Like the Antarctic ice sheet, the Greenland ice sheet is a dynamic polar
region where the atmosphere, temperature and ocean currents force changes
to the balance of the ice sheet. Andrews: In the Arctic we have a
wide variety of glaciers and ice caps, but the largest
glacier is the Greenland ice sheet. And it's composed of a number of different
outlet glaciers and land-terminating glaciers.
When an ice sheet is in balance, the amount of snow coming in
is equal to the amount of melt and calving
that is going out. In Greenland, unlike Antarctica,
we have a situation where we have large amounts of melt and large amount of calving.
So that Greenland is losing mass regularly every melt season. And
the accumulation during the winter does not balance that
mass loss that occurs during the summer. Atmospheric currents
play a really important role in directing warm
bodies of air onto the ice sheet. And as the
jet stream moves from the west across the Greenland ice sheet,
it can add a substantial amount of moisture and warmth
to the surface of the ice sheet and cause
increased or elevated surface melting. Surface water
on the Greenland ice sheet only flows a small distance on the surface.
It eventually will reach a crevasse or a moulin,
which is this large vertical conduit that is named after
the windmill in French, and that is because it makes this
large whooshing sound whenever water goes in. They act
to drain large volumes of water. Almost all of the surface melt that occurs
on the ice sheet to the bed of the ice sheet. VO: The ocean
surrounding Greenland also impacts the changes to the ice sheet.
Andrews: Warm ocean currents from the south travel along the edges of the Greenland
ice sheet. And as it travels along the edge of the ice sheet, this water
can intrude into these fjords along
the periphery. And this intrusion of warm water
can then interact with the front of the outlet glaciers, which can
increase the amount of melting, it can speed the rate of calving,
and can substantially influence the dynamics of outlet
glaciers. This imbalance in the ice sheet is
continuing to grow. This increase in melt intensity and
extent alters the surface reflectance of the ice sheet,
which we call surface albedo. VO: The ice sheet's albedo helps cool the planet
by reflecting solar energy back into space. The ICESat-2 satellite
will measure the changes in thickness of the ice sheets, which will help us understand how
changes in the reflective nature of the polar regions could affect climate.
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