Bjorn Stevens directs the Climate Physics Department of the Max Planck Institute for Meteorology in Hamburg. His research has advanced the scientific understanding of how atmospheric water vapor, clouds, and aerosols influence Earth’s climate and climate change. Stevens is among the most cited scientists in the broad field of climate physics world wide, and has initiated and led some of the most influential field studies and modeling initiatives over the past two decades. Stevens co-authored the chapter on clouds and aerosols in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report and served as a joint lead coordinator for the World Climate Research Programme's Grand Challenge on Clouds, Circulation, and Climate Sensitivity. Stevens was a post-doctoral fellow with the Advanced Study Program at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, from 1996 to 1998. He then received a Humboldt Fellowship to conduct research at the Max Planck Institute for Meteorology from 1998 to 1999. In 1999. He joined the Department of Atmospheric Sciences at the University of California, Los Angeles (UCLA), as an assistant professor, and was promoted to the rank of full professor in 2007. In 2008, Stevens returned to the Max Planck Institute for Meteorology as a Director and Scientific Member, and as Managing Director for two terms (2011-2014, 2021-2024) Through his leadership at the Max Planck Institute for Meteorology and his research, Stevens continues to contribute profoundly to the field of climate science, enhancing the understanding of atmospheric processes and their implications for global climate change.
In the past years km and finer scale models have been used to simulate, rather than model, the global earth system. This capability unveils much of the climate system’s dark matter. In the context of climate science, dark matter refers to gestalt constructs like rain-storms, wind-storms, topographic features, and ocean eddies, which are familiar locally, but which are assumed to play no role globally. This assumption, sometimes called large-scale determinism (LSD), has underpinned climate modelling since its very beginning. The new km-scale simulation capacity makes it possible to test for violations of LSD. In my talk I will discuss ongoing efforts to test for LSD-violation. These include studies of cloud organization, land-sea circulation systems, tropical storms, ocean eddies, and 1-100 km scale topographically induces flow regimes. I will additionally outline progress toward global hm scale simulations, and the scientific challenges such a capability can be expected to address, including efforts to understand the limits of predictability of the second kind.