Tree-Ring Evidence for Climatic Changes in Western North America From 1500 A.D. to 1940 A.D.

Abstract

Introduction: The details of the climatic history of the United States during recent centuries are not known. In this period, as in more ancient times, there is much indirect evidence of significant changes of climate. Dendroclimatic analysis represents an especially promising source of information on the chronology and character of such climatic changes, especially those in the semiarid regions of western North America. It is the purpose of this report to present: (1) some recent analyses of the climatic factors influencing ring growth; (2) a brief discussion of the current theory concerning the model of tree growth and climate and (3) a first approximation of synoptic dendroclimatological patterns from 1500 A.D. to 1940 A.D. using 26 selected tree-ring chronologies from western North America. This material is being circulated to professionals in related fields in hopes that they may compare these results with their own findings and make appropriate criticisms. The authors welcome any suggestions, especially those pertaining to correlation or lack of correlation of the maps with other lines of evidence. The paper is to be presented at the VII International Congress of the International Association for Quaternary Research which meets at Boulder, Colorado, during August of 1965. The analyses of the tree growth relationships were sponsored in part by the National Geographic Society and the U. S. Department of Interior, National Park Service, through the Wetherill Mesa Archeological Project. The authors are indebted to past and present staff at the Laboratory of Tree-Ring Research for the development of the regional tree-ring chronologies, and to the Numerical Analysis Laboratory, The University of Arizona, for free computing time and services. They are also indebted to James A. Erdman, Maurice E. Cooley, Nicholas Matelas, and Julie McMahan, who assisted in various phases of the project.