Eric J. Steig & David P. Schneider University of Washington C. 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 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 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

Methodology Reconstruct the climate field by summing over the reconstructed PCs

“Known” Data Proxy Data Satellites: complete spatial coverage to 1982 Weather stations: Continuous temporal records to 1961; back to 1901 on limited basis

Methodology AVHRR PCs (“known”) Weather Stations Calibration Interval “proxy” Weather Stations Full Data Set “proxy” Reconstructed PCs

Calibration/Verification statistics (correlation coefficients) Calibration ( ) = 0.77 (monthly) = 0.77 (annual) = 0.91 (5-year averages) Verification ( ) = 0.61 (monthly) (weather stations) = 0.54 (annual) = 0.71 (5-year averages) Verification ( ) = 0.66 (monthly) (Vostok) = 0.60 (annual) How well does it work?

Reconstruction AVHRR Data

Reconstruction of Vostok Temperatures

Figure from Rutherford/Mann shows fraction of data availability

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.

Implications for Deep Drilling Site Selection

Modes of Variability: Modern vs. LGM Figure from Camille Li et al. CCM3 experiments.

Figure after Lea, Science 297 (2002). Super ENSO and Global Climate Oscillations at Millennial Time Scales Lowell Stott, Christopher Poulsen, Steve Lund, and Robert Thunell Science : 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 : Long term ENSO changes?

SOI vs. AVHRR temperature

Calibration Statistics (r)

PCs vs. Variance