A. dell'Aquila, M. Felici, V. Lucarini, P.M. Ruti, A. Speranza, R. Vitolo
Extreme value statistics of mid-latitude atmospheric variability 
with present-day and increased CO2 concentration
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ABSTRACT.  The General Circulation Model ECHAM4.6 is run under perpetual January 
conditions with two different values of CO2: the present 
concentration and five times as much. For each case, time series of 
two indexes of mid-latitude wave activity are computed. The mean 
activity of baroclinic waves and of planetary waves decreases 
slightly, following the decrease of the mean baroclinicity of the 
system. Inference of extreme values is performed by estimating the 
parameters of the Generalised Extreme Value (GEV) distribution from 
sequences of maxima over data blocks of fixed length extracted from 
the time series. The sensitivity and goodness-of-fit of the inferences 
are assessed by various graphical and numerical tools. The results 
reveal no marked differences in the statistics of extreme values 
between the cases with 1 and 5 CO2 and also suggest that the often 
invoked approach of relating changes of the extremes to changes in the 
mean and standard deviation of the bulk statistics is not reliable. 
Maps corresponding to the dates of the extremes (block maxima) of the 
indexes show that the relative weight of the wave activity of the 
Atlantic sector increases with CO2 concentration.