International Polar Year 2007–2008 - WMO

PA R T T WO: IPY SCIENCE PR O G R A M
2.4 Greenland Ice Sheet and Arctic Glaciers
Lead Author:
Ian Allison
Contributing Authors:
Maria Ananicheva, David Burgess, Prasad Gogineni, Jon-Ove Hagen, Volker Rachold,
Martin Sharp and Henning Thing
Reviewer:
Barry Goodison
Background
The Arctic Climate Impact Assessment (ACIA, 2005),
which was released at the time that IPY 2007–2008 was
being planned, provided an exhaustive compilation of
the ongoing warming in the Arctic and the consequent
decrease in sea ice, increased surface melt on the
margins of the Greenland Ice Sheet, shrinking Arctic
glaciers, degradation of permafrost, and many impacts
on ecosystems, animals and people. The Arctic was
observed to be warming much faster than temperate
regions of the planet, possibly because of the positive
surface albedo feedback whereby reduced sea ice, in
particular, increases solar heat absorption. There were
indications that, in the decade prior to IPY, the rate of
reduction of many Arctic terrestrial ice masses had
accelerated.
The IPY Framework document (Rapley et al., 2004)
clearly identified determination of the status and
change to Arctic ice as a key objective. The total
terrestrial ice volume in the Arctic is estimated at 3.1
million km 3 (Dowdeswell and Hagen, 2004), or about
8 m of sea level equivalent, most of which is in the
Greenland ice sheet, the largest body of freshwater
ice in the Northern Hemisphere. Greenland will be
highly susceptible to continued warming over coming
decades and centuries, and quantification of the ice
sheet mass balance and the consequent changes to
global sea level were a key goal of IPY.
Improved estimates of the Greenland mass balance
would be based upon a variety of techniques including
large-scale surface and airborne observational
projects, in conjunction with space observations.
Satellite-borne sensors would provide a unique snapshot
and new satellite systems available during IPY
included the laser altimeter on ICESat and the Gravity
Recovery and Climate Experiment (GRACE) satellite
mission. Airborne and over-snow surveys would also
image ice sheet internal features and, together with
the ground measurements, could be used to link the
data records from the major deep ice core sites on the
ice sheet. Automatic instruments would be deployed
in remote regions by air or during over-snow surveys.
As noted above, the future response and stability
of Greenland to ongoing warming need to be better
understood to project future global sea level rise.
Warming above a certain “threshold” level will cause
the surface mass balance of the ice sheet to become
negative every year, with more mass lost by surface
melt than is gained from snowfall. The ice sheet
would thus thin and reach a state of “irreversible”
decline. This mass loss from surface processes could
be compounded by increased ice discharge to the
ocean. Over the past decades, many of Greenlands
fast-flowing glaciers and ice streams have accelerated
dramatically, with observations showing that ice
discharge can double within one to two years, and may
also be slowed. The dynamic processes controlling the
discharge are poorly understood, but possible causes
are the impact of relatively warm ocean currents
on the stability of glacier termini and the effect of
surface melt water penetrating to the glacier base and
enhancing ice flow by lubrication. These issues were
also identified as IPY topics.
The Greenland Ice Sheet contains an important
archive of palaeoclimatic information within the ice.
Previous deep ice core drilling and analysis programs
in Greenland have provided an outstanding record of
s C I e n C e P r o g r a m 215