The Paleoclimatic Perspective:
Paleoclimate-proxy data enhance the possibility of studying the nature and causes of past climate variability such as drought, especially with regards to severe multi-year events on time scales of decades to centuries. Such a perspective is necessary if reliable methods of forecasting and management are to be developed. For example, long drought histories are needed to develop useful probabilistic models to determine the risk of experiencing different classes of drought intensity and duration under future scenarios. As population and development patterns change under the spectre of a changing global climate, it is useful to be armed with knowledge about the true long-term variability of moisture availability in order to avoid disastrous shortages. With this, and related research projects, we use long tree ring records to overcome the most significant difficulty encountered when using the available instrumental records alone to model drought in the US, mainly the limited time span covered by such records. It is often not possible to know if the instrumental records are long enough to include the full range of drought variability likely to occur in any given region of the US in the future. Therefore, long tree-ring chronologies, when analysed carefully, help to increase the odds of capturing low-frequency trends in climate that are greater than the length of the instrumental data. Only through such an approach can regional populations be prepared for all contingencies based on a sound and sober understanding of the regional climate variability.
This projects objective is “to develop a network of drought-sensitive tree-ring chronologies for the eastern United States, derived primarily from two species of long-lived conifer: eastern red cedar (Juniperus virginiana) and eastern white cedar (Thuja occidentalis)”. Aside from the more spatially-restricted bald cypress (Taxodium distichum) found in the bottomlands of the southeastern US (e.g., Stahle et al., 1985; Stahle and Cleaveland, 1996), these two species represent the best opportunities for developing time series that cover the past 500-1000 years for the eastern US. This is due to the existence of relict sites in marginal locations that have escaped the loggers axe and other disturbances both natural and anthropogenic. Previous work by the Cliff Ecology Group at the University of Guelph in Canada showed the great potential for long records from Thuja in the Great Lakes region (e.g., Larson and Kelly, 1991; Kelly et al., 1994) and also for Juniperus in the Northeast (Larson, 1997). Following up on this concept, we explored cliff locations throughout the eastern US, and found both species growing in locations from West Virginia to New Hampshire, and westward to Wisconsin. Chronologies developed from this project were incorporated into a network used by Cook et al. (2004) to reconstruct North American drought, allowing for the extension of the reconstructions in the northeastern region back to AD 1500 or earlier in regions where it was not previously possible to do so. In addition, our chronologies were included in the expanded network used to produce the North American Drought Atlas.
Reconnoitring by air, potential cliff sites along the west shore of the Door Peninsula, Wisconsin.