HR: 16:00h
AN: GC54B-01 INVITED    [Abstracts]
TI: Permanent El Nino Conditions in the Early Pliocene, the Poleward Heat Transport Paradox, and Contemporary Global Warming.
AU: * Fedorov, A V
EM: alexey.fedorov@yale.edu
AF: Yale University, Department of Geology and Geophysics, KGL, 210 Whitney Ave, New Haven, CT 06511, United States
AU: Brierley, C
EM: christopher.brierley@yale.edu
AF: Yale University, Department of Geology and Geophysics, KGL, 210 Whitney Ave, New Haven, CT 06511, United States
AB: Proxy temperature records show that in the early Pliocene, approximately 3 to 5 million years ago, the tropics were characterized by permanently warm El Nino-like conditions. The equatorial Pacific was as warm as in the east as it is in the west today, and the zonal SST gradient along the equator was significantly reduced or absent. Concurrently, major coastal upwelling regions were up to 10 degrees C warmer than they are today. The globally averaged temperatures of the Earth's surface were also substantially higher. This climate state persisted even though the external factors that control climate were essentially the same as at present and the Earth was experiencing greenhouse conditions similar to today's, with the concentration of CO2 in the atmosphere comparable to present day values. Thus far, there is no satisfactory explanation for the climate state of the Pliocene, especially for the climate conditions in the tropics and subtropics. State-of-the-art climate models fail to reproduce a permanent El Nino even when forced by CO2 concentrations many times larger than those estimated for the early Pliocene. Predicting the impact on the tropics of global warming caused by anthropogenic factors also remains a serious challenge for climate scientists. Coupled general circulation models yield a wide range of possible scenarios for the region, but many suggest a slightly higher likelihood of an El Nino-like state in global warming. Efforts to predict future global warming should benefit enormously from a better understanding of the state of permanent El Nino which imposes a strong dynamical constraint on both oceanic and atmospheric circulations. Modeling permanent El Nino with atmospheric and oceanic GCMs reveals a poleward heat transport paradox: Calculations with ocean-only models suggest that a permanent El Nino should correspond to a reduced poleward heat transport by the ocean. This is related to a deeper thermocline in the eastern equatorial Pacific, which leads to a smaller ocean heat intake in the equatorial region. However, calculations with atmospheric GCMs suggest a weaker poleward heat transport by the atmosphere and, consequently, a strengthening of the ocean heat transport. This contradiction implies that there should be an additional mechanism for the poleward heat transport, which is absent or under-resolved in the current generation of general circulation models. This factor explains why climate models cannot replicate a permanent El Nino, and also questions whether climate GCMs can model adequately the impacts of global warming.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4522 ENSO (4922)
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting