Antarctic ice-sheet melting provides negative feedbacks on future - - PowerPoint PPT Presentation

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Mar 12, 2023 324 likes •462 views

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) Universit catholique de Louvain, Institut

SLIDE 1

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

n future global warming

SLIDE 2

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?

SLIDE 3

Tool: L0VECLIM earth system model

ECBILT

QG, T21, 3 levels

ISM

10km 31 levels

CLIO

GCM, 3°x3°, 20 levels

VECODE

SLIDE 4

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) 140 3000 280 1120 CTRL Year 4xCO2

AGIS GIS AIS

SLIDE 5

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

GIS AGIS CTRL AIS fixed SAT in summer: fixed-CTRL (2900-3000) Grounded AIS mass balance

Ablation Accumulation

SLIDE 6

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

SLIDE 7

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

SLIDE 8

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)

NADW

AABW NADW

AABW

CTRL fixed AGIS AIS GIS

NADW export at 30°S

Poster XY0162 on Friday

SLIDE 9

Climate-ice sheet feedback

Temperature
Precipitation

Ice-sheet melting Climate

Elevation and

Albedo (+)

Freshwater

input into the

ceans (-)
…

Sign? Amplitude?

SLIDE 10

Climate-ice sheet feedback

Ice-sheet melting Climate

Sea-level rise = Grounded ice-sheet melting + Thermal expansion in the oceans

SLIDE 11

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 elevation

AGIS

(uncoupled)

SLIDE 12

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

SLIDE 13

Thank you ! Thank you !

Mailto: swingedo@cerfacs.fr

Mailto: swingedo@cerfacs.fr Web: http://dods.ipsl.jussieu.fr/dssce/public_html/index.html Web: http://dods.ipsl.jussieu.fr/dssce/public_html/index.html Poster XY0162 on Friday, Swingedouw et al.