Paul Crutzen: 1933-2021

Paul Crutzen, who shared a Nobel Prize in 1995 for his work identifying chemical agents that damaged Earth’s protective ozone layer, died Jan. 28. He was 87.

Crutzen’s affiliations among multiple research centers around the world included a professorship at Scripps Institution of Oceanography at UC San Diego, where he took part in some of the most ambitious field campaigns ever to understand the impacts of pollution on global climate. He was a proponent of research on the feasibility of geoengineering — the mitigation of climate change effects through large-scale projects —and was perhaps most famous for his suggestion that the current period of geological history has been so dominated by the effect of human activity on natural systems that it should be termed the “Anthropocene” in recognition.

“This is one of the saddest days for me. He was my closest friend for decades,” said Scripps Oceanography climate and atmospheric scientist Veerabhadran Ramanathan, who recruited Crutzen to join Scripps’ faculty as a part-time professor in 1991. “In my view, he is the most creative and original scientist geosciences has ever produced and did the most to protect the planet from human impacts through his science. I have had many, many moments when I witnessed his creativity, genius thoughts, and warm friendliness from personal interactions with him since 1978.”

Scripps Oceanography geochemist Ray Weiss noted that Crutzen’s research in the 1970s showed that the atmospheric trace gas nitrous oxide is broken down by ultraviolet light in the stratosphere, and that its breakdown products then destroy the Earth’s protective ozone layer through powerful catalytic chemical reactions.  This work led to the discovery by Mario Molina and F. Sherwood Rowland that the stratospheric breakdown products of man-made chlorofluorocarbons pose a similar and even more potent threat to the stratospheric ozone layer.  This synergy among the three scientists led to their receipt of the 1995 Nobel Prize in Chemistry, and to the establishment of the Montreal Protocol on Substances that Deplete the Ozone Layer, one of the most successful international environmental treaties of all time.

During his time at Scripps, Crutzen designed and conducted with Ramanathan the Indian Ocean Experiment, or INDOEX, in the late 1990s, which led to the discovery of soot-laden atmospheric brown clouds over south Asia. The multiyear experiment involved several research centers around the world and established the significant contribution to global warming of agents besides carbon dioxide, the chief human-generated driver of climate change.

“I worked with Paul as a fellow member of the science committee of the International Geosphere Biosphere Program, a part of the international Global Change Program.” said UC San Diego’s Vice Chancellor for Marine Science Margaret Leinen. “He was not only a great leader in his own field, but his unbounded creativity challenged old ideas and ways of doing science at exactly the right time -- when we were struggling to understand how to grapple with the interconnectedness of climate and global change and their impacts on society.”

“Paul was a great scientist,” said UC San Diego Chancellor Pradeep K. Khosla. “His early career work in atmospheric chemistry during the 1970s was instrumental in demonstrating that human activity could affect the stratospheric ozone layer. Three years after coming to UC San Diego, Paul shared the 1995 Nobel Prize in Chemistry with UC San Diego’s Mario Molina and UC Irvine’s F. Sherwood Rowland for their work on ozone depletion. Their groundbreaking research seeded innumerable studies on ozone and solidified UC San Diego’s reputation as a prestigious, global research leader. Paul’s commitment to expanding human knowledge about one of the most crucial scientific issues of our time continues to inspire scientists around the world and countless UC San Diego students. Our university mourns the loss of a true pioneer.” 

Crutzen’s was a major voice in describing the effect society had on the planet. In 1982, he opined on what a “nuclear winter” would look like in the aftermath of a nuclear war, a scenario in which the planet would be largely uninhabitable less because of the level of radioactivity but more because of the strong atmospheric cooling that would take place because of a global proliferation of smoke caused by burning forests, oil storage facilities, and other locales that would prevent sunlight reaching the planet’s surface.

Born in Amsterdam on Dec. 3, 1933, Crutzen did not start out as an atmospheric scientist. His initial career was in civil engineering and from there he moved on to become a computer programmer at the Department of Meteorology at Stockholm University in Sweden. He was fascinated by this field of science and studied it while continuing in his job, acquiring a PhD in meteorology with distinction in 1968. Crutzen and his long-time colleague and friend Henning Rodhe both studied with Bert Bolin, a meteorologist who was later involved in establishing the Intergovernmental Panel on Climate Change of the United Nations.

After the period in Stockholm, Crutzen taught and did research at various institutions, among them the University of Oxford, the National Center for Atmospheric Research (NCAR) in Boulder, Colo., Colorado State University, and the University of Chicago.

Crutzen was a research associate in the former Ocean Research Division at Scripps from 1979 to 1984.  In 1980, he became director of the Atmospheric Chemistry Department at the Max Planck Institute for Chemistry in Mainz, Germany. He rejoined Scripps Oceanography as an adjunct professor in 1991 and remained associated with the institution until his retirement in 2008. He continued his scientific activities for many years afterward.

Crutzen published over 360 peer-reviewed scientific journal articles, another 135 scientific publications in research journals, and 15 books. He was one of the most highly cited scientists in the world, was bestowed numerous awards and honors, and was a member of many scientific academies, such as council member of the Pontifical Academy of Sciences, and an honorary member of the German National Academy of Natural Sciences Leopoldina.

Crutzen is survived by his wife Terttu, his daughters Ilona and Sylvia, and three grandchildren.

• The Max Planck Institute in Mainz, Germany contributed to this story.

TRIBUTES

I’ve worked with Paul starting in 1984 and he has been a wonderful mentor, collaborator, and friend ever since. In 1987, he brought me to the Max Planck Institute for Chemistry in Mainz to work side by side with him as director at the Institute and we worked there on many joint projects and papers.

– Meinrat Andreae, research affiliate, Scripps Institution of Oceanography at UC San Diego, Director Emeritus at the Max Planck Institute for Chemistry

Paul is another environmental giant that we have lost. Sadly, he is the last of three pioneers who dedicated his life to protecting our planet (Rowland, Molina, and Crutzen). He set an example for future generations to follow in how to use basic science to protect both the planet and humans.

– Kimberly Prather, distinguished professor of atmospheric chemistry, UC San Diego

In addition to being among the most far thinking and creative Earth scientists of our time, Paul Crutzen was also a truly humble and caring human being whose time was given as freely to a struggling student as to the most distinguished of his peers.  His passing is a great loss for us all.

– Ray Weiss, distinguished professor emeritus, Scripps Institution of Oceanography, UC San Diego