‘Genial genius’ alerted world to threats of nuclear winter and ozone depletion
Ironically for a man of serene and gentle demeanour, Paul Crutzen was best known for an abrupt interjection. He made it at a conference of the International Geosphere-Biosphere Programme, held in Cuernavaca, Mexico, in February 2000, where his fellow scientists kept referring to the present geological epoch as the ‘‘Holocene’’, the period of stable climatic conditions that began 12,000 years ago.
It seemed obvious to Crutzen that that period of stability was now over; not only had greenhouse gas emissions warmed the planet by more than half a degree since preindustrial times, a far larger spike than any natural variation in the Holocene, but humanity had radically altered the planet in many other ways – by cutting down forests, driving species to extinction, and dousing crops with fertiliser. To refer to the present day as the Holocene was to elide this abrupt transition in Earth’s history. So he said: ‘‘No, we’re no longer in the Holocene but in the Anthropocene.’’
The word had occurred to him in the moment. It combined the Greek words for ‘‘human’’ and ‘‘recent’’, and encapsulated the idea that he had been studying all his career, that humanity is now so powerful that it acts as a geological force, reshaping the planet’s lands and seas. ‘‘Everyone was shocked,’’ he recalled, ‘‘but it seems to have stuck.’’ He suggested this new epoch began in 1784, when James Watt’s invention of the steam engine kicked off the industrial revolution.
Throughout his career Crutzen discovered multiple ways in which humanity risked damaging the planet or was already damaging it. In 1970, while working in the department of meteorology at the University of Stockholm, he published the first paper to mention the damage to the ozone layer by human activity.
It detailed his discovery that nitrous oxide, a gas produced by soil bacteria, is so stable it can rise all the way up to the stratosphere, about five miles. Once there, it passes one of its two oxygen atoms on to three-atom molecules of ozone, breaking the ozone down into two pairs of atoms.
He showed that humanity, by use of fertilisers, was stimulating the production of nitrous oxide and thereby inadvertently destroying the ozone layer, the shield that protects us from the sun’s carcinogenic ultraviolet rays. The next year he raised concerns that the nitrous dioxide emissions from new supersonic planes, flying in the stratosphere, could damage the ozone layer even further. They were never built in large numbers.
Crutzen’s research laid the foundation for the work of the two men who would share the Nobel prize in chemistry with him in 1995, Mario Molena and Frank Sherwood Rowland. They discovered that the ozone layer was also being damaged by a group of chemicals called chlorofluorocarbons (CFCs), used in fridges and aerosol sprays.
When a group of British researchers discovered a hole in the ozone layer over the Antarctic in 1985, Crutzen alerted policymakers to the need to quickly phase out CFCs. He pursued his research out of curiosity, not out of a sense that he had to save the world. Yet when his research portended that the world needed saving, he shared that news sedulously. Thanks in no small part to him, CFC production was restricted by the Montreal Protocol, signed in 1987, and the ozone hole is now closing.
The second environmental disaster to which Crutzen alerted the world was a hypothetical one, the nuclear winter. In 1982 he wrote a paper with John Birks, a student, entitled Twilight at Noon ,in which they demonstrated that nuclear war would kill billions of people not only in the instant of catastrophe, but in the dark months afterwards, as large quantities of sunlight reflecting ash drifted above wilting crops. The concept was named ‘‘nuclear winter’’ by Richard Turco, the atmospheric scientist, and popularised by Carl Sagan. ‘‘It’s really no fun to think about the consequences,’’ said Crutzen, ‘‘but when I look back it’s probably almost the most important work I have done.’’
Although the moral of much of Crutzen’s research is that humanity meddles with nature at its peril, he worried that more meddling might be necessary to avert the coming dangers of the Anthropocene.
Specifically, he feared that if we did not cut our greenhouse gas emissions rapidly enough to avoid disruptive climate change, we might have to turn down the planet’s thermostat by a risky method called ‘‘geoengineering’’. This would involve pouring sulphates into the stratosphere to reflect a portion of the sun’s energy back into space. Nobody knows exactly what the consequences of this would be, though they could include disrupting the Indian monsoon and reopening the ozone hole. In short, it would be a further step into the Anthropocene, which Crutzen believed we should take carefully, and only as a last resort.
Paul Jozef Crutzen was born in Amsterdam in 1933, the son of Anna, who worked in a hospital kitchen, and Josef, a waiter in a restaurant. ‘‘It was not an easy start,’’ Crutzen said of his childhood, which was disrupted by World War II. His interest in sciences was sparked by reading the stories of Jules Verne and he also developed a fascination with bridges.
In the winter of 1944 famine befell the Netherlands. ‘‘Many died of hunger and disease, including several of my schoolmates,’’ he recalled. Taking his final exams in 1951 while under a fever, he failed to get the grades required for a university stipend, so trained as a civil engineer. During a break from national service he went walking in the Swiss Alps where he met Terttu Soininen, a student at the University of Helsinki. They married in 1958, had two daughters, Ilona and Sylvia, and settled in Sweden because it was in between Finland and the Netherlands.
Crutzen had long wanted to change tack towards academia and in 1958, spotting that the department of meteorology at the University of Stockholm was in need of a computer programmer, took his chance. Although he knew nothing about meteorology when he began, he studied on the job, gained his PhD in 1968 and went on to specialise in stratospheric chemistry.
Having taken up research positions at the universities of Oxford and Boulder, Colorado, in 1980, he became the director of the atmospheric chemistry department of the Max Planck Institute for Chemistry in Mainz, Germany, and stayed in that role for 20 years.
Crutzen, who was described by one colleague as a ‘‘genial genius’’, was suspicious of scientists who seemed full of themselves; he thought a knowledge of how little we understand about the natural world should make one modest. Although his main hobby was his work, he also enjoyed piano recitals and was a surprisingly nimble table tennis player into his sixties.
Crutzen ... thought a knowledge of how little we understand about the natural world should make one modest.