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Climate and Beavers in Yellowstone National Park (USA)
Persico, L. and Meyer, G. 2009. Holocene beaver damming, fluvial geomorphology, and climate in Yellowstone National Park, Wyoming. Quaternary Research 71: 340-353.

What was done
The authors used "beaver-pond deposits and geomorphic characteristics of small streams to assess long-term effects of beavers and climate change on Holocene fluvial activity in northern Yellowstone National Park," which feat was accomplished by comparing "the distribution of beaver-pond deposit ages to paleoclimatic proxy records in the Yellowstone region."

What was learned
Persico and Meyer report that "gaps in the beaver-pond deposit record from 2200-1800 and 700-1000 cal yr BP are contemporaneous with increased charcoal accumulation rates in Yellowstone lakes and peaks in fire-related debris-flow activity, inferred to reflect severe drought and warmer temperatures (Meyer et al., 1995)." In addition, they note that "the lack of evidence for beaver activity 700-1000 cal yr BP is concurrent with the Medieval Climatic Anomaly, a time of widespread multi-decadal droughts and high climatic variability in Yellowstone National Park (Meyer et al., 1995) and the western USA (Cook et al., 2004; Stine, 1998; Whitlock et al., 2003)," while we note that the lack of evidence for beaver activity 2200-1800 cal yr BP is concurrent with the Roman Warm Period. In both of these instances, the two researchers concluded that the severe droughts of these periods "likely caused low to ephemeral discharges in smaller streams, as in modern severe drought [our italics]," implying that the Medieval and Roman Warm Periods were likely just as dry and warm as it is today.

What it means
Once again, these findings suggest there is nothing unusual, unnatural or unprecedented about the degree of warmth and drought of the Current Warm Period, in contrast to what climate alarmists continually claim. And the fact that there was more than 100 ppm less CO2 in the air of those earlier warm and dry periods than there is today suggests that something other than CO2 could well be responsible for the equivalent warmth and dryness of today, while the regular recurrence of such conditions suggests that their cause is a cyclical phenomenon of nature that is independent of the activities of the planet's human population.

Cook, E.R., Woodhouse, C.A., Eakin, C.M., Meko, D.M. and Stahle, D.W. 2004. Long-term aridity changes in the western United States. Science 306: 1015-1018.

Meyer, G.A., Wells, S.G. and Jull, A.J.T. 1995. Fire and alluvial chronology in Yellowstone National Park - climatic and intrinsic controls on Holocene geomorphic processes. Geological Society of America Bulletin 107: 1211-1230.

Stine, S. 1998. Medieval climatic anomaly in the Americas. In: Issar, A.S. and Brown, N. (Eds.). Water, Environment and Society in Times of Climatic Change. Kluwer Academic Publishers, pp. 43-67.

Whitlock, C., Shafer, S.L. and Marlon, J. 2003. The role of climate and vegetation change in shaping past and future fire regimes in the northwestern US and the implications for ecosystem management. Forest Ecology and Management 178: 5-21.

Reviewed 1 July 2009