Zhengyu Liu

The 2025 Milutin Milanković Medal is awarded to Zhengyu Liu for outstanding contributions to our understanding of global climate change by combining theoretical approaches, the development and use of a hierarchy of models, and model-data comparisons.

Zhengyu Liu received his PhD in 1991 in Physical Oceanography from the Massachusetts Institute of Technology. He then moved to Princeton University as a Postdoctoral Fellow before accepting a faculty position at the University of Wisconsin where he advanced to become Professor by 2002. In 2017, he moved to Ohio State University where he is the Max Thomas Professor of Climate Dynamics.

In his early career, Zhengyu Liu developed theoretical models to explain the characteristics of the ventilated thermocline, the mysterious annual cycle in the eastern equatorial Pacific, the emergence of decadal variability through oceanic processes, double gyre dynamics and extratropical/tropical interactions.

Zhengyu Liu became interested in palaeoclimate in the mid-1990s, when he provided the first modeling insights into the emergence of the Green Sahara and the orbital-scale modulation of the African monsoon system. He was one of the first to show the role of the ocean in mid-Holocene simulations and how it affected monsoon characteristics, first in Africa and then globally. He didn’t limit his interest to ocean questions but also considered vegetation feedbacks and made original contributions to the debate on the end of the African Humid Period in Africa. Using a hierarchy of models, from conceptual to fast global coupled models, he proposed that the vegetation changes are a response to the changes in high frequency variability and not a direct trigger of the change through climate-vegetation feedback.

Taking on another palaeoclimate challenge, Zhengyu Liu pioneered the use of GCMs for long, multi-millennial climate simulations, transforming the palaeoclimate modelling field. He launched and spearheaded the very successful Trace modeling project (later SynTrace-21), which attempted for the very first time to conduct a transient deglacial model simulation using a state-of-the art Coupled General Circulation Model. This created an unprecedented synergy among disciplines in the United States and worldwide, and this effort represents one of the first major projects that successfully integrated palaeoclimate disciplines.

Zhengyu Liu further advanced this transient palaeo-modelling approach by using water isotope-enabled models. This research has led to a much deeper understanding of the Asian palaeo-monsoon system and its sensitivity to external forcings. By entraining the speleothem community in this research, he also helped to refine interpretations of their isotopic signals beyond the simple amount-effect paradigm. This work is particularly important because it has laid the dynamical foundation for understanding how one of the largest hydrological systems in the world reacts to perturbations.

As one of the leading and most innovative and influential climate dynamicists worldwide and serving as an intellectual leader at the intersection among climate dynamics, Earth system modelling, and palaeoclimate reconstruction,Zhengyu Liu is exceptionally deserving of the 2025 Milutin Milanković Medal.