Eric J' Steig

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Reconstruction of Antarctic climate through the
Holocene and beyondmethodology, and
implications for deep ice core site selection
WAIS Workshop September, 2003
Eric J. Steig David P. Schneider
University of Washington
C. A. Shuman
NASA/Goddard
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Past climate variability and change
Deep Ice Cores
Array of Shallow Ice Cores
Time
Antarctic Weather Stations
Satellite Observations
Numerical Weather Reanalyses and Mesoscale
Modeling
Space
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Question 2. How has the climate changed over
WAIS during the past 200-500 years ?

• Goal Use ITASE ice cores to answer this
• Problem interpretation of ice cores requires
  reliable calibration against the instrumental
  record, but the instrumental record is too short
  and too sparse
• Solution use statistical methods to extend an
  estimate of the instrumental record as far back
  as we can

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Modern interannual temperature variability
Figure after Schneider, Steig, Comiso, in press
(J. Climate)
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Methodology
Obtain basis functions (time series and
associated spacial patterns) of variability using
orincipal component analysis of known climate
Determine empirical relationship between proxy
variables (e.g. ice cores) and known climate data
Use that relationship to extend climate basis
functions farther back in time
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Methodology
Reconstruct the climate field by summing over the
reconstructed PCs
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Known Data Proxy Data
Weather stations Continuous temporal records to
1961 back to 1901 on limited basis
Satellites complete spatial coverage to 1982
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Methodology
AVHRR PCs (known)
Weather Stations Calibration Interval proxy
Weather Stations Full Data Set proxy
Reconstructed PCs
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How well does it work?
Calibration/Verification statistics (correlation
coefficients) Calibration (1982-1999) 0.77
(monthly)
0.77 (annual)
0.91 (5-year averages) Verification
(1961-1981) 0.61 (monthly) (weather stations)
0.54 (annual)
0.71 (5-year averages) Verificat
ion (2000-2002) 0.66 (monthly)
(Vostok) 0.60 (annual)
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AVHRR Data
1982
1984
Reconstruction
1982
1984
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Reconstruction of Vostok Temperatures
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Reconstruction of Vostok Temperatures
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Figure from Rutherford/Mann shows fraction of
data availability 1960-1999.
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Implications for ITASE cores
Reconstructed instrumental records provide larger
data set for calibration of ice core proxy
variables. Reconstructed records are long enough
to allow for decade-to-decade as well as
interannual comparison. Reconstructions are
inherently filtered to emphasize large-scale
variability. Prediction ice core records will
better reflect the PCs of the temperature field
than with raw temperature, due to uncorrelated
noise in both.
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Implications for Deep Drilling Site Selection
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Modes of Variability Modern vs. LGM
Figure from Camille Li et al. CCM3 experiments.
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Long term ENSO changes?
Super ENSO and Global Climate Oscillations at
Millennial Time Scales Lowell Stott, Christopher
Poulsen, Steve Lund, and Robert Thunell Science
2002 297 222-226. El Niño-Like Pattern in Ice
Age Tropical Pacific Sea Surface
Temperature Athanasios Koutavas, Jean
Lynch-Stieglitz, Thomas M. Marchitto, Jr., and
Julian P. Sachs Science 2002 297 226-230.
Figure after Lea, Science 297 (2002).
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SOI vs. AVHRR temperature
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Calibration Statistics (r)
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PCs vs. Variance