Crutzen , Paul

(1933–) Dutch meteorologist

Crutzen first worked in Sweden, at Stockholm University, moving in 1974 to the National Oceanic and Atmospheric Administration and the National Center for Atmospheric Research in Boulder, Colorado. In 1980 he moved to Germany, where he has since served as director of the Department of Atmospheric Chemistry at the Max Planck Institute for Chemistry, Mainz.

It began to be suspected in the 1950s that the concentration of ozone in the stratosphere was lower than expected. In 1970 Crutzen argued that nitrous oxide, arising from the use of nitrogen-rich fertilizers and the combustion of fossil fuels, could be responsible. As it was relatively unreactive, nitrous oxide could rise unchanged into the stratosphere, where, under the influence of ultraviolet radiation, it could initiate a series of reactions that would lead to the conversion of ozone into molecular oxygen.

Little notice was taken of Crutzen's argument – if only because it was felt that the amount of nitrous oxide produced was too insignificant to cause any noticeable depletion of the ozone layer. The debate, however, was revived by the growing fear in the early 1970s that a proposed armada of supersonic transport aircraft (SSTs) would emit large quantities of nitrous oxide from their exhausts. Consequently the anti-SST lobby seized upon Crutzen's work.

In fact, the SSTs were never constructed. Soon after, Crutzen's warnings were overshadowed by the greater threat from the chlorofluorocarbons (CFCs), first identified in 1974 by F. Sherwood Rowland and Mario Molina, with whom Crutzen shared the 1995 Nobel Prize for chemistry.

Crutzen was also one of the first scientists to warn of the dangers of a ‘nuclear winter’. In 1982, two years before Carl Sagan and his colleagues published their famous paper on the subject, Crutzen argued that fires lit by large nuclear explosions would be extensive enough to generate massive amounts of smoke, which, added to the dust produced by the bomb, would profoundly restrict the amount of sunlight reaching the ground.