What was done
The author reviews what many people have learned about many aspects of climate in the vicinity of Lake Baikal, which is situated in a rift zone in southeastern Sibera (between 51°28' to 55°47'N and 103°43' to 109°58'E) and is the world's deepest lake, containing some 20% of the globe's freshwater resources.

What was learned
Among a vast array of other important information, Mackay reports that productivity in Lake Baikal "exhibits millennial-scale variability." Focusing on the most recent full cycle of this oscillation (plus just a tad more), he says that "based on diatom composition alone, three significant zones could be recognized, coincident with the broad features of the MWP [Medieval Warm Period], the LIA [Little Ice Age] and the period of recent warming."

Beginning with the first of these climatic intervals, Mackay states that "between c. AD 850 and 1200, S. acus dominated the assemblage, most likely due to prevailing warmer and wetter climate that occurred in Siberia at this time, which is reflected in high early summer temperatures derived from tree ring studies (Naurzbaev and Vaganov, 2000)." Then, between c. AD 1200 and 1400, there was a transition to "increased winter severity and snow cover on the lake, which is reflected in cooler early Siberian summers."

These conditions persisted until modern warming began, which "in the Lake Baikal region started as early as c. AD 1750," according to Mackay. What is more, he says that these data "mirror instrumental climate records from Fennoscandia for example, which also show over the last 250 years positive temperature trends and increasing early summer Siberian temperature reconstructions."

What it means
In the concluding words of Mackay's synthesis of what scientists have learned to this point in time, "warming in the Lake Baikal region commenced before rapid increases in greenhouse gases, and at least initially, is therefore a response to other forcing factors such as insolation changes during this period of the most recent millennial cycle (e.g. Beer et al., 1996)." In fact, since the warming began so far in advance of rapid increases in greenhouse gases (some two full centuries), we can essentially discount these gases as having been responsible for the majority of the warming that has taken the earth to the level of warmth it enjoys today.

References
Beer, J., Mende, W., Stellmacher, R. and White, O.R. 1996. Intercomparisons of proxies for past solar variability. In: Jones, P.D., Bradley, R.S. and Jouzel, J. (Eds.), Climate Variations and Forcing Factors of the Last 2000 Years. Springer-Verlag, Berlin, Germany, pp. 501-517.

Naurzbaev, M.M. and Vaganov, E.A. 2000. Variation of early summer and annual temperature in east Taymir and Putoran (Siberia) over the last two millennia inferred from tree rings. Journal of Geophysical Research 105: 7317-7326.