claim: The 'decline' refers to a decline in northern tree-rings, not global temperature, and is openly discussed in papers and the IPCC reports.
evidence: The implications of the decline are discussed in Chapter 2 of the IPCC Third Assessment Report, and in Chapter 6 of the 2007 IPCC Fourth Assessment Report ( AR4 ) which describes discussion of various possible reasons for the divergence which does not affect all the trees, and says that there is no consensus about the cause.