Variability in the El Nino - Southern oscillation through a glacial-interglacial cycle

The El Nino-Southern Oscillation (ENSO) is the most potent source of intera nnual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change, Here we use annually banded corals from Papua New Guinea to show that ENSO has exi sted for the past 130,000 years, operating even during "glacial" times of s ubstantially reduced regional and global temperature and changed solar forc ing. However, we also find that during the 20th century ENSO has been stron g compared with ENSO of previous cool (glacial) and warm (interglacial) tim es. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing b y precessional orbital variations.