Episode 9: Bjorn Stevens

Deep Convection

Bjorn Stevens’ main scientific interest is in the role of clouds in the climate system. He established himself early in his career as a leader in the study of marine stratus-topped boundary layers. That eventually led him to a broader climate research agenda. And since about 2008, Bjorn heads one of the world’s most prominent climate modeling labs, the Max Planck Institute for Meteorology in Hamburg. In that position, with his team there and many collaborators, he has produced an enormous volume of important research, and that’s not to mention the countless additional studies that use the data his lab contributes to the CMIP archives.
Bjorn’s personal story is as fascinating as his professional achievements. Born in Germany, he first moved to the US when he was only a few months old, and from then on he and his family kept moving a lot for his father’s work. Because of that, his education ended up being “a bit of a patchwork”, but he soon realized that he felt drawn to the beauty of math and science:

“Science opened itself up as something that I seemed reasonably good at, and I felt the rewards of doing it. It had this wonderful mix of being creative work, and it had an aesthetic to it. It involved many different skills from writing to analyzing to programming, so it was just something I […] realized and enjoyed, and I had a certain amount of success that allowed me to continue.”

Bjorn did indeed continue, from his PhD at Colorado State and early career at NCAR and UCLA, to his current position as managing director of the Max Planck Institute for Meteorology in Hamburg. His research covers many topics, but a particular focus have been clouds—he has studied them as a modeler and as a theorist, and he has led many field campaigns to collect data that improve our understanding of these elusive yet critical components of the climate system.

“How does precipitation affect the clouds? There were some simple hypotheses at the time […] which didn’t make sense to me, and so I tried to understand how drizzle affects the development of the cloud layer. So that was mostly my PhD thesis, and at that time I was really concerned with how to use models to come up with ideas that we could test in observations. So I think that’s also an enduring aspect of the way I think about things, which is not to use models to provide answers but to use models to tell us how to look at nature differently.”

Bjorn’s leadership role in the global climate science community goes well beyond his astonishing scientific productivity. He has a unique gift for starting, leading and facilitating important and sometimes difficult scientific conversations.
And currently, Bjorn is doing this in a bigger way than ever before, as he leads an international effort to develop the Earth Virtualization Engine, or EVE. EVE is conceived as a large international collaboration, taking CERN—the particle physics facility—as a model. EVE’s proposed mission is to develop kilometer-scale, that is, ultra high-resolution global climate models, using the biggest computers that exist, and use them to support climate services worldwide. You’ll hear Adam and Bjorn spend quite a bit of time talking about that towards the end of their conversation.

The interview with Bjorn Stevens was recorded in September 2023. Image credit: MPI-M, D. Ausserhofer

• Bjorn’s website at Max-Planck-Institut