An Orbitally Driven Tropical Source for Abrupt Climate Change*

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Abstract
Paleoclimatic data are increasingly showing that abrupt change is present in wide regions of the globe. Here a mechanism for abrupt climate change with global implications is presented. Results from a tropical coupled ocean–atmosphere model show that, under certain orbital configurations of the past, variability associated with El Niño–Southern Oscillation (ENSO) physics can abruptly lock to the seasonal cycle for several centuries, producing a mean sea surface temperature (SST) change in the tropical Pacific that resembles a La Niña. It is suggested that this change in SST would have a global impact and that abrupt events such as the Younger Dryas may be the outcome of orbitally driven changes in the tropical Pacific.