NZ vs S. Hemisphere temperatures

The “Seven-Station Series” (7SS) constituting the official New Zealand Temperature Record (NZTR) is analysed and compared with the Southern Hemisphere (SH) temperature record using an interesting new data analysis technique called Empirical Mode Decomposition (EMD).

UPDATE 1, 10 JAN 2011, 22:28 NZDT

Analysis of temperature trends usually employs extrinsic data smoothing techniques such as regression, moving average and Fourier filtering, but there is a more appropriate technique available.

Empirical mode decomposition (EMD) is an intrinsic data analysis technique now being used across a number of disciplines, including climatology. You can find out more from these two background papers: On the trend, detrending, and variability of nonlinear and nonstationary time series (Wu et al., 2007)(pdf) and Analysis of Temperature Change under Global Warming Impact using Empirical Mode Decomposition (Molla et al., 2007)(pdf). If you want to study EMD in detail, there’s a lot of help available — even a free command line utility.

EMD uses a sifting algorithm that filters the data until an overall adaptive trend (monotonic residual) is revealed. The first paper linked above shows how a decadal trend was also extracted from the global record but the 100-year 7SS time-frame used here is too short to do the same. A longer 7SS record would probably reveal an intermediate decadal trend similar to that presented plus an overall trend that cannot be extracted (by this author) from the 7SS at its current length. Continue Reading →