Why some Antarctic glaciers are disappearing faster than we thought
Melting Antarctic ice could cause sea levels to rise more than three feet this century, say a pair of climate scientists who added a fast and frightening sequel to the previously known story of how certain glaciers collapse. Read related article: Antarctic loss could double expected sea level rise by 2100, scientists say

Melting from below
Scientists have long known that glaciers resting under sea level can be unstable if they rest on a downward sloping sea bed.
Warmer ocean currents erode the glacier’s base from below. The grounding line retreats downhill and, as it does, even more of the glacier is exposed to warm water. It melts more and flows faster.
1.
Previous profile
of ice sheet
Thinning
Receding
Previous edge
of ice shelf
Ice front
Ice flow
Ice shelf
Glacier,
or ice sheet
Glacial
retreat
1
Ocean currents
Continental
shelf
Diagram is schematic
Shearing from cliffs
Now, researchers have identified two new processes that can make this still worse.
Warm air, rain and meltwater cause fissures in the shelf, which breaks away from the glacier in large swaths. Eventually, only vertical ice cliffs remain.
2.
Temperatures
above freezing
Crevassing,
hydrofracturing
3
2
Unstable
cliffs
(Around
300 ft.)
Glacial
retreat
Ocean currents
3.
As warm water continually eats away at the glacier’s base, the unstable cliff faces above the water line shear off under their own massive weight.
A dangerous situation
Current data comes from three relatively small places, where ice cliffs are about 300 feet tall: Antarctica’s Crane Glacier and two glaciers in Greenland. The researchers predict that if the same type of accelerated collapse occurs — as they suspect — throughout Antarctica, it could cause sea levels to rise nearly 50 feet by 2500.
Ice shelves
Ice rests below sea level (less stable)
Ice rests over sea level (more stable)
Crane
Glacier
RONNE ICE SHELF
ANTARCTICA
South Pole
WEST
ANTARCTICA
Amundsen Sea
ROSS ICE SHELF
0
800
MILES

Melting from below
Previous profile
of ice sheet
Receding
Scientists have long known that glaciers resting under sea level can be unstable if they rest on a downward sloping sea bed.
Previous edge
of ice shelf
Thinning
Ice front
Ice flow
Ice shelf
1.
Warmer ocean currents erode the glacier’s base from below. The grounding line retreats downhill and, as it does, even more of the glacier is exposed to warm water. It melts more and flows faster.
Glacier,
or ice sheet
Glacial
retreat
1
Ocean currents
Continental
shelf
Diagram is schematic
Shearing from cliffs
Now, researchers have identified two new processes that can make this still worse.
Temperatures
above freezing
Crevassing,
hydrofracturing
3
2
2.
Warm air, rain and meltwater cause fissures in the shelf, which breaks away from the glacier in large swaths. Eventually, only vertical ice cliffs remain.
Unstable
cliffs
(Around
300 ft.)
Glacial
retreat
Ocean currents
3.
As warm water continually eats away at the glacier’s base, the unstable cliff faces above the water line shear off under their own massive weight.
A dangerous situation
Current data comes from three relatively small places, where ice cliffs are about 300 feet tall: Antarctica’s Crane Glacier and two glaciers in Greenland. The researchers predict that if the same type of accelerated collapse occurs — as they suspect — throughout Antarctica, it could cause sea levels to rise nearly 50 feet by 2500.
Crane
Glacier
RONNE ICE SHELF
WEST
ANTARCTICA
Amundsen Sea
ROSS ICE SHELF
Ice shelves
Ice rests below sea level (less stable)
0
800
Ice rests over sea level (more stable)
MILES

Melting Antarctic ice could cause sea levels to rise more than three feet this century, say a pair of climate scientists who added a fast and frightening sequel to the previously known story of how certain glaciers collapse.
Shearing from cliffs
Melting from below
Now, researchers have identified two new processes that can make this still worse.
Scientists have long known that glaciers resting under sea level can be unstable if they rest on a downward sloping sea bed.
1.
2.
Warmer ocean currents erode the glacier’s base from below. The grounding line retreats downhill and, as it does, even more of the glacier is exposed to warm water. It melts more and flows faster.
Warm air, rain and meltwater cause fissures in the shelf, which breaks away from the glacier in large swaths. Eventually, only vertical ice cliffs remain.
3.
As warm water continually eats away at the glacier’s base, the unstable cliff faces above the water line shear off under their own massive weight.
Previous profile
of ice sheet
Thinning
Receding
Previous edge
of ice shelf
Temperatures
above freezing
Crevassing,
hydrofracturing
3
Ice front
Ice flow
2
Ice shelf
Unstable
cliffs
(Around
300 ft.)
Glacier,
or ice sheet
Glacial
retreat
1
Glacial
retreat
Ocean currents
Ocean currents
Continental
shelf
Diagram is schematic
A dangerous situation
Current data comes from three relatively small places, where ice cliffs are about 300 feet tall: Antarctica’s Crane Glacier and two glaciers in Greenland. The researchers predict that if the same type of accelerated collapse occurs — as they suspect — throughout Antarctica, it could cause sea levels to rise nearly 50 feet by 2500.
Crane
Glacier
RONNE ICE SHELF
ANTARCTICA
South Pole
Ice shelves
WEST
ANTARCTICA
Ice rests below sea level (less stable)
Amundsen Sea
Ice rests over sea level (more stable)
ROSS ICE SHELF
0
800
MILES
SOURCE: "Contribution of Antarctica to Past and Future Sea-Level Rise," by Robert M. DeConto and David Pollard, in Nature, NASA, British Antarctic Survey Geodata Portal.