The Dust Bowl (for our international members it was the American midwest/southwest that was plagued by drought and dust storms that was caused by a combination of CLIMATE (a series of drought years starting in 1930; the dust storms started a year later; and the rains returned by the end of 1939); GOVERNMENT POLICIES (the Homestead Act of 1862 and the Kincaid Act of 1904 opened up 160-acre plots of land to an influx of inexperienced farmers who were not given any real guidance about how to use the land they were claiming); and HUMAN CONTRIBUTIONS (these farmers believed that "rain follows the plow," so they believed that even though the area did not have regular and adequate rainfall, there would be more rain somehow once they started plowing the fields; they did not know anything about rotation of crops or leaving fields fallow for a year, so they wore out the earth with their crops, and that left the land with no natural vegetation to hold what little rain there was, etc., etc.).
So... to review: the area that became knowns as "the Dust Bowl" was already predisposed to have a lack of regular annual rainfalls that would support the farmers in general. The land was opened to many "amateurs" who didn't know how to farm and who had superstitious beliefs that guided their actions. The lack of "good farming techniques" that were unknown at that time exacerbated the other factors.
Therefore, I'd have to say that the change in the climate was part nature (drought years) but those were exacerbated by HUMAN FACTORS, just like today. Yes, the tendency is that climate WILL change slowly as years go by, and there is an ebb and flow to much of it. But when you add HUMAN CONTRIBUTIONS that literally change the environment factors that would otherwise would tend to moderate the changes... you get what we're getting now:
"Extreme Nature on Steroids Supplied by Humankind."