What was done
The USA's 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 United States (Karl et al., 1987; Soule, 1992). Laird et al. examined the historical record of drought in this region in an attempt to establish a baseline of natural drought variability, which could help in attempts to determine if current and future droughts might be anthropogenically influenced. In doing so, they examined a high-resolution sediment core from Moon Lake, North Dakota (46.86°N, 98.16°W), which provided a sub-decadal record of salinity (drought) over the past 2300 years.

What was learned
Laird et al.'s analysis revealed that the Northern Great Plains were relatively wet during the final 750 years of the 2300-year record. In fact, in the 1550 prior years, they determined that "recurring severe droughts were more the norm," and that they were "of much greater intensity and duration than any in the 20th century," including the great Dust Bowl drought of the 1930s.

What it means
In light of Laird et al.'s discovery that there have been "no modern equivalents" to Northern Great Plains droughts experienced prior to AD 1200, it would appear that 20th-century global warming has done nothing to exacerbate drought conditions in this part of the world. Therefore, any claims to the contrary are clearly incorrect.

References
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.

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.