Reference
Arseneault, D. and Payette, S. 1997. Reconstruction of millennial forest dynamics from tree remains in a subarctic tree line peatland. Ecology 78: 1873-1883.
What was done
Tree-ring and growth-form sequences obtained from more than 300 spruce remains buried in a presently treeless peatland located near the tree line in northern Québec were analyzed to produce a proxy record of climate for this region between 690 and 1591 AD.
What was learned
Over the course of this 900-year time period, the trees of the region experienced several episodes of suppressed and rapid growth, indicative of both colder and warmer conditions, respectively, than those of the present. Cooler (suppressed growth) conditions prevailed between 760-860 and 1025-1400 AD, while warmer (rapid growth) conditions were prevalent between 700-750, 860-1000, 1400-1450 and 1500-1570 AD.
Analysis of the warm period between 860 and 1000 AD led the authors to conclude that the warmth experienced in northern Quebec during this time period coincided with the Medieval Warm Period that was experienced across the North Atlantic and Northern Europe, which "exceeded in duration and magnitude both the 16th and 20th century warm periods identified previously [by other scientists] using the same methods." Furthermore, on the basis of the current annual temperatures at the author's study site and the northernmost 20th century location of the forest, which is presently 130 km south of the author's study site, the author concludes that the "Medieval Warm Period was approximately 1°C warmer than the 20th century."
What it means
The results of this study demonstrate the natural oscillatory nature of climate in the subarctic region of North America. Furthermore, they demonstrate that current temperatures are still about 1°C lower than they were during the Medieval Warm Period. The results also indicate that even if it warms by yet another degree or so in the next few decades or coming century, such warming would not be proof of the current politically-correct theory of CO2-induced global warming. It would simply prove what everyone has know for a long time now, i.e., that climate naturally oscillates, independent of the actions of man.