:: it relies on proxy data such as tree rings ::
And, according to a disciple of the Goracle, here’s how that proxy works (this is NOT from a scientist, just a “true believer” in CACA - see tag).
Larger rings indicate a warmer period because the tree is assumed to have a longer growing period. They can process more nutrients over a longer period between dormancy periods.
Get that? Larger rings show an increase of CO2 in the atmosphere and an increase in CO2 indicates a warmer period.
I thought larger rings also indicated more water available to grow with so that water and temperature are interactive. The most interesting measure is the number of stoma (?) in the leaves which are fewer when there is more CO2