Overline: Obituary Paul Crutzen

Headline: Visionary Scientist and Supporter of the IASS: Prof. Dr. Paul Crutzen

Paul J. Crutzen was one of the most important Earth system scientists of the twentieth century. Born in Amsterdam in 1933, Crutzen wished to become a scientist from his earliest days. Financial constraints compelled him to first train as a civil engineer.  At the age of twenty-five, he was finally able to take up a position as a programmer at Stockholm University, where he helped to develop and operate the first numerical weather prediction model at the Institute of Meteorology (1959-1966). The role of atmospheric ozone was a particular focus of Crutzen's work and in 1968 he earned his doctorate with a ground-breaking thesis on this topic. From there, his career developed in leaps and bounds: from 1977-1980 he led the Atmospheric Chemistry Department at the National Center of Atmospheric Research (NCAR) in Boulder, Colorado. Following this, he served as the Director of the Department of Atmospheric Chemistry at the Max Planck Institute for Chemistry (MPIC) in Mainz from 1980 to 2000.

A prescient pioneer

Paul Crutzen's early work deepened our understanding of stratospheric ozone chemistry. He investigated the formation of the Antarctic ozone hole and the effect of supersonic aircraft on the Earth's ozone shield. Crutzen was among the first scientists to publish on the massive loads of airborne pollutants originating from sources such as forest fires and oceanic cargo shipping. He was instrumental in recognizing the growing importance of air pollution in Southern Asia and the long-range transport of pollutants across the Indian Ocean. In 1995, together with Mario J. Molina and Frank Sherwood Rowland, he was awarded the Nobel Prize in Chemistry for his findings on the role of nitrogen oxides in the depletion of stratospheric ozone. Crutzen's research addressed an even broader range of issues: he published key works on the threat of a "nuclear winter" (1982) and on the impacts of emissions of nitrous oxide (N2O) – a potent greenhouse gas – from agro-biofuel production (2008).

Paul Crutzen's publication in 2006 on the potentials and risks of climate geoengineering as a means of cooling the climate by injecting particles into the stratosphere is particularly relevant to the IASS.  As part of our critical analysis of climate geoengineering, IASS researchers published a special issue of the journal Earth's Future in 2016:. Spanning 19 scientific articles, the issue traces and evaluates the dynamic development of this research field in the decade since Crutzen's ground-breaking paper.

The Anthropocene: A milestone in the debate on sustainability

Paul Crutzen's work around the concept of the "Anthropocene" was perhaps his most important contribution to the IASS. Although the term was coined in the 1920s, it was Paul Crutzen, together with Eugene F. Stoermer, who widely popularized its usage in the early 2000s.  The Anthropocene refers to the current geological epoch, which is characterized by the planetary scale of human influences on the composition and function of Earth ecosystems and life forms. Paul Crutzen highlighted humankind’s shared responsibility arising from these circumstances, lending new impetus to debates around sustainability. The IASS, whose mission is to pave the way towards sustainable societies, shares this perspective and conducts research on the grand challenges (so-called "wicked problems") of the Anthropocene.

Paul Crutzen's close links to the IASS were both professional and personal. He was a long-standing colleague of IASS Founding Director Professor Klaus Töpfer, who was the Minister of the Environment in the state of Rhineland-Palatinate during Crutzen's tenure in Mainz. In addition to this, he was the doctoral supervisor of IASS Scientific Director Professor Mark Lawrence, and continued to interact with him regularly and share his wisdom over the many years. As recently as 2017, the two co-authored an essay on the ethical aspects of climate geoengineering research.

In 2013, in recognition of his dedicated support of the Institute during its founding years and his contributions to our understanding of the Earth system in the Anthropocene, the IASS appointed Paul Crutzen as its inaugural "Honorary Senior Fellow", a special distinction awarded to only a select few researchers.
Paul Crutzen was more than a brilliant scientist: He was a very enthusiastic, kind, and generous person who will be fondly remembered by all those who knew him. We will miss Paul immensely and will be forever grateful for the many years of fruitful collaboration with him. We wish to extend our sincere condolences to his family, especially his wife Terttu, and to his many friends and colleagues.