Ice in the Sea
Source: NASA
Summary
Sea ice plays a key role for climate and is important as habi-
tat 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 sub-
stantially during the last 30 years; Antarctic sea ice is de-
creasing in some areas, but overall it has shown a slight
Annual maximum
increase during this period. Climate models project further
sea-ice extent in
both hemispheres
decreases in sea-ice extent in the Arctic during this century
Sea ice: ice found at sea which has originated from the freez-
and comparable decreases in Antarctic sea-ice extent. There
ing of sea water. Sea ice may be discontinuous pieces (ice
are uncertainties attached to the rate at which these changes
floes) moved on the ocean surface by wind and currents,
will occur, and there is a risk of tipping points being crossed
driven together into a single mass (pack ice), or a continu-
and abrupt reductions in sea ice occurring. To reduce these ous sheet attached to the coast (land-fast ice).
uncertainties, more large-scale continuous observations
are needed, especially of ice and snow thickness.
Sea ice, Arctic and Antarctic (annual minimum ~ maximum):
Area Covered (million square km) 19 ~ 27
Ice Volume (million cubic km) 0.019 ~ 0.025
Changes to sea ice will have major impacts on both the
Potential Sea-level Rise (cm) 0
physical and biological environment at all scales from
Source: IPCC 2007
1a
global to regional. The reduction in albedo (reflection of
solar radiation) resulting from less ice cover is a feed-
back mechanism that accelerates the rate that sea ice de- Introduction to sea ice
clines and also the rate at which Earth warms. Changes
in sea ice contribute to altering the ocean thermohaline Seen from space, the Earth is dominated by the colours
circulation, especially in the North Atlantic. blue, white, and grey-brown. Blue from the ice-free ocean
surfaces, white from snow, ice and clouds, and grey-
Sea ice is a complex environment with a diversity of habi- brown from snow-free and ice-free land surfaces. The
tats and seasonal variation to which life in the polar seas brighter the colour, the more the sun’s rays are reflected
is closely adapted. Many species are now being affected by back into space, and the less the Earth warms up. An im-
changes in sea ice in the Arctic, and, if the changes con- portant part of the Earth’s white surface area is sea ice.
tinue, there is a strong risk of species extinctions. There
is a range of direct consequences of changes in sea ice for In the Arctic, winter sea ice extends over an area of approx-
economies and human well-being – including threats to imately 15 million km
2
at its peak in March and up to 7
indigenous cultures and opening of new sea routes and million km
2
in September, at the end of the summer melt
economic opportunities. season. Corresponding numbers for the Southern Ocean
64 GLOBAL OUTLOOK FOR ICE AND SNOW
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