Friends and Colleagues Reveal the Warm, Funny Paul Crutzen Behind the Nobel Prize

Paul J. Crutzen won the 1995 Nobel Prize in Chemistry for unraveling the chemical machinery of stratospheric ozone, coined the term Anthropocene, and helped launch the modern science of nuclear winter. Yet a new collection of personal recollections published in the History of Geo- and Space Sciences argues that the man behind those achievements is often lost when the story is told purely through his publications. Rolf Müller of Forschungszentrum Jülich, together with Lennart Bengtsson, John Birks, John Burrows, Ruprecht Jaenicke and the late Richard S. Stolarski, has gathered anecdotes from colleagues who knew Crutzen intimately, painting a portrait of a scientist who was as generous, humorous and stubbornly curious as he was brilliant.

The biographical frame is striking in itself. Born in Amsterdam on 3 December 1933, Crutzen began his career as a bridge-building engineer before pivoting to meteorology in Stockholm, where he completed his doctorate and, in 1973, the Filosofie doktor, roughly equivalent to a habilitation. After stints at NOAA and NCAR in Boulder, Colorado, where he became a director in 1977, he moved in 1980 to the Max Planck Institute for Chemistry in Mainz as director of the Air Chemistry Department. He remained a Dutch citizen throughout his life, married Terttu Soininen in 1958, and raised two daughters. He died in Mainz on 28 January 2021, leaving behind what his colleagues describe as a lineage of scientific children, grandchildren and even great-grandchildren trained under his mentorship.

His scientific range was extraordinary. In 1970 he first described the nitrogen-oxide-driven ozone-loss cycle in the stratosphere, and he warned that a fleet of supersonic aircraft could damage the ozone shield through their NOx emissions. He traced how nitrous oxide from the troposphere ascends into the stratosphere to form reactive nitrogen, and he was among the first to work out the photochemical mechanisms that create ozone in the lower atmosphere. Later he contributed key ideas on the chemistry of the Antarctic ozone hole, showed how biomass burning and aerosol particles reshape tropospheric chemistry, and, with John Birks, calculated that smoke from a nuclear war could plunge the planet into what became known as nuclear winter. In 2006 an essay of his reignited the geoengineering debate, and in 2000 he co-founded the journal Atmospheric Chemistry and Physics, a pioneer of open access and transparent peer review.

The anecdotes collected by Müller and his co-authors reveal how these landmark results emerged from an intensely human style of working. Lennart Bengtsson recalls a phone call in the summer of 1995 in which Crutzen asked, with characteristic indirectness, whether Bengtsson could arrange an invitation to that year’s Nobel Prize ceremonies in Stockholm. Bengtsson, who knew things he was not permitted to reveal, could only say he would work on it and was confident matters would resolve themselves. They did, of course, and by December Crutzen was in Stockholm sharing the chemistry prize with Mario Molina and F. Sherwood Rowland.

Other memories underline Crutzen’s instinctive kindness. John Birks met him on a flight from Illinois to Washington, discovered mid-journey that his checked bag would not follow him to the destination, and scrambled to recheck it during a stopover. As the cabin door was about to close with Birks still off the plane, Crutzen persuaded the flight attendants to hold the aircraft. Birks later followed Crutzen from the University of Colorado to Mainz for a sabbatical, and the two eventually reunited to study the atmospheric effects of asteroid impacts. John Burrows, who first encountered Crutzen at a NATO winter school in the Italian Dolomites in 1977, remembers the senior scientist delivering the second half of a lecture series on a broken leg sustained skiing down the Marmolada in bad weather, filling young researchers with enthusiasm for stratospheric and tropospheric ozone chemistry.

Burrows, who joined Crutzen’s new department in Mainz in late 1981, describes a science manager who led by example and was, in his words, a why-not person rather than a why person, a calculated risk-taker who listened carefully to the ideas of others. It was over a coffee-time discussion in 1983 that Burrows suggested the differential optical absorption spectroscopy technique, developed by Dieter Perner and Ulrich Platt, could be adapted for space-borne spectrometers. Crutzen backed the idea, and although the first proposal to ESA failed, it paved the way for the SCIAMACHY and GOME satellite instruments that transformed atmospheric remote sensing. Crutzen advised Burrows to keep space experiments well focused and to manage expectations realistically, and he liked to call SCIAMACHY sky magic. He also served as a government adviser on the German Bundestag’s Enquete Commission on protecting the Earth’s atmosphere from 1987 to 1991, work that helped shape national and European support for ozone research at a time when West Germany alone accounted for more than ten percent of global consumption of long-lived ozone-depleting substances.

Not every memory is flattering, and that is part of the charm. Rich Stolarski of NASA Goddard recalls borrowing the code of Crutzen’s two-dimensional atmospheric model in the 1980s, only to find it littered with cryptic comments such as a note that there seemed to be too much diffusion in the upper stratosphere, followed by an abrupt halving of the eddy diffusion coefficient. Stolarski eventually gave up on the punch cards, concluding that while many colleagues wrote better code, Crutzen was an artist who wrote programs to test ideas; for him the idea, not the code, was the goal. Stolarski also remembers a 1970 AGU meeting where the then-unknown Crutzen projected a slide of chemical equations that came up out of focus, cheerfully explaining that he merely wanted to impress the audience with how many reactions his model contained.

The chemistry itself produced memorable exchanges. After Stolarski and Ralph Cicerone presented work on stratospheric chlorine at a 1973 meeting in Kyoto, Crutzen sat down with Stolarski and walked through a series of equations suggesting chlorine might actually increase ozone. He later admitted he spent several months trying to prove it, an effort Stolarski now regards as thoroughness rather than waste, since it verified that no simple mistake had been made. Decades later, Monte Carlo uncertainty calculations showed that chlorine-driven ozone increase was theoretically conceivable only if the rate of the OH plus HO2 reaction were vanishingly small, which laboratory measurements subsequently ruled out. The episode captures Crutzen’s method: test every idea, including your own doubts, against the chemistry.

Life in Mainz had its frictions. Ruprecht Jaenicke recounts that the Max Planck Society hesitated over Crutzen’s appointment, perhaps because of his unusual career path, and that the University of Mainz long refused to recognize his Swedish Filosofie doktor as habilitation-equivalent, addressing him as Dr. rather than Professor even after he had held professorships in Chicago and San Diego. Only shortly before the Nobel Prize was he made an Honorarprofessor. Meanwhile the university chemists of the era dismissed atmospheric trace constituents as scientifically negligible, so Crutzen relied on the outstanding atmospheric chemist Peter Warneck to supervise doctoral students. Rolf Müller adds lighter touches: colleagues piled important papers on Crutzen’s chair during his travels, only for him to sweep the entire heap aside and sit down to discuss science; and when pressed for model plots for a 1992 paper on Antarctic ozone chemistry, he replied with self-irony that he already knew the outcome of the simulations but needed the plots for the paper.

Perhaps the most vivid scene comes from Jülich in February 1996. Müller had invited his former boss to give a seminar, only for the date to coincide with Fettdonnerstag, the carnival day when costumed revelers traditionally cut off men’s ties. The institute’s directors hesitated to welcome a brand-new Nobel Laureate amid the festivities, but rescheduling was impossible given Crutzen’s packed calendar. The lecture hall filled, partly with people in costume, to hear him speak on halogen chemistry in the troposphere. A few minutes in, the doors swung open and a band of witches advanced with an enormous pair of scissors, only to find that Crutzen was not wearing a tie. He resumed his lecture after about five minutes with the words that he hoped he could now focus on his talk again. That blend of scientific intensity and unflappable good humor, his colleagues conclude, was inseparable from the achievements: a modest man, always impatient for new results, who kept one piece of work with him even on family holidays, and who, when a university president credited the Nobel Prize to his institution, quietly observed that what counts, in any case, is the future.

Subject of Research: Personal recollections of Nobel laureate atmospheric chemist Paul J. Crutzen by his friends and colleagues

Article Title: Paul J. Crutzen – interactions with friends and colleagues

Article References: Müller, R., Bengtsson, L., Birks, J., Burrows, J., Jaenicke, R., & Stolarski, R. S. (2025). Paul J. Crutzen – interactions with friends and colleagues. History of Geo- and Space Sciences, 16(2), 31-40. https://doi.org/10.5194/hgss-16-31-2025

Image Credits: AI Generated

DOI: 10.5194/hgss-16-31-2025

Keywords: Paul Crutzen, atmospheric chemistry, ozone, Nobel Prize, Anthropocene, nuclear winter, stratosphere, SCIAMACHY, Max Planck Institute for Chemistry, biography, history of science, geoengineering