Last month I posted some information on the rate of change for seasonal anomalies and thought I'd give a little more detail about the calculations involved. One starts with the NOAA Global Land Anomaly and computes the annual averages for the years for which the data is available (1880 to 2012).
One then computes the differences from the monthly averages and sorts the results by month. One can then do a linear fit for each month to get the coefficients for the lines of best fit.
If one looks at the fit for Aug one sees that there is a steady rate of decrease for the 133 years that were used.
As shown in the previous post the rates for the year roughly follows a sinusoidal curve. The maximum rate of change appears to be 0.24 °C per century.
The peak rate of increase in Feb and the rate of decrease in Aug are of the same magnitude for the sinusoidal curve and the average for the curve is 0. The sum of alpha and beta also average to zero since the yearly average is by definition equal to zero. The steady rates of change are evidence of a long term decrease in the difference between the Aug and Feb anomalies.
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