A paper published today in Quaternary Science Reviews is the first to reconstruct droughts in California and the Southwest US for the past 3000 years and clearly demonstrates drought conditions were far more severe and persistent in the distant past than during recent history. In fact, the paper demonstrates drought at the end of the record is at some of the lowest levels of the past 3,000 years and far more extreme epic droughts in the US Southwest/California have persisted for periods of 300-500 years at least three times over the past 3 millennia.
The authors find wet conditions are associated with more frequent El Ninos, and droughts with periods having fewer El Ninos. Although some climate scientists such as Kevin Trenberth have claimed AGW will cause more frequent El Ninos [and thus less drought], the El Nino reconstruction in this paper shows the frequency of El Ninos in the past 3000 years has been persistently much higher and much lower than the present for periods lasting several hundred years each.
Bottom line is that this paper demolishes claims that current California drought conditions are relatively "extreme" or linked to man-made CO2, as well as claims that man-made CO2 controls the frequency of natural El Ninos.