Evaluation of Sea-ice in the Max Planck Institute Earth System Model

Kurzfassung

Polar sea-ice reacts rapidly to climate changes and is therefore a good indicator for climate conditions in a warming world. To understand the Earth’s climate, several climate models are being developed. In 2007 most ofthe modelsparticipating in thethird phaseof the Coupled Model Intercomparison Project (CMIP3) underestimated the decline of Arctic sea-iceextent, which iswell constrained by satelliteobservations since the late 1970s.ThenewMax Planck Institute Earth System Model (MPI-ESM), whose predecessor model also participated in CMIP3, provides several improvements regarding the simulation of sea-ice. In this thesis,sea-ice in the MPI-ESMis evaluated with observations and projections for the 21stcentury are analyzed for different scenarios. Simulated sea-ice is comparedto the observational datasets from the Advanced Microwave Scanning Radiometer -Earth Observing System (AMSR-E) in addition to observations from the National Snow and Ice Data Center (NSIDC) andfromthe Hadley Centre Sea Ice and Sea Surface Temperature (HadISST).Inthe Arcticregion, the MPI-ESM realistically simulates the observed seasonal cycle, thespatial distributionand the summer-time trendof sea-ice extent. The model’s large internal inter-annual variability is in good agreement with the observations. The MPI-ESM provides different future scenarios depending on the atmospheres greenhouse gas concentration. Under the Representative Concentration Pathways (RCP)2.6 scenario an Arctic ice-free summer can still be avoided, while the RCP 8.5 projection simulates a strong sea-ice decrease and an ice-free summerduring the second half of the 21stcentury.The seasonal cycle of Antarctic sea-ice extent is realistically simulated by the MPI-ESM, but the total sea-ice amount is substantially underestimated. The relatively small simulated summer-time trend in the Southern Hemisphere sea-ice is in agreement withobservations. The RCP 2.6 projection showsa decrease of March Antarctic sea-ice inthe first and an increase of sea-ice inthe second half of the 21stcentury. The simulationof RCP 8.5 projects a further decrease during the 21stcentury and the possibility of an ice-free Antarctic summer by the end of the century.Overall, the MPI-ESM simulates Arctic sea-ice in agreement with observations. The causesfor the biases in Antarctic sea-ice should be investigatedin a future work.