Peter U. Clark

The 2024 Milutin Milanković Medal is awarded to Peter U. Clark for exceptional contributions to reconstructing and understanding how the past climate, ice sheets and sea level responded to perturbations, with a perspective on future committed changes.

Peter Clark received his PhD in geology from the University of Colorado, Boulder in 1984. He is a Distinguished Professor of Earth, Ocean, and Atmospheric Sciences at Oregon State University.

For more than three decades, Peter Clark has contributed to advancing our knowledge of glacial-interglacial variations, especially in relation to glacial chronologies and reconstructions of sea level and ice sheets, global and regional surface temperature, and the interplay between deglacial freshwater fluxes and ocean circulation. Through his large data synthesis efforts and key collaborations with the modeling community, his achievements have helped the palaeoclimate research to uncover strong evidence on how the climate system operates.

Building on the importance of subglacial dynamics to ice flow, Peter Clark explored how bedrocks influenced ice-sheet topography. This line of thinking led to the well-known ‘regolith hypothesis’ in 1996, which posits that the mid-Pleistocene transition from 40 to 100-kyr glacial cycles occurred as soft bed gave way to hard bed and produced slower, thicker ice sheets. He then turned his attention to ice margins and expanded on the freshwater explanation for the Younger Dryas with his compelling ‘routing hypothesis’ which proposes that rerouting of continental drainage from ice sheets was a key component of ocean circulation variability and abrupt climate change. Observing a major freshwater event, the Meltwater Pulse-1a sea level jump during the Northern Hemisphere Bølling-Allerød warming, he proposed the importance of meltwater sourced from the Antarctic Ice Sheet. Collaborating with the modern sea level community, he suggested that the fingerprinting technique could provide a test for the origin of Meltwater Pulse-1a, an approach that has since become ubiquitous in palaeo-sea level studies.

Peter Clark developed ice sheet and glacier chronologies around the world and integrated these with existing datasets to produce global climate narratives, frequently testing with model simulations. His work led to a global compilation of ice margin constraints to define the timing and expression of the Last Glacial Maximum, as well as proxy data syntheses and transient modeling to explain how Milanković forcing triggered a cascade of events responsible for the last termination.

Peter Clark’s work has also been significant from a past-to-future perspective. He is a pioneer of long-term projections of future sea level change, and has argued for their use in guiding policies, serving as Coordinating Lead Author of the Sea Level Change Chapter of the Intergovernmental Panel on Climate Change (IPCC) Working Group 1, Fifth Assessment Report. His papers with collaborators have provided a bridge between future climate and sea level change by explaining polar ice sheet mass loss during past warm periods.

His continued groundbreaking and influential contributions to the understanding of how the Earth’s climate system operates and responds to perturbations and his outstanding service bridging the gap between the palaeoclimate and future climate communities, make Peter Clark exceptionally deserving of the 2024 Milutin Milanković Medal.