On the credibility of climate predictions

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Mike Jr.

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Sep 13, 2008, 6:27:16 AM9/13/08
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http://www.itia.ntua.gr/en/docinfo/864/

This is a peer-reviewed paper.

"... the models of the IPCC Third Assessment Report have projected
future climate starting from 1990; thus, there is an 18‐year period
for which comparison of model outputs and reality is possible. In
practice, the climatic model outputs are downscaled to finer spatial
scales, and conclusions are drawn for the evolution of regional
climates and hydrological regimes; thus, it is essential to make such
comparisons on regional scales and point basis rather than on global
or hemispheric scales. In this study, we have retrieved temperature
and precipitation records, at least 100‐year long, from a number of
stations worldwide. We have also retrieved a number of climatic model
outputs, extracted the time series for the grid points closest to each
examined station, and produced a time series for the station location
based on best linear estimation. Finally, to assess the reliability of
model predictions, we have compared the historical with the model time
series using several statistical indicators including long‐term
variability, from monthly to overyear (climatic) time scales."

The companion presentation can be found here.
http://www.itia.ntua.gr/getfile/850/2/documents/2008EGU_ClimatePredictionPr_.pdf

"20.Conclusions
* All examined long records demonstrate large overyear variability
(long‐term fluctuations) with no systematic signatures across the
different locations/climates.
* GCMs generally reproduce the broad climatic behaviours at different
geographical locations and the sequence of wet/dry or warm/cold
periods on a mean monthly scale.
* However, model outputs at annual and climatic (30‐year) scales are
irrelevant [sic] with reality; also, they do not reproduce the natural
overyear fluctuation and, generally, underestimate the variance and
the Hurst coefficient of the observed series; none of the models
proves to be systematically better than the others.
* The huge negative values of coefficients of efficiency at those
scales show that model predictions are much poorer that an elementary
prediction based on the time average.
* This makes future climate projections not credible.
* The GCM outputs of AR4, as compared to those of TAR, are a
regression in terms of the elements of falsifiability they provide,
because most of the AR4 scenarios refer only to the future, whereas
TAR scenarios also included historical periods."

--Mike Jr

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