A Millennium of Climate Change in Western Canada
Edwards, T.W.D., Birks, S.J., Luckman, B.H. and MacDonald, G.M. 2008. Climatic and hydrologic variability during the past millennium in the eastern Rocky Mountains and northern Great Plains of western Canada. Quaternary Research 70: 188-197.
The four researchers report that "high inferred winter temperatures ~AD 1100-1250 stand out in particular, corresponding with the Medieval Climate Anomaly," adding that the "climate shifted broadly in western Canada from warm in winter and atmospherically moist during the growth season during medieval times to being cool in winter and atmospherically dry during the growth season in the subsequent Little Ice Age." Nevertheless, they note that "independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern Rockies," while during the Medieval Warm Period there was "evidence for reduced discharge in rivers draining the eastern Rockies and extensive hydrological drought in neighboring western USA." Finally, they write that "declining streamflow in rivers draining the eastern Rockies over the past century (Rood et al., 2005) may indicate that conditions are in the process of returning to a similar state [italics added]," which suggests that the Current Warm Period has not yet achieved the more extreme climatic status of the Medieval Warm Period.
The results of this study from western Canada clearly delineate the classic cycling of climate that brought the earth the Medieval Warm Period and subsequent Little Ice Age, as well as the 20th-century transition to the Current Warm Period, all independent of the air's CO2 content. In fact, Edwards et al.'s data clearly indicate that both the minimum temperature of winter and the yearly average of the winter minimum and summer maximum temperature were greater during the Medieval Warm Period than they were during the late 20th century, between which times the air's CO2 concentration rose by approximately 100 ppm and still could not force a temperature increase equal to that of a thousand years ago.
Rood, S.B., Samuelson, G.M., Weber, J.K. and Wyrot, K.A. 2005. Twentieth-century decline in streamflows from the hydrographic apex of North America. Journal of Hydrology 306: 215-233.