A new paper now in open review in the journal Climate of the Past suggests that “modern sample bias “has “seriously compromised” tree-ring temperature reconstructions, producing an “artificial positive signal [e.g. 'hockey stick'] in the final chronology.”Huh. Pretty hard to see bias as driving that, just a reflection that the universe is a tricky place that we (mostly) poorly understand. I wonder what sort of biases are in ice core data? They're obviously highly dependent on precipitation levels as well as temperature.
Basically, older trees grow slower, and that mimics the temperature signal paleo researchers like Mann look for. Unless you correct for this issue, you end up with a false temperature signal, like a hockey stick in modern times. Separating a valid temperature signal from the natural growth pattern of the tree becomes a larger challenge with this correction.
Dang it. And I thought that the science was settled.