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The Medieval Warm Period in Northern Chile
Elbert, J., Wartenburger, R., von Gunten, L., Urrutia, R., Fischer, D, Fujak, M., Hamann, Y., Greber, N.D. and Grosjean, M. 2013. Late Holocene air temperature variability reconstructed from the sediments of Laguna Escondida, Patagonia, Chile (45°30'S). Palaeogeography, Palaeoclimatology, Palaeoecology 369: 482-492.

The authors write that "climate and environmental reconstructions from natural archives are important for the interpretation of current climatic change," but they note in this regard that "few quantitative high-resolution reconstructions exist for South America, which is the only land mass extending from the tropics to the southern high latitudes."

What was done
In a study designed to partially fill this data void, Elbert et al. analyzed sediment cores from two adjacent lakes in Northern Chilean Patagonia - Lago Castor (45°36'S, 71°47'W) and Laguna Escondida (45°31'S, 71°49'W) - for total organic carbon and total nitrogen concentrations, as well as biogenic silica (bSi) flux, which they "compared with meteorological data from the CRU TS 3.0 reanalysis data set (Mitchell and Jones, 2005; 0.5°x0.5° grid cell 45°S/72°W)," while further noting that "radiometric dating (210Pb, 137Cs, 14C-MS) suggests that the cores reach back to c. 900 BC (Laguna Escondida) and c. 1900 BC (Lago Castor).""

What was learned
The team of ten scientists (nine Swiss and one Chilean) report that the temperature record they developed "compares well with the multi-decadal temperature variability documented in the few paleo-temperature archives available in southern South America." And that record shows, as may be seen in the figure below, that the peak warmth of the Medieval Warm Period was about 2.9°C greater than the most recent of sediment-derived Current Warm Period temperatures.

Figure 1. Reconstructed annual temperature anomalies, with respect to the 20th-century mean, which also just happens to occur shortly after the beginning of the 20th century and at its end, as derived for Laguna Escondida. Adapted from Elbert et al. (2013).

What it means
Once again, and for a region of the earth far removed from the North Atlantic Ocean and the lands that surround it, we have evidence for the existence of the Medieval Warm Period and its significant exceedance of the warmth of the Current Warm Period, clearly suggesting that there is nothing unusual, unnatural or unprecedented about earth's current level of warmth, nor is there any compelling reason to attribute the essentially non-existent 20th-century warming at Laguna Escondida to the concomitant increase in the atmosphere's CO2 concentration, for there was little to no increase in the air's CO2 content during the development of the much greater peak warmth (~2.9 °C) that was experienced at that location back in the middle of the MWP.

Mitchell, T.D. and Jones, P.D. 2005. An improved method of constructing a database of monthly climate observations and associated high-resolution grids. International Journal of Climatology 25: 693-712.

Reviewed 31 July 2013