Volcanic and solar forcing of the tropical Pacific over the past 1000 years

The response of El Nino to natural radiative forcing changes over the past 1000 yr is investigated based on numerical experiments employing the Zebiak-Cane model of the tropical Pacific coupled ocean-atmosphere system. Previously published empirical results demonstrating a statistically significant tendency toward El Nino conditions in response to past volcanic radiative forcing are reproduced in the model experiments. A combination of responses to past changes in volcanic and solar radiative forcing closely reproduces changes in the mean state and interannual variability in El Nino in past centuries recorded from fossil corals. The dynamics of El Nino thus appear to have played an important role in the response of the global climate to past changes in radiative forcing.