Bo Li, NCAR, Boulder, CO, USA

The Uncertain Hockey Stick: A Statistical Perspective on the

Reconstruction of Past Temperatures

The past temperature is reconstructed based on the proxies which is known to preserve the climate evolution. There are many kinds of proxies in term of temporal resolution, e.g., tree rings represent climate information at the interannual to decadal time scale, while bore-hole data record climate signals at multi-decadal or longer time scales. We propose to integrate proxies of different time resolution by Hierarchical Bayesian Models (BHM) in reconstructing the past temperature. BHMs are built by three hierarchies which isolate the statistical errors of the proxy data from the underlying temperature process. The data hierarchy describes the measurement error of the proxies conditional on the true temperature. The process hierarchy models the true temperature process and the priors complete the hierarchy. We produce ensemble reconstructions of Northern Hemisphere (NH) average temperature for the past millennium based on tree ring and borehole based proxies.