We review results of recent and ongoing research in using long, exactly dated, annual tree-ring chronologies to study and reconstruct past El Niño/Southern Oscillation (ENSO) variability and forcing. The research covered here includes (1) the development and testing of long teak chronologies from Indonesia for ENSO signals; (2) the reconstruction of the Tahiti–Darwin Southern Oscillation Index (SOI) using tree-ring chronologies from North America and Java; (3) the recent discovery of some tree species suitable for developing tree-ring chronologies from ENSO-sensitive regions of East Africa; (4) the discovery of long-term ENSO forcing of climate in the midto high-latitude Southern Hemisphere from a tree-ring reconstruction of the summer transpolar sea-level pressure (SLP) index; and (5) the characterization of the ENSO teleconnection with drought in the United States and its temporal stability in a network of long drought reconstructions from tree rings.
The El Niño/Southern Oscillation (ENSO) is the most important known cause of interannual climate variability on Earth (see, e.g., Ropelewski and Halpert 1987; Kiladis and Diaz 1989). El Niño/Southern Oscillation has exhibited large changes in amplitude and phase of the annual cycle and in the frequency and intensity of warm and cold events during the past 100 years of instrumental observation. Dynamic models of ENSO have successfully anticipated some recent ENSO activity (Cane et al. 1986) and have also simulated dramatic amplitude modulation of warm events on decadal to century timescales (Cane et al. 1995).