Everyone is fascinated by climate and by history. Both can be studied over a wide range of spatial and temporal scales, ranging from small areas and single years to continents and thousands of years. The reconstruction of how climate has varied in time and space over the past 11 500 years of the Holocene has been a major challenge for natural scientists for the past 200 years. Such reconstructions were probably motivated initially by natural curiosity about the past and the attractive and even seductive idea of "secrets of the past". Today such reconstructions are vitally important in the current debate about recent climate change and global warming, because reconstructions of past climate provide a powerful means of assessing the magnitude and rate of natural climate variability over the perspective of the past 11 500 years at a range of spatial and temporal scales from small areas to continents and from single years to centuries and millennia.

There has been enormous progress in reconstructing the history of Holocene climate since the pioneering investigations by Dau (1829) in Denmark. Progress in science, like climate and almost all other phenomena in the natural world, varies continuously in time and space. Historians of science (e.g. Kuhn 1970) suggest that the temporal continuum of gradual directional scientific progress is interrupted by abrupt changes, so-called paradigm shifts. Science is thought to progress by the gradual accumulation of observations and data within a basic agreed intellectual framework (Kuhn's "normal science") until a "revolution" occurs and the basic research framework or paradigm of the old conceptual structure is overturned and a new research framework or paradigm rapidly develops and becomes the new

Holocene climate research -progress, paradigms, and problems

"normal" science. The spatial patterns of scientific progress are less explored by science historians, but Crane's (1972) "invisible college" effect is clearly important. In this, major researchers and their laboratories develop as nuclei of scientific influence through their methodologies, publications, presentations, research students, and visiting researchers. Visitors assimilate the methods and concepts of the center they have visited, and transfer the learning and experience to their own laboratory and research group. Patterns of scientific progress can often only be explained, in part at least, by the "invisible college" effect and by considering who was where when. For example, many developments in Quaternary pollen analysis in the past 50 years are only explicable in terms of the "invisible college" effect (Birks 2005).

Holocene climate research has witnessed several major paradigm shifts in the past 200 years as a result not only of new ideas and conceptual breakthroughs, but also because of new and improved techniques, studies of different climate proxies, increased scientific rigor, improved project design, increased quantification, greater attention to detail, and investigations in different geographic areas and climate regimes (e.g. low latitudes, high latitudes, high altitudes, arid areas). The effects of "invisible colleges" and the inevitable geographic concentration of research effort were clearly important in the development of Holocene climate research, especially in the early pioneering stages.

This chapter provides a historical overview of progress and associated paradigm shifts in Holocene climate research. My review is inevitably incomplete for several reasons. First, it reflects my geographic parochialism as there is an inevitable bias towards areas where I have had some direct research interest and experience. Second, it reflects a methodologic bias with an inevitable bias towards terrestrial proxies and Holocene terrestrial paleoecology of which I have had some direct experience. Third, the recent primary literature is so vast that I have mainly cited recent reviews and books rather than original research papers to keep the bibliography a manageable size. Fourth, I pay greatest attention to the early pioneering studies and research stages and the early publications than to the later stages, several of which are being actively pursued today by many researchers. This concern with the pioneering studies is because there is an increasing tendency in these days of the Internet and electronic sources, such as Wikipedia, for the early primary literature and the early pioneering researchers to be forgotten, or at least largely ignored. I apologize for any major omissions in the geographic areas, methodologic developments, research studies, and literature discussed here, and for any unevenness in my accounts of the different stages in Holocene climate research.

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