Climate of the Past
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http://www.clim-past.net/2/167/2006/cp-2-167-2006.pdf
167
185
2006-10-26
Inter-hemispheric linkages in climate change: paleo-perspectives for future climate change
J. Shulmeister
james.shulmeister@canterbury.ac.nz
D. T. Rodbell
M. K. Gagan
G. O. Seltzer
Department of Geological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Department of Geology, Union College, Schenectady, NY 12308, USA
Research School of Earth Sciences, The Australian National University, Canberra 2000, ACT, Australia
Department of Earth Sciences, Heroy Geology Lab, University of Syracuse, Syracuse NY 13244, USA
deceased
The Pole-Equator-Pole (PEP) projects of the PANASH (Paleoclimates of the
Northern and Southern Hemisphere) programme have significantly advanced our
understanding of past climate change on a global basis and helped to
integrate paleo-science across regions and research disciplines. PANASH
science allows us to constrain predictions for future climate change and to
contribute to the management of consequent environmental changes. We
identify three broad areas where PEP science makes key contributions.
<br><br>
1. <i>The pattern of global changes.</i> Knowing the exact timing of
glacial advances (synchronous or otherwise) during the last glaciation is
critical to understanding inter-hemispheric links in climate. Work in PEPI
demonstrated that the tropical Andes in South America were deglaciated
earlier than the Northern Hemisphere (NH) and that an extended warming began
there ca. 21 000 cal years BP. The general pattern is consistent with
Antarctica and has now been replicated from studies in Southern Hemisphere
(SH) regions of the PEPII transect. That significant deglaciation of SH
alpine systems and Antarctica led deglaciation of NH ice sheets may reflect
either i) faster response times in alpine systems and Antarctica, ii)
regional moisture patterns that influenced glacier mass balance, or iii) a
SH temperature forcing that led changes in the NH. This highlights the
limitations of current understanding and the need for further fundamental
paleoclimate research.
<br><br>
2. <i>Changes in modes of operation of oscillatory climate systems.</i>
Work across all the PEP transects has led to the recognition that the El
Niño Southern Oscillation (ENSO) phenomenon has changed markedly through
time. It now appears that ENSO operated during the last glacial termination
and during the early Holocene, but that precipitation teleconnections even
within the Pacific Basin were turned down, or off. In the modern ENSO
phenomenon both inter-annual and seven year periodicities are present, with
the inter-annual signal dominant. Paleo-data demonstrate that the relative
importance of the two periodicities changes through time, with longer
periodicities dominant in the early Holocene.
<br><br>
3. <i>The recognition of climate modulation of oscillatory systems by
climate events.</i> We examine the relationship of ENSO to a SH climate event,
the Antarctic cold reversal (ACR), in the New Zealand region. We demonstrate
that the onset of the ACR was associated with the apparent switching on of
an ENSO signal in New Zealand. We infer that this related to enhanced zonal
SW winds with the amplification of the pressure fields allowing an existing
but weak ENSO signal to manifest itself. Teleconnections of this nature
would be difficult to predict for future abrupt change as boundary
conditions cannot readily be specified. Paleo-data are critical to
predicting the teleconnections of future changes.
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