What was done
The authors developed a history of changes in the level of Lake 259 (Rawson Lake, 49°40'N, 93°44'W) within the Experimental Lakes Area of northwestern Ontario, Canada, based on a suite of near-shore gravity cores they analyzed for diatom species identity and concentration, as well as organic matter content.

What was learned
Laird and Cumming report there was "a distinct decline in lake level of ~2.5 to 3.0 m from ~800 to 1130 AD." This interval, in their words, "corresponds to an epic drought recorded in many regions of North America from ~800 to 1400 AD," which they say "is often referred to as the Medieval Climatic Anomaly or the Medieval Warm Period, and encompasses 'The Great Drought' of the thirteenth century (Woodhouse and Overpeck, 1998; Woodhouse, 2004; Herweijer et al. 2007)." They also note that the Canadian prairies are currently "experiencing reductions in surface-water availability due to climate warming and human withdrawals (Schindler and Donahue, 2006)," and that "many regions in the western U.S. have experienced water supply deficits in reservoir storage with the recent multi-year drought (Cook et al., 2007)." However, they say "these severe multi-year drought conditions pale in comparison [our italics] to the many widespread megadroughts [our italics] that persisted for decades and sometimes centuries [our italics] in many parts of North America over the last millennium (Woodhouse, 2004)."

What it means
The close association between the severity and duration of drought and warmth throughout the affected region of North America suggests that the degree of warmth during the Medieval Warm Period in the Experimental Lakes Area of Canada was likely much greater than the degree of warmth so far experienced there during the Current Warm Period.

References
Cook, E.R., Seager, R., Cane, M.A. and Stahle, D.W. 2007. North American drought: reconstructions, causes, and consequences. Earth Science Reviews 81: 93-134.

Herweijer, C., Seager, R., Cook, E.R. and Emile-Geay, J. 2007. North American droughts of the last millennium from a gridded network of tree-ring data. Journal of Climate 20: 1353-1376.

Schindler, D.W. and Donahue, W.F. 2006. An impending water crisis in Canada's western prairie provinces. Proceedings of the National Academy of Sciences, USA 103: 7210-7216.

Woodhouse, C.A. 2004. A paleo-perspective on hydroclimatic variability in the western United States. Aquatic Science 66: 346-356.

Woodhouse, C.A. and Overpeck, J.T. 1998. 2000 years of drought variability in the central United States. Bulletin of the American Meteorological Society 79: 2693-2714.