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.