Dendrochronology in climatology - The state of the art

The current state of dendrochronology's contributions to climatology is surveyed, with an emphasis on the extent to which its actual and potential strengths are being used, and its weaknesses recognized and surmounted. After the growth in climatologists' interest in the potential of dendrochronology to contribute to their field is described, a brief account is given of the development of dendroclimatology over the past quarter-century. The strengths and weaknesses of tree rings as natural archives of climate variability are discussed. The greatest strengths are: the capability to date tree rings to the calendar year with a very high degree of confidence; the existence of large geographic-scale patterns of common year-to-year tree-ring variability; the development of very extensive, shared networks of tree-ring chronologies meeting common standards; the surprising effectiveness of very simple linear models of tree-ring/climate relationships; and the growing understanding of the mechanisms leading to variability in tree-ring features. The greatest weaknesses are that: tree-ring chronologies only capture a fraction of climate variability; their response may be limited to specific seasonal "windows"; some do not respond directly to a single monthly or even seasonal climate variable; they may not record the climate variables of interest to climatologists; their use to reconstruct past climate is based on the assumption that the same factors, acting in the same way, controlled the formation of tree rings in the past as in the twentieth century; and, the techniques used to remove non-climatic variability, such as that caused by tree age/size trend and interactions with neighbors, limit the faithful representation of climate variations on centennial and longer time scales in many cases. The manner in which these strengths have been used, and these weaknesses addressed, is discussed. The overall assessment is that the state of the art of dendrochronology in climatology is vibrant, with much robust debate and innovative work.