Global Outlook for Ice and Snow: Chapter 5 - Ice in the sea

Sea ice plays a key role for climate and is important as habitat
and for human activities and economies. Observations
show and models indicate that climate and sea-ice regimes
are changing. Sea-ice extent in the Arctic decreased substantially
during the last 30 years; Antarctic sea ice is decreasing
in some areas, but overall it has shown a slight
increase during this period. Climate models project further
decreases in sea-ice extent in the Arctic during this century
and comparable decreases in Antarctic sea-ice extent. There
are uncertainties attached to the rate at which these changes
will occur, and there is a risk of tipping points being crossed
and abrupt reductions in sea ice occurring. To reduce these
uncertainties, more large-scale continuous observations
are needed, especially of ice and snow thickness.