Chen, L., Zonneveld, K.A.F. and Versteegh, G.J.M. 2011. Short term climate variability during the "Roman Classical Period" in the eastern Mediterranean. Quaternary Science Reviews 30: 3880-3891.
What was done
In order to gain some insight into the character and potential forcing of short-term climatic and oceanographic variability in the southern Italian region of the Mediterranean Sea during the Roman Classical Period (60 BC - 200 AD), the authors developed a high temporal resolution (4-year) sea surface temperature (SST) history based on a dinoflagelate cyst record obtained from a well-dated sediment core retrieved from a site in the Gulf of Taranto located at the distal end of the Po River discharge plume (39°50.07'N, 17°48.05'E).
What was learned
Chen et al. report that SST reconstructions based on the composition of dinoflagellate cysts recovered from the sediment core "suggest high stable temperatures between 60 BC and 90 AD followed by a decreasing trend between 90 AD and 200 AD." And "consistent to earlier findings for the region," as they continue, they say that "local air temperature during the Roman Period might have been warmer than that of the 20th century." Also of note, they say "the observation of strong 11 years cyclicity in our records together with a strong visual correlation of our temperature and river discharge records with the global variation in Δ14C anomalies suggest that solar activity might have been an important climate forcing factor during this time."
Also of more than passing interest is the three researchers' observation that their "reconstruction of relatively warm stable climatic conditions corresponds to the time of the 'Pax Romana'," i.e., the long period of relative peace and minimal expansion by military force experienced by the Roman Empire in the 1st and 2nd centuries AD.
What it means
Once again we have more evidence for (1) the rule-of-thumb proposition that warmer times have generally been more peaceful times throughout human history, (2) the likelihood that the high stable temperatures between 60 BC and 90 AD may well have been warmer than those of the 20th century, and (3) the likelihood that solar variability may have been "an important climate forcing factor during this time."