Hasselmann, Klaus

Klaus Hasselmann, in full Klaus Ferdinand Hasselmann, (born October 25, 1931, Hamburg, Germany), German oceanographer who was awarded the Nobel Prize for Physics in 2021 for the foundational progress he and Japanese-born American meteorologist Syukuro Manabe made in developing scientific models of Earth’s climate, quantifying variability, and predicting global warming. Hasselmann and Manabe shared the prize with Italian physicist Giorgio Parisi.

In 1934 Hasselmann and his family emigrated from Hamburg to England, where he spent his childhood in Welwyn Garden City in Hertfordshire. They returned to Hamburg after World War II. Hasselmann studied physics and mathematics at the University of Hamburg and graduated in 1955, after completing a thesis on isotropic turbulence. He continued his work in physics and fluid dynamics at the University of Göttingen and at the Max Planck Institute of Fluid Dynamics, earning a Ph.D. from the University of Göttingen in 1957.

He served as a research assistant at the Institute of Naval Architecture at the University of Hamburg from 1957 to 1961 before accepting a professorship at the Institute of Geophysics and Planetary Physics and Scripps Institution of Oceanography, University of California, San Diego, from 1961 to 1964. He then returned to the University of Hamburg, where he would spend the majority of his career. After a short visiting professorship at the Woods Hole Oceanographic Institution in Massachusetts from 1970 to 1972, Hasselmann earned the rank of full professor for theoretical geophysics and served as managing director at the university’s Institute of Geophysics until 1975, when he became the founding director for the Max Planck Institute for Meteorology in Hamburg, where he served as director until 1999. He also served as the scientific director at the German Climate Computing Centre, also in Hamburg, from 1988 to 1999.

Hasselmann’s seminal work in 1976 involved the creation of a stochastic climate model that shows how weather disturbances could be integrated into larger, more stable atmospheric and ocean circulation patterns to produce changes in climate. In other words, he showed how weather that appears as noise and that can change rapidly and chaotically can be incorporated into a model to frame longer-term climate changes. This model led him to consider how warming signals generated by human activities, such as those produced from greenhouse gas emissions and their effects on temperature, could be separated from the background noise of natural climate variability. In 1979 he published statistical techniques that allowed climate scientists to identify the presence and relative strength of these warming signals. This work became the basis for attribution studies—which seek to explain the links between human activities that contribute to climate change and specific weather and climate events, such as tropical cyclones (hurricanes), droughts, extreme rainfall events, and the pattern of rising global average temperatures—that appear frequently in national and global climate risk assessments that help to guide climate policy.

Among Hasselmann’s many accolades, he is the recipient of the Sverdrup Gold Medal of the American Meteorological Society (1971), the Symons Memorial Medal of the Royal Meteorological Society (1997), and the Vilhelm Bjerknes Medal of the European Geophysical Society (2002). Hasselmann has either authored or co-authored more than 175 scientific publications and has contributed to six books, including Ocean Wave Modeling (1985) and Reframing the Problem of Climate Change: From Zero Sum Game to Win-Win Solutions (2012).