Continental-scale temperature variability in PMIP3 simulations and PAGES 2k regional temperature reconstructions over the past millennium

摘要

Estimated external radiative forcings, model results, and proxy-based climatereconstructions have been used over the past several decades to improve ourunderstanding of the mechanisms underlying observed climate variability andchange over the past millennium. Here, the recent set of temperaturereconstructions at the continental-scale generated by the PAGES 2k projectand a collection of state-of-the-art model simulations driven by realisticexternal forcings are jointly analysed. The first aim is to estimate theconsistency between model results and reconstructions for eachcontinental-scale region over the time and frequency domains. Secondly, thelinks between regions are investigated to determine whether reconstructedglobal-scale covariability patterns are similar to those identified in modelsimulations. The third aim is to assess the role of external forcings in theobserved temperature variations. From a large set of analyses, we concludethat models are in relatively good agreement with temperaturereconstructions for Northern Hemisphere regions, particularly in the Arctic.This is likely due to the relatively large amplitude of the externallyforced response across northern and high-latitude regions, which results ina clearly detectable signature in both reconstructions and simulations.Conversely, models disagree strongly with the reconstructions in theSouthern Hemisphere. Furthermore, the simulations are more regionallycoherent than the reconstructions, perhaps due to an underestimation of themagnitude of internal variability in models or to an overestimation of theresponse to the external forcing in the Southern Hemisphere. Part of thedisagreement might also reflect large uncertainties in the reconstructions,specifically in some Southern Hemisphere regions, which are based on fewerpalaeoclimate records than in the Northern Hemisphere.