Department of Environmental Sciences
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Seminar Abstracts
Environmental Sciences Seminar Abstract            

  Revisiting Mid-Holocene ENSO
Tony Broccoli
Rutgers University

The El Nino-Southern Oscillation (ENSO) phenomenon is a major source of climate variability on interannual time scales. Centered in the equatorial Pacific Ocean, ENSO has a profound impact on weather and climate throughout the tropics and an influence that extends to higher latitudes. Because of the widespread impacts of ENSO, there is considerable interest in potential changes in ENSO variability that may result from anthropogenic climate change. Whether ENSO variability will strengthen or weaken in the future remains highly uncertain, as a consensus among climate models has yet to emerge. Thus evidence of past changes in ENSO variability is valuable for understanding the mechanisms that might lead to such changes and for constraining climate model simulations. Reduced ENSO variability during the mid-Holocene epoch, a period from about 5,000 to 7,000 years ago, has been indicated by some proxy climate records. This interpretation has also been supported by some climate simulations. The putative source of reduced mid-Holocene ENSO variability is the seasonal redistribution of solar radiation associated with slow and subtle changes in the shape of Earth's orbit. The response of tropical Pacific climate to such orbital forcing is investigated in a simulation with the GFDL CM2.1 coupled atmosphere-ocean model and the evidence for reduced mid-Holocene ENSO variability is reexamined.


Last updated: 02/18/2010