HR: 09:15h
AN: PP51E-06    [Abstracts]
TI: Mounting Mid-Pliocene Paradoxes, Mounting Concern About Climate Sensitivity
AU: * Chandler, M A
EM: mac59@columbia.edu
AF: Columbia University, CCSR/GISS, 2880 Broadway, New York, NY 10025, United States
AU: Dowsett, H
EM: hdowsett@usgs.gov
AF: U. S. Geological Survey, 926A National Center, Reston, VA 20192, United States
AU: Dwyer, G
EM: gsd3@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC 27708, United States
AU: Jonas, J
EM: jjonas@giss.nasa.gov
AF: Columbia University, CCSR/GISS, 2880 Broadway, New York, NY 10025, United States
AU: Shukla, S
EM: sonalips16@gmail.com
AF: Columbia University, CCSR/GISS, 2880 Broadway, New York, NY 10025, United States
AB: The warm interval of the middle Pliocene continues to vex proxy data and climate modelers with its unusual combination of much warmer than modern sea surface temperatures, reduced ice sheet mass and consequent sea level rise, together with atmospheric carbon dioxide amounts that are within the error bars of present day values. Coupled ocean atmosphere GCMs simulating the mid-Pliocene have characteristically been incapable of producing sea surface temperatures at high latitudes that are as warm as those portrayed by the PRISM2 global data set, while simultaneously maintaining relatively unchanged tropical SSTs. Alkenone data for the east equatorial Pacific, and reanalysis of Mg/Ca proxies may show that warmer tropical SSTs were indeed present at this time, but it remains to be seen whether or not proxy paleo-CO2 data can be reinterpreted to lend modelers a forcing mechanism that would generate such warm ocean temperatures. Further complicating the Pliocene scenario is the fact that deep ocean temperature data that are now becoming available may not present a smoking gun that would be suggestive of ocean circulation intensification. This may not prove to be paradoxical to prior interpretations of carbon isotope ratios, which seemed indicative of increased NADW production, but once again a mechanism (increased ocean heat transport) that may have been consistent with much warmer North Atlantic SSTs, might be at odds with proxy data. Regardless, coupled models seem locked into solutions that show warming climates are generally accompanied by a weakening of the North Atlantic circulation. Thus, one of the few negative feedbacks that we consistently find in global warming scenarios is triggered in a location where the mid-Pliocene warm SST anomaly peaks. These paradoxes are explored using one of the latest versions of the GISS GCM (Model III). With the mid-Pliocene the most recent period in which global warmth approached something like late 21st century projections, we should perhaps be concerned that our closest global warming analog is telling us that our best models are not sensitive enough.
DE: 0429 Climate dynamics (1620)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0798 Modeling
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting