Here’s another model output oddity that I noticed from a plot and confirmed with a direct screensave. In January 2100, the SH values for an NCAR PCM run, as archived at KNMI, (expressed as an anomaly here) jumps 2.5 deg C from 0.3 deg C to 2.81 deg C, before relaxing to lower values over the next few years. The NH has an offsetting problem with 45-90N dropping over 2 deg C in Jan 2100. Overall it seems to average out. (Did I hear someone say that it therefore “doesn’t matter”?)
The problem occurs exactly in January 2100 and one can hardly help wondering whether something has been spliced somewhere along the way – a model version of the Hansen Y2K problem. Again, I do not know whether this is an artifact of how KNMI handles the data extraction or whether it’s a property of the model.