What was done
Five 60-cm sediment cores were retrieved from the eastern Gotland Basin in the central Baltic Sea (~56°55'-57°15'N, 19°20'-20°00'E) and analyzed for a variety of physical, chemical and biological properties.

What was learned
The authors report that "during the Medieval Warm Period, from about AD 900 to 1250, the hydrographic and environmental conditions were similar to those of the present time," while "during the period from about 1250 to 1850" -- which they refer to as the cold phase and which they note includes the Little Ice Age -- they say that "the environmental conditions of the central Baltic Sea were distinctly different," as "both the productivity of the planktonic ecosystem as well as the preservation of organic matter in the sediments improved during the warm periods." In addition, analyses of lignin compounds in the sediment cores -- which they say "can be used to characterize terrigenous organic matter from plants" -- pointed to the Medieval Warm Period possibly being warmer than the Current Warm Period.

What it means
Once again, we have yet another study -- such as we discover essentially every week (see our Medieval Warm Period Project) -- which indicates that it is likely no warmer now than it was a thousand years ago, when there was 100 ppm less CO2 in the air than there is today; and this fact suggests that there is no compelling reason why we should believe that the bulk of today's warmth had to have been caused by the increase in atmospheric CO2 concentration that occurred in the interim.