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Decadal and Multidecadal Changes in Precipitation in Chesapeake Bay
Reference
Cronin, T., Willard, D., Karlsen, A., Ishman, S., Verardo, S., McGeehin, J., Kerhin, R., Holmes, C., Colman, S. and Zimmerman, A.  2000.  Climatic variability in the eastern United States over the past millennium from Chesapeake Bay sediments.  Geology 28: 3-6.

What was done
The authors studied the salinity gradient across sediment cores from the Chesapeake Bay, the largest estuary in the United Sates, in an effort to examine precipitation variability in the surrounding watershed over the past 1000 years.

What was learned
A high degree of decadal and multidecadal variability between wet and dry conditions was noted throughout the 1000-year record, where regional precipitation totals fluctuated between 25 to 30%, often in "extremely rapid [shifts] occurring over about a decade."  However, precipitation over the last two centuries in the Chesapeake Bay watershed was on average greater than the eight centuries previous, with the exception of the Medieval Warm Period (1250-1350 A.D.) when the climate was "extremely wet."  It was also determined that this region has experienced several "mega-droughts" lasting from 60-70 years in length, some of which "were more severe than twentieth century droughts."

What it means
Because both wetter and drier climates have occurred naturally in the Chesapeake Bay watershed region in the past, there is no reason not to believe that such conditions will naturally recur in the future, even over a period of a few short years.  Yet, just as soon as the precipitation balance tips to one side or the other, you can be sure there will be those who will be all too eager to attribute the change to increased atmospheric CO2, when such attribution is clearly unwarranted.


Reviewed 15 March 2000