OES Director's Group


The OES Director’s Research Group, which is led by Jochem Marotzke and Johann Jungclaus, investigates the dynamics and climate impacts of large-scale ocean variability and climate change. We focus on understanding mechanisms that relate ocean and atmosphere variations on sub-daily to centennial time-scales. We apply theory and model systems of various complexity ranging from Integrated Assessment Models (IAMs) and conceptual modelsto General Circulation and Earth System Models (ESMs) in idealised and realistic set-ups at various resolutions. For numerical experimentation, we are establishing ICON as our standard research tool. Through collaborations through the Cluster of Excellence Climate, Climatic Change, and Society (led by UHH) and Prof. Manfred Milinski from the MPI for Evolutionary Biology, the Director furthermore performs research on climate–economy interactions.


Time series of annual GMST anomalies (relative to 1961–1990) simulated by the Max Planck Institute Grand Ensemble in the historical and representative concentration pathway 4.5 simulations (red) and GMST HadCRUT4 observations (black circles), shown for the period 1850–2017. The red shading represents the ensemble spread within the 12.5th to 87.5th percentile range, while the red lines represent the ensemble maximum and minimum. (b) Rank histogram of the total count of each rank (binned for 11 members centered on the rank indicated, note that bins 1 and 101 are single bins for this purpose) for HadCRUT4 GMST observations shown as a member of the Max Planck Institute Grand Ensemble. GMST = global mean surface temperature. Figure from Maher et al. (2019).


The current scientific focus of the group is centered on the following themes:

Climate variability and change on interannual to multi-decadal time-scales

Our group has led the exploitation of the MPI Grand Ensemble (MPI-GE). The MPI-GE was the first single-model initial-condition large ensemble (SMILE) run with a comprehensive set of future scenarios, and it is still the SMILE with the largest number of realizations. This combination has enabled, among other themes, the first computation of the probability that emissions reductions cause changes in important climate trends during the fifteen years following the reductions. Furthermore, we have established that the internal variability and forced response of globally averaged surface temperature has a realistic magnitude in MPI-GE.

People: J. Marotzke, S. Milinski, D. Olonschek, C. Hedemann, J. Jungclaus, N. Maher*

Projects: H2020 CONSTRAINT, University of Hamburg CliCCs


Ocean dynamics and decadal to multi-decadal variability

We investigate the role of ocean dynamics in shaping low-frequency variability. We use coupled simulations at various resolutions and idealized experiments to assess the connections of the large-scale ocean circulation with variability modes. A focus is on the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic gyre circulation with phenomena like Atlantic Multidecadal Variability or the North Atlantic “Warming Hole” in global warming simulations.

People: J. Jungclaus, A. Gronholz, D. Matei, K. Lohmann, O. Gutjahr, P. Keil*, J. Oelsmann*, R. Hand*, R. Ghosh*

Projects: H2020 PRIMAVERA, H2020 ATLANTOS, H2020 BlueAction, JPI Climate/Belmont RoadMap


Ocean-atmosphere interactions in high-resolution simulations

Applying global ICON set-ups with very high resolution, we investigate small-scale processes, for example the interaction of an evolving hurricane with the underlying eddy field, in the ocean-atmosphere system. We investigate the role of Tropical Instability Waves for upper ocean mixing and air-sea exchanges.

People: J. Marotzke, J. Jungclaus, A. Kumar, M.S. Specht, N. Brüggemann+


Tropical-midlatitude-Arctic linkages

We investigate dynamical processes linking Arctic-midlatitude weather and climate in climate model simulations and reanalyses. We study oceanic and atmospheric pathways linking tropical, midlatitude and Arctic regions, and their implications for interannual-to-decadal climate predictions, as well as North Atlantic atmospheric and oceanic circulation response to global warming.

People: D. Matei, E. Tyrlis, K. Lohmann, E. Manzini, N. Specht*, Y. Dai*, R.Ghosh*

Projects: H2020 Blue-Action project, JPI Climate/Belmont InterDec and RoadMap


Conceptual and Theoretical Climate Dynamics

This theme focuses on the processes and mechanisms that control the state of the climate system – whether from idealized models such as aqua-planets, from reduced complexity models with changing CO2 concentrations, or from theoretical analysis of planetary waves in the ocean.  The main focus is on changes in the ocean circulation due to changed boundary conditions.

People: Jochem Marotzke, M. Rugenstein*, T. Rohrschneider, L. Ramme, B. Mayer

Projects: University of Hamburg CliCCs


Climate-economy interactions

The Director’s group is aiming at advancing understanding of how uncertainties and variabilities in natural and social processes interact by prototypically generating more plausible scenarios of climate futures. Climate change occurs over longer periods of time, and, as a result, social actors, for example from politics and business, are often unable to directly react to actual climate events. They have to rely on scientific predictions as to which changes are likely under climate change. Not only does the global climate system vary spatially and temporally, the social systems, which in turn are influenced by other policy fields, also differ. This allows for different social reactions to variabilities and uncertainties in climate and social systems.

People: J. Marotzke, C. Li

Projects: University of Hamburg CliCCs


Near-term predictions

To what extent are multi-year forecasts of the climate system possible?  By starting model simulations with the best-guess of the current state of the ocean and atmosphere, this research theme investigates the accuracy of climate forecasts, both from limitations of the models and from the inherent variability of the climate system. The projects anchored in the Director’s group cooperate closely with the Decadal Climate Prediction working group, but focus on oceanic aspects. In particular, we investigate the benefits of an eddy-resolving ocean model set-up for improving forecast skills.

People: J. Jungclaus, O. Gutjahr, D. Matei, K. Lohmann

Projects: BMBF RACE-Synthese, H2020 BlueAction


Model Development and Support

The OES director’s group participates in the development of the ICON-O ocean model and the Earth System Model ICON-ESM with the goal of establishing the new-generation model ICON-ESM as the standard research tool at the MPI-M. We contribute to the further development through improved parameterizations in collaboration with the Numerical Model Development Group and the Theoretical Oceanography department of Hamburg University.

People: J. Jungclaus, H. Haak, S. Lorenz, O. Gutjahr, N. Brüggemann+

Projects: H2020 PRIMAVERA, DFG Transregio “Energy Transfers”


+ guest

* former group member