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The Medieval Warm Period in Southern Patagonia, Argentina
Reference
Haberzettl, T., Fey, M., Lucke, A., Maidana, N., Mayr, C., Ohlendorf, C. Schabitz, F., Schleser, G.H., Wille, M. and Zolitschka, B.  2005.  Climatically induced lake level changes during the last two millennia as reflected in sediments of Laguna Potrok Aike, southern Patagonia (Santa Cruz, Argentina).  Journal of Paleolimnology 33: 283-302.

What was done
Working with five sediment cores extracted from Laguna Potrok Aike (5158'S, 7023'W), which is one of the few permanently water-filled lakes in the dry-lands of southern Patagonia, Argentina, the authors analyzed a host of proxy climate indicators.

What was learned
Haberzettl et al. write that "the sediment record of Laguna Potrok Aike reveals an unprecedented sensitive continuous high resolution lake level, vegetation and climate record for southern Patagonia since AD 400."  This history indicates that the climate of the region fluctuated rapidly from the beginning of the record right up to the start of the Medieval Climatic Anomaly (MCA, which was proposed by Stine (1998) to have begun at about AD 870).  This interval of time corresponds with the Dark Ages Cold Period of Europe.  It was followed, of course, by the MCA, or what Europeans called the Medieval Warm Period, which was most strongly expressed in the Laguna Potrok Aike data from AD 1240 to 1410, during which period maxima of total inorganic carbon (TIC), total organic carbon (TOC), total nitrogen (TN), carbon/nitrogen ratio (C/N) and δ13Corg indicated, in the words of the ten researchers, "low lake levels and warm and dry climate."

Thereafter, as the scientists continue, "the MCA ends during the 15th century" and is "followed by the so called 'Little Ice Age'."  Last of all, "in the course of the 20th century," they report that "Laguna Potrok Aike reacted like many other Patagonian lakes with a lake level lowering after 1940, culminating in 1990, and followed by a subsequent rise and recession."

With respect to "the question of whether it was warmer during [this period] than during the 20th century," Haberzettl et al. say "there is evidence for lower lake levels during the MCA than today in every proxy [our italics]," and that "the existence of lower lake levels in former times was demonstrated by seismic studies which revealed hitherto undated fossil lake level terraces ca. 30 m below the present lake level (Zolitschka et al, 2004)."   In addition, they say that "TOC and TN as proxies reflecting productivity also show higher values during the MCA than today," even though "present TOC and TN values are elevated due to anthropogenic eutrophication." Consequently, they conclude that "this altogether implies that it might have been warmer during [AD 1240 to 1410] than today."

What it means
Once again, and contrary to worn-out climate-alarmist claims, we find evidence for the existence of a likely warmer-than-present Medieval Warm Period -- far, far away from lands that border the North Atlantic Ocean and at a time when the atmosphere's CO2 concentration was much, much lower than it is today -- all of which suggests there is no compelling reason to believe that any of the planet's current warmth is due to the current elevated level of atmospheric CO2.

References
Stine, S.  1998.  Medieval Climatic Anomaly in the Americas. In: Issar, A.S. and Brown, N. (Eds.), Water, Environment and Society in Times of Climatic Change.  Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 43-67.

Zolitschka, B., Schabitz, F., Lucke, A., Wille, M., Mayr, C., Ohlendorf, C., Anselmetti, F., Ariztegui, D., Corbella, H., Ercolano, B., Fey, M., Haberzettl, T., Maidana, N., Oliva, G., Paez, M. and Schleser, G.H.  2004.  Climate changes in Southern Patagonia (Santa Cruz, Argentina) inferred from lake sediments - the multi-proxy approach of SALSA.  PAGES News 12(2): 9-11.

Reviewed 8 June 2005