American Scientist

The Discovery of Global Warming. Spencer R. Weart. x + 228 pp. Harvard University Press, 2003. $24.95.

The Discovery of Global Warming is a slim volume that seeks to explore a huge and vitally important subject. Understandings of global warming are of major significance for science, for public policy and for the interaction between the two. The science of climate change is diffuse, complex and interdisciplinary—"not one story but many parallel stories," as the author, Spencer R. Weart, assures us in his preface. He identifies two aims: to explain in tracing the history how the development of the science led to the understandings we now have, and to explore the interactions between science and society at large when a piece of very complex science has important social consequences.

It would be impossible in the compass of a single short volume to deal comprehensively with such questions. Weart does not achieve the impossible, but what he does achieve is very impressive. He recognizes the difficulties in two ways. His treatment, although it seeks to provide an overview across the spectrum of the science, is openly selective, subjective and somewhat episodic. This keeps the account readable and interesting. What is more important, he makes available a much larger amount of supplementary material in electronic form, at http://www.aip.org/history/climate. This Internet resource consists of a series of cross-linked essays on various themes within the book's scope, along with a large set of references to scientific papers and reviews, secondary historical sources, books on related topics and links to other relevant Web sites.

Weart's task is further complicated by the fact that there can be no straightforward account of global climate change. Many factors are known to be involved, and others may well yet be identified. We know the relative importance of some of the factors; others are still a matter of uncertainty or controversy. We need to consider changes of the Earth's axis, possible solar variability, the role of water vapor and clouds in the atmosphere, atmospheric carbon dioxide, other trace gases. We also need to gauge the effects of air and ocean circulation, exchange of materials between atmosphere and oceans and between atmosphere and biosphere, and radiative changes associated with changing color of the Earth's surface and with aerosols in the various atmospheric regions. The relevant scientific investigations include such diverse areas as developing computer models for circulation, measuring and modeling chemical reaction and material exchange, accurately monitoring climatic variables and chemical compositions, finding methods of obtaining evidence about past climate, accounting theoretically for past variations, accurately identifying the effects of changing climate on ecosystems, associated biological feedbacks and more.

Weart's book steers a remarkable course through these complexities. The material is faithfully presented as a series of historical developments of the scientific understandings. In some cases these developments themselves are complex: Work that was flawed, or ideas that were demonstrably wrong, nevertheless led to the emergence of new attitudes, new insights or new methods.

The early episodes are seen largely and appropriately as a series of challenges to the idea of the "balance of nature." The author shows how deeply the notion that Earth systems are stable and self-correcting permeated scientific thought until the mid 20th century. The persistence of this sort of thinking is presented as the major factor in the scientific reluctance to accept the likelihood of major and continuing climate change.

Balancing the treatment of different areas of science while covering a large and complex problem is no easy task, and the choice of focus is always a very personal thing. If anything, Weart could be held to account for an overemphasis on physics and meteorology at the expense of biology and particularly chemistry. For several of the most important decades, the only certainties in the whole debate were that levels of atmospheric carbon dioxide were unnaturally high and increasing, and that this gas was potentially a major forcing factor in atmospheric warming. Weart does not ignore these aspects—they are thoroughly filled out in the supplement and treated briefly in the book, where, in my view, they could rightly have claimed more emphasis and depth of coverage.

The work could also be seen as rather limited in exploring the social and political connections. The influence of the science and the scientific debates on policy development is well treated, but the feedback of social and political attitudes and decisions into the science is only dealt with superficially.

Consider the place of ozone depletion in the story. Scientifically, the link with climate change is a subtle one. Weart mentions the role of the ozone investigations in drawing attention to human-generated trace gases in the atmosphere. He does not mention the importance of the ozone problem in getting scientists from different disciplines talking together. Nor does he take up the point that the ozone negotiations provided negotiators with a dress rehearsal in producing international protocols prior to tackling what was seen, even then, as the more important challenge of global climate change. But maybe that oversight is understandable: There is simply not the scope for a thorough examination in a work of this nature. Likely for the same reason, the author declares his general optimism about public policy outcomes in the medium term but produces no deep argument to justify such optimism.

There are a few rather strange omissions in minor areas. For example, Weart's discussion of volcanic aerosols starts with Benjamin Franklin's association of a cold summer in Europe with an eruption in Iceland. It then jumps to the late 19th century, when "most scientists believed that volcanic eruptions could indeed affect large regions, even the entire planet." There is no mention of the huge Tambora eruption in Indonesia in 1815, which resulted in a spring and summer so cold that 1816 was known as the "year without a summer." Even in the supplementary material Tambora rates no mention, although the relatively minor climatic effects of the much smaller Krakatoa eruption in 1883 are noted. It is also strange that in an extensive bibliography, Frances Drake's accurate and thoroughly accessible account Global Warming (Edward Arnold, 2000) is not included.

These criticisms, though, are all fairly minor. This volume provides a balanced historical overview of the science of global climate change, clearly earning a place as a key work for anyone interested in the topic. Taken with the supplementary material, the account is comprehensive. The story presented is easy and enjoyable to read; Weart puts a human face on the science without descending into journalistic cliché. The book is also noteworthy for its approach and innovation as a historical work dealing with recent and complex science.—Maureen Christie, History and Philosophy of Science, University of Melbourne