Hans A. Oeschger

1997 Roger Revelle Medal Winner

Physics Institute, University of Bern, Switzerland

Hans A. Oeschger was awarded the Roger Revelle Medal at the AGU Fall Meeting Honors Ceremony, which was held on December 10, 1997, in San Francisco, California. The Revelle Medal is given for sustained and continued superior contributions to the science of climate dynamics and to predictions of expected climate changes. The citation and response are given here.


“Roger Revelle would be proud to learn that Hans Oeschger was to receive the medal bearing his name, because Hans’ research has encompassed so many important aspects of the Earth’s carbon cycle. So would the late Fritz Houtermans, who served as Oeschger’s professor and inspired him to a career of leadership in isotope geochemistry. During his 40-year long career in the Physics Department at the University of Bern, Hans, together with his colleagues and students, has pioneered many innovations that have led to a better understanding of how the carbon cycle currently operates, how it might have differed during glacial time, and how human activity might alter it in the future.

“A few of the accomplishments covered by his 200+ professional publications include: The measurement of 14C first in the mid-1950s by ultra-low-level counting and then by accelerator mass spectrometry in the mid-1980s with the Eidgenossische Technische Hochschule Zurich group; with Siegenthaler, the modeling of bomb 14C and fossil fuel CO2 uptake by the ocean using the box diffusion model; with Berner and Stauffer, the first measurements of the CO2 content of glacial age air trapped in ice cores; with Loosli, measurements of the 39Ar distribution in the deep ocean; and the realization that the record preserved in Greenland ice required that the Earth’s climate system have multiple states of operation.

“In addition to his superb scientific contributions, Hans can take credit for nurturing the careers of many, many young scientists. Among these are Martin Heimann, now at the Max Planck Institute in Hamburg; Martin Wahlen, now at the University of California, San Diego, in La Jolla; Hugo Loosli in Bern; Jürg Beer at EAWAG in Zurich; and, of course, the late Uli Siegenthaler.

“In his quiet way, Hans has consistently pushed for two goals in the world’s scientific-political arena. First, he was a strong advocate of ice core research in both polar regions. Second, he felt strongly that by loading the atmosphere with greenhouse gases, mankind was putting the Earth’s climate at risk. In hopes that this loading might be eased, he pushed for the strongest possible language in international documents such as the International Panel on Climate Change report.

“I might sum up by saying that Hans’ career provides an exemplary example of what society expects of us; namely, excellent innovative research, but with an eye toward discoveries that yield benefits to mankind and to the preservation of the environment.”

—WALLACE BROECKER, Lamont-Doherty Earth Observatory, Columbia University, Palisades, N.Y.


“I am deeply moved to be honored with the AGU’s Revelle Medal. I met Roger Revelle for the first time in 1958, during my stay in La Jolla. I had a chance to meet him many times again at meetings related to the carbon cycle and the human impact on it. He also visited Bern several times, and he attended the ICSU Conference 1986 in Bern at which it was decided to conduct the International Geosphere-Biosphere Programme (IGBP).

“At all the turning points on my way from studying developments in low-level counting to Earth system science, there were outstanding personalities. A special role was played by my doctor “father,” F. G. Houtermans. He was full of ideas that reached out much beyond the traditional borders of physics; intrigued by W. F. Libby’s work on 14C and 3H in nature, he told me to set up a radiocarbon laboratory.

“When I visited La Jolla in 1958, I had a great chance to meet many brilliant scientists and to get a feeling for the potential of geochemical studies in many scientific fields. Concerning the carbon cycle, Dave Keeling just started the Mauna Loa CO2 measurements and Hans Suess and I made the first 14C measurements on bicarbonate samples from deep Pacific Ocean water samples.

“I began to realize the great potential of natural radioactive and stable isotope studies for so many scientific fields. Together with Johannes Geiss, I analyzed the radioactivity in meteorites and later also in lunar samples (3H). H. Loosli succeeded in measuring the radioactive isotopes 37Ar, 39Ar, and 81Kr in atmospheric samples, the latter two for the first time. Ar37 measurements provided information on underground nuclear weapon testing, Ar39 complemented the measurements of other tracers in the sea and 39Ar and 81Kr analyses helped to determine the age of underground water. However, it also became evident that the specific radioactivity of long-lived natural radioisotopes is often too small for routine measurements. The introduction of the high-sensitivity accelerator mass spectrometry (AMS) enabled us to overcome some of the difficulties. The accelerator at the ETH in Zürich was adjusted for AMS and Jürg Beer from our laboratory was able to start 10Be measurements on ice core samples.

“Our attention was also drawn to the potential of natural ice as an archive for information on Earth system phenomena. At a meeting in Austria, I met Chet Langway. We identified common interests and planned to work together. With the addition of Willi Dansgaard in Copenhagen, a collaboration between the United States, Switzerland, and Denmark evolved. We successfully drilled to bedrock at the Radar Station Dye 3 in South Greenland and recovered ice samples dating back into the Eemian interglacial. This activity lead to the deep drilling projects by GRIP and GISP 2 on the summit of the Greenland ice sheet in the 1990s. Parallel to these studies, Claude Lorius and his team studied the ice cores from the Russian Vostok Station in Antarctica.

“In 1972, at a Radiocarbon Conference, the observed CO2 increase was discussed and the question was raised about how well one understands the uptake of excess CO2 by the ocean. Simple extrapolation indicated that toward the middle of the next century the atmospheric CO2 concentration might double and, based on basic physical knowledge, global temperature would then increase by the order of 3°C with dangerous anthropogenic consequences.

“How well can one estimate the atmospheric CO2 increase for given CO2 emission scenarios? To overcome the limitations of the box models of the carbon cycle used at that time, we introduced a diffusive deep ocean box. This made possible much better simulations at the observations, the CO2 increase for the estimated emissions, the 14C distribution (produced by cosmic rays and from nuclear weapon tests) in the system, and the 14C dilution due to the 14C-free fossil CO2. We were convinced that for given CO2 emission scenarios, atmospheric CO2 with high probability would follow the box diffusion model estimates.

“At an ERDA meeting in Miami at the end of the 70s the issue of the increasing atmospheric CO2 concentration and its consequences were discussed. It would be very important to know the preindustrial atmospheric CO2 concentration and the increase before the atmospheric measurements began. Though the chances for success seemed small, we decided to provide the answer by analysis of the air occluded in ice samples of known age.

“On an ice core drilled at Siple Station, Antarctica by a U.S.-Swiss team, my collaborators B. Stauffer, A. Nettel, and J. Schwander measured the CO2 concentrations back to preindustrial times and found values around 280 ppm, followed by an increase to values overlapping the Mauna Loa data. These early values agree surprisingly well with those obtained later by U.S., French and Australian teams.

“In samples from Camp Century and Byrd Station taken somewhat earlier, W. Berner and B. Stauffer had found CO2 concentrations of the occluded air in glacial ice that were significantly lower than those in samples from Holocene ice. Could it be that during the glacial periods the atmospheric CO2 concentrations had been lower than during the present interglacial period? Lorius and Delmas also obtained lower glacial CO2 concentrations and in their studies of the Vostok ice, by now this has been confirmed in half a dozen polar ice cores with different physical and chemical characteristics. This hardly expected result inspired studies of how the CO2 variations could have been caused by changes in the carbon system and to what degree they were responsible for the interhemispheric climatic coupling during glacial-interglacial cycles.

“The ice core studies provided additional unexpected results. In the Greenland ice cores, rapid variations of δ18O in H2O between a cold and a mild climate were observed by W. Dansgaard and his team, and the other analyzed parameters also showed similar switches between two states. Based on Wally Broecker’s lectures on the conveyor belt and its control, it appeared to us that these transitions might reflect the turning off and on of the North Atlantic Deep Water formation. W. S. Broecker discussed this idea in a paper in Nature in 1985, and an intensive search for similar events in other natural archives began.

“In the frame of global change science, it became evident that in addition to the physical system, Earth’s climate is also controlled by the biogeochemical systems, and the ICSU decided on the occasion of its General Assembly 1986 in Bern to conduct an International Geosphere-Biosphere Programme (IGBP). The IGBP would complement the World Climate Research Programme (WCRP) in the attempt to assess the consequences of the human impact on the Earth system. In the Commissions of the IGBP, together with J. A. Eddy, we emphasized the importance of paleo- information, and in the beginning of the 1990s, it was decided to conduct a past global changes (PAGES) core project. Together with H. Zimmerman and the members of the Scientific Steering Committee, a scientific program was designed.

“To the IPCC Assessment of Climate Change, which appeared to be very important to us, we made contributions based on paleoinformation. The Bern carbon cycle model of U. Siegenthaler and F. Joos is used to make predictions of future atmospheric CO2 concentrations for assumed CO2 emission scenarios.

“Looking back, I am full of thanks to my collaborators, scientists, and skilled technicians; we were often called the Bern team. Special thanks are due to T. Riesen and U. Schotterer for their interest and support over the decades. I am very satisfied that my successor, Thomas Stocker, with my former collaborators and new ones, continues the work in much the same sense shown here, and adds the modeling dimension. Close model-data interaction is the logical continuation of the earlier work. Results and ideas from our team were always received with great interest and encouragement by our American friends, especially Chet Langway and Wally Broecker. Without this resonance, many things would not have been possible.

“To summarize, to reduce the uncertainties, we need to adequately document and analyze the global geophysical experiment being conducted by human beings, as R. Revelle and H. S. Suess have pointed out. However, we also need to learn from the experiments that nature has conducted in the past and that are recorded as trace constituent concentrations and isotopic signatures in Earth system components in natural archives. To understand the isotope information in past and present Earth system events is an important challenge of Earth system science.

“Real progress in this field will make it possible for society to act based on foresight. The anticipated climate change is only one of the great problems with which society is faced; the thorough way climate change is assessed by the scientific community may serve as an example for addressing other grand challenges.”

—HANS A. OESCHGER, Physics Institute, University of Bern, Switzerland