Hans Oeschger’s letter to ESPR

Jaworowski’s article in ESPR is so hard to locate, it wouldn’t be too unreasonable to suspect that the journal is not eager now for people to take much notice of it. But it did get noticed by one giant in climate science — Hans Oeschger.
Prof. Oeschger was the founder of the Division of Climate and Environmental Physics at the Physics Institute of the University of Bern. His name is attached to the Oeschger Counter that enabled Carbon-14 dating to be applied to geophysical problems, and to the Dansgaard-Oeschger 1,500 year cycle of slow cooling and abrupt warming observed in sediments and ice cores. He was active and influential in climate science until his death in 1998. His assessment of the Jaworowski article was blunt.

ESPR – Environ Sci. & Pollut. Res. 2 (1) 1995, pp. 60-61
Ancient Atmosphere

It is with great hesitation that I write in reply to the paper by JAWOROWSKI, this paper deserves little attention. But unfortunately, he has succeded in publishing similar articles in journaIs and thus has induced considerable confusion regarding the reconstruction of ancient atmospheric compositions by the analysis of air occluded in polar ice of known age. We hope that this reply will help to clarify the issue. JAWOROWSKI is correct in one point. The glacier studies of ice cores are fundamental for one of the most important issues of the century and are of great importance for succeeding centuries.

I have been personally involved in the development of this field since its inception. In the early stages I was involved directly in experiments; later the experimental and analysis work was conducted by my collaborators and students. ii in this article I speak of “we”, I refer to the ice core team at the University of Bern. In the following I first give a short overview of the history of ice core research.

Although we knew since the nineteen fifties that human activities might change the climate of the Earth, it was not until the mid seventies we realised that mankind was faced with a serious problem. Using a new model for the exchange of CO2 between atmosphere and ocean, we were able to consistently describe the uptake excess of CO2 by the ocean, as well as the distribution in the ocean of 14C produced by cosmic radiation, and 14C stemming from nuclear weapon tests. We became convinced that, for the expected future anthropogenic CO2 emission, the atmospheric CO2 concentration would rise in a predictable manner. (In fact, using the estimated actual fossil CO2 emissions as input, the CO2 increase of the past 20 years corresponds to within 10% of the predictions based on such models.) At that rime an urgent question concerned the preindustrial atmospheric CO2 concentration and the early history of the CO2 increase, but also the question of whether the atmospheric CO2 concentration of the preindustrial time was stable or whether there were also natural variations in CO2 concentration.

The US-CO2 programme was planned at an ERDA meeting in Miami in the late seventies. At that time we proposed a reconstruction of the CO2 history by measuring the gases trapped in polar ice. This idea was met with a great deal of scepticism and we were aware that the changes for success were limited because of a wide spectrum of problems, including those which JAWOROWSKI describes in his paper. On the other hand, we were aware of the urgency of the greenhouse problem and concerned that the science community would fail to conduct the most relevant studies aimed at the assessment of the rising greenhouse effect.

The project to reconstruct the history of the greenhouse gases was conducted; it was, and is, very successful – much above expectation. The CO2 concentrations measured on the SIPLE core, Antarctica, serve as a measure of that success. They illustrate (JAWOROWSKI, Fig. 5 a, p. 168) the history of atmospheric CO2 increase since the middle of the 18th century. Another important result was the observation of low CO2 concentrations of the gases extracted from ice-age ice. The low glacial CO2 concentrations have been confirmed in ice cores with different physical and chemical properties both from Greenland and Antarctica and independently from 13C measurements on carbonate of foraminifera shells in ocean cores and, yet again, more recently in moss samples.

Now to the paper of JAWOROWSKI: For years he emphasizes only the difficulties of these studies, formulates the underlying assumptions which sometimcs are only partly fulfilled and criticizes the work performed hitherto in an unscrupulous manner. He does this without any appreciation for the development of expertise in this field over several decades. Thus he extrapolates from contamination problems in improvised pioneering experiments in the late sixties to more recent (1992) similar experiments on the Greenland ice cap for which special equipment was developed. Some of his statements are drastically wrong from the physical point of view, e.g. the statement that CO2 at 70 m depth in the ice begins to change into solid clathrates. Another example concerns the gas-occlusion process in firn and young ice. This process has been studied in detail theoretically and experimentally. The theory of diffusion of gases in firn and the occlusion at the firn-ice transition has been confirmed impressively by the detection of a gravitational enrichment of the heavier gases and of the heavier isotopes of a gas. This enrichment depends, in the first instance, on the depth of the firn-ice transition. It enables the reconstruction of the history of gas enclosure depth during the last glacial-interglacial cycle. But JAWOROWSKI maintains that the age of the ice and that of the occluded gases are the same and shifts the CO2 increase revealed from studies of the SIPLE core (Fig. 5 a) – which in the uppermost part overlaps convincingly with the atmospheric measurements by ca. 100 years back in time (assuming identical ages for the ice and the gases in the ice). Fig. 5 b speaks for itself; why should there be such a drastic increase of CO2 and of CH4 (Fig. 5 a) in the middle of the 19th century?

The teams of researchers involved in ice core studies have a high standing within the scientific community. The early increases of the greenhouse gases are used to initiative the models simulating climatic change and help to understand the source and sink problem related to the greenhouse gas increases of the last 150 years. The low glacial greenhouse concentrations are an essential boundary condition for climate modelling experiments of the Earth during a glacial period. The papers by JAWOROWSKI, and the one by HEYKE quoted in this paper, are not taken seriously by the science community. The problem with these publications is that a broader circle of persons interested in the Global Change issue will receive the impression that the assessment of the problem is partly based on doubtful information, that there are serious weaknesses in experimental procedures, that the whole Global Change problem does not need to be taken so seriously and that there is no urgency regarding the control of CO2 emission. The time lost now is crucial for attempts to limit the anthropogenic climatic change to a range with more absorbable negative consequences.

The study of the history of Earth system parameters is an on-going process; an increasing number of laboratories have become involved and interact with each other. As it is the case in any field of science, the state of art is continuously critically assessed and attempts are made to improve the quality of the research. Ice-core information is fundamental for the assessment of one of the most urgent problems of our time. Based on my experience during decades of involvement in this field, I consider the chances as very small that the major findings from greenhouse gas studies on ice cores are fundamentally wrong; and I find the publications of JAWOROWSKI not only to be incorrect, but irresponsible.

Hans Oeschger, Ph. D. Professor of Physics
Physical Institute
University of Bern
Chl-3012 Bern, Switzerland

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