There's a video on YouTube, Gwynne Dyer -- Geopolitics in a Hotter World (2010) ( https://www.youtube.com/watch?v=Mc_4Z1oiXhY ), which very briefly touches on it IIRC. I'm talking about the bit that starts at 8m30s on the video, but I highly recommend watching the whole thing (or at leas the 1-hour talk part - the Q&A is practically inaudible for me).

Basically, the IPCC doesn't publish studies - they study compilations of studies, every 4-5 years. And when they start compiling, they have a cut-off date at the very start and only use studies that have been both completed and have passed peer review from before that date.

Meanwhile, the studies themselves have the same problem - they obviously can't start the study with incomplete data and update the data as they go. The studies need to start with data that finished before they started the study.

And on top of that, they're necessarily a reserved body (Icd say "conservative" but that's ambiguous in politics) - IPCC is run by a bunch of governments trying to figure out the bare minimum of emissions reduction they need to commit to, to not be negligent - they don't want to hear bad news unless it's certain.

The end result is that the data in the report is 10+ years out of date.