From greenhouse to icehouse world

The Earth system on tectonic time scales

The long-term evolution from hothouse to icehouse conditions during the Cenozoic (last ~65 million years) is characterized by step-like glaciations of the high latitudes that represent the initial roots for our present climate with bi-polar glaciation and large equator-to-pole temperature differences. Hence, the Cenozoic can serve as a unique test-bed to form a quantitative, process-based understanding of the underlying mechanisms, feedbacks and thresholds of these global scale changes. In this context our research aims to differentiate between classic hypotheses for glaciations that involve e.g. tectonic changes and associated changes in ocean circulation or declining atmospheric CO2 in combination with the Earth’s orbital configuration.

Research on the climate of the Cenozoic can widen our perspective to dynamical components in the climate system that may rapidly swing to a new climate state if global temperature raise beyond a critical threshold. This component of our research therefore closes the loop between past naturally forced and future human forced warm climates.

Studying climate of the Cenozoic is demanding both with regard to the collection of climate reconstructions as well as from the viewpoint of climate model capabilities. The latter is enabled by dedicated model development work that led to the establishment of the Alfred Wegener Institute Earth System Model that extends the simulation of the Earth System from the classical coupled atmosphere-ocean dynamics towards consideration of dynamics in vegetation and ice sheets. Combining the needs for sufficient spatial resolution to resolve details of past geographies in our simulations on the one hand, and of sufficient computational efficiency for the necessary long-term model integration on the other hand, is facilitated by a novel numerical approach in the ocean model FESOM. 

The figure shows a land-sea configuration during the Middle Miocene (~15 million years ago) as incorporated in a complex Earth System Model. For example changes in oceanic gateways such as the Pacific-Atlantic connection and the Atlantic-Indian Ocean gateway via the Mediterranean are thought to represent critical factors for the global scale climate evolution during the Cenozoic (last ~65 million years).

Examples from our research:

Klages, J. P. , Salzmann, U. , Bickert, T. , Hillenbrand, C. D. , Gohl, K. , Kuhn, G. , Bohaty, S. , Titschack, J. , Müller, J. , Frederichs, T. , Bauersachs, T. , Ehrmann, W. , van de Flierdt, T. , Simoes Pereira, P. , Larter, R. D. , Lohmann, G. , Niezgodzki, I. , Uenzelmann-Neben, G. , Zundel, M. , Spiegel, C. , Mark, C. , Chew, D. , Francis, J. E. , Nehrke, G. , Schwarz, F. , Smith, J. A. , Freudenthal, T. , Esper, O. , Pälike, H. , Ronge, T. , Dziadek, R. , Afanasyeva, V. , Arndt, J. E. , Ebermann, B. , Gebhardt, C. , Hochmuth, K. , Küssner, K. , Najman, Y. , Riefstahl, F. and Scheinert, M. , Science Team of Expedition PS104, 2020: Temperate rainforests near the South Pole during peak Cretaceous warmth , Nature, 580 (7801). doi: 10.1038/s41586-020-2148-5.

Guo, D., Wang, H., Romanovsky, V. E., Haywood, A. M., Pepin, N., Salzmann, U., Sun, J., Yan, Q., Zhang, Z., Li, X., Otto-Bliesner, B. L., Feng, R., Lohmann, G., Stepanek, C., Abe-Ouchi, A., Chan, W.-L., Peltier, W. R., Chandan, D., von der Heydt, A. S., Contoux, C., Chandler, M. A., Tan, N., Zhang, Q., Hunter, S. J. and Kamae, Y. (2023): Highly restricted near‐surface permafrost extent during the mid-pliocene warm period, Proceedings of the National Academy of Sciences, 120(36), doi:10.1073/pnas.2301954120 

Hossain, A. , Knorr, G. , Jokat, W. and Lohmann, G. (2021): Opening of the Fram Strait led to the establishment of a modern-like three-layer stratification in the Arctic Ocean during the Miocene , arktos . doi: 10.1007/s41063-020-00079-8

Lohmann, G. , Knorr, G. , Hossain, A. and Stepanek, C. (2022): Effects of CO2 and Ocean Mixing on Miocene and Pliocene Temperature Gradients , Paleoceanography and Paleoclimatology, 37 (2) . doi: 10.1029/2020PA003953

Stephen Barker, Lorraine E. Lisiecki, Gregor Knorr, Sophie Nuber Polychronis C. Tzedakis: Distinct roles for precession, obliquity, and eccentricity in Pleistocene 100-kyr glacial cycles, Science (2025). DOI:10.1126/science.adp3491

Niu, L., G. Knorr, U. Krebs-Kanzow, P. Gierz, G. Lohmann, 2024: Rapid Laurentide Ice Sheet growth preceding the Last Glacial Maximum due to summer snowfall. Nat Geo., DOI:10.1038/s41561-024-01419-z

 

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