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

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

Feb 16, 2023 233 likes •473 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

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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
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SLIDE 2

Major ice sheets on the Earth

  • Greenland

Grounded ice is equivalent to 7 m

  • f sea-level rise

Area of 2 millions km² (81% ice covered)

  • Antarctica

Grounded ice is equivalent to 61 m

  • f sea-level rise

Area of 14 millions km² (98% ice covered)

Huge ice shelves

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SLIDE 3

Thermohaline circulation and climate

  • Thermohaline circulation (THC):

Oceanic circulation related to temperature and salinity gradient

  • Past abrupt climate changes related to

changes in the THC (Younger Dryas, McManus et al. 2004) due to massive ice-sheet melting in the North Atlantic

  • Southern Ocean have also

experienced massive ice-sheet melting (Kanfoush et al. 2000), which could explain some warm periods in the North Atlantic (Bølling-Allerød, Weaver et al. 2003)

  • Future of the THC: no Antarctic ice-

sheet melting in most models

Schneider et al., 2007

NADW AABW

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SLIDE 4

Outlines

What could be the effect of Antarctic Ice-Sheet (AIS) melting

  • n long term global warming ?
  • Can the AIS melt in the future ?
  • What will be its effect on surface temperature ?
  • What will be its effect on ocean circulation ?
  • What are the implications for the projections of sea-level

rise ?

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SLIDE 5

Tools: L0VECLIM earth system model

ECBILT

QG, T21, 3 levels

ISM

10km 31 levels

CLIO

GCM, 3°x3°, 20 levels

VECODE

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SLIDE 6

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

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SLIDE 7

Cryospheric response in scenarios

  • After 500 years the AIS

begins to loose mass in scenarios (0.14 Sv into the Southern Ocean in AIS after 3000 years)

  • Lag due to the large

thermal inertia of the Southern Ocean (same lag for sea-ice cover reduction in the south)

  • Greenland looses mass

after a century and has totally melted in 3000 years in GIS

CTRL AGIS fixed GIS GIS fixed AIS AGIS AIS AGIS AIS fixed GIS

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SLIDE 8

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

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SLIDE 9

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

  • Why such an increase

under global warming in AABW production?

AABW export at 30°S

CTRL AGIS AIS GIS fixed

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SLIDE 10

Explanation for the AABW enhancement in scenarios without AIS melting

  • SST increases in the

Southern Ocean

  • As the SSS, which

increases surface density at some places, which increases AABW production

  • This increase in SSS is

mainly due to changes in sea-ice freshwater forcing

4XCO2 fixed - CTRL after 3000 years

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SLIDE 11

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

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SLIDE 12

Mean SAT

Climate-ice sheet interactions

Why such different climatic responses?

CTRL fixed AGIS

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SLIDE 13

Climate-ice sheet feedback

  • Temperature
  • Precipitation

Ice-sheet melting Climate

  • Elevation and

Albedo (+)

  • freshwater

input into the

  • ceans (-)
  • …

Sign?

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SLIDE 14

Climate-ice sheet feedback: a sea- level rise viewpoint

Ice-sheet melting Climate

Sea-level rise = Melting of the ice sheets + Thermal expansion of the oceans

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SLIDE 15

Greenland ice sheet

  • « on line »: GIS melts as much as 7.9

m sea-level rise equivalent in 3000 years

  • « off line »: GIS melts as much as 3.4

m sea-level rise equivalent in 3000 years

  • Strong positive feedback: elevation

and albedo feedbacks dominate over negative feedbacks

  • Thermal expansion contribution: 1.5 m

«on line», 1.2 m «off line» = slight negative feedback

  • Total positive feedback of 4.6 m sea-

level rise equivalent

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SLIDE 16

Antarctic ice sheet

  • « on line »: AIS melts as much as

3.2 m sea-level rise equivalent

  • « off line »: 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 « on line »; 1.2 m « off line » = important negative feedback

  • Total negative feedback of 5.5 m

Température de l’océan : on line – off line

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SLIDE 17
  • 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

feedbacks implying climate interactions

  • For all these reasons AIS has to be coupled

interactively in coupled models for long-term climate projections

Conclusions

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SLIDE 18

Outlooks

  • Test the robustness of the former processes within

an ensemble of parameter set in LOVECLIM

  • Evaluate the AIS melting effect in other models (by

isolating its effect through an experimental design similar to ours)

  • Understand the mechanisms for the “bipolar oceanic

seesaw” (under debate since a paper from Seidov et

  • al. 2005)
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SLIDE 19

Thank you !

Mailto: swingedouw@astr.ucl.ac.be

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

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SLIDE 20
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SLIDE 21

Greenland ice sheet

  • « on line » : GIS melts as much as 7.9 m

sea-level rise equivalent in 3000 years

  • « off line » : GIS melts as much as 3.4 m

sea-level rise equivalent in 3000 years

  • Strong positive feedback : elevation and

albedo feedbacks dominates over freshwater input feedback

  • Thermal expansion contribution : 1.5 m

«on line», 1.2 m «off line» = slight negative feedback

  • Total positive feedback of 4.6 m sea-

level rise equivalent

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SLIDE 22

Antarctic ice sheet

  • « on line » : AIS melts as much as

3.2 m sea-level rise equivalent

  • « off line » : 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 « on line » ; 1.2 m « off line » = important negative feedback

  • Total negative feedback of 5.5 m

Température de l’océan : on line – off line