An Introduction to the Greenland Ice Sheet

The Greenland ice sheet covers ~80% of Greenland’s 2.2

million km2 area. It is thought to have formed around 2 million

years ago when glaciation in the Northern hemisphere became

extensive.

Currently, it holds around 2.9 million km3 of ice – about 7

metres of potential sea level rise.

Since the 1980s the ice sheet has had a negative mass balance.

This means it has been losing ice more quickly than it has been

gaining it. These losses have recently accelerated: during the last

five years the ice sheet has lost almost 300 km3 more ice each

year than it has gained.

Melting from 1979 to 2011 – the ice

sheet has melted more intensively over

the last decade than previously.

The larger the text, the stronger the melting.

Warm water from the Atlantic ocean

can reach the edges of the ice sheet,

undercutting and melting the ice.

Snow falls and collects in the ice

sheet interior – the accumulation

zone. Over time the snow compacts,

turning into ice. Around 680 km3 of

ice collect each year.

Where glaciers flow into the ocean,

chunks of ice fracture off the glacier front.

The faster a glacier flows, the more icebergs

tend to be produced, so more ice is lost.

Iceberg calving accounts for about 50% of ice

loss from Greenland.

Meltwater from the ice sheet runs

off into the ocean. About 50% of ice

from Greenland is lost as water. Most

runoff happens during high summer.

Outlet glaciers around Greenland are

concentrated streams of ice flowing very quickly

towards the ocean. Jakobshavn Isbrae (see map)

flows at speeds in excess of 15km per year. It

drains roughly 10% of Greenland's annual ice loss.

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? What we don’t know

• How the world’s climate will change

• The exact causes of glacier sliding and iceberg calving in relation to

climate change

• How quickly the ice sheet will change over the coming decades and

centuries

What we do know

• Approximately how much ice is currently being lost by melting and iceberg

calving

• In response to a warming climate, the ice sheet will continue to lose mass

• Ice sheet models suggest that an arctic warming of 3oc could be enough to

lead to a complete loss of the ice sheet

During the summer, ice at lower

altitudes melts. In the ablation zone

there is more melting than snowfall. The

water collects into lakes and streams. Often,

this water can get to the ice sheet bed. This

is important in changing the speed at which

the ice above flows and slides. See the next

board for more details...