The IPCC’s justification for tossing Briffa’s trees after 1960 was that they were made defective by too much CO2, and didn’t match the surface record – i.e. were too producing readings too low.
This is utter nonsense on all counts. More CO2 would cause more growth, and thus produce wider tree rings and produce false readings which were too high, not too low.
But the biggest BS is the claim that Briffa’s trees didn’t match thermometer readings. The graph below shows untampered US data on top of Jones, Briffa, et. al 1998.
There was actually quite a good match between Briffa’s trees and the raw data. It wasn’t until Hansen, Karl et al started tampering with the data that the mismatch appeared.
So they tampered with the data, then tossed Briffa’s trees because they didn’t match the tampered data, then used the tampered data in place of Briffa’s trees.
Enron would blush at such accounting fraud.