PARENT SESSION
Oral Session #33: Climate Change. Presiding: A. Peterson.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas E.
Climatic interpretation of 20th-century tree-ring patterns in high-elevation conifers.
Bunn, Andrew1, Graumlich, Lisa1, Urban, Dean2, 1 2
ABSTRACT- Millennial-length networks of annually-resolved proxies of past climate derived from tree rings, ice cores, and historical records play a pivotal role in assessing the role of greenhouse warming in current Northern Hemisphere climate trends. The most critical and most controversial data source in these analyses are tree-ring records from high elevation conifers in western North America that display a progressive trend in growth that may reflect rising atmospheric carbon dioxide levels. Here we analyze an augmented, multi-species tree-ring database from western North America to assess the degree to which 20th century growth trends reflect climatic variation. Using non-parametric ordination and cluster analyses, we decompose the variability at annual to decadal time scales into two dimensions, both of which are significantly correlated to temperature and precipitation variation. We examine rates and trajectories of change and find that the pattern of high elevation conifer growth rates during the last half of the 20th century have no analog in the past 1000 years.
KEY WORDS: climate, tree-rings, ordination, Sierra