Background
The United States' Northern Great Plains is an important agricultural region of North America, providing a significant source of grain both locally and internationally. Because of its location, it is also susceptible to extreme droughts that tend to persist longer than in any other region of the country (Karl et al., 1987; Soule, 1992); and because of this fact, it is probably as good a place as any to look for a manifestation of the climate-alarmist claim (Gore, 2006; Mann and Kump, 2008) that global warming will usher in a period of more frequent and intense drought.

What was done
Based on diatom-inferred salinity and Mg/Ca ratios in ostracode calcite derived from sediment cores taken at three sites in North Dakota (USA) -- Moon Lake, Coldwater Lake and Rice Lake -- the authors constructed three 2000-year histories of lake-water salinity in order to infer regional patterns of drought.

What was learned
"From the vantage point of the 20th century," in the words of Fritz et al., "the three North Dakota sites suggest that droughts equal or greater in magnitude to those of the Dust Bowl period were a common occurrence during the last 2000 years and that severe droughts may have been frequent for multiple decades within this period." Interestingly, they also report that "both the Medieval Period and Little Ice Age were hydrologically complex, and there is no clear evidence to suggest that either interval was coherent or unusual in effective moisture relative to long-term patterns." In addition, they report that "studies from the northern Great Plains and western North America (Cook et al., 1997; Dean, 1997; Laird et al., 1996; Yu and Ito, 1999) have shown a correlation between solar forcing and centennial- and decadal-scale drought patterns." Thus, they conclude that "solar variability may influence the duration of dry periods through its impact on convective activity and circulation (Rind and Overpeck, 1993)."

What it means
In light of climate-alarmist predictions of intensified drought conditions in a warming world, many people would assuredly claim that any new period of intensified drought on America's Northern Great Plains would be a vindication of those prognostications ... and probably of other climate-alarmist contentions as well. It is clear from the work of Fritz et al., however, that such need not be the case; for everything bad that happens need not be the result of rising atmospheric CO2 concentrations, as the study here described clearly demonstrates.

References
Cook, E.R., Meko, D.M. and Stockton, C.W. 1997. A new assessment of possible solar and lunar forcing of the bidecadal drought rhythm in the western United states. Journal of Climate 10: 1343-1356.

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

Gore, A. 2006. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. Roldale, Emmaus, Pennsylvania, USA.

Karl, T., Quinlan, F. and Ezell, D.S. 1987. Drought termination and amelioration: its climatological probability. Journal of Climate and Applied Meteorology 26: 1198-1209.

Laird, K.R., Fritz, S.C., Maasch, K.A. and Cumming, B.F. 1996. Greater drought intensity and frequency before AD 1200 in the Northern Great Plains, USA. Nature 384: 552-555.

Mann, M.E. and Kump, L.R. 2008. Dire Predictions: Understanding Global Warming. DK Publishing Inc., New York, New York, USA.

Rind, D. and Overpeck, J. 1993. Hypothesized causes of decade to century scale climate variability: Climate model results. Quaternary Science Reviews 12: 357-374.

Soule, P.T. 1992. Spatial patterns of drought frequency and duration in the contiguous USA based on multiple drought event definitions. International Journal of Climatology 12: 11-24.

Yu, Z.C. and Ito, E. 1999. Possible solar forcing of century-scale drought frequency in the northern Great Plains. Geology 27: 263-266.