- Sea ice extent
- Area of ocean with at least a set fraction of ice cover. The standard yardstick for the pack. Peaks in late winter, bottoms out in late summer.
- Albedo
- Fraction of sunlight a surface reflects. Snow and ice: high. Open water and bare tundra: low. Loss of ice lowers albedo and the ocean warms faster.
- Multiyear ice
- Sea ice that has survived at least one summer melt. Thicker, fresher, stronger than first-year ice. The part of the pack in fastest decline.
- Permafrost
- Ground that stays at or below freezing for at least two consecutive years. Can be rock, sediment, or ice-rich soil. Covered by a thin layer that thaws each summer.
- Active layer
- The top of the ground that thaws in summer and refreezes in winter. Deepening as summers lengthen.
- Thermokarst
- Land surface collapsing as ground ice melts. Pits, slumps, lakes, drained lakes. Fast, uneven thaw.
- Marine-terminating glacier
- A glacier whose front stands in the sea. Loses ice by calving and by melting where it meets warm water. Greenland's fast outlets are all of this type.
- Polar Code
- The International Maritime Organization's code for ships in polar waters. Covers hull, equipment, training, and environmental measures.
- Arctic Council
- Intergovernmental forum of the eight Arctic states, with Indigenous peoples' organisations as Permanent Participants. Discusses environment and sustainable development, not military matters.
- Northern Sea Route
- The passage along Russia's Arctic coast from the Kara Gate to the Bering Strait. Administered under Russian rules, escorted in ice.