What was done
The authors developed a high-resolution record of ocean and climate variations during the late Holocene in the Fram Strait (the major gateway between the Arctic and North Atlantic Oceans, located north of the Greenland Sea), based on detailed analyses of a sediment core recovered from a location (78°54.931'N, 6°46.005'E) on the slope of the western continental margin of Svalbard, based on analyses of organic-walled dinoflagellate cysts that permit the reconstruction of sea-surface conditions in both summer and winter. These latter reconstructions, in their words, "were made using two different approaches for comparison and to insure the robustness of estimates." They were "the modern analogue technique, which is based on the similarity degree between fossil and modern spectra" and "the artificial neural network technique, which relies on calibration between hydrographical parameters and assemblages."

What was learned
Bonnet et al. report that the sea surface temperature (SST) histories they developed via the two techniques they employed were "nearly identical and show oscillations between -1°C and 5.5°C in winter and between 2.4°C and 10.0°C in summer," and their graphical results indicate that between 2500 and 250 years before present (BP), the mean SSTs of summers were warmer than those of the present about 80% of the time, while the mean SSTs of winters exceeded those of current winters approximately 75% of the time, with the long-term (2250-year) means of both seasonal periods averaging about 2°C more than current means.

The highest temperatures of all were recorded in the vicinity of 1320 cal. years BP, during a warm interval that persisted from about AD 500 to 720 during the very earliest stages of the Medieval Warm Period (MWP), when the peak summer and winter temperatures of the MWP both exceeded the peak summer and winter temperatures of the first several years of the 21st century by about 3°C.

What it means
These several observations, as well as the many similar findings we have described in our Medieval Warm Period Project, clearly indicate there is nothing unusual, unnatural or unprecedented about the world's current level of warmth, which further suggests there is no compelling reason to attribute the Little Ice Age-to-Current Warm Period transition to the concomitant historical increase in the air's CO2 content.