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Eric J. Steig & David P. Schneider
University of WashingtonC. A. Shuman
NASA/Goddard
WAIS Workshop
September, 2003
Reconstruction of Antarctic climate through the
Holocene and beyond:methodology, and
implications for deep ice core site selection
Past climate variability and change
Satellite Observations
Numerical Weather Reanalyses and Mesoscale Modeling
Antarctic Weather Stations
Array of Shallow Ice Cores
Deep Ice Cores
Time
Space
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
Modern interannual temperature variability
Figure after Schneider, Steig, Comiso, in press (J. Climate)
Methodology
€
T = λ k
k=1
K
∑ ukTvk
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
€
Ux = yshort
Use that relationship to extend climate basis functions farther back in time
€
ˆ U x = y long
Methodology
€
ˆ T = λ k
n=1
NPCs
∑ ˆ u kTvk
Reconstruct the climate field by summing over the reconstructed PCs
“Known” Data Proxy Data
Satellites: complete spatial coverage to 1982
Weather stations:Continuous temporal recordsto 1961; back to 1901 onlimited basis
MethodologyAVHRR PCs
(“known”)
Weather StationsCalibration Interval“proxy”
Weather StationsFull Data Set“proxy”
ReconstructedPCs
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)
Verification (2000-2002) = 0.66 (monthly) (Vostok) = 0.60 (annual)
How well does it work?
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.
Modes of Variability: Modern vs. LGM
Figure from Camille Li et al. CCM3 experiments.
Control EOF1 of Z500 (21%)
10 m contours
Control EOF2 of Z500 (14%)
LGM EOF1 of Z500 (31%)
LGM EOF2 of Z500 (16%)
Figure after Lea, Science 297 (2002).
Super ENSO and Global Climate Oscillations at Millennial Time ScalesLowell Stott, Christopher Poulsen, Steve Lund, and Robert Thunell Science 2002 297: 222-226.
El Niño-Like Pattern in Ice Age Tropical Pacific Sea Surface TemperatureAthanasios Koutavas, Jean Lynch-Stieglitz, Thomas M. Marchitto, Jr., and Julian P. Sachs Science 2002 297: 226-230.
Long term ENSO changes?