Arctic Oscillation index shows notable correlation with surface temperatures as given by Hadley Centre ISST (ice and sea surface temperature) dataset.
hadISST is a continuous gridded dataset with lots of infilling and extrapolation. Caveat emptor.
Data used here was ISST from 70-90N.
It is obvious , at least in the earlier part of the record that there is a close correlation but with punctual phase shifts.
Post 1997 the correlation is a lot less, however there are sufficient features to allow alignment of the two and detect at least two later phase shifts. The period is more speculative due to the poorer correlation.
The latter two sections have been shifted vertically to allow better visual comparison. This does not affect the determination or the value of the shifts.
estimated shift events dates ( hadISST timescale ) : 1988.8 1994.5 1998 2006.8
There may be justification for a fifth phase shift at 2003.5 , the phase at the bottom of that rise shifts off. Though with the lack of notable features it would be hard to align the phase of that segment.
