Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations

TLDR

The study aims to reconstruct hemispheric temperatures over the past millennium while explicitly addressing uncertainties and caveats. The authors employ proxy data networks, building on recent studies, to perform the temperature reconstructions. Although expanded uncertainties prevent decisive conclusions before AD 1400, the 20th‑century warming—highlighted by the warmest decade in the 1990s and the warmest year in 1998—stands out against a millennial‑scale cooling trend consistent with long‑term astronomical forcing.

Abstract

Building on recent studies, we attempt hemispheric temperature reconstructions with proxy data networks for the past millennium. We focus not just on the reconstructions, but the uncertainties therein, and important caveats. Though expanded uncertainties prevent decisive conclusions for the period prior to AD 1400, our results suggest that the latter 20th century is anomalous in the 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.