Tomas Milanovic made an interesting post on Climate Etc.
One area he covered was Tsonis et al (2007). “He identifies the 5 fields with 5 oceanic oscillations and quantifies every field by a single number (index). He doesn’t formulate it that way and it is extremely unlikely that a 3D field can be relevantly represented by a single number, but the paradigm is on the right track” – Milanovic.
He may be pointing at adding dimensions to each of the 5 oscillations. I am not sure if a climate index value is made more dimensional by adding the current slope or its recent change in slope.