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Limits of historical reconstructions using
indirect evidence
Limits of historical reconstructions using
indirect evidence
Hans von Storch, Eduardo Zorita, Julie Jones, Institute for Coastal Research, GKSS Research Centre, GermanyFidel González-RoucoUniversity Complutense Madrid, Spain
Hans von Storch, Eduardo Zorita, Julie Jones, Institute for Coastal Research, GKSS Research Centre, GermanyFidel González-RoucoUniversity Complutense Madrid, Spain
9IMSC, Cape Town24-28. May 2004
ECHO-G simulations „Erik den Røde” (1000-1990)
and “Christoph Columbus” (1550-1990)
with estimated volcanic, GHG and solar forcing
1675-1710vs. 1550-1800
Reconstruction from historical evidence, from Luterbacher et al.
Late Maunder Minimum
Model-based reconstuction
Christoph CErik dR
Both, Erik den Røde and Christoph Columbus generate temperature variations considerably larger than standard reconstructions (Mann, Jones …).
The simulated temperature variations are of a similar range as derived from NH summer dendro-data and from terrestrial boreholes.
For the present context, it does not really matter how „good“ the historical climate is reproduced by Erik den Røde and Christoph Columbus
.
The model data provide a laboratory to test MBH and other methods.
pseudo-proxies: grid point SAT plus white noise
red: mimicking largest sample used in MBHblue: hypothetic additional data to obtain better coverage.
Testing the MBH method
Mimicking MBH?
Estimated NH SAT from terrestrial deep soil temperature (TDST) in Erik den Røde.
Conclusion, 1
• Erik den Røde, an effort to simulate the response to estimated volcanic, GHG and solar forcing, 1000-2000.
• Low-frequency variability in Erik den Røde > Mann, Jones, & mainstream, but ~ Esper, boreholes, (some) instrumental data
Conclusion, 2
• Erik den Røde-data used to test MBH and borehole approaches.
• Randomized grid-point SAT (i.e. white noise added) is used as pseudo proxy.
• MBH method, based on regression, gives significant underestimation of low-frequency NH mean SAT.
• Direct averaging of randomized local data results in considerably smaller errors in NH mean SAT.
Conclusion, 3
• When using Erik den Røde-data and pseudo-proxy data, which share a correlation of about 0.5 with the grid point data, the best guess resembles the MBH estimate (incl. the ±2σ confidence band).
• The problem is common to ALL regression based methods, trained with temporal high-resolution data – except if the correlations are really high.
• A reliable reconstruction of centennial time scales requires either really high correlation, or process-based inverted data (e.g., borehole inversions), or local instrumental data.
Testing with HadCM3 simulation
Erik
HadCM3
Data provided by Simon Tett.