Harold S. Johnston

1998 Roger Revelle Medal Winner

University of California, Berkeley

Harold S. Johnston was awarded the Roger Revelle Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 8, 1998, in San Francisco, California. The medal recognizes sustained and continued superior contributions to the science of climate dynamics and to predictions of expected climate changes.


“It is an honor and a pleasure to introduce Harold S. Johnston, the 1998 recipient of AGU’s Roger Revelle Medal. The Revelle Medal recognizes outstanding contributions to our understanding of atmospheric processes or other key elements of the climate system. Professor Johnston’s research on atmospheric chemistry and chemical kinetics is a model for elegance, creativity, and accuracy; his recognition of the potential for human activities to contribute to global change stands as a landmark in the history of atmospheric science; and his tireless dedication to educating the public and policy-makers about careful scientific analysis of the impact of aviation on the stratosphere has been extraordinary. For these reasons, it is especially fitting that we recognize his numerous accomplishments with the Revelle Medal.

“Johnston is most widely recognized for his landmark paper that appeared in Science in 1971 and the studies that followed, which showed that nitrogen oxides emitted by aircraft directly into the stratosphere might cause substantial depletion of the Earth’s ozone layer. He was thrust into the public spotlight with the publication of this paper, which was controversial both because of its profound scientific conclusion that human activities could have a rapid environmental impact on a global scale and because of its implicit challenge to unfettered industrial activity. Johnston is known for his unflappable intellectual honesty, even in the face of the harsh public criticism that followed this paper. He has continued to work toward an honest, unbiased, and responsible discussion of the effects of stratospheric aircraft. In this, he is motivated by a deep personal commitment about the responsibilities of scientists (especially those of us who work at public institutions) to the public that pays our salaries. The extraordinary insights presented in this 1971 paper, as well as Johnston’s efforts to communicate the results to the public and policy-makers, led to a transformation in the state of stratospheric science, spurring the initial development of modern programs of stratospheric observation and modeling.

“Johnston’s contributions to atmospheric chemistry also encompass fundamental work in kinetics. His pioneering studies of the theory of elementary chemical reactions have established cornerstones for the foundation of modern reaction rate theory. For example, he and his colleagues have focused attention on the importance of local properties in influencing the reaction rate; this is a piece of work beautiful in its elegance and simplicity. He and coworkers demonstrated to many doubters the usefulness of the activated complex theory for simple gas phase reactions when low-frequency vibrations were no longer neglected. The series of studies of kinetic isotope effects coupled with studies directed specifically at deducing the importance of tunneling furnish a foundation upon which the field is still building. He has also contributed significant new experimental methods, including a sophisticated development in the direct study of transient intermediates. In his beautiful work on the fundamental kinetics of nitrogen oxides he systematically examined and quantified the chemistry of NO, NO2, NO3, N2O5, and HNO3. These laboratory studies of nitrogen oxide photochemistry constitute a body of work that paved the way for rapid progress in atmospheric chemistry related to these gases. Indeed, no other single individual has contributed so much to the understanding of the chemistry of molecules of importance in the atmosphere.

“Johnston’s deep understanding of the role of elementary mechanisms in atmospheric chemistry is evident throughout his career. Early on, Johnston recognized the genius of Haagen-Smit’s proposal that Los Angeles smog was created by photochemistry of organic compounds. In 1952, Johnston proposed that free radical reactions were at the heart of this chemical mechanism, a concept we now take for granted. In the years since, Johnston’s work has continued to demonstrate the importance of elementary photochemical processes and free radical catalysis in building an accurate description of atmospheric composition and in understanding the actual and potential effects of human activity on the atmosphere. His 1978 article in Reviews of Geophysics and Space Physics (still one of the most lucid and concise introductions to issues in stratospheric photochemistry) and his September 1998 Journal of Geophysical Research paper on the oxidation of CH4 exemplify his insightful approach.

“Harold Johnston has been recognized numerous times for his contributions. He was elected to the National Academy of Sciences in 1965 and was awarded the 1983 Tyler Award (together with Mario J. Molina and 1994 Revelle Medal winner F. Sherwood Rowland) and the President’s National Medal of Science in 1997. In 1988, he was selected as the University of California Faculty Research Lecturer–the highest distinction of the Academic Senate at Berkeley. It is with great pleasure that I present to you, my colleague and the Revelle Medal recipient for 1998, Harold Johnston.”

—RONALD COHEN, University of California, Berkeley


“I am deeply grateful to receive the Roger Revelle Medal from the American Geophysical Union. During the last 30 years I have seen brilliant creative scientists turn my narrow specialty of gas phase chemical kinetics into a global atmospheric science, and I am indebted to them for my being here today. I never met Roger Revelle, but over the years I have been aware of his outstanding research in oceanography and climate and his broad scientific statesmanship. One thing his work and mine have in common is respect for and use of radioactive carbon 14 data, obtained after the atmospheric nuclear bomb tests of 1961-1962. Revelle measured carbon 14 to study motions in the ocean. My coworkers and I used carbon 14 data to test models with respect to air motions in the stratosphere.

“Nuclear bombs were tested in the atmosphere on a large scale from 1954 to 1959 and from 1961 to 1962. From 1955 to 1971, the Atomic Energy Commission measured, among other things, the vertical profile of excess carbon 14 at several latitudes, using aircraft below 20 km and balloons above 20 km. From 1959 to 1969, the balloons sampled at only one latitude: 30°N. These measurements had high national priority, there was fear of impending nuclear war, and no money was spared to determine where and how long radioactive bomb products remained in the atmosphere and where and when they fell out as Telegadas et al., reported in 1971 and 1972. Bound as chemically inert carbon dioxide, carbon 14 provides a unique, ideal, inert-gas tracer in the stratosphere. If repetition of this experimental study of atmospheric motions were permitted today, it would surely cost much more than a billion dollars.

“In 1974, most atmospheric models were one dimensional, with atmospheric motions determined by a vertical eddy diffusion function, Kz. When Richard Lindzen heard of the great variation of results among the one-dimensional modelers, he said, ?Why don’t you pay some attention to the physics of the problem?’ According to Don Hunten, Lindzen gave some advice and Hunten took Lindzen’s general theory, drew a simplified shape that a vertical profile of Kz should have, fitted it to observed vertical distributions of methane and nitrous oxide, and from then on made no further changes and used no adjustable parameters. The Kz functions for nine models were used to calculate the evolution of carbon 14 profiles at 30°N from 1963 to 1971 and, except for Hunten’s, all models failed as Johnston et al., reported in the Journal of Geophysical Research in 1976. Johnston and his coworkers compared calculations based on Hunten’s model to observed carbon 14 from April 1963 to November 1970 and found remarkably successful agreement between those observations and Hunten’s model.

“In 1992-1993, 11 two- or three-dimensional models were used to predict the two-dimensional distributions of carbon 14, and where the predictions overlapped observations, showed that the models had vertical transport that was much too fast. Between 1964 and 1966, all models showed a rapidly rising altitude of maximum mixing ratio from 21 to more than 40 km, whereas the measured values increased slowly from 21 to 25 km as Prather and Remsberg indicated in a NASA publication in 1993 and Kinnison et al. reported in the Journal of Geophysical Research in 1994. The two-dimensional observations at five latitudes for fall 1970 and spring 1971 reported by Telegadas et al. in 1972 show a strong upward flux of low carbon 14 air above the tropics (originating in the troposphere) and indicate a flow of this not rapidly mixed air above 30 km directed laterally and poleward, a feature that all of the models underestimated.

“High-quality stratospheric measurements, such as those for carbon 14, retain their value indefinitely, but high-quality stratospheric models need to be modified every year or so.

“These early carbon 14 documents are now difficult to find, and there is danger that these valuable reports will become extinct. To provide anyone interested in the full body of organized data, I have made copies of Telegadas’ two reports, and I will mail them to anyone who sends me a stamped return-addressed envelope, with enough size and postage for 16 oz.

—HAROLD S. JOHNSTON, University of California, Berkeley