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Precipitation History of the USA's Bighorn Basin
Gray, S.T., Fastie, C.L., Jackson, S.T. and Betancourt, J.L.  2004.  Tree-ring-based reconstruction of precipitation in the Bighorn Basin, Wyoming, since 1260 A.D.  Journal of Climate 17: 3855-3865.

What was done
In the words of the authors, "cores and cross sections from 79 Douglas fir (Pseudotsuga menziesii) and limber pine (Pinus flexillis) trees at four sites in the Bighorn Basin of north-central Wyoming and south-central Montana were used to develop a proxy for annual (June-June) precipitation spanning 1260-1998 A.D."

What was learned
Gray et al. report that "the reconstruction exhibits considerable nonstationarity, and the instrumental era (post-1900) in particular fails to capture the full range of precipitation variability experienced in the past ~750 years."  More specifically, they say that "both single-year and decadal-scale dry events were more severe before 1900," and that "dry spells in the late thirteenth and sixteenth centuries surpass both [the] magnitude and duration of any droughts in the Bighorn Basin after 1900."

What it means
In the introduction to their paper, Gray et al. comment that studies from throughout the world "demonstrate that the instrumental record is often insufficient for capturing the full range of precipitation variability possible in a given area (Cook and Evans, 2000)."  Such was also found to be the case in their study, as they indicate that "single- and multi-year droughts regularly surpassed the severity and magnitude of the 'worst-case scenarios' presented by the 1930s and 1950s droughts."  Hence, if 20th-century global warming had any effect at all on Bighorn Basin precipitation, it was to make it less extreme rather than more extreme, in contradiction of the fervent claims of the world's climate alarmists.

Cook, E.R. and Evans, M.  2000.  Improving estimates of drought variability and extremes from centuries-long tree-ring chronologies: A PAGES/CLIVAR example.  CLIVAR Exchanges, Vol. 5, No. 1, PAGES Newsletter, Vol. 8, No. 1, International CLIVER Project Office, Southampton, United Kingdom, pp. 19-12.

Reviewed 8 December 2004