Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations

Building on recent studies, we attempt hemiWarm Epoch (though Lamb, examining evidence mostly spheric temperature reconstructions with proxy data netfrom western Europe, never suggested this was a global works for the past millennium. We focus not just on the phenomenon). We here apply the methodology detailed by reconstructions, but the uncertainties therein, and imporMBH98 to the sparser proxy data network available prior tant caveats. Though expanded uncertainties prevent decito AD 1400, to critically revisit this issue, extending NH sive conclusions for the period prior to AD 1400, our results reconstructions as far back as is currently feasible. We also suggest that the latter 20th century is anomalous in the reevaluate earlier estimates of uncertainties in the NH series. context of at least the past millennium. The 1990s was the warmest decade, and 1998 the warmest year, at moderately high levels of confidence. The 20th century warming counters a millennial-scale cooling trend which is consistent with' long-term astronomical forcing.