The biggest pitfall of early temperature readings from Derham and others may not be the reliability of the readings, but rather that there are so few of them, and that they cover such a small patch of the Earth's surface. (discovermagazine.com)
The researchers used the measured temperatures from these two sites and the isotope data from the ice core from the overlapping time period (a method called «scaling») to quantitatively reconstruct earlier temperature variations. (sciencenordic.com)
Why is there computer code in the Climategate files that artificially adjusts earlier temperatures lower and later higher? (realclimate.org)