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The Medieval Warm Period and Little Ice Age in Russia and Elsewhere
Krenke, A.N. and Chernavskaya, M.M. 2002. Climate changes in the preinstrumental period of the last millennium and their manifestations over the Russian Plain. Isvestiya, Atmospheric and Oceanic Physics 38: S59-S79.

What was done
The authors present an impressive review of what is known about the Medieval Warm Period and Little Ice Age, both throughout the world in general and within Russia in particular. The review is based upon written historical evidence, glaciological evidence, hydrologic evidence, dendrological data, archaeological data and palynological data.

What was learned
With respect to the world as a whole, the authors conclude that, "concerning the Medieval Warm Period (MWP), it is currently known that, from the 9th century to, apparently, the mid-15th century, the climatic conditions were warmer than during most of the subsequent five centuries, including the early 20th century." In some places, in fact, it was even warmer during the MWP than it was during the latter part of the 20th century. For example, the authors note that "the northern margin of boreal forests in Canada was shifted by 55 km [north] during the MWP, and the tree line in the Rocky Mountains in the southern United States and in the Krkonose Mountains was higher by 100-200 m than that observed at the present time [our italics]."

With respect to the temperature reconstructions of Mann et al. (1998, 1999), the two members of the Russian Academy of Sciences say "the temperature averaged over the 20th century was found to be the highest among all centennial means, although it remained within the errors of reconstructions for the early millennium." However, they pointedly remind us that "one should keep in mind that the reconstructions of the early period were based nearly entirely on tree-ring data, which, because of the features of their interpretation, tend to underestimate low-frequency variations, so the temperatures of the Medieval Warm Period were possibly underestimated," after which they go on to provide yet additional evidence for that conclusion, reporting that "the limits of cultivated land or receding glaciers have not yet exceeded the level characteristic of the early millennium."

Concentrating on data from within Russia, the authors report large differences in a number of different variables between the period of the Little Ice Age and the preceding Medieval Warm Period. With respect to the annual mean temperature of northern Eurasia, they report an MWP to LIA drop on the order of 1.5C. They also say that "the frequency of severe winters reported was increased from once in 33 years in the early period of time, which corresponds to the MWP, to once in 20 years in the LIA," additionally noting that "the abnormally severe winters [of the LIA] were associated with the spread of Arctic air masses over the entire Russian Plain." Finally, the authors note that the data they used to draw these conclusions were "not used in the reconstructions performed by Mann et al.," which perhaps explains why the Mann et al. temperature history of the past millennium does not reproduce the Little Ice Age nearly as well as does the more appropriately derived temperature history of Esper et al. (2001).

What it means
The authors began their paper by noting that "an analysis of climate variations over 1000 years should help ? reveal natural multicentennial variations possible at present but not detectable in available 100-200-year series of instrumental records." In this endeavor, they were highly successful; and their efforts have helped expose the bankruptcy of the climate-alarmist claim that the warming of the 20th century is outside the realm of natural variability and must therefore be due to anthropogenic CO2 emissions. Indeed, their work reveals that much larger temperature changes have occurred naturally over the past millennium than what occurred over the 20th century, which latter rate and degree of change is typically described by climate alarmists as "unprecedented" over the past millennium. Last of all, and in contradiction of another of Mann et al.'s contentions, the authors unequivocally state, based on the results of their comprehensive study of the relevant scientific literature, that "the Medieval Warm Period and the Little Ice Age existed globally."

Esper, J., Cook, E.R. and Schweingruber, F.H. 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2253.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Reviewed 23 July 2003