The Climate Analysis Center discontinued the SST product we'd been using and offered an optimum interpolation product in its place. The new product (NMC Monthly) has been computed over all ocean areas on a 1x1 degree grid and extends back to November 1981. For details on the new product, see the NMC Monthly Documentation.
We chose to combine our original data and this new product as follows. We retained our CAC data from Jan 1970 through Oct 1981 and and then regridded the new product to match the old 2x2 grid from Nov 1981 through the present. A new climatology was computed for the period Jan 1970 through December 1985 and then used to recompute all the anomalies for the entire period. All other procedures (i.e. smoothing) were kept the same.