海氷
Sea ice in the arctic is currently in decline in area, extent, and volume, and has been accelerating during the early twenty‐first century, with a decline rate of −4.7% per decade (it has declined over 50% since the first satellite records). It is also thought that summertime sea ice may cease to exist sometime during the 21st century. This sea ice loss constitutes one of the main drivers for surface-based Arctic amplification. Sea ice area refers to the total area covered by ice, whereas sea ice extent is the area of ocean with at least 15% sea ice, while the volume is the total amount of ice in the Arctic.