[jansan]

In this paper from 1999 it is claimed that the global temperature between 1961 and 1990 was 14.0°C (14.6°C for the northern hemisphere and 13.4°C for the southern hemisphere). https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999...

[busymom0]

In my original comment I pointed that out:

> Sometime between 1997 and 1998, they started claiming the avg to be 14 degree C instead of 15.

So far, I haven't read any valid reasoning on why this happened out of nowhere.