In 1992, the IPCC issued a Supplementary Report to the 1990 Assessment Report, which visited some of the multiproxy topics in chapter C. Again, I’ll provide some extended excerpts: The main summary stated:
Warming over the past few decades is primarily due to an increase of night-time rather than day-time temperatures. These change appear to be partly related to increases in cloudiness but other factors cannot be excluded (p 17)
The Executive Summary to Chapter C stated:
It is still not possible to attribute with high confidence all or even a large part of the observed global warming to the enhanced greenhouse effect. On the other hand it is not possible to refute the claim that greenhouse-gas enhanced climate change has contributed substantially to the observed warming.
There is one page on paleoclimate studies. Cook et al  re Tasmania and Norton et al.  re New Zealand are mentioned with the caveat that:
“no allowance has been made in these or similar studies for the possible fertilization effect of twentieth century increases in carbon dioxide (CO2) on tree growth, neglect of which might lead to an overestimate of recent warming"
Given the dependence of MBH98 results on trees argued to be most affected by CO2 fertilization, it will be interesting to track this issue into SAR and TAR. They report some then recent oxygen isotope measurements from Antarctica as follows:
Oxygen isotope measurements from the northern Antarctic Peninsula have been interpreted as evidence of warmer temperatures during the nineteenth century compared with the twentieth century (Aristarain et al 1990). However the isotope/temperature link is weak both physically and statistically (Peel, 1993) and accumulation rate changes which are more directly related to in situ temperatures point to cooler conditions in the 19th century (Jones et al 1992).
I haven’t worried through oxygen isotope data, but I am very suspicious about overuse of Thompson’s dO18 tropical data, where rain-out effect is conflated with temperature effects. It would be interesting to see exactly why the Aristarain results are dropped from multiproxy studies, while Thompson’s get used canonically. The IPCC then mentions some Chinese studies (Wang and Wang, 1992; Wang et al. 1991) – these turn up in Bradley and Jones  as well. While the 1990 IPCC had been skeptical of tree ring results, Briffa’s Tornetrask study (discussed in detail elsewhere on this blog) gets highlighted next as follows:
Briffa et al  have expanded the analysis presented in an earlier paper [Briffa et al, 1990] where they use tree-ring data to reconstruct summer temperatures for northern Fennoscandia since AD500. Their new analysis is designed to highlight greater than century scale variability which was largely removed by the analysis procedure they used previously. They find good evidence in this region for a Medieval Climatic Optimum (S7, 202) around 870-1110, another warm period around 1360-1570 and a Little Ice Age (S7, 202) period around 1570-1750.
They then refer to new articles on long instrumental series at De Bilt and Central England (van Engelen and Nellestijn, 1992; Parker et al, 1992) and using coral proxy data to reconstruct precipitation in Queensland (Lough, 1991). Section C4 discusses detection and attribution, but does not discuss the question of attribution of past centennial-scale climate change, which had concerned IPCC 1990. They point out that progress in the "fingerprint" detection of an enhanced greenhouse effect is "very difficult" and that no definitive paper on detection has appeared since the 1990 IPCC Scientific Assessment. They point out that:
“it remains to be proved that the greenhouse signal is sufficiently distinguishable from other signals to be detected except as a gross increase in tropospheric temperature that is so large that other explanations are not likely (see S8)."