TREE-RING EVIDENCE OF THE WIDESPREAD EFFECTS OF EXPLOSIVE VOLCANIC-ERUPTIONS

Tree-ring evidence from 97 sites over North America and Europe are use d to develop a chronology of widespread cool summers since 1600. Avera ging annual maximum-density information from the chronologies provides an index that correlates with Northern Hemisphere summer temperatures to 0.44 over 1851-1975. A number of the extreme low density years occ ur in both North America and Europe, suggesting a common response to h igh-frequency forcing. The analysis was repeated with ring-width infor mation but the results are markedly less coherent. Of the five common extreme low-density years (1601, 1641, 1669, 1699 and 1912) four are k nown to be coincident with the year or year following major volcanic e ruptions. Other extreme low density indices in the continental series are also dearly coincident with known volcanoes. ?he density indices c learly demonstrate great potential for quantifying the climate effecti veness and perhaps establishing precise calendar dates of large explos ive volcanoes.