Reference
Siklosy, Z., Demeny, A., Szenthe, I., Leel-Ossy, S., Pilet, S., Lin, Y. and Shen, C.-C. 2009. Reconstruction of climate variation for the last millennium in the Bukk Mountains, northeast Hungary, from a stalagmite record. Quarterly Journal of the Hungarian Meteorological Service 113: 245-263.
What was done
The authors conducted a complex trace element and stable carbon and oxygen isotope analysis of a stalagmite recovered from a cave (Kiskohat Shaft) located in northeast Hungary at the southern rim of the Bukk Highland (48°4.086'N, 20°29.422'E), with dating provided by twelve 230Th-234U determinations made along the growth direction of the stalagmite.
What was learned
Siklosy et al. determined that the highest oxygen isotope values occurred around AD 1000-1150, which interval they identified as the Medieval Warm Period, while the coldest years, which they associated with the Little Ice Age, prevailed from about AD 1550 to 1700. Another striking aspect of their results was the 50-year period from approximately AD 1450-1500, which was almost as warm as the Medieval Warm Period. This warm interval has also been observed in a number of other paleoclimate studies; and we have christened it the "Little" Medieval Warm Period, about which more can be read in the reviews we have posted under this heading in our Subject Index.
What it means
As ever more evidences of the Little Medieval Warm Period are discovered, it is beginning to look like the Medieval Warm Period proper and the earlier Roman Warm Period were not the only eras to exhibit surface air temperatures that may have equaled or eclipsed those of the late 20th century. And we would be remiss in not noting that all of those earlier warm eras achieved their enhanced thermal status without any help from elevated atmospheric CO2 concentrations, which were fully 100 ppm less than they are today at those earlier times. Hence, there is ample reason to believe that whatever caused the warmth of those prior eras could well be maintaining the warmth of the present era, which -- if true -- would relieve CO2 of that undeserved credit.