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WalterF It’s not a model, it’s a reconstruction of 692 proxy systems responding to temperature changes (e.g. tree rings, coral, marine sediment), from across 49 countries.
Here’s the paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6675609/
Here are details regarding the 692 samples used: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5505119/
Although, you mention models; climate models can be very accurate. Here’s a study of various models dating back as far as 1970 that were found to be “indistinguishable” from what actually happened: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085378