Let’s have a little fun, and predict the global average temperature (land+ocean) for the next few months. We’ll base the prediction on GISS data, so this will be a prediction for the upcoming temperature according to GISS.



For those interested in the gory details (those who just want the numbers can skip this paragraph), I’ll model GISS global land+ocean temperature as a function of MEI (the multivariate el Nino index), volcanic forcing according to Amman et al., solar forcing (represented by monthly sunspot numbers), a linear trend in time, and a “residual annual cycle” which I’ll model as a 2nd-order Fourier series. I’ll allow for a lag in the influence of MEI, volcanic forcing, and solar forcing. I’ll fit the model using observed data from 1975 to the present. I’ll further model the residuals as an AR() process.

The model gives an excellent approximation to the observed temperature data:

The model as a whole explains 76% of the variance in global temperature since 1975. It’s worth noting that the linear time trend in this model (which is an approximation of the influence of man-made global warming) is 0.0172 deg.C/yr.

Using the model to forecast the next 3 months gives this:

For those who want numbers, the predictions are (all error ranges are 95% confidence intervals):

August: 0.53 +/- 0.21

September: 0.59 +/- 0.22

October: 0.57 +/- 0.23

Place your bets!