An assessment of the possible effects of volcanic eruptions on North American climate using tree-ring data, 1602 to 1900 A.D.

Seasonal and annual temperature reconstructions derived from western North American semi-arid site tree-ring chronologies are used to examine the possible spatial response of North American climate to volcanic eruptions within the period 1602 to 1900. Low-latitude eruptions appear to give the strongest response. Cooling of the annual average temperatures in the central and eastern United States is reconstructed to follow volcanic eruptions with warming in the western states. The magnitude and spatial extent of the reconstructed cooling and warming varies seasonally. The warming that occurs in the west is strongest and most extensive in winter while the cooling in the east is most marked in summer. These results are based on reconstructed climate records which contain error terms unrelated to climatic factors. The suggested pattern of response to volcanic forcing is, however, supported by four independent temperature/proxy temperature series within the area of the temperature reconstructions. Additional support is provided by three independent series lying outside the area which suggest that the temperature spatial response may extend to the north beyond the area covered by the tree-ring reconstructions.