Transcript
Page 1: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Didier Swingedouw (1), Fichefet T. (1), Huybrechts P. (2), Goosse H. (1), Driesschaert E, Loutre M.-F (1),

(1) Université catholique de Louvain, Institut d’Astronomie et de Géophysique Georges Lemaître, Belgium(2) Vrije Universiteit Brussel, Department of geography, Belgium

Antarctic ice-sheet melting

provides negative feedbacks

on future global warming

Page 2: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Rahmstorf . 2002

Antarctic ice sheet, THC and climate

Antarctic ice sheet (AIS) : 61 m of potential sea-level rise

Thermohaline circulation (THC): Oceanic circulation related to temperature and salinity gradient

Freshwater input in the Southern Ocean can explain warm periods in the North Atlantic (Bølling-Allerød, Weaver et al. 2003)

Future of the THC: no Antarctic ice-sheet melting in most IPCC models

NADW

AABW

Can the AIS melt in the future?

What could be the climatic impact of this melting?

Can this melting stabilize the North Atlantic THC?

Are the AIS-climate interactions important for sea-level rise projections?

Page 3: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Tool: L0VECLIM earth system model

ECBILTQG, T21, 3 levels

ISM10km

31 levels

CLIOGCM, 3°x3°, 20 levels VECODE

Page 4: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Experimental design

We analyse several scenario simulations at 4XCO2

Without any ice-sheet melting (fixed)

With ice-sheet melting from both Greenland and Antarctic ice sheets (AGIS)

With melting from Greenland ice sheet only (GIS)

With melting from Antarctic ice sheet only (AIS)

Sans

CO2 (ppm)

0140 3000

280

1120

CTRL

Year

4xCO2

AGISGISAIS

Page 5: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

AIS response

AIS looses mass after a few centuries

Important warming over Antarctica after 3000 years

Lag due to large thermal inertia in the Southern Ocean

Freshwater input up to 0.14 Sv in the Southern Ocean after 3000 years in AGIS and AIS

GISAGISCTRL AISfixed

SAT in summer: fixed-CTRL (2900-3000)

Grounded AIS mass balance

Ablation

Accumulation

Page 6: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Temperature response in scenarios

The north is warming, the south is cooling

SAT: AGIS-fixed

AIS melting reduces the Climate Sensitivity by 10%

Surface Air Temperature (SAT) AGIS-fixed: years 2900-3000

a) SAT

b) Sea-ice thickness

Because of sea-ice differences

Page 7: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

AABW cell response in scenarios

The AABW cell weakens the first 300 years

Then it recovers

It stabilizes around CTRL value with AIS melting

And 25% over CTRL value without AIS melting

AABW export at 30°S

CTRL

AGIS

AIS

GIS

fixed

Page 8: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

NADW cell response in scenarios

NADW cell weakens more with GIS melting (Driesschaert et al. 2007), while AIS melting reduces this weakening

An illustration of the « bipolar ocean seesaw » process from Stocker et al. (1992)

NADWAABW

NADWAABW

CTRL

fixed

AGIS

AIS

GIS

NADW export at 30°S

Poster XY0162 on Friday

Page 9: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Climate-ice sheet feedback

• Temperature

• Precipitation

Ice-sheetmelting

Climate

• Elevation and Albedo (+)

• Freshwater input into the oceans (-)

•…

Sign?

Amplitude?

Page 10: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Climate-ice sheet feedback

Ice-sheetmelting

Climate

Sea-level rise

=

Grounded ice-sheet melting

+

Thermal expansion in the oceans

Page 11: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

AIS-climate feedback after 3000 years

AIS coupled with climate: AIS melts as much as 3.2 m sea-level rise equivalent

AIS uncoupled with climate: AIS melts as much as 10.0 m sea-level rise equivalent

Strong negative feedback: freshwater input feedback dominates over the others

Thermal expansion contribution:

2.3 m when coupled; 1.2 m when fixed

Total negative feedback of 5.7 m

Ocean Temperature: AGIS-fixed

fixed

(coupled)

AIS elevationAGIS

(uncoupled)

Page 12: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

AIS melting reduces global warming especially in the Southern Hemisphere

AIS melting reduces the Atlantic THC weakening

AIS melting is governed by a strong negative feedback implying climate interactions

For all these reasons, AIS has to be coupled interactively in climate models for long-term projections

Conclusions

Page 13: Antarctic ice-sheet melting  provides negative feedbacks  on future global warming

Thank you !Thank you !

Mailto: [email protected]: [email protected]

Web: http://dods.ipsl.jussieu.fr/dssce/public_html/index.htmlWeb: http://dods.ipsl.jussieu.fr/dssce/public_html/index.html

Poster XY0162 on Friday,

Swingedouw et al.


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