Divergence problem in Japanese tree-ring records

It is a critical issue in tree-ring based climatic reconstructions to search for possible causes of divergence between tree-ring and temperature records. The divergence problem has been evidenced mainly by ring-width and density records from circumpolar northern forest sites. In this study, we compiled recently developed tree-ring chronologies in Japan. We performed running correlation analysis between the ring-width data and local climate records. A decreased temperature sensitivity since 1960s was observed in ring-width data for Hinoki cypress trees in central Japan. It was suggested that the divergence at this location was cased by anthropogenic SO2 emission that increased rapidly until 1970 and by then decreased gradually. On the other hand, a Japanese cedar chronology in north-eastern Japan showed stable response to April temperature and increased sensitivity to February, March and May temperatures. Adding some other forest sites to these, we present some conclusions with regards to the current understanding of the divergence problem in Japan.