1. Summary 26 September 2012 Core Theme 2: Assessing sources of uncertainty in ocean analyses and forecasts Lead: Steffen M Olsen (DMI), Co-lead: H. Drange (NERSC) Participants: UiB, GEOMAR, UPMC-LOCEAN, MET-O, NERSC, DMI, MPG

2. CT2 overview, Hamburg THOR 2012 Collaborative work: Paper on the historical hosing experiments now online - Swingedouw et al. 2012, Clim. Dyn. New coordinated sensitivity simulations using RCP8.5 scenarios completed - Five model-member ensemble. Analysis and interpretations initialized - CT2 hands-on workshop in Paris, May 2012. Developments: New model based estimate of plausible future GIS mass loss available from MPI Deliverables months 48 D34 WP2.1: Updated evaluation of ocean state estimates (CT3 obs) D35 WP2.2 & 2.3: Recommendation of model developments to improve future THC forecasts D34 concludes also on D04 (ongoing throughout the project) CT2: Assessing sources of uncertainty…

3. CT2 overview, Hamburg THOR 2012 RCP8.5 hosing experiments Setup and models RCP8.5 over the period 2006-2100 0.1 Sv distributed around Greenland for the period 2050-2090 Four models: EC-Earth, MPI-ESM, HadCM3, IPSLCM5A-LR, BCM2 Hosing relative to 2050 Hosing-RCP8.5

4. CT2 overview, Hamburg THOR 2012 AMOC response to hosing

5. CT2 overview, Hamburg THOR 2012 Preliminary conclusions Smaller impact than under historical (and Stouffer et al. 2006) but not negligible: around 1 Sv at 26°N (1.5 Sv for the max) in 40 years. (equivalent to around 0.05 PW decrease at 26°N in HT) Deep convection already ceased south of the GSR (Labrador Sea) in all model by year 2050. In the strongly forced experiment (RCP8.5) the deep ocean apears decoupled and the ocean impact of hte hosing is confined to the upper ~ 800m Apparently reduced AMOC sensitivity to GrIS melting in a warming climate!

6. CT2 overview, Hamburg THOR 2012 Greenland's response and interaction within a fully coupled ice sheet-earth system for the near-future Christian Rodehacke, Miren Vizcaino, Uwe Mikolajewicz ESM: ECHAM6 T63/MPIOM GR15 (T63L47GR15L40) Ice sheet model: mPISM (SIA+SSA) Greenland: Resolution horizontal 10 km, vertical 40 m Ctrl: Control Run for pre-industrial state: pCO 2 =284ppm abrupt: immediate increase to 4xpCO 2 1pct: Gradual pCO 2 increases by1% per year until 4xpCO 2, then constant 1pct_alone: same as 1pct but ice sheet melt water is from Ctrl

7. CT2 overview, Hamburg THOR 2012 GrIS melting under global warming Ctrl, abrupt, 1pct, 1pct_alone Ice mass loss rate (mSv) Thickness anomalies (m) grow shrink Equilibrium lines Ctrl 1pct Ice thickness 1pct – Ctrl : 350yr 1pct Ctrl abrupt 0yr 200yr 350yr

8. CT2 overview, Hamburg THOR 2012 GrIS melting under global warming abrupt 1pct_alone 1pct Ctrl Stronger radiative forcing results ultimately in a weaker AMOC In the first 200yr the additional melt water hardly affects the AMOC AMOC

9. CT2 overview, Hamburg THOR 2012 CT2 activities will continue after Thor - joint analysis and publication on the RCP8.5 exercise. - intercation with CT3 on exploiting Thor observations in ocean state estimates and analysis. Note the CT2 multi model data archive of historical and RCP8.5 hosing experiments.

10. THOR is a project financed by the European Commission through the 7th Framework Programme for Research, Theme 6 Environment, Grant agreement 212643 http://ec.europa.eu/index_en.htm http://ec.europa.eu/index_en.htm