Ulrike Lohmann

The 2025 Vilhelm Bjerknes Medal is awarded to Ulrike Lohmann for outstanding research on cloud-climate interactions; integrating microscale processes and satellite data with global models to assess the radiative effects of clouds on the Earth system.

Lohmann is a pioneer in the field of aerosol-cloud interactions. Her research and scientific leadership has focused on quantifying how the effects of clouds on the climate system through their effects on the Earth’s radiative balance and distribution of precipitation are modified by human influence through the role of aerosol particles. This has been, and continues to be a long-standing grand challenge in atmospheric sciences. Lohmann’s approach has been to focus on developing and improving physical understanding of the system and to use this to inform improved representation and quantification of the effects.

Her pioneering contributions to warm-phase aerosol-cloud-climate interactions include the first comprehensive uncertainty estimate of the cloud-mediated forcing of anthropogenic aerosol emissions. Early in her career she developed an aerosol scheme for the ECHAM climate model, the basis of which remains in wide use today. She was one of the first to use satellite-based remote sensing of clouds to constrain global model representation of their radiative effects. She identified the importance of aerosol modification of ice clouds in the climate system, and recognised very early that there was a lack of microscale observations and process based knowledge that was preventing improvements in global models being made. To remedy this, she initiated an integrated programme of research that brought together laboratory studies, advances in instrumentation and field observations to improve knowledge of ice nucleating particles, responsible for glaciating many clouds. Her leadership of multiple large research programmes since has focused on growing fundamental knowledge through these approaches and using it to dramatically improve the way ice and mixed-phase clouds are now considered in global climate models. She has made numerous contributions to her field, many of which are seminal works that have transformed our understanding of this important system, which have found broad use throughout the atmospheric research community.

Lohmann is an inspiring leader. She has played a major role in the IPCC assessment cycles and has striven to ensure her work and that of others has been used to inform policy at a number of levels. She has been hugely influential in establishing the careers of the next generation of researchers in her field, many of whom are now leading scientists in universities and research institutes across the world. She has played a particularly important role in encouraging the next generation of female atmospheric scientists, by acting as an excellent role model, through her mentorship and guidance of young researchers, and through her approach to team management

Ulrike Lohmann is very worthy recipient of the 2025 Vilhelm Bjerknes Medal for her major contributions to the field of aerosol-cloud-climate interactions and developmental of the fundamental physical knowledge that has underpinned them. This holistic approach has been exceptional and has inspired a new generation of researchers in what remains a grand challenge of atmospheric sciences.