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Canadian and U.S. Droughts of the Medieval Warm Period
Volume 16, Number 5: 30 January 2013

In introducing a study of theirs that was recently published in Global Change Biology, Laird et al. (2012) write that "future extreme droughts, similar to or more extreme than the 'dust-bowl' 1930s, could be the most pressing problem of global warming," citing Romm (2011) and noting, for comparison, that "droughts of unusually long duration" or mega-droughts that occurred during the Medieval Climate Anomaly (MCA) [= Medieval Warm Period] "lasted for several decades to centuries thus dwarfing modern-day droughts," as reported by Seager et al. (2007) and Cook et al. (2010).

Noting further that "one of the predictions of increasing temperatures is decreased lake levels and river flows (Schindler and Lee, 2010)," the eight researchers go on to say that "analysis of longer-term records of past water levels can provide a context for informing water managers on the inherent natural variability of lake levels and their sensitivity to climate change," which is something that is of extreme importance to the entire world. And so they proceed to describe a pertinent study they conducted on six lakes spread across a 250-km transect of the Winnipeg River Drainage Basin of northwest Ontario, Canada, where the land-based pollen data of Viau and Gajewski (2009) suggest the presence of warmer temperatures during the MCA.

The six diatom-inferred decadal-scale two-millennia-long drought records, which Laird et al. developed for the six lakes they studied, revealed that what they call "periods of synchronous change" had occurred across all of the six lakes throughout "a period of prolonged aridity during the MCA (c. 900-1400 CE)." And they state that this "general synchrony across sites suggests an extrinsic climate forcing (Williams et al., 2011)," with the MCA being part of a set of what they call "inherent natural fluctuations."

In further support of this conclusion, Laird et al. write that "a widespread external forcing must be large enough for regional patterns to emerge." And they report, in this regard, that in the Nebraska Sandhills "an analysis of five topographically closed lakes indicated relative coherency over the last 4000 years, particularly during the MCA with all lakes indicating lake-level decline (Schmieder et al., 2011)." In addition, they indicate that "in Minnesota, sand deposits in Mina Lake indicate large declines in lake level during the 1300s (St. Jacques et al., 2008), high eolian deposition occurred from ~1280 to 1410 CE in Elk Lake (Dean, 1997) and δ18O from calcite indicated an arid period from ~1100 to 1400 CE in Steel Lake (Tian et al., 2006)," while "in Manitoba, the cellulose δ18O record from the southern basin of Lake Winnipeg indicated severe dry conditions between 1180 and 1230 CE, and a less-severe dry period from 1320 to 1340 CE (Buhay et al., 2009)." And they add that relatively warm conditions during the MCA "have been inferred from pollen records in the central boreal region of Canada and in Wisconsin," citing Viau and Gajewski (2009), Viau et al. (2012) and Wahl et al. (2012).

These impressive and temporally-coherent findings have several important implications; but the one that is most germane to climatology is that if future extreme droughts, such as those that occurred during the MCA, could indeed be the "most pressing problem" of projected future global warming, as many climate alarmists contend, then it logically follows that (1) the Medieval Warm Period must have been far more extreme in terms of both high temperature values and their duration than anything yet experienced during the Current Warm Period, and (2) the preceding observation is strong evidence that warming considerably in excess of what has been experienced to date in our day and age can readily occur without any help from rising atmospheric CO2 concentrations, which were more than 100 ppm less during the Medieval Warm period than they are today, as is additionally - and convincingly - demonstrated by the great multitude of quantitative and qualitative findings of a host of scientists who have studied both the Medieval and Current Warm Periods throughout the entire world, which findings further suggest that (3) the development of the planet's Current Warm Period may be due to something that is totally unrelated to anthropogenic CO2 emissions.

Sherwood, Keith and Craig Idso

Buhay, W.M., Simpson, S., Thorleifson, H., Lewis, M., King, J., Telka, A., Wilkinson, P., Babb, J., Timsic, S. and Bailey, D. 2009. A 1000 year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics. Journal of Quaternary Science 24: 426-436.

Cook, E.R., Seager, R., Heim Jr., R.R., Vose, R.S., Herweijer, C. and Woodhouse, C. 2010. Mega-droughts in North America: placing IPCC projections of hydroclimatic change in a long-term palaeoclimate context. Journal of Quaternary Science 25: 48-61.

Dean, W.E. 1997. Rates, timing and cyclicity of Holocene eolian activity in north-central US: evidence from varved lake sediments. Geology 25: 331-334.

Laird, K.R., Haig, H.A., Ma, S., Kingsbury, M.V., Brown, T.A., Lewis, C.F.M., Oglesby, R.J. and Cumming, B.F. 2012. Expanded spatial extent of the Medieval Climate Anomaly revealed in lake-sediment records across the boreal region in northwest Ontario. Global Change Biology 18: 2869-2881.

Romm, J. 2011. The next dust bowl. Nature 478: 450-451.

Schindler, D.W. and Lee, P.G. 2010. Comprehensive conservation planning to protect biodiversity and ecosystem services in Canadian boreal regions under a warming climate and increasing exploitation. Biological Conservation 143: 1571-1586.

Schmieder, J., Fritz, S.C., Swinehart, J.B., Shinneman, A., Wolfe, A.P., Miller, G., Daniels, N., Jacobs, K. and Grimm, E.C. 2011. A regional-scale climate reconstruction of the last 4000 years from lakes in the Nebraska sand hills, USA. Quaternary Science Reviews 30: 1797-1812.

Seager, R., Graham, N., Herweijer, C., Gorodn, A.L., Kushnir, Y. and Cook, E. 2007. Blueprints for medieval hydroclimate. Quaternary Science Reviews 26: 2322-2336.

St. Jacques, J.M., Cumming, B.F. and Smol, J.P. 2008. A 900-year pollen-inferred temperature and effective moisture record from varved Lake Mina, west-central Minnesota, USA. Quaternary Science Reviews 27: 781-796.

Tian, J., Nelson, D.M. and Hu, F.S. 2006. Possible linkages of late-Holocene drought in the North American midcontinent to Pacific Decadal Oscillation and solar activity. Geophysical Research Letters 33: 10.1029/2006GL028169.

Viau, A.E. and Gajewski, K. 2009. Reconstructing millennial-scale, regional paleoclimates of boreal Canada during the Holocene. Journal of Climate 22: 316-330.

Viau, A.E., Ladd, M. and Gajewski, K. 2012. The climate of North America during the past 2000 years reconstructed from pollen data. Global and Planetary Change 84-85: 75-83.

Wahl, E.R., Diaz, H.F. and Ohlwein, C. 2012. A pollen-based reconstruction of summer temperature in central NorthAmerica and implications for circulation patterns during medieval times. Global and Planetary Change 84-85: 66-74.

Williams, J.W., Blois, J.L. and Shuman, B.N. 2011. Extrinsic and intrinsic forcing of abrupt ecological change: case studies from the late Quaternary. Journal of Ecology 99: 664-677.