Evaluation of recent extremes in high northern latitude temperatures is better undertaken in the longer term context afforded by the paleoclimate record. Determining the probability that an event like the 2010 Russian heat wave is unprecedented requires a statistical treatment that permits for the imputation of temperatures in space, accounts for uncertainties in the instrumental and proxy observations, and permits for a probabilistic assessment of extreme values. In addition, the recent divergence of tree ring proxies from instrumental temperatures must be accounted for in any assessment of past extremes. While there is a rich tradition in the paleoclimate literature of describing recent observations as unprecedented, in this talk I present the first reconstruction that meets each of these necessary conditions for making inferences on extremes. I describe a recently developed Bayesian Hierarchical Model for inferring past climate, and apply it to the instrumental record and proxy observations from trees, ice cores, and lake sediments to reconstruct Arctic and sub-Arctic temperature anomalies over the last 600 years. Results show that the summer of 2010 was with virtually certainty (p>0.99) the warmest in the last 600 years in Western Russia and very likely (p>0.9) the warmest in Western Greenland and the Canadian Arctic as well, while the modern rate of centennial-scale warming has only recently exceeded in magnitude the rate of cooling in the 1600s. The multi-proxy approach demonstrates that the recent tree ring divergence is unique to the last 600 years, and consistent (but less significant) results are obtained when tree ring records are excluded.
Wednesday, April 25, 2012 - 10:00am
Croul Hall, Room 3101