Tree-ring evidence of the widespread effects of explosive volcanic eruptions

Tree-ring evidence from 97 sites over North America and Europe are used to develop a chronology of widespread cool summers since 1600. A number of the extreme low density years occur in both North America and Europe, suggesting a common response to high-frequency forcing. Of the five common extreme low-density years (1601, 1641, 1669, 1699 and 1912) four are known to be coincident with the year or year following major volcanic eruptions. Other extreme low density indices in the continental series are also clearly coincident with known volcanoes.