Arctic and Antarctic Sea Ice Today

Sea ice is frozen ocean water. It grows and retreats with the seasons in both polar regions, shaping exchanges of heat between the ocean and atmosphere and providing habitat for specialized ecosystems. The live display above places the latest available Arctic and Antarctic measurements alongside their recent seasonal paths and longer-term references.

A single day’s value should be read as one point in a noisy, evolving record. Winds can spread the ice apart or compact it, storms can alter its edge, and satellite processing can be affected by meltwater, surface conditions and missing observations. Climate interpretation depends on sustained changes across seasons and decades rather than one daily rise or fall.

Sea-ice extent and area

Sea-ice extent is the total area of ocean in which at least a defined proportion—commonly 15 percent—of each satellite grid cell is covered by ice. A grid cell that meets the threshold counts in full toward extent, even if some open water remains inside it.

Sea-ice area attempts to count only the estimated ice-covered fraction of each grid cell. Area is therefore normally smaller than extent and can respond differently when ice becomes dispersed or compacted. Both are useful, but numbers from the two measures should not be compared as though they were equivalent.

The dashboard identifies the measure being displayed. NSIDC’s widely used Sea Ice Index emphasizes extent because it is generally more robust for a consistent long-term satellite record.

The Arctic seasonal cycle

Arctic sea ice normally reaches its greatest extent near the end of Northern Hemisphere winter, commonly in March. It then melts through spring and summer and usually reaches its annual minimum in September. The precise dates and values vary from year to year.

The annual minimum is an important indicator, but it does not describe every property of the ice cover. Thickness, age, volume, concentration and regional distribution also matter. A broad region of thin first-year ice can have a similar extent to more resilient multiyear ice while responding differently to weather and ocean heat.

The Antarctic seasonal cycle

Antarctic sea ice follows the opposite calendar because it surrounds the South Pole. It normally reaches a minimum around February and a maximum around September. Its geography is also different: Antarctic ice grows outward from a continent into the Southern Ocean, while much of Arctic sea ice is contained within an ocean bordered by continents.

Those differences affect circulation, winds and seasonal behavior. Arctic and Antarctic trends should be examined separately. Adding the two extents into a single “global sea ice” number can conceal important and physically distinct changes in each hemisphere.

What daily movement means

The ice edge can shift because of both thermodynamic processes—freezing and melting—and dynamic processes such as wind and ocean currents. Strong winds may compact ice into a smaller extent without immediately melting the same amount of ice. They may also push floes apart, temporarily increasing the region that crosses the concentration threshold.

For that reason, researchers often use a five-day running average to make the seasonal pattern easier to see. Daily observations remain valuable, particularly near a seasonal minimum or maximum, but small changes should not be overinterpreted.

Comparing the latest value with history

A useful comparison includes the same calendar date in previous years and a multi-decadal median or average calculated from a stated reference period. The reference period matters. As the climate changes, a median based on older decades can differ from one based on recent years.

Satellite observations provide a consistent near-complete record beginning in late 1978. Earlier observations exist from ships, aircraft and other sources, but they are less spatially complete and are not directly interchangeable with the modern passive-microwave record.

Sea ice, land ice and sea level

Sea ice already floats in the ocean, so its melting does not directly raise global mean sea level in the same way as melting land ice. Glaciers and the Greenland and Antarctic ice sheets are land ice; when they lose mass to the ocean, sea level rises.

Sea-ice loss still has important consequences. Bright ice reflects much of the incoming sunlight, while darker open water absorbs more energy. Changes in sea ice affect ecosystems, coastal exposure, travel conditions and interactions between the ocean and atmosphere. Sea ice can also influence—but should not be confused with—the behavior of nearby ice shelves and glaciers.

Methodology and sources

The live module uses the National Snow and Ice Data Center Sea Ice Index and its daily data and image archive. The product derives sea-ice concentration from passive-microwave satellite observations and provides consistent Arctic and Antarctic extent and concentration records.

ARGO.net displays the latest published values, historical comparison series and simple differences where appropriate. We do not independently retrieve raw satellite radiances or produce a separate operational sea-ice analysis. NSIDC documentation and source files remain authoritative.

Daily data may be revised during quality control. NSIDC notes that short-term weather effects and measurement limitations can produce variability, so its contextual reporting commonly uses a five-day running average. The dashboard’s data-refresh timestamp is separate from the date on which ARGO editors last reviewed this explanation.

Limitations

• Recent daily observations may be preliminary or later revised.
• Extent is threshold-based and is not the same as ice area, thickness or volume.
• Coastal effects, melt ponds and unusual surface conditions can complicate satellite retrievals.
• Small daily changes may reflect winds or processing noise rather than net melting or freezing.
• A value for one hemisphere—or one date—does not by itself establish a global climate trend.

Update log

• July 2026: ARGO Sea Ice Today launched with Arctic and Antarctic observations, seasonal context and an explanation of extent, area and measurement limitations.