An orbitally driven tropical source for abrupt climate change

Paleoclimatic data is increasingly showing that abrupt change is present in wide regions of the globe. Here we present a mechanism for abrupt climate change with global implications. Results from a tropical coupled ocean-atmosphere model show that under certain orbital con gurations of the past, variability associated with El Ni~ no/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 Paci c which resembles a La Ni~ na. We suggest 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 Paci c.