This map shows how sea ice in the Arctic has changed from 1980 to 2023. Each year is marked with a different color, starting with dark blue for 1980 and ending with white for 2023. The data come from the National Snow and Ice Data Center (NSIDC), which used to collect information every day until it was decommissioned under Trump administration cuts in 2025. The areas shown on the map are the maximum extent, or largest ice-covered areas, for that year. The Arctic Sea Ice Extent (max by year) project has been helping people understand frozen parts of Earth since 1976.

Sea ice forms when ocean water gets cold enough, about -1.8°C (28.8°F) depending on its salinity. This usually happens in the fall and winter in both the Arctic and Antarctic. Sea ice starts as ice crystals that form on particles, like microbes or fine sediment material, in the upper waters and then “clump” together and float to the surface to form a slushy layer called “grease ice”. This layer continues to grow in thickness and extent through winter, reaching its largest area in March for the Arctic and September for the Antarctic. Sea ice is important because it reflects the sun’s rays and prevents the sun’s heat from being absorbed by the ocean. It also provides a crucial habitat for an entire ice-dependent ecosystem—from algae and zooplankton to seals and polar bears—and is relied upon as a seasonal highway and hunting ground for communities living along the Arctic coastline.

Sea ice formation also plays an important role in driving ocean currents that are responsible for moving heat from the equator to the poles. As polar waters cool, they get denser and sink below the surface, this draws warmer, less dense water from the equator towards the poles to replace it in what’s referred to as a giant ocean conveyor belt.

The changes in sea ice thickness and extent show that the planet is getting warmer. Arctic sea ice extent has been shrinking by more than 12% every decade since 1979, and in 2025 and 2026, the sea ice reached record-low levels in winter.

Explorer Kristina Brown - Bridging Earth and Ocean Sciences

Marine biogeochemist and National Geographic Explorer Kristina Brown is partnering with the people of Gjoa Haven to study the ecosystem of nearby Sherman Basin in Nunavut, Canada. The Sherman Basin’s unique geography and climate makes it an important habitat for mammals like caribou, muskox, and bearded seals. Fish like Arctic char and whitefish are also abundant.

Inuit Elders and Youth are helping Dr. Brown understand why these types of wildlife, which have been an important source of food for thousands of years, thrive in this area. Dr. Brown uses scientific sampling tools to see how changing oceanographic conditions may impact the Basin. She is also working with Youth from the Gjoa Haven community so that they can conduct ocean research and share the information they gather with scientists and community Elders.

Dr. Brown’s project is part of the National Geographic and Rolex Perpetual Planet Arctic Ocean expedition. This is a multi-year project to study how climate change is impacting the Arctic.

Thinking Geographically

Using a digital map with decades of data allows us to quickly experience changes over time. We can see the max ice line move every five years by turning the map layers on and off.

Click the Map layers tool to see all the layers available. Turn off (uncheck) the 2023 data. You can now see the 1980 line. Progressively turn on the layers to move forward in time. Observe the changes. What ocean areas seem to change the most?

Change the basemap to “environment.” Change the map from 2D to 3D and rotate the globe so that you are looking straight at the North Pole.

Click the map layers tool to see all the layers available. Turn off (uncheck) the 2023 data. You can now see the 1980 line. Turn on the layers to move forward in time. Observe the changes again. What is different about this view to better understand changes?