Paradigm shifts in late-Holocene climatology?

Abstract

The climatic consequences of major increases in the concentration of atmospheric carbon dioxide were calculated over 100 years ago, but only during the last two decades have the effects of human-induced increases in various atmospheric gas concentrations become a concern of a wide range of scientists. The near-century delay between the propounding of the theory and the widespread recognition of the consequences for climate of continuing human activities implies a recent shift in either the perspectives or in the interests of researchers. Here we use citation indices to discern a major shift in the focus of research into climatic change. Scientific findings in the 1970s and early 1980s are identified as a trigger to the development of wider scientific concern over human-induced climatic warming, while the period from 1988 to 1991 at first sight appears to represent a major paradigm shift. However, it is suggested here that an inferred change in scientific emphasis was caused primarily by a combination of (1) new evidence from ocean and ice cores, particularly concerning the relationship between past atmospheric gas concentrations and climatic change; (2) the availability and application of new tools, notably a new generation of General Circulation Models (GCMs); (3) attribution of human causation for other environmental problems; (4) a changing science research agenda, driven by political and funding considerations; and (5) the contemporary recording of apparently increased 'global' temperatures, which reversed a previously recorded cooling trend. We caution that the pre-eminence and longevity of the 'global warming' thesis is vulnerable either to meteorological data that do not fit with model scenarios, or to the rise or resurrection of other notions on the primary forcing factors in climatic change. To obtain a clear perspective on late-Holocene climatic change, it will be necessary to evaluate palaeoclimate data that derive from a wide range of complementary sources-sedimentological, biological, archaeological and documentary-and to compare the magnitude, rate and frequency of past climatic changes implied in those data with recorded twentieth-century 'global' changes and projected twenty-first-century scenarios.