The Effect on slope using base period from 1931 to 1995

As requested for WUWT here is a plot of linear curve fit to plots of the same data referenced to 30 year periods from 1931 to 1995
eg. base periods
1931 to 1961
1945 to 1975
1995 to 2012* THIS DOES NOT GIVE SUFFICIENT YEARS BUT IS PLOTTED.

Only stations returning over 15  reference base years were used as noted on the normal plot. The stations in this data set are from the UK

So it looks as if the slope changes by over 10% but 1961 to 1991 gives one of the lower slopes. Choosing 1931 the slope (deg C per year) is near the maximum!

The Effect Of Anomaly reference period on Temperature Plots

Much rubbish is talked in some locations about how the reference period for anomaly plots is chosen to to create worse temperature rises than reality.

Here is a plot showing monthly data from UK station temperatures. These are converted into anomalies by taking 30 Januarys from the start year, averaging the temperature and then subtracting this from each January to create an anomaly. This is repeated for each month to create the full plot.

This method shows how met. stations are warming and allows a reasonable average anomaly to be calculated over dissimilar (envirnonmentally) stations. It also removes the annual fluctuation in temperature reducing the need to filter this out.

The plot shows 5 different start years from 1951 to 1991 (the latter only having 20 years averaged for the anomaly calculation.

As can be seen all that happens is the plot gets shifted up and down the chart. The wiggles and the slope are constant.

NO ADDITIONAL WARMING is created by changing the reference period. The reference period is not relevant unless the distribution of temperatures throughout the year changes.