ASK TOM: What caused the extreme drought during the "Dust Bowl" years?

Dear Tom,
The extreme drought persisting in the Great Plains is reminiscent of the Dust Bowl years of the 1930s. What was the cause then? El Nino? La Nina?

– Richard Miller, Chicago

Dear Richard,

The drought of the 1930s (and resultant “Dust Bowl”) was a seven-year event of varying intensity with 1930, 1934 and 1936 the worst years. Researchers have offered theories as to the cause, but none has been definitive.

The causes might never be known. The atmosphere wasn’t monitored by weather balloons back then, so we don’t have information about wind patterns and jet stream configurations. The drought occurred over such an extended period that no single El Nino or La Nina event (which usually runs only a year or two) or sunspot cycle (11 years) adequately explains the drought period.