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Like the Antarctic ice sheet, the Greenland ice sheet is a dynamic polar

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region where the atmosphere, temperature and ocean currents force changes

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to the balance of the ice sheet.
Andrews: In the Arctic we have a

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wide variety of glaciers and ice caps, but the largest

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glacier is the Greenland ice sheet. And it's composed of a number of different

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outlet glaciers and land-terminating glaciers.

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When an ice sheet is in balance, the amount of snow coming in

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is equal to the amount of melt and calving

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that is going out. In Greenland, unlike Antarctica,

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we have a situation where we have large amounts of melt and large amount of calving.

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So that Greenland is losing mass regularly every melt season. And

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the accumulation during the winter does not balance that

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mass loss that occurs during the summer. Atmospheric currents

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play a really important role in directing warm

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bodies of air onto the ice sheet. And as the 

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jet stream moves from the west across the Greenland ice sheet,

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it can add a substantial amount of moisture and warmth

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to the surface of the ice sheet and cause

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increased or elevated surface melting. Surface water

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on the Greenland ice sheet only flows a small distance on the surface.

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It eventually will reach a crevasse or a moulin,

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which is this large vertical conduit that is named after

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the windmill in French, and that is because it makes this

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large whooshing sound whenever water goes in. They act

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to drain large volumes of water. Almost all of the surface melt that occurs

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on the ice sheet to the bed of the ice sheet.
VO: The ocean

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surrounding Greenland also impacts the changes to the ice sheet.

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Andrews: Warm ocean currents from the south travel along the edges of the Greenland

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ice sheet. And as it travels along the edge of the ice sheet, this water

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can intrude into these fjords along

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the periphery. And this intrusion of warm water

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can then interact with the front of the outlet glaciers, which can 

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increase the amount of melting, it can speed the rate of calving,

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and can substantially influence the dynamics of outlet

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glaciers. This imbalance in the ice sheet is

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continuing to grow. This increase in melt intensity and

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extent alters the surface reflectance of the ice sheet,

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which we call surface albedo.
VO: The ice sheet's albedo helps cool the planet

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by reflecting solar energy back into space. The ICESat-2 satellite

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will measure the changes in thickness of the ice sheets, which will help us understand how

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changes in the reflective nature of the polar regions could affect climate.

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