What was done
Changes in temperature and/or precipitation were inferred from plant macrofossils, pollen, fungal spores, testate amebae and peat humification in peat monoliths collected from the Valle de Andorra about 10 km to the northeast of Ushuaia, Tierra del Fuego, Argentina (54° 45' S latitude).  Value-enhanced by an improved ¹⁴C wiggle-match dating technique, the new chronologies were compared with other chronologies of pertinent data from both the Southern and Northern Hemispheres in an analysis that helped the authors come to their final important conclusions.

What was learned
Mauquoy et al. report finding evidence for a period of warming-induced drier conditions from AD 960-1020 that "seems to correspond to the Medieval Warm period (MWP, as defined in the Northern Hemisphere)."  They note that "this interval compares well to the date range of AD 950-1045 based on Northern Hemisphere extratropical tree-ring data (Esper et al., 2002)," and they thus conclude that this correspondence "shows that the MWP was possibly synchronous in both hemispheres, as suggested by Villalba (1994)."

What it means
Once again, we have evidence far removed from the site of origin (North Atlantic Ocean) of the concept of the Medieval Warm Period, demonstrating the truly global nature of this prior period of warmth that equals or exceeds that of the present without the benefit of today's supposedly enhanced greenhouse effect, which climate alarmists claim is primarily due to the 100-ppm increase in the air's CO2 concentration that has occurred over the intervening millennium, but more particularly over the last century.  The global expression of this prior period of significant warmth bears witness to the fact that the high CO2 concentrations of today need not be the source of our present global warmth, since whatever caused the high global temperatures of the Medieval Warm Period may well be the cause of the high global temperatures of today.  And that cause is not CO2.

References
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.

Villalba, R.  1994.  Tree-ring and glacial evidence for the Medieval Warm Epoch and the 'Little Ice Age' in southern South America.  Climatic Change 26: 183-197.