Biographical
Born on 25th October 1931, Klaus Hasselmann is one from the founding generation of modern climate research. It was not foreseeable during and after his studies of physics and mathematics at the Universität Hamburg that he would shape this field as one of the pioneers. Since the then fashionable fields of physics, such as quantum field theory, with their abstract concepts seemed too difficult to him, he sought a thesis in the field of fluid dynamics, with Professor Karl Wieghardt. There he came across a topic that was to shape his scientific life: the unsolved problem of turbulence calculation. Turbulence occurs as a phenomenon in many ways in liquids and gases, especially in the oceans and the atmosphere.
At the desk in the Pavillion, 1989.
Credit: Hasselmann
Through this research, Hasselmann came into contact with stochastics and so-called nonlinear processes. Nonlinear systems are characterized by the fact that they do not respond to a manipulation in a “rigid”, linear way, but their response can, for example, be disproportionately strong. Thus, such a nonlinear bicycle would not accelerate as much as a normal bicycle when pedaled harder, just as the “linear” gear ratio would dictate, but would accelerate much faster. Such systems exist everywhere in nature. However, the physical formulas describing their behavior are difficult to solve exactly — usually only in more or less tricky approximation methods.
Hasselmann refined the mathematical toolbox he needed for this during his doctoral work at the University of Göttingen and at the Max Planck Institute for Flow Research there in 1955-57. He received his doctorate in 1957 and married the soon-to-be mathematician Susanne Barthe — with whom he would later also collaborate scientifically. During his subsequent assistantship with Wieghardt at what was then the Institute of Naval Architecture at the Universität Hamburg, he stumbled upon his first major research topic: ocean waves. The task was to calculate how ships react to waves.
Ocean waves consist of a superposition of many partial waves with different wavelengths. Consequently, in physical terms, they have a “spectrum”, a mathematical distribution of different wavelengths. As a wave propagates, the energy stored in it shifts within this spectrum between the wavelengths involved. Thus, a choppy storm sea freshly stirred up by the wind becomes a long-wave old swell after some time. However, this energy exchange between different wavelengths is nonlinear, which made its calculation so difficult. Hasselmann, as a young researcher, succeeded in solving the problem with the help of a complicated, five-dimensional integral [Hasselmann1962].
This first feat attracted attention at a presentation in the U.S. and resulted in an offer from the eminent American-Austrian oceanographer Walter Munk. Hasselmann accepted and from 1961 to 1964 was first Assistant, then Associate Professor at the Institute of Geophysics and Planetary Physics and at the Scripps Institution of Oceanography in La Jolla, California, USA. During this time, he also participated in a large-scale field experiment conducted by Munk in the Pacific Ocean. It investigated how waves generated by winds, over, say, the South Pacific reach Alaska as old swell.
The contact to Hamburg did not break off during this formative period. His habilitation followed there in 1963, and in the years that followed Hasselmann worked his way up to full professor at the Universität Hamburg. During his Hamburg years, he also sought new subject areas in which to apply his skills, which led him and his first research group temporarily into plasma physics, where he collaborated with his former fellow students Gerd Wibberenz and Wolfgang Kundt. Hasselmann also recruited his first own working group from Kundt’s graduates.
From 1970 to 1972, he spent a second period in the USA, as a professor at the Woods Hole Oceanographic Institution. During this time, the so-called “Sonderforschungsbereich 94“ (“Special Research Area 94” or SFB94 for short) was founded in Hamburg, and after his return in 1972, he became the spokesman of SFB94. This developed into a large-scale, international field experiment in the North Sea called JONSWAP (Joint North Sea Wave Project). It explored in great detail how waves are generated by wind and later become swells. The JONSWAP ocean wave spectrum measured in the process is still of great importance today. “Previously, it had been assumed that a steady wind would result in a fully mature swell,” explains Dirk Olbers, who was a young researcher on the measurement campaign at the time: “But the JONSWAP spectrum showed that the swell never fully matured!” As a result, this spectrum is still used today as the “gold standard” in prediction models for sea state forecasting.
After 1972, Hasselmann became professor for theoretical geophysics in Hamburg. During this time, the president of the Max Planck Society, Reimar Lüst, contacted him and suggested that he become the future director of a Max Planck Institute dedicated to climate research. In 1975, Hasselmann became the founding director of the Max Planck Institute for Meteorology in Hamburg. The term “climate research” still seemed too new as a scientific field at the time, so it was avoided in the institute’s name as a matter of caution.
The choice of Hasselmann for such an important position was quite controversial because he did not originally come from the field of meteorology. It was clear to him that he would now have to deliver a scientific paper that showed him to be competent in the new field of research. To do this, he again drew on his profound knowledge of stochastics and nonlinear systems. He developed the theory of stochastic climate models introduced above and published it in 1976 [Hasselmann 1976]. This revolutionary work proved, as already explained, that the climate does not simply respond rigidly to external influences, but that it is variable by itself, the driving force being the “noise” in the weather.
In 1979, the famous paper showing how the “fingerprint” of man could be traced in the climate followed [Hasselmann 1979]. During this time, Hasselmann ensured that the institute grew by recruiting many young, talented scientists — at that time still predominantly male — and that it became too cramped on the two floors in the Hamburg Geomatikum. New premises were needed. So, a pavilion was built opposite the Geomatikum, a provisional arrangement that was then used much longer than originally intended and was demolished only in 2013.
In front of the pavillion 1990.
Credit: MPI-M
During the first few years, computers did not yet play such a central role at the new Max Planck Institute. Of course, climate models were already being developed, but Hasselmann was initially concerned with establishing the scientific basis for climate research. This meant that work was still mainly done with pencil and paper. In the 1980s, however, it became clear that the models now to be developed had to be more complex and therefore required much more powerful computers. Since Max Planck Institutes were supposed to be lean and scientifically flexible, the solution was to establish a separate German Climate Computing Centre, the “Deutsches Klimarechenzentrum”. Its funding was provided by the Federal Ministry of Education and Research. With the tactical help of Hartmut Graßl, Hasselmann succeeded in bringing the DKRZ to Hamburg and became its first scientific director in 1988. The technical director of the DKRZ was one of his former junior researchers, Wolfgang Sell.
This period also saw a change in the statutes of the Max Planck Institute for Meteorology, driven by Hasselmann, which introduced a directorate of equals, with three leading scientists. Hartmut Graßl and Lennart Bengtsson, who had previously been director of the European Centre for Medium-Range Weather Forecasts in Reading, UK, became Hasselmann’s first colleagues. This allowed him to hand over responsibility and concentrate more on his own research.
With the ever-improving data and models, Hasselmann’s teams led by then-postdoc Gabriele Hegerl and former postdoc Ben Santer finally succeeded in a series of important papers to prove the “fingerprint” of human activity [Hasselmann1993, Hegerl1996, Santer1996, Hegerl1997, Hasselmann1997]. These scientific publications established that greenhouse gases emitted by humans are undoubtedly responsible for global warming as an observable signal.
In addition to climate research, Hasselmann was also enormously productive in other fields. Starting in the late 1970s, he was involved as a scientific advisor in the design of the European Space Agency’s ERS-1 research satellite. This satellite was intended to measure ocean waves from orbit. It was launched in 1991 and provided valuable global data, which was analyzed by a team working for Hasselmann, among others.
Moreover, the ocean waves led to a joint research project with his wife. After a 15-year break because of their three children, Susanne Hasselmann had completed her interrupted degree in mathematics and now wanted to return to research. In a small team, the couple developed the wave model WAM (for Wave Model) [WAMgroup 1988]. This model was so successful that it is now used by many meteorological institutes around the world for operational sea state forecasts. The Hasselmanns’ work therefore not only helps to keep ships on a safe course, the forecasts based on WAM have also become popular with the surfing community.
Klaus Hasselmann also never lost touch with the fundamental questions of physics. Through the mathematical methods he used, there were many cross-connections to other research areas in physics in any case. One example is the famous Feynman diagrams, which graphically describe the various interactions between elementary particles. Mathematically related to this are the interaction rules between colliding waves that Hasselmann had worked out.
On the occasion of his 60th birthday, to the surprise of the guests, he gave a lecture on a new particle physics theory on which he had been working for some time. This metron theory should overcome some fundamental weaknesses from which the existing physical quantum field theories suffer in Hasselmann’s view. After his retirement in 1999, he devoted himself entirely to his Metron project, until today. But the great researcher who, with impressive intelligence and light-footedness, has spent his life switching extremely successfully between different fields of research — this is where he failed. The particle physics community still does not accept the Metron approach. In this respect, too, Hasselmann’s career is somewhat reminiscent of that of Albert Einstein, who invested his last decades of research in vain in a field theory that failed to gain acceptance.
However, there is also a decisive difference in the lives of the two renowned scientists. Einstein became increasingly lonely in old age. Klaus Hasselmann, on the other hand, is supported by the large network of friendships he has built up over the course of many decades. And he is a family man. During the award ceremony for the Nobel Prize in Physics, which was held in a small circle only because of the Corona lockdown, Bjorn Stevens was amused to observe how Klaus Hasselmann much preferred to occupy himself with his great-grandchildren than to follow the ceremony.
The networker and „emperor“
Emeritus Dinner with Wolfgang Sell, Lennart Bengtsson and Frau Susanne Hasselmann November 1999.
Credit: Hasselmann
If one follows not only the facts but also the comments, stories and anecdotes from the large circle of people who got to know Klaus Hasselmann more closely, then very striking character traits of the researcher emerge. This is especially true of the characteristics of an extraordinarily independent mind and a versatile, inquisitive thinker. Moreover, there is a rare fearlessness with which Hasselmann never flinched from the adventure of radically deviating from a supposedly predefined career path. A typical physicist of his generation would probably have ended up in particle physics, high-energy physics, and stayed there. In fact, Hasselmann has always been very interested in fundamental physics, as he demonstrated late in his career.
His scientific adventurousness is also reflected in the advice and impulses he gave to the young scientists around him. A suitable anecdote is told by Peter Lemke, who, among other things, was the first German to chair the joint steering committee of the World Climate Research Program (WCRP) and, until his retirement in 2014, headed the Department of Climate Sciences at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Bremerhaven. For an expedition of the research vessel “Polarstern” planned for the summer of 1989, he was to replace the absentee leader of a research team on board. As a theoretician, however, he had doubts as to whether he should accept the offer, since it involved experiments, measurements. Since he was still employed at the Max Planck Institute for Meteorology, he asked Klaus Hasselmann for advice. Hasselmann replied, “If I were you, it’s obvious — go along and learn how to collect data and how to interpret it!” For Hasselmann, there was no question that Lemke should take this leap and grow from it, had he done so himself.
In any case, Hasselmann had no qualms about throwing young researchers into the deep end of what were for them new fields of research. His life’s journey is accompanied by many anecdotes of doctoral students or postdocs who were sent around the world by Hasselmann as representatives and who then found themselves in high-profile rounds of the leading scientists in the field.
„He has always seen people’s potential,” says Dirk Olbers, who was one of a group of young graduate students of Professor Wolfgang Kundt whom Hasselmann “hijacked” after his return from Cambridge to set up his research in Hamburg, as he told von Storch [1, S. 48]. With JONSWAP, Hasselmann unceremoniously threw the physicist Olbers into the deep end of oceanography research. Later, Olbers became a professor and went to the Alfred Wegener Institute as a climate researcher, thus setting an example for the many successful scientific careers that Hasselmann has fostered.
This leads to Hasselmann’s next outstanding character trait, that of the sociable networker, the humanitarian and — in a positive sense — also manhunter, who discovered talents with a fine intuition and knew how to win them over. Many of them he let go after an intensive period of cooperation. In the background and without their knowledge, he often ensured that they were strategically placed in attractive scientific positions. In this way, he wove a network that allowed intensive scientific exchange, to the benefit of all involved. Other talents remained and accompanied Hasselmann throughout their scientific lives. These include Ernst Maier-Reimer as a central figure at the institute. “He became the guru of numerical modeling,” recalls Dirk Olbers. Maier-Reimer was also instrumental in developing the institute’s first global climate model, which was, after the Princeton model, the second of its kind in the world at the time,” says Olbers.
Of course, even a great scientist is occasionally wrong, as Olbers knows from his own experience. In the 1980s, Tim Barnett, one of Hasselmann’s first doctoral students from his time in La Jolla, came to the institute as a guest. He brought with him 14 years of area-wide wind data from the Pacific Ocean, “a very unusual data set at the time,” Olbers says. Mojib Latif, a young researcher at the institute, then came to Olbers with the idea of inputting that data into the institute’s ocean model and seeing if it produced anomalies in ocean currents off America’s coasts that had become known as El Niño. “Klaus Hasselmann was not enthusiastic about the suggestion,” Olbers recalls, “but we did it anyway with Maier-Reimer, and the result was El Niño.” With this work, Mojib Latif was able to launch his impressive scientific career, and Hasselmann was also quick to acknowledge the success. Together with Graßl, Latif also took on the task of communicating the climate issue to the public — something Hasselmann was happy to let them do. As a result, both of them became much better-known public figures than he was himself. Latif, who has also been president of the Academy of Sciences in Hamburg since 2021, is now Germany’s best-known climate researcher.
60th Birthday, Rissen 1991
Credit: Hasselmann
Anyone with good arguments never had any problems with the emperor — the “Kaiser”. This nickname goes back to Hasselmann’s confident and friendly demeanor, with which he was able to win people over quickly. In von Storch’s book [1, p. 144f], Ben Santer, who conducted research at the Max Planck Institute from the late 1980s to the early 1990s, recounts a joint flight with Hasselmann to a scientific meeting in Boulder, Colorado. On the international flight to Denver, Hasselmann asked the flight attendants if there were two quiet seats available in business class – they had to work on some important scientific research. With his incomparable confident manner, Hasselmann got the upgrade, even though they had both booked one class below. It was on this flight that Hasselmann drafted the foundations of his later “fingerprint” paper, which would appear in 1997 [2]. [Hasselmann 1997].
Hasselmann’s sociability also included singing in choirs together with his wife. During his research stay in La Jolla it was a madrigal choir, and later in Hamburg the Altona Singakademie. Gerbrand Komen was also unceremoniously introduced to the latter by the Hasselmanns. Hasselmann had invited Komen to the institute as a guest for the summer of 1983, and due to a lack of housing, the Hasselmanns had accommodated him and his entire family in their house in Kayhude. After Komen’s family had to go back to the Netherlands, he was brought into the choir by the Hasselmanns so that he would not miss his family so much. When he needed a black suit for a concert, Hasselmann lent him his own wedding suit, which fit perfectly.
This anecdote [1, p. 150] says a lot about Klaus Hasselmann as a friend and family man. His own family, however, did not always have an easy time with the hyperactive scientific nomad. In von Storch’s book [1, p. 117ff], Susanne Hasselmann tells of a party in Hamburg at which each guest was supposed to introduce themselves with a drawing. Klaus Hasselmann drew himself as a man smoking a pipe and traveling the globe in a rocking chair. Susanne Hasselmann then added herself as an appendage, clutching the chair with one hand and dragging the three children and a suitcase behind her with the other. And yet, in retrospect, she describes the time at his side as “the richest life one could ever dream of“.
Klaus Hasselmann’s love of traveling and cosmopolitanism may also have its roots in his childhood. In 1934, his parents emigrated from the Nazis to England, where he spent his years at school. It was not until 1949 that the family returned to Hamburg. This shaped a citizen of the world for whom it was only natural to be on the move. “He was never there, always on the road,” recounts Dirk Olbers: “And when he came back, he gave seminar lectures in which there was always something new.” This stimulating atmosphere around Hasselmann, however, also demanded discipline, Olbers says: “You had to be careful to stay on your own topic.” But this also meant that Hasselmann always brought new impulses into his working groups, keeping them well informed about the latest scientific trends.
Gabriele Hegerl, who today teaches as a professor for climate research at the University of Edinburgh and as a postdoc was significantly involved in Hasselmann’s important “fingerprint” work, learned three essential practical things of life from him [1, p. 137ff]. These are listed here in the conclusion because they aptly describe Hasselmann’s personality. The first lesson is accuracy in the preparation of scientific papers. Von Storch’s book is full of anecdotes about how Hasselmann would pick apart drafts of scientific papers and have them rewritten until the last minute and until he was finally satisfied. This is seamlessly matched by lesson number two, to do important things “really well.“
The third lesson is that research and life offer a wealth of possibilities. If one threatens to get stuck in one thing, one should try “something crazy.” This describes another of Hasselmann’s character traits, his optimism. This optimism also applies to humankind as a whole in challenging times. Hasselmann assumes that our species will not only acknowledge the problem of climate change, but also find solutions.
This article is based on interviews conducted by the author with companions and climate researchers, and in important passages on Hans von Storch’s book “From Decoding Turbulence to Unveiling the Fingerprint of Climate Change: The Science of Klaus Hasselmann”. In it, many scientists have their say who could not be included here due to lack of space.
For the full details, please refer to the source.
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Source:
https://mpimet.mpg.de/en/institute/the-nobel-prize-in-physics-2021
