Hanhijarvi,S., Tingley, M.P. and Korhola, A. 2013. Pairwise comparisons to reconstruct mean temperature in the Arctic Atlantic Region over the last 2,000 years. Climate Dynamics 41: 2039-2060.
With earlier multi-proxy climate reconstruction methods facing "problems with varying temporal resolutions of the proxy data," according to the authors, they introduced "a new reconstruction method that uses the ordering of all pairs of proxy observations within each record to arrive at a consensus time series that best agrees with all proxy records," after which "the resulting unitless composite time series is subsequently calibrated to the instrumental record to provide an estimate of past climate."
What was done
After developing and testing their new climate reconstruction method that they called PaiCo, Hanhijarvi et al. applied it to a newly-assembled collection of 27 high-quality proxy data to reconstruct the mean temperature of the Northernmost Atlantic region," which they christened the Arctic Atlantic.
What was learned
The ultimate take-home message of the three researchers is contained in the final sentence of their paper's abstract: "The Arctic Atlantic reconstruction features temperatures during the Roman Warm Period and Medieval Climate Anomaly that are comparable [to] or even warmer than those of the twentieth century, and coldest temperatures in the middle of the nineteenth century, just prior to the onset of the recent warming trend [italics added]."
What it means
Once again, we have another study of real-world data, which suggests that the warmest intervals of both the Roman and Medieval Warm Periods may well have been warmer than the warmest interval of the Current Warm Period, suggesting that there is nothing unusual, unnatural or unprecedented about the planet's current level of warmth.