from accelerating the melt, according to NASA scientists. Despite this recent plateau, the summer minimum remains well below the long-term average.

Across the Arctic, the ice that remains is younger and thinner. Observations show a decline in multiyear ice—that which survives at least one melt season—leaving an Arctic dominated by thinner first-year ice. Winter ice is also shrinking. The March 2026 maximum statistically tied the 2025 maximum for the lowest in the satellite record.

Cycles of natural variability such as the Arctic Oscillation are known to play a role in Arctic sea ice extent, but the decline observed throughout the satellite record cannot be explained by natural variability alone. Natural variability and rising global temperatures have worked together to melt greater amounts of Arctic sea ice. Scientists have projected an essentially ice-free Arctic could occur at least once before the middle of the 21st century.

Seeing Through the Clouds

To determine sea ice extent, scientists rely on satellites with passive microwave sensors that measure the microwave energy Earth naturally emits. Sea ice emits more of this energy than open water, so it stands out in microwave images. Because microwaves pass through clouds, the satellites can observe sea ice regularly, regardless of weather.

The record began in 1978 with data collected by NASA’s Nimbus-7, followed by Defense Meteorological Satellite Program (DMSP) satellites starting in 1987 and NASA’s Aqua satellite between 2002 and 2011. Starting in 2025, scientists began using observations from the Japan Aerospace Exploration Agency’s GCOM-W satellite. The white circle at the center of each image is the “pole hole,” north of which satellite sensors have historically been unable to collect data. The sea ice estimates assume that this hole is ice-filled.

NASA Earth Observatory images by Michala Garrison, using data from the National Snow and Ice Data Center.

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September 12, 2026

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References & Resources

• IPCC (2021) Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Accessed October 6, 2026.
• NASA Earthdata (2026, October) Sea Ice. Accessed October 6, 2026.
• NASA Earth Observatory (2026, October 6) World of Change: Arctic Sea Ice. Accessed October 6, 2026.
• NASA Earth Observatory (2016, September 16) Sea Ice. Accessed October 6, 2026.
• NASA Earth Science (2026, September 23) Arctic Sea Ice Reaches 2026 Annual Minimum Extent. Accessed October 6, 2026.
• National Snow and Ice Data Center (2026, September 23) Arctic sea ice minimum ties for tenth lowest. Accessed October 6, 2026.
• National Snow and Ice Data Center (2026, March 26) Arctic sea ice record low maximum strikes again. Accessed October 6, 2026.

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Greenland is capped with a vast ice sheet that spans 1.7 million square kilometers (656,000 square miles) and measures more than 3 kilometers (1.9 miles) at its thickest point. Below all this ice lies a landscape human eyes have never seen directly. But a newly developed method for mapping this hidden bedrock has produced the most detailed and accurate view of it yet.

The new map reveals an expansive network of valleys carved into the surface beneath the Greenland Ice Sheet. Many of the features formed well before most of the ice above them existed, offering new context for the island’s geologic history—and potentially helping scientists refine projections of the ice sheet’s future. Scientists described the newly mapped valleys in a NASA-led paper published in Geophysical Research Letters.

The map, shown above, was derived from a method called Ice Flow Perturbation Analysis. As ice flows over a valley or ridge, the topography leaves a faint signature on the ice surface. Satellites map the ice surface in fine detail, and scientists can use these subtle bumps and dips to infer the shape of the landscape buried below. The work aims to improve future versions of BedMachine Greenland, a high-resolution dataset of the terrain beneath the ice sheet.

Using the technique, researchers manually mapped 1,943 subglacial valleys beneath the Greenland Ice Sheet, about a third of which are newly identified. About half of the valleys included in BedMachine Greenland, primarily near the ice sheet’s edge, are now known to extend farther inland than that map indicates, in some cases by hundreds of kilometers.

Some aspects of the new map align with the current understanding of how Greenland’s landscapes formed. For instance, many of the valleys appear to begin in the southern and eastern highlands, where the ice sheet is thought to have first formed. Near the eastern highlands, the map reveals a mountain range beneath the ice, with interconnected valleys and relief that increases toward the coast. These alpine-style landforms may have survived under the ice since at least the Pliocene.

Other aspects of the topography are more puzzling. The analysis indicates numerous valleys, especially in the west-central region, that are long, straight, and consistently aligned in a southwest-northeast direction. This orientation suggests a tectonic influence, generating preferential pathways along which water could flow and valleys could form. “That’s a riddle to us,” said Joe MacGregor, a NASA cryospheric scientist and co-author of the study. “Greenland is justifiably usually treated as a rigid block of old rock that is simply translated as needed to accommodate the motion and interactions of other tectonic plates.”

Separately, the angles at which the valleys branch offer another insight into their origin. Their relatively wide branching angles suggest that surface water didn’t act alone; instead, a widespread groundwater network—seeping upward and eroding the surrounding rock—likely helped carve the valleys before the ice sheet formed.

Mapping these valleys matters for understanding the ice sheet, which has continued to dramatically reshape the landscape. Ice flow concentrates in valleys, where it forms glaciers that eventually calve into fjords at the periphery of the ice sheet. This creates a reinforcing cycle: ice funneling through a valley gets thicker, thicker ice flows faster, and faster flow carves the valley even deeper.

This carving power is especially evident along western Greenland. MacGregor likened it to the glacially incised landscape at Yosemite, with Greenland’s western coast resembling, as he put it, “El Capitan after El Capitan.”

Studying the valleys also matters for the ice sheet’s future. Because the relationship between ice flow and valleys is well understood, scientists expect that as the ice sheet retreats, flow will continue to concentrate wherever the valleys already are. “The better we understand the topography now,” MacGregor said, “the better sense we’ll have of what it will look like in the longer term—beyond the next decade or two—as faster ice flow propagates into Greenland’s interior.”

NASA Earth Observatory map by Lauren Dauphin using data from Chartrand et al. Story by Kathryn Hansen.

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Bedrock Map

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References & Resources

• Chartrand, A. M., et al. (2026) A Vast Valley Network Beneath the Greenland Ice Sheet. Geophysical Research Letters, 53 (13), e2026GL122028.

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