Ice-related items as selected from the Glossary (Annex I of the AR4)
(see the pdf
file, 0.5 MB for the full Annex I)
The boundary between the region on a glacier
where there is a net annual loss of ice mass (ablation area) and that
where there is a net annual gain (accumulation area). The altitude of
this boundary is referred to as equilibrium line altitude.
A mass of land ice that flows downhill under gravity
(through internal deformation and/or sliding at the base) and is
constrained by internal stress and friction at the base and sides. A
glacier is maintained by accumulation of snow at high altitudes,
balanced by melting at low altitudes or discharge into the sea. See
Equilibrium line; Mass balance.
A general term referring to all types of ice contained
in freezing and seasonally frozen ground and permafrost (Van
The junction between a glacier or ice sheet
and ice shelf; the place where ice starts to float.
An ice age or glacial period is characterised by a
long-term reduction in the temperature of the Earth's climate,
resulting in growth of continental ice sheets and mountain glaciers
A dome shaped ice mass, usually covering a highland area,
which is considerably smaller in extent than an ice sheet.
A cylinder of ice drilled out of a glacier or ice sheet.
A mass of land ice that is sufficiently deep to cover
most of the underlying bedrock topography, so that its shape is
mainly determined by its dynamics (the flow of the ice as it deforms
internally and/or slides at its base). An ice sheet flows outward from
a high central ice plateau with a small average surface slope. The
margins usually slope more steeply, and most ice is discharged
through fast-flowing ice streams or outlet glaciers, in some cases
into the sea or into ice shelves floating on the sea. There are only
three large ice sheets in the modern world, one on Greenland and
two on Antarctica, the East and West Antarctic Ice Sheets, divided
by the Transantarctic Mountains. During glacial periods there were
A floating slab of ice of considerable thickness extending
from the coast (usually of great horizontal extent with a level or
gently sloping surface), often filling embayments in the coastline of
the ice sheets. Nearly all ice shelves are in Antarctica, where most
of the ice discharged seaward flows into ice shelves.
A stream of ice flowing faster than the surrounding ice
sheet. It can be thought of as a glacier flowing between walls of
slower-moving ice instead of rock.
The warm periods between ice age glaciations. The
previous interglacial, dated approximately from 129 to 116 ka, is
referred to as the Last Interglacial (AMS, 2000)
Last Glacial Maximum (LGM)
The Last Glacial Maximum refers to
the time of maximum extent of the ice sheets during the last glaciation,
approximately 21 ka. This period has been widely studied because the
radiative forcings and boundary conditions are relatively well known
and because the global cooling during that period is comparable with
the projected warming over the 21st century.
Last Interglacial (LIG)
Little Ice Age (LIA)
An interval between approximately AD 1400
and 1900 when temperatures in the Northern Hemisphere were
generally colder than today's, especially in Europe.
Mass balance (of glaciers, ice caps or ice sheets)
between the mass input to the ice body (accumulation) and the mass
loss (ablation, iceberg calving). Mass balance terms include the
Specific mass balance:
net mass loss or gain over a hydrological
cycle at a point on the surface of a glacier.
Total mass balance (of the glacier):
The specific mass balance
spatially integrated over the entire glacier area; the total mass a
glacier gains or loses over a hydrological cycle.
Mean specific mass balance:
The total mass balance per unit area
of the glacier. If surface is specified (specific surface mass balance,
etc.) then ice flow contributions are not considered; otherwise, mass
balance includes contributions from ice flow and iceberg calving.
The specific surface mass balance is positive in the accumulation
area and negative in the ablation area.
Medieval Warm Period (MWP)
An interval between AD 1000 and
1300 in which some Northern Hemisphere regions were warmer
than during the Little Ice Age that followed.
Any form of ice found at sea that has originated from the
freezing of seawater. Sea ice may be discontinuous pieces (ice floes)
moved on the ocean surface by wind and currents (pack ice), or a
motionless sheet attached to the coast (land-fast ice). Sea ice less
than one year old is called first-year ice. Multi-year ice is sea ice that
has survived at least one summer melt season.
The process by which characteristic landforms result
from the thawing of ice-rich permafrost or the melting of massive
ground ice (Van Everdingen, 1998).
Van Everdingen, R. (ed.): 1998. Multi-Language Glossary of
Permafrost and Related Ground-Ice Terms, revised May
2005. National Snow and Ice Data Center/World Data Center
for Glaciology, Boulder, CO, http://nsidc.org/fgdc/glossary/.