Dangers of multiyear averaging in analyses of longterm climate trends
Abstract
Multiyear averaging in studies seeking longterm trends can be risky and misleading. It is shown here that a change of 1 year in the starting point of the averaging done in generating a multiyearaverage sequence can make a dramatic difference in the appearance of the sequence, even including whether the apparent trend is upward or downward. An example is given in which the same time series, when grouped to 3year averages by starting in turn at the first, second, and third points of the series, yields one 3yearaverage sequence that is monotonically increasing, a second 3yearaverage sequence that is monotonically decreasing, and a third 3yearaverage sequence that has constant values. Furthermore, it is proven in general that such series can be created for nyear averages for any integer n > 2, and can be extended to exceed any desired length. Finally, historical seaice data from Iceland are used to illustrate with a longterm climate data set the misrepresentation of climate statistics which can occur through selective multiyear averaging.
 Publication:

Climate Dynamics
 Pub Date:
 June 1989
 DOI:
 10.1007/BF00207398
 Bibcode:
 1989ClDy....4...39P