Climate change: where is the hockey stick? evidence from millennial-scale reconstructed and updated temperature time series.

The goal of this paper is to test on a millennial scale the magnitude of the recent warmth period, known as the “hockey-stick”, and the relevance of the causative anthropogenic climate change hypothesis advanced by several academics and worldwide institutions. A select batch of ten long-term climate proxies, included in the NOAA 92 PCN dataset all of which running well into the nineties, is updated to the year 2011 by means of a Time-Varying Parameter Kalman Filter SISO model for state prediction. This procedure is applied by appropriately selecting as observable one out of the HADSST2 and of the HADCRUT3 series of instrumental temperature anomalies available since the year 1850. The updated proxy series are thereafter individually tested for the values and time location of their four maximum non-neighboring attained temperatures. The results are at best inconclusive, since three of the updated series, including Michael Mann’s celebrated and controversial tree-ring reconstructions, do not refute the hypothesis, while the others quite significantly point to different dates of maximum temperature achievements into the past centuries, in particular those associated to the Medieval Warm Period.