The climate of coastal British Columbia is regulated by the proximity of the Pacific Ocean, which imparts a maritime climate to this region through a complex suite of forcing processes. Nevertheless, there is a growing recognition that the climate of this region is not static and that shifts between climatic states have occurred not only repeatedly but often abruptly. There is strong evidence showing that the North Pacific underwent a massive reorganization following the winter of 1976, and was accompanied by wide-scale circulation pattern changes that influenced natural systems from glacier mass balance states to streamflow conditions throughout western North America. The accompanying changes had devastating repercussions for a variety of ongoing fishery, water resource and forestry management strategies.

Dendroclimatic research undertaken at the University of Victoria Tree-Ring Laboratory (UVTRL) has shown that the 1976-1977 climate shift was not unique and that similar events have occurred at least eleven times during the past 400 years (Gedalof and Smith 2001). Significantly, our analyses indicate that another regime-scale shift in the North Pacific is almost certainly imminent. If this proves to be the case, it suggests that the observed climate of the Twentieth Century may not be representative of longer-term variability in the North Pacific ocean-atmosphere system.

High-resolution archives of past climate fluctuations are clearly required to detect and assess major climatic changes. In coastal British Columbia, the climate sensitivity of several long-lived tree species offers an opportunity to develop overlapping records of environmental change that potentially span the last millennium (Smith and Laroque 1998; Laroque and Smith 1999; Gedalof and Smith 2001). While this record will not be matched in detail or length by the glaciological record, recent studies confirm there is dendroglaciological evidence of Little Ice Age (LIA) glacier activity within the Coast Mountains that offers a complimentary climate-related signal (Smith and Laroque 1996; Smith and Desloges 2000). Reconstructions focused on identifying the common climate forcing mechanisms should permit the development of a robust proxy mass balance records (Lewis and Smith 1999).

Based on these findings, our ongoing research is designed to reconstruct the recent climate history of the Coast Mountains of British Columbia using tree ring data. The overall goals are to:

develop a network of high elevation tree-ring sites within the Coast Mountains. Chronologies and climate reconstructions developed from these data will provide a perspective on local climatic environments (growing season temperature and winter snowpacks. develop a corollary network of coastal moisture-sensitive sites that provide information on precipitation and precipitation variability).

complete a broader-scale analysis (synoptic dendroclimatology) of the tree-ring data to offer insights into regional/global relationships. It is anticipated that tree-ring data sets will be developed to reflect spatial and temporal patterns encompassing the range of natural climate variability of large scale atmospheric and ocean circulation patterns over the last millennium. document Little Ice Age glacial histories to assess linkages between mass balance fluctuations and climatic changes within the last millennium.

assess the different reconstructions of past climates and relate these to our understanding of the controls of climate variability.

Tree-ring, climate and glacier records will be used to reconstruct the recent climate history of the British Columbia Coast Mountains ( Smith and Desloges 2000, Lewis 2001). Because each of these indices differ in the timing and change they record, a regional tree-ring network is being compiled to isolate the common forcing mechanisms. Shown below is the network of tree-ring chronologies that we have been collected (1993-2001), largely at high elevation treeline sites, in the southern and central Coast Mountains of British Columbia by various UVTRL researchers.

E-mail : Dan Smith smith@uvic.ca