1. Contribution of MPI to CLIMARES Erich Roeckner, Dirk Notz Max Planck Institute for Meteorology, Hamburg

2. Suggestion: Apply procedure analogous to that of the FP6 ENSEMBLES project ‘Stream 1‘: Global climate simulations to be done for the IPCC AR5 (data available for impact studies by the end of year 2010) ‘Stream 2‘ Additional simulations with improved model - focus on sea ice (data available by the end of year 2011)

3. Model to be used for stream1 Atmosphere: ECHAM6 (T159L95) including the stratosphere (top at 80km height) Ocean: MPI-OM (0.4°,L80) Sea ice: dynamic/thermodynamic (zero-layer) Aerosols: interactive or prescribed (not yet decided) Carbon cycle: included

4. The IPCC AR5 Earth System Model ECHam6 (Roeckner et al., 2003), interactive runoff and glacier calving scheme. Land surface JSBACH (Raddatz et al., 2007), Dynamic Vegetation (Brovkin et al., 2009) New Radiation Resolution: T63L47 and T159/L95 OASIS 3.0 coupler MPIOM (Marsland et al., 2003), C-Grid, z-level, partial cells, BBL parameterization Hibler-type sea ice model incl. snow and fractional ice cover Conformal mapping grid: Tri-polar: Resolution: 1°L40, 0.4°L80 Ocean biogeochemistry module HAMOCC5 (Wetzel et al., 2007)

5. Model experiments (stream 1 = AR5) Hindcasts (1960 to 2005) using observed GHG and aerosol concentrations (or emissions) Forecasts until 2035 (RCP4.5*) starting from different observed (assimilated) ocean initial states Projections until 2100 and beyond (”centennial”) Number of realizations envisaged: ≥ 5 * Representative concentration pathways reaching 4.5 W/m 2 radiative forcing by year 2100

6. Model experiments (stream 2) Repeat some of the stream 1 simulations with an updated model, including new components Multi-layer sea-ice model (see contribution D. Notz) New parameterization of sea-ice albedo (Pedersen et al. JGR 2009)

7. New sea-ice model An improved representation of first- year sea-ice formation An improved representation of salt fluxes from ice Multi-layer, multi-category sea-ice thermodynamics Improved albedo scheme (Pedersen et al., 2009) At MPI, we are currently developing a new sea-ice model. It will include:

8. Sea-ice albedo defined separately for snow on ice (depends on snow aging) bare ice (function of ice thickness) melt ponds (depth, fractional area for FYI, MYI) and specified differently for direct, diffuse, visible, near-infrared radiation Few results from an earlier model version...

9. Annual cycle of Arctic sea-ice fractions ECHAM5/MPI-OM (T31L19) Snow on ice ponds bare ice

10. Simulated (min, max, mean) and observed melt pond fractions (f) obs1 for whole Arctic (1998)... SSM/I (IARC) obs2 for Beaufort and Chukchi Seas (Tschudi et al, 2004)

11. Mean Arctic surface albedo (including sea-ice and leads) Obs: Laine JGR 2004 (AVHRR 1982-1998) %

12. Expected outcome in climate change experiments (hypothesis to be checked) Enhanced sea-ice albedo feedback as a result of extended melt ponds simulated (and observed) on first year ice (FYI) Climate warming ==> MYI decreases, FYI increases ==> melt pond area increases ==> summer albedo decreases ==> enhanced absorption of sunlight ==> further warming

13. Planned work within WP 110 Simulations with the new coupled model will be used within WP 110 to provide all partners with ● Distribution of ice thickness and ice concentration throughout the entire Arctic Ocean ● Uncertainty ranges of future sea-ice evolution ● Impact of changes in future anthropogenic GHG emissions on the expected sea-ice evolution ● Future changes within the Arctic climate system (Air and water temperature, precipitation, wave patterns (-> coastal erosion), changes in storm activity etc.) ● Manpower: 1 Post Doc for 2 years and 1 PhD for 3 years