Introduction: The climate of any region sets the tempo of indigenous life styles and largely dictates the scale and type of economic activity that can be sustained. In Arizona, we are subject to perhaps more climatic restraints than are many other areas, due to the high air temperatures in summer and the rather low yearly rainfall. But, weather is variable; and its sum total -- climate -- is not unchanging either. Thus, in planning the future direction economic activity should take, prospects for changes in climate should be considered. In this paper we attempt to marshal the best evidence available to outline the possibilities for Arizona's future climate. We hope that the information will prove useful to those who must make the difficult decisions that will shape the character of our state in the years to come.

Millennial length temperature and precipitation reconstructions from tree rings are developed for the northern Arizona region and applied to questions regarding the nature of the cultural-environmental interface in the northern Southwest, the role of explosive volcanism as a forcing mechanism in temperature variability, and the state of late 20th century climate compared to the range of natural variability of the past. A 2660-year long bristlecone pine tree-ring chronology from high elevation in the San Francisco Peaks of northern Arizona is calibrated with instrumental annual mean-maximum temperature data to reconstruct temperature. Three 1400-year long lower elevation tree-ring chronologies, developed from both living trees and wood from archaeological sites on the Colorado Plateau, are calibrated with instrumental precipitation data (October-July) to reconstruct precipitation. The juxtaposition of these two reconstructions yields paleoclimatic insights unobtainable from either record alone. Results include the identification of wet, dry, cool, and warm intervals and the identification of periods of high and low variance in temperature and precipitation. Population movement into the Flagstaff area in the second half of the 11th century is attributed to relatively warm wet conditions. The role of temperature decline in the 13th century merits additional consideration in the prehistoric regional abandonment of the Four Corners area. Many of the reconstructed cold periods are linked to explosive volcanism. The second half of the 20th century is the warmest in the period of record, and extremely warm/wet conditions have persisted since 1976.