What was done
The authors devised a classification scheme for four important climatic conditions (drought, thunderstorm occurrence, cold season precipitation, and precipitation to potential evapotranspiration ratio) that favor the existence of the tall grass prairie -- or True Prairie (TP), as they call it -- of the central United States.  Then, for the period 1895-2000, they assessed the spatial and temporal variability of these conditions with archived meteorological data from the U.S. National Climatic Data Center.

What was learned
The authors say their analysis "did not reveal any long-term trends in most climate-year types, although there were significant decadal-scale fluctuations, most notably a high frequency of drought-type years in the 1930s and 1950s."  They also report "there is no indication of a major shift in conditions that would be more or less conducive to maintaining the TP."  In fact, they state that "the average climate dimensions of the century appear to be similar to those in substantial portions of preceding millennia when the tall grass prairie existed."  Hence, they conclude that the climatic events of the 20th century "serve as a useful sample that could have occurred in many discrete centuries of the Holocene since about 6,000 YBP [years before present]."

What it means
For the period of time that climate alarmists typically describe as having experienced a change in global climate that is unprecedented over the past one to two millennia, Kunkel and Changnon find that the climate of a large portion of the central United States was not materially different from that which occurred there periodically over the past 6000 years.  Nothing too "unprecedented" here!