"Mann argues that Esper's tree-ring measurements come from high latitudes and reflect only summer temperatures"

Tree rings suggest Roman world was warmer than thought - environment - 10 July 2012 - New Scientist

Long-term temperature reconstructions often rely on the width of tree rings: they assume that warmer summers make for wider rings. Using this measure, it seems that global temperatures changed very little over the past two millennia. Such studies are behind the famous "hockey stick" graph, created by Michael Mann of Pennsylvania State University in University Park, which shows stable temperatures for a millennium before the 20th century...Mann argues that Esper's tree-ring measurements come from high latitudes and reflect only summer temperatures. "The implications of this study are vastly overstated by the authors," he says

Video: "Hide The Decline II" - Minnesotans For Global Warming

The tree ring data was very thin
You shoulda chopped more trees instead of hugging them.
Ignoring the snow and the cold and a downward line
Hide the decline (hide the decline)

Oh Climategate
Medieval Warming now is gone
And the Maunder Minimum
Hide the decline (hide the decline)
Hide the decline (hide the decline)