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

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),

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

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  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

  2. NADW AABW Rahmstorf . 2002 Antarctic ice sheet, THC and climate 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? • 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

  3. ECBILT QG, T21, 3 levels CLIO GCM, 3°x3°, 20 levels ISM 10km 31 levels VECODE Tool: L0VECLIM earth system model

  4. CO2 (ppm) 1120 4xCO2 CTRL 280 Sans 0 140 3000 Year AGIS GIS AIS 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 fromAntarctic ice sheet only (AIS)

  5. CTRL AGIS fixed AIS GIS AIS response Grounded AIS mass balance Ablation • 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 Accumulation SAT in summer: fixed-CTRL (2900-3000)

  6. AGIS-fixed: years 2900-3000 a) SAT b) Sea-ice thickness SAT: AGIS-fixed The north is warming, the south is cooling Because of sea-ice differences Temperature response in scenarios Surface Air Temperature (SAT) AIS melting reduces the Climate Sensitivity by 10%

  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 AIS AGIS CTRL GIS fixed

  8. AABW NADW NADW AABW NADW cell response in scenarios NADW export at 30°S AIS • 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) CTRL fixed AGIS GIS Poster XY0162 on Friday

  9. Climate-ice sheet feedback Ice-sheet melting • Elevation and Albedo (+) • Freshwater input into the oceans (-) • … • Temperature • Precipitation Sign? Amplitude? Climate

  10. Ice-sheet melting = Grounded ice-sheet melting + Thermal expansion in the oceans Climate Climate-ice sheet feedback Sea-level rise

  11. AIS elevation Ocean Temperature: AGIS-fixed • Thermal expansion contribution: 2.3 m when coupled; 1.2 m when fixed • Total negative feedback of 5.7 m AGIS AIS-climate feedback after 3000 years (coupled) • 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 fixed (uncoupled)

  12. Conclusions • 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

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

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