Natural Variability in the GMST record

What is the natural variability in the surface temperature record?

One way to explore this is to take the temperature record and subtract all the known non-random forcings and fluctuations.  What's left over is our best guess at natural variation.

I did this with the HADCRUT global land/ocean temperature dataset from 1881 thru 2010. The known forcing that I used were:

• CO2
• TSI
• LOD
• ENSO (using two different ENSO indexes for comparison purposes)

The result looks like this:

Using the NINO34 ENSO dataset the standard deviation is 0.105503°C
Using the CTI ('Cold Tongue Index') the standard deviation is 0.107541°C

With global warming since pre-industrial at approximately 1°C, natural variation is not the answer.  It's known forcings -- and CO2 is most of that answer.

We should also check the sensitivity of the analysis to the various datasets used.  In the first analysis we looked at two different ENSO indexes.  A second analysis replaces the HADCRUT gmst data with the BEST gmst dataset.  The results are the same to within a few thousandths of a degree:

One other analysis that might be of interest is to gauge how 'The Tidal Model of ENSO' that Paul Pukite has developed fares in this regard.  I have one of his model spreadsheets at hand and so I went back to the first analysis using HADCRUT and substituted the model output for the CTI:

For this application, the model output works as well as the NINO34 dataset to within 4 ten-thousandths of a degree and actually slightly better than the CTI.