A Pioneer in Environmental Physics

Hans Oeschger (1927 - 1998)

Hans Oeschger, Climate and Environmental Physicist of international stature passed away on December 25, 1998 after long illness. Oeschger's research of the Earth System was based on the modern methods of physics. He and his team in Bern have produced numerous important results which helped develop the young branch of Environmental Physics into a respected science. Professor Oeschger was the founder of the Division of Climate and Environmental Physics at the Physics Institute of the University of Bern in 1963 and remained its director until his retirement in 1992.

Trained as a nuclear physicist at ETH Zurich, he worked toward his PhD at the University of Bern under the guidance of Professor F. G. Houtermans. In 1955 he built a device to measure weak radioactivity. This counter, now referred to as "Oeschger Counter" had a lower background than any other available instrument which enabled the application of the carbon-14 method to geophysical problems. Together with Houtermans he built the first 14C-Dating Laboratory in Switzerland and brought it to international reputation. Oeschger was the first to date the "age" of Pacific deep water. The Oeschger Counter was the leading instrument for many years which enabled the Oeschger's team to measure the activity of a host of naturally occurring radioisotopes (3H, 14C, 26Al, 37Ar, 39Ar, 81Kr, 85Kr). With this method they quantified exchange processes between different components of the Earth System.

From the Past to the Future

In 1962 Oeschger started to determine the tritium content of firn and ice, and utilized them as archives of environmental information. His participation and leading involvement in numerous expeditions to Greenland and Antarctica from 1964 to 1992 gave his laboratory direct access to polar ice cores. The analytical methods, as well as the drilling techniques, Oeschger and his team developed, allowed them to produce an unprecedented reconstruction of climate changes of the last 150,000 years.

Oeschger was a pioneer and leader in ice core research. In collaboration with his colleagues he was the first to measure the glacial-interglacial change of atmospheric CO2. They showed in 1979 that the atmospheric concentration of CO2 during the glacial was almost 50% lower than today. Furthermore, they analysed the CO2 changes during the last 1000 years and demonstrated that the dramatic increase of the last 200 years was a direct consequence of the burning of fossil fuels. These two results are now cornerstones of global change research.

Hans Oeschger was deeply troubled by the potential of an increased greenhouse effect caused by the steady increase of atmospheric CO2. He was a concerned citizen who took seriously his responsibility as a scientist towards society. He said: The worst for me would be, if there were serious changes in the next 5 to 10 years and we scientists are helpless and did not have the courage to point at these dangerous developments early. In addition to his many public lectures, he was also a Lead Author of the First Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), a report which was the basis of the Earth Summit in Rio de Janeiro (1992) and the subsequent Conferences of the Parties.

However, Hans Oeschger extracted even more surprises from the polar ice cores. Together with his colleagues Chester C. Langway (USA) and Willi Dansgaard (DK), he documented a series of abrupt climate changes in the Greenland ice cores. Stable isotope measurements on lake carbonates in Lake Gerzensee (near Bern) demonstrated that these abrupt changes are not only local or regional changes in Greenland but they are large climatic changes of at least hemispheric extent. Today 24 of these events have been documented during the last glacial. The community now refers to them as Dansgaard-Oeschger events, and they are found in many different paleoclimate archives (lake and sea sediments, tropical ice cores etc.). Already in 1984 Oeschger recognized the important role of the ocean circulation for an explanation of abrupt climate change and used the physical analogy of a flip-flop system. Triggered by small perturbations, the ocean circulation could switch from one mode of operation to another.

Based on these insights, he was early to point out that also the anthropogenic increase of CO2 could represent such a perturbation and lead to changes in the ocean circulation. Although his early warning signals and concerns have often been greeted by disbelief, the latest results both from observations and high-resolution paleoclimate archives are an impressive testimony to his early insight about global warming.

Physics and Transdisciplinarity

Hans Oeschger considered the Earth as a system. Its processes can be understood by scientists only if they are open to other ways of approaching the problems. Oeschger crossed the disciplinary boundaries long before inter- and transdisciplinarity have become buzz words. However, he was also firm in pointing out the fact that successful transdisciplinary research requires inspiration from the disciplinary research at the highest level. The wide respect for Hans Oeschger's work is not least based on his fundamental contributions to physics during many years.

His scientific achievements were widely honored. He received the Harold Urey Medal (1987), the Seligman Crystal (1991), the Marcel-Benoist Prize (1991), the Tyler Prize for Environmental Achievement (1996) and the Revelle Medal of the American Geophysical Union (1997). He was Member of the Leopoldina, the Academia Europaea and a foreign Member of the US Academy of Sciences.

Hans was excellent in conveying his enthusiasm for the scientific quest to understand the Earth System in its entire complexity to his colleagues and students. Modern environmental physics owes much to Hans Oeschger. His contributions to paleoclimatology made this initially descriptive field a quantitative science, in which changes of environmental conditions are given numbers and units. Hans has produced results and shared his way of thinking which will lead us on our way long after he is gone. Hans Oeschger was a pioneer in Earth System Science; his work and his inspiration will be remembered. Those privileged to have worked or shared his ideas with him will not forget his friendship.

Thomas Stocker
Climate and Environmental Physics
University of Bern